Thongchai Thailand

 

 

FIGURE 1: SEASONAL CYCLE OF THE CLOUD DATACLOUD-SEASONAL-CYCLE

 

FIGURE 2: CLOUD AND TEMPERATURE ANOMALIES AND THEIR DETRENDED SERIESMONTHLY-ANOMALIES&DETRENDED

 

FIGURE 3: MONTHLY TIME SCALE: CORR=-0.5682DETCORR=0.09554MONTHLY-CORR-DETCORR

 

FIGURE 4: ANNUAL TIME SCALE: SOURCE DATA FOR EACH CALENDAR MONTHANNUAL-SOURCE

 

FIGURE 5: ANNUAL TIME SCALE: DATA FOR EACH CALENDAR MONTH DETRENDEDANNUAL-DET

 

FIGURE 6: ANNUAL TIME SCALE: CORRELATION AND DETRENDED CORRELATIONCORR-DETCORR

 

  1. It has been proposed in various climate change blogs that a negative correlation between cloud cover and temperature (HadCRUT4 global mean temperature anomalies) explains the observed warming prior to the year 2000 and the hiatus in warming since the year 2000 [LINK] . It is shown that the HadCRUT4 monthly mean temperature anomalies are negatively correlated with monthly mean cloud cover and this relationship is developed into a climate model that explains changes in surface temperature in terms of incident solar radiation, the heat trapping effect of carbon dioxide, and the effect of cloud cover. This model is then validated by its ability to faithfully reproduce the HadCRUT4 global mean temperature anomaly series.
  2. Monthly time scale: The analysis is carried out at a monthly time scale considered valid because the temperature data are anomalies with the seasonal cycle removed; but no attention is paid to the possibility that the cloud data may contain a seasonal cycle. In Figure 1 above, a plot of the mean cloud cover shows a strong seasonal cycle with low cloud cover in the Northern summer and higher cloud cover in the Northern fall, spring, and winter. This seasonal cycle implies that at a monthly time scale the source cloud data may not be used directly but must be deseasonalized to conform with the deseasonalized temperature anomalies.
  3. Monthly time scale: Deseasonalized cloud data are computed by subtracting the mean seasonal cycle from the data. These cloud anomalies and the HadCRUT4 temperature anomalies are shown in Figure 2 along with their corresponding detrended series. The correlation between the cloud cover anomalies and the temperature anomalies is found to be r = -0.562, a strong negative correlation in support of the hypothesis derived from these data that warming is driven by low cloud cover.
  4. Monthly time scale: It is noted, however, that spurious correlations in time series data imposed by long term trends do not imply a responsiveness of Y to changes in X at the time scale of interest. The Tyler Vigen website contains many examples to demonstrate this spurious correlation property of time series data [LINK] . In this case, to detect the responsiveness of temperature to cloud cover at a monthly time scale, net of the effect of long term trends, it is necessary to remove the long term trends from the data with a detrending procedure as explained in this brief lecture by Alex Tolley [LINK] .
  5. Monthly time scale: The detrended data are shown in Figure 2 (in red) and their correlation is displayed graphically in the second frame of Figure 3. This graphic shows that no correlation at a monthly time scale remains when the effect of long term trends is removed. The strong negative correlation seen in the source data of  r=-0.562 turns out to be an artifact of long term trends. At a monthly time scale a statistically insignificant correlation of r=0.09554 remains and the negative sign, essential for the theory that low cloud cover causes warming, is gone. Thus, though the required negative correlation is seen in the source data, detrended analysis shows that it has no implication in terms of responsiveness of temperature to cloud cover at a monthly time scale.
  6. Annual time scale: The corresponding analysis is presented at an annual time scale for each of the twelve calendar months separately. This analysis option does not require the computation of deseasonalized anomalies because the calendar months are not combined. Instead we test the hypothesis that the monthly mean temperature is responsive to monthly mean cloud cover from one year to the next. The results are presented in Figure 4 to Figure 6.
  7. Annual time scale: Strong statistically significant negative correlations are seen in the source data for the eleven calendar months from February to December from r=-0.5 to r=-0.7 as seen in the left frame of Figure 6. However, these correlations are artifacts of long term trends and do not represent responsiveness of temperature to cloud cover at an annual time scale as can be seen in the right frame of Figure 6 where all the statistically significant negative correlations have vanished.
  8. This analysis shows that the spurious correlation in the source data created by long term trends that does not imply responsiveness at an annual or monthly time scale, has been misinterpreted by the authors of the blog posts in terms of an inverse causal relationship between cloud cover and surface temperature. Of course correlation even at the time scale of interest does not imply causation but that condition is more clearly stated as “correlation is a necessary but not sufficient condition for causation”. Here we have addressed the necessity condition and do not claim the sufficient condition.
  9. All data and computational details used in this work are available for download from an online data archive:  [LINK]

 

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CLIMATEREFUGEES

 

  1. 1997, THE BBC MAKES THE CASE FOR THE KYOTO PROTOCOL:  Twenty years of hard data from meteorological stations and nature show a clear warming trend. Growth rings in Mongolian and Canadian trees are getting wider. Butterflies in California are moving to higher ground once too cold for butterflies. Stalactites in Britain are growing faster. The growing season for crops in Australia is getting longer. Permafrost in Siberia and Canada is melting. The evidence is there anywhere you look. A warming rate is one 1C per century is enough to wreak havoc. The cause is the greenhouse effect of CO2 emissions from fossil fuels as well as CFCs and HCFCs that trap heat. The effect is being compounded as deforestation simultaneously removes trees that absorb CO2. Some scientists are skeptical but the majority view is that the greenhouse effect is real and it requires urgent action. This conclusion rests on the results from sophisticated computer simulation models that give the best possible information on this topic even though they are not perfect. These models are giving us scary accounts of the future and we should be paying attention. The IPCC tell us that melting ice and thermal expansion of oceans will cause the sea level to rise one meter by 2037 and inundate low lying areas and island nations. Extreme weather events will become common. El Nino and La Nina cycles will become more extreme. There will be millions of climate refugees driven from their home by global warming. Some regions of the world will become hotter, others colder, some wetter, others drier. Entire weather systems will be dramatically altered. The Gulf Stream will switch off making Europe colder. Tropical diseases such as malaria will ravage the world as vectors migrate to higher latitudes and altitudes. Some wheat farmers may be able to grow more wheat but the net effect of global warming is overwhelmingly negative.
  2. 2001, GLOBAL WARMING NOW UNSTOPPABLE:  A 500-member IPCC led by Sir John Houghton issued the most authoritative report on global warming so far. It contains the following alarming findings: so much CO2 has already been injected into the air that global warming is “already unstoppable”; the world is warming at an accelerating rate; tens of millions of people around the world will be driven from their homes in the coming decades to become climate change refugees; governments must take urgent action to reduce carbon dioxide emissions; climate change is now so rapid that it is not possible for us to adapt to these changes; human ecosystems and biodiversity will all be affected and it will affect the world economy; the temperature rise in the next 100 years will be between 1.4C and 5.8C, significantly higher than previously thought; “there is new and stronger evidence that most of the warming observed over the past 50 years is attributable to human activities; human influences will continue to change atmospheric composition throughout the 21st century; global warming will persist for many centuries by virtue of the CO2 we have already put into the air; change caused by humans is far greater than the changes due to nature; global warming is caused by carbon dioxide trapping heat.
  3. 2008: SEA LEVEL RISE INUNDATES ATOLL AND CREATES CLIMATE REFUGEES: Climate scientists say that man-made global warming has caused a rise in the sea level sufficient to inundate an atoll in Kiribati, a chain of 33 such islands, and created climate refugees. More info: http://chaamjamal.blogspot.com/2008/06/reference-atoll-leader-asks-australia.html 
  4. 2009: BANGLADESH HIT WITH CYCLONES AND CLIMATE REFUGEES: Bangladeshis displaced by Cyclone Sidr in 2007 are “climate refugees” because they have been rendered homeless by a climate change event that was caused by carbon dioxide emissions from fossil fuels and it suggests that cyclones like Sidr will continue to ravage this poverty stricken nation unless we forge a plan in Copenhagen and do away with fossil fuels. More info: http://chaamjamal.blogspot.com/2009/10/reference-climate-refugees-add-strain.html
  5. 2009: SEA LEVEL RISE SINKING SOUTH PACIFIC ATOLLS: Our use of fossil fuels causes global warming. Global warming causes sea level rise. Sea level rise causes South Pacific atolls to become inundated. The inundation of these islands creates climate refugees. More info: http://chaamjamal.blogspot.com/2009/10/worlds-first-climate-refugees-age-july.html
  6. 2018: CLIMATE CHANGE AND ITS STAGGERING REFUGEE CRISIS: Today’s research confirms that massive migration into the millions—combined, as always, with a multitude of other effects—will be an inevitable consequence of global warming.  https://www.yesmagazine.org/issues/mental-health/climate-change-and-its-staggering-refugee-crisis-20181017
  7. 2018: A NEW U.N. CLIMATE REPORT SAYS THAT A GLOBAL CRISIS COULD OCCUR AS SOON AS 2040: Scientists concluded that the most disastrous effects of climate change could occur by 2040 if greenhouse gas emissions occur at the current rate. These effects include coastlines wiped out by sea levels, widespread drought and poverty, and hordes of displaced climate refugees. It said that 50 million people in the United States, Bangladesh, China, Egypt, India, Indonesia, Japan, the Philippines, and Vietnam will be exposed to flooding. https://www.vogue.com/article/un-climate-change-report-crisis-by-2040
  8. 2018: BILL AND MELINDA GATES FOUNDATION TO HELP CLIMATE REFUGEES: There are 800 million people in developing countries who depend on subsistence farming to make a living, and many of the 143 million people who the World Bank estimates will become climate refugees by 2050 are subsistence farmers. That is how the Bill and Melinda Gates Foundation, which does not rank among the leaders in climate-related giving, is proceeding. It sat out of the $4 billion collective philanthropic pledge but it is making grants to help farmers with small plots of land in the poorest countries like Tanzania and Niger cope with “diseases, pests and drought from a changing climate.” https://www.theweathernetwork.com/news/articles/foundations-are-making-climate-change-a-bigger-priority/115841
  9. 2018: CHANGING CLIMATE FORCES GUATEMALANS TO MIGRATE: Guatemala is consistently listed among the world’s 10 most vulnerable nations to the effects of climate change. Increasingly erratic climate patterns have produced year after year of failed harvests and dwindling work opportunities across the country, forcing more and more people like Méndez López to consider migration in a last-ditch effort to escape skyrocketing levels of food insecurity and poverty. During the past decade, an average of 24 million people each year were displaced by weather events around the world. Although it’s unclear how many of those displacements can be attributed to human-caused climate change, experts expect this number to continue to rise. https://www.nationalgeographic.com/environment/2018/10/drought-climate-change-force-guatemalans-migrate-to-us/
  10. 2018:  TYPHOON YUTU CLIMATE REFUGEES: The strongest storm recorded anywhere on the planet this year has caused “catastrophic” damage on the Northern Mariana Islands, a US commonwealth in the northern Pacific Ocean, northeast of Guam. Super Typhoon Yutu reached speeds of up to 255 km/h before it slammed into the islands of Saipan, Tinian, and Rota on Thursday creating havoc and climate change refugees.  https://www.irinnews.org/news/2018/10/26/typhoon-yutu-refugee-investment-and-climate-dragons-cheat-sheet
  11. 2018: CLIMATE REFUGEES IN THE USA: When Americans think of “climate refugees,” the source locales are likely to be low-lying island states, or desertification-prone regions of Africa, India and China; possibly portions of Bangladesh or Central America, where the monsoons are growing ominously larger. It’s time to look closer to home. A provocative package by The Guardian’s Oliver Milman makes that counterpoint  clear from the opening headline: “America’s era of climate mass migration is here.” Think of the rising sea encroaching on Miami Beach, of course, but also Virginia Beach. Think of the Alaskan communities small in size but large in number, sinking into softening permafrost or washing away with the coastline. Remember the thousands displaced from New Orleans by Hurricane Katrina, many to the Houston area, where a dozen years later Hurricane Harvey repeated the process. https://www.minnpost.com/earth-journal/2018/10/great-reads-on-algal-poison-factories-american-climate-refugees-and-more/
  12. 2018: GOVT MAY CHANGE IMMIGRATION LAWS TO TAKE CLIMATE CHANGE REFUGEES: Jacinda Ardern has revealed to Newshub she isn’t ruling out New Zealand taking climate refugees. “We’re looking at creating an immigration plan that looks to the Pacific, and what options there might be within the existing arrangements.” Climate refugees are people displaced from their homes because of the impact of climate change. The existing refugee quota is being lifted from 1000 to 1500 in 2020, an increase announced recently after public in-fighting between the Government’s coalition partners. https://www.newshub.co.nz/home/politics/2018/09/govt-may-change-immigration-settings-to-take-climate-change-refugees.html
  13. 2018: THE GLOBAL CLIMATE REFUGEE CRISIS HAS ALREADY BEGUN: When Hurricane Florence struck the shores of North and South Carolina and Virginia, more than a million evacuees fled their homes seeking shelter from the storm. For some, there will be no return home, as their homes are damaged beyond repair or beyond what they can afford to repair. All these displaced people are not simply evacuees fleeing a dangerous hurricane. They are climate refugees. There are a couple of reasons why climate change is creating a new category of refugee. First, climate change contributes to rising seas. As ocean water warms, it expands. That, along with simultaneous increased melting of the world’s mountain glaciers and the Greenland and Antarctic ice sheets, contributes to rising sea levels. Sea level rise is already one factor producing climate refugees around the world.  https://thehill.com/opinion/energy-environment/409002-the-global-climate-refugee-crisis-has-already-begun

 

 

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PETM-BIOTA

 

PALEOCENE-EOCENE THERMAL MAXIMUM 55 MILLION YEARS AGO

 

 

WHAT WE KNOW FROM PALEO CLIMATOLOGY

  1. Time, duration, & data: Paleoclimate data from carbonate and organic matter deposits in terrestrial and ocean sediments show that there was a 10,000 year (or so) period of global warming about 55 to 56 million years ago where the Paleocene age ends and the Eocene age begins. The warming is found in the atmosphere, in sea surface temperature, and in the deep ocean.
  2. Global Warming: Temperatures in the deep ocean rose by 4ºC from 11ºC to 15ºC while sea surface temperature (SST), estimated from oxygen isotope excursion and Mg/Ca records, warmed by 8ºC to 10ºC with temperatures as high as 33ºC in the mid-latitudes and 23ºC in the Arctic. Global mean surface temperatures rose by 5ºC to 9ºC. Although these changes are described as “abrupt” in the long paleo context, it should be noted that a warming of 10ºC over a period of  10,000 years corresponds to a warming rate of 0.1ºC per century compared with our current warming rate of 0.5ºC/century.
  3. Carbon Isotopic excursion: The data also show that over the same period of time, there were isotopic excursions of carbon13. (An isotopic excursion is a temporary divergence from the long term average.) In the 10,000-year excursion, carbon13 levels in both oceans and atmosphere fell by 0.2% to 0.4% from the norm. It is significant that the carbon isotope excursion is found in both the atmosphere and the oceans. The excursion implies that carbon in the current carbon cycle had been combined with carbon from a distant past.
  4. Oceanic oxygen depletion: Warming of deep waters was followed by oxygen deficiency in the deep ocean as seen in the extinction of 30–50% of deep‐sea benthic foraminiferal species. Oxygen depletion implies that warming was associated with oxidation of some kind.
  5. Ocean Acidification: Coincident with oceanic oxygen depletion, a rapid decline in pH and evidence of shoaling of the calcite compensation depth down to depths greater than 3km of the ocean are found in the data. The data indicate a very large global oxidation event in the ocean that generated large quantities of carbon dioxide.
  6. Increase in Atmospheric Carbon Dioxide: Atmospheric CO2 levels estimated from oxygen17 isotopic signatures in tooth enamel show a large uncertainty range from 230 to 630 ppm that is thought to have increased by more than 70% in course of the 10,000-year PETM event. The attempt to describe the observed warming in terms of the greenhouse effect of atmospheric CO2 and thereby to draw theoretical parallels with the current warming episode has not yielded useful results because it yields gross anomalies in terms of climate sensitivity and also because some of the warming events recorded came before the increase in atmospheric CO2.

 

 

WHAT WE DON’T KNOW BUT HAVE THEORIES FOR

  1. What was the large deep-ocean oxidation event that warmed the ocean, depleted its oxygen, increased its inorganic carbon concentration, injected carbon dioxide into the atmosphere? The main body of research points to methane hydrates as the source of the carbon. It is proposed that the the hydrates were dissociated into methane by unspecified heat sources possibly geothermal, that then caused the methane to oxidize thus consuming the ocean’s oxygen and generating even more heat in a chain reaction. It is clear however, that much of the methane survived into the atmosphere where their further oxidation by atmospheric oxygen continued. An alternative theory identifies the mantle as a direct source of both carbon and heat (Svenson 2004). At least one study (Kent 2003) has presented evidence that bears the signature of a comet strike that may have initiated the ocean warming, carbonification, and oxidation sequence.
  2. What was the role of the greenhouse effect of atmospheric carbon dioxide? The proposed heat trapping effect of atmospheric CO2 could not have initiated the PETM warming because the oceanic carbon enrichment and oxidation events preceded the rise in atmospheric CO2; and the rise in atmospheric CO2 is poorly quantified. Also, using the IPCC climate sensitivity range of ECS = [1.5, 4.5] in conjunction with the best guess for the rise in atmospheric CO2 concentration does not explain the amount of surface warming. It is therefore possible that other sources of heat, possibly geothermal, may have been at work.
  3. Does the rate of carbon dioxide injection into the atmosphere compare with that of the current episode of anthropogenic global warming? Paleo climatology likes to refer to it as “a massive carbon injection”  and indeed a great deal of carbon dioxide was injected into the atmosphere; but the time frame is very long as these things occurred over 10,000 to 20,000 years compared with the century of two in today’s time scale. Currently, the CO2 injection rate is around 10 GTCY (gigatonnes of carbon equivalent per year). The corresponding figures for the PETM event is somewhere between 0.2 and 0.6 GTC per year. Yet, if the total amount injected had occurred in 100 years instead of 10,000 years, the corresponding annual rate would have been 20 to 60 GTCY.
  4. Is there an analogy between AGW and PETM that will give us better insight and understanding of AGW and help us to design better climate action and climate adaptation policies? This analogy is often claimed in the popular press and there may be some generalities about warming that will be useful to us but there are gross departures in the details of the two events that make it difficult to draw a parallel that can relate events in one to events in the other. For example, the the PETM event started in a world that was already much warmer than today’s world so that there was little or no ice/snow albedo and thermal dissociation of deep ocean hydrates were more plausible; and the flora and fauna along with the carbon cycle were very different. But the more fundamental issue is that while the AGW event is thought to have been initiated and driven by humans digging up and burning fossil fuels, the PETM event was initiated by nature in the deep ocean where inexplicably, an enormous amount of carbon was released possibly from the ocean bed either from methane hydrates or from the mantle. The oxidation of the carbon simultaneously consumed the ocean’s oxygen, caused ocean acidification, and caused atmospheric CO2 to rise. The parallel between these events and AGW often drawn by climate activists, require that these sequence of events in reverse – starting with CO2 release by humans into the atmosphere – can be understood in PETM terms.
  5. The role of the earth’s internal geothermal heat in climate: The current episode of climate change is understood purely in terms of solar radiation arriving at the top of the atmosphere and the proposed role of carbon dioxide emissions from the use of fossil fuels in leveraging surface temperature. There is no role in this mechanism for the earth itself either in terms of its internal geothermal heat or of natural emissions of carbon from within the earth itself. The PETM is a cautionary tale in this regard because there, the predominant role of the earth’s internal heat and carbon emissions are acknowledged. The possible role of the earth itself in the current event is discussed in three related posts [Ocean Heat Content] ,  [Unprecedented Warming of the Arctic] [Carbon Cycle Measurement Problems Solved with Circular Reasoning] .
  6. What was the impact of the PETM events on the flora and fauna? Mass extinctions of some species (benthic foraminifera) and expansion of other species (subtropical dinoflagellates) are recorded in the paleo data. The most dramatic change and the one most relevant to humans is that the PETM is credited with the rapid expansion of mammals on land and the first appearance of the modern orders of mammals. For details please see the various works of Paleontologist Philip Dean Gingerich.

 

 

PETM BIBLIOGRAPHY

 

Featured Authors

Gerald Dickens, James Zachos, Philip Gingerich, & Dennis Kent

 

  1. 1995: Dickens, Gerald R., et al. “Dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the Paleocene.” Paleoceanography and Paleoclimatology10.6 (1995): 965-971. Isotopic records across the “Latest Paleocene Thermal Maximum“ (LPTM) indicate that bottom water temperature increased by more than 4°C during a brief time interval (<104years) of the latest Paleocene (∼55.6 Ma). There also was a coeval −2 to −3‰ excursion in the δ13C of the ocean/atmosphere inorganic carbon reservoir. Given the large mass of this reservoir, a rapid δ13C shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere. However, a direct consequence of warming bottom water temperature from 11 to 15°C over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic CH4 hydrate at locations with intermediate water depths. In terms of the present‐day oceanic CH4 hydrate reservoir, thermal dissociation of oceanic CH4 hydrate during the LPTM could have released greater than 1.1 to 2.1 × 1018 g of carbon with a δ13C of approximately −60‰. The release and subsequent oxidation of this amount of carbon is sufficient to explain a −2 to −3‰ excursion in δ13C across the LPTM. Fate of CH4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the LPTM.
  2. 1997: Dickens, Gerald R., Maria M. Castillo, and James CG Walker. “A blast of gas in the latest Paleocene: Simulating first-order effects of massive dissociation of oceanic methane hydrate.” Geology 25.3 (1997): 259-262. Carbonate and organic matter deposited during the latest Paleocene thermal maximum is characterized by a remarkable −2.5‰ excursion in δ13C that occurred over ∼104 yr and returned to near initial values in an exponential pattern over ∼2 × 105 yr. It has been hypothesized that this excursion signifies transfer of 1.4 to 2.8 × 1018 g of CH4 from oceanic hydrates to the combined ocean-atmosphere inorganic carbon reservoir. A scenario with 1.12 × 1018 g of CH4 is numerically simulated here within the framework of the present-day global carbon cycle to test the plausibility of the hypothesis. We find that (1) the δ13C of the deep ocean, shallow ocean, and atmosphere decreases by −2.3‰ over 104 yr and returns to initial values in an exponential pattern over ∼2 × 105 yr; (2) the depth of the lysocline shoals by up to 400 m over 104 yr, and this rise is most pronounced in one ocean region; and (3) global surface temperature increases by ∼2 °C over 104 yr and returns to initial values over ∼2 × 106 yr. The first effect is quantitatively consistent with the geologic record; the latter two effects are qualitatively consistent with observations. Thus, significant CH4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum. This conclusion is of broad interest because the flux of CH4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present-day anthropogenic CH4 sources.
  3. 2002: Thomas, Deborah J., et al. “Warming the fuel for the fire: Evidence for the thermal dissociation of methane hydrate during the Paleocene-Eocene thermal maximum.” Geology30.12 (2002): 1067-1070.  Dramatic warming and upheaval of the carbon system at the end of the Paleocene Epoch have been linked to massive dissociation of sedimentary methane hydrate. However, testing the Paleocene-Eocene thermal maximum hydrate dissociation hypothesis has been hindered by the inability of available proxy records to resolve the initial sequence of events. The cause of the Paleocene-Eocene thermal maximum carbon isotope excursion remains speculative, primarily due to uncertainties in the timing and duration of the Paleocene-Eocene thermal maximum. We present new high-resolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells from Ocean Drilling Program Site 690 (Weddell Sea, Southern Ocean), demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface-water warming. Both of these findings support the thermal dissociation of methane hydrate as the cause of the Paleocene-Eocene thermal maximum carbon isotope excursion. Furthermore, the data reveal that the methane-derived carbon was mixed from the surface ocean downward, suggesting that a significant fraction of the initial dissociated hydrate methane reached the atmosphere prior to oxidation.
  4. 2001: Katz, Miriam, et al. Uncorking the bottle: What triggered the Paleocene/Eocene thermal maximum methane release?   Paleoceanography 16.6 (2001): 549-562. The Paleocene/Eocene thermal maximum (PETM) was a time of rapid global warming in both marine and continental realms that has been attributed to a massive methane (CH4) release from marine gas hydrate reservoirs. Previously proposed mechanisms for this methane release rely on a change in deepwater source region(s) to increase water temperatures rapidly enough to trigger the massive thermal dissociation of gas hydrate reservoirs beneath the seafloor. To establish constraints on thermal dissociation, we model heat flow through the sediment column and show the effect of the temperature change on the gas hydrate stability zone through time. In addition, we provide seismic evidence tied to borehole data for methane release along portions of the U.S. continental slope; the release sites are proximal to a buried Mesozoic reef front. Our model results, release site locations, published isotopic records, and ocean circulation models neither confirm nor refute thermal dissociation as the trigger for the PETM methane release. In the absence of definitive evidence to confirm thermal dissociation, we investigate an alternative hypothesis in which continental slope failure resulted in a catastrophic methane release. Seismic and isotopic evidence indicates that Antarctic source deepwater circulation and seafloor erosion caused slope retreat along the western margins of the North Atlantic in the late Paleocene. Continued erosion or seismic activity along the oversteepened continental margin may have allowed methane to escape from gas reservoirs trapped between the frozen hydrate‐bearing sediments and the underlying buried Mesozoic reef front, precipitating the Paleocene/Eocene boundary methane release. An important implication of this scenario is that the methane release caused (rather than resulted from) the transient temperature increase of the PETM. Neither thermal dissociation nor mechanical disruption of sediments can be identified unequivocally as the triggering mechanism for methane release with existing data. Further documentation with high‐resolution benthic foraminiferal isotopic records and with seismic profiles tied to borehole data is needed to clarify whether erosion, thermal dissociation, or a combination of these two was the triggering mechanism for the PETM methane release.
  5. 2002: Bralower, Timothy J. “Evidence of surface water oligotrophy during the PaleoceneEocene thermal maximum: Nannofossil assemblage data from Ocean Drilling Program Site 690, Maud Rise, Weddell Sea.” Paleoceanography 17.2 (2002): 13-1. Nannoplankton assemblages at Ocean Drilling Program Site 690 (Maud Rise, Weddell Sea) experienced an abrupt and dramatic transformation at the onset of the Paleocene‐Eocene Thermal Maximum (PETM) at ∼55 m.y. The major assemblage shift suggests a change from colder, more productive surface waters to warmer, more oligotrophic conditions. Significant restructuring of assemblages during the later part of the PETM indicates that nannoplankton communities were not stable and that surface water conditions changed, although they remained warm and oligotrophic. Combined with benthic foraminiferal assemblage data, nannoplankton assemblage results suggest increased sequestration of nutrients in shelf environments and starvation of the open ocean. Although the PETM was a short‐lived event, it appears to have had long‐term effects on nannoplankton, leading to the extinction of Fasciculithus, a dominant Paleocene genus. The Cretaceous and early Paleogene was a time of remarkable transformation of marine communities [e.g., Vermeij, 1977]. Some of the most dramatic evolutionary changes took place in the protistans. Groups such as the diatoms and planktic foraminifera became fundamental parts of marine food chains during this time. Other groups such as the calcareous nannoplankton and radiolarians underwent wholesale changes in species composition and assemblage structure. The underlying causes of the long‐term evolutionary changes that took place are not well understood [e.g., Roth, 1987; Leckie, 1987; Leckie et al., 2002]. Research over the last decade, however, has established that these groups were also affected by environmental changes that took place over short timescales. In particular, short‐lived (<1 m.y.) global warming events sparked significant biotic turnover in association with dramatic changes in global carbon cycling [e.g., Schlanger et al., 1987; Leckie, 1989; Elder, 1991; Kennett and Stott, 1991; Coccioni et al., 1992; Erba, 1994; Koch et al., 1995; Kelly et al., 1996; Thomas and Shackleton, 1996; Aubry, 1998; Premoli Silva and Sliter, 1999; Premoli Silva et al., 1999]. One of the most extreme and abrupt warming episodes occurred close to the Paleocene/Eocene boundary at ∼55 Ma [Kennett and Stott, 1991; Bralower et al., 1995; Thomas and Shackleton, 1996]. This event, which is known as the Paleocene‐Eocene Thermal Maximum (PETM) [e.g., Zachos et al., 1993], lasted for a period of ∼210 kyr [Norris and Röhl, 1999; Röhl et al., 2000]. The deep and surface oceans warmed by ∼5° and ∼4°–8°C, respectively, during the PETM. The carbon isotopic composition of the ocean and atmosphere decreased by 3–4‰ coeval with the warming event, suggesting a massive perturbation to the global carbon cycle [Kennett and Stott, 1991; Koch et al., 1992; Bains et al., 1999; Norris and Röhl, 1999]. The large magnitude and rate of onset of the carbon isotope excursion (CIE) are most consistent with the sudden dissociation of methane hydrates from continental shelves and slopes [Dickens et al., 1995, 1997; Katz et al., 1999]; CH4 would have immediately contributed to greenhouse warming. The PETM climatic changes affected biota on a global scale, triggering abrupt turnover of benthic and planktic organisms in the ocean [e.g., Kennett and Stott, 1991; Kelly et al., 1996; Speijer and Morsi, 2002], and the rapid radiation of mammals on land [e.g., Gingerich et al., 1980; Maas et al., 1995; Hooker, 1996; Clyde and Gingerich, 1998]. Deep‐sea environmental changes led to an abrupt extinction in benthic foraminiferal communities [e.g., Thomas, 1990; Pak and Miller, 1992; Thomas and Shackleton, 1996; Thomas, 1998]. This benthic foraminiferal extinction (BFE) event [e.g., Tjalsma and Lohmann, 1983] has been well documented in a range of different environments and latitudes [e.g., Kaiho et al., 1996; Speijer et al., 1996]. The response of surface‐dwelling marine organisms to PETM environmental changes appears to have been fundamentally different: tropical planktic foraminifers radiated dramatically during this event [Kelly et al., 1996, 1998]. There have been few high‐resolution investigations of the response of phytoplankton groups such as the calcareous nannoplankton to the PETM. Most previous investigations have considered only long‐term changes in assemblages through the late Paleocene‐early Eocene interval [e.g., Aubry, 1998]. Interpretations of geochemical and biotic investigations disagree as to whether the PETM was characterized by increased or decreased surface water productivity. Tropical plankton at Pacific Site 865 suggests increased oligotrophy [Kelly et al., 1996]; benthic foraminiferal assemblages in open ocean sites also suggest reduced food supply under oligotrophic surface water conditions, whereas assemblages in marginally marine and shelf sites are interpreted as indicating high food supply likely as a result of eutrophic conditions [Thomas and Shackleton, 1996; Speijer and Schmitz, 1998; Thomas, 1998; Thomas et al., 2000]. A widespread bloom of the dinoflagellate Apectodinium in sections deposited in coastal environments is also consistent with high productivity [Crouch et al., 2001]. Bains et al. [2000] interpreted an increase in Ba accumulation rates in the PETM at several open‐ocean sites as evidence for high productivity; these authors concluded that elevated productivity led to increased CO2 draw down, curbing a potential runaway greenhouse. To attempt to resolve the contrast between biotic and geochemical proxies of productivity and to more fully constrain the effects of the PETM on marine phytoplankton, we have carried out a detailed study of calcareous nannofossil assemblages across the PETM at Site 690 (Maud Rise, Weddell Sea; Figure 1). This site contains one of the highest‐quality deep‐sea records of the PETM event. Upper Paleocene sediments are composed of ooze representing nannofossil zone NP9, planktic foraminiferal zones AP4 and AP5, and part of magnetic polarity zone C24r [Aubry et al., 1996]. White to pale brown lithologic cycles caused by oscillations of CaCO3 and clay content appear to correspond to precessional orbital rhythms [Röhl et al., 2000]. These cycles can be used to construct a timescale for Site 690 [Cramer, 2001; D. Thomas, manuscript in preparation, 2002], allowing us to monitor paleoceanographic changes at millennial resolution.
  6. 2003: Kent, Dennis V., et al. “A case for a comet impact trigger for the Paleocene/Eocene thermal maximum and carbon isotope excursion.” Earth and Planetary Science Letters 211.1-2 (2003): 13-26. We hypothesize that the rapid onset of the carbon isotope excursion (CIE) at the Paleocene/Eocene boundary (∼55 Ma) may have resulted from the accretion of a significant amount of 12C-enriched carbon from the impact of a ∼10 km comet, an event that would also trigger greenhouse warming leading to the Paleocene/Eocene thermal maximum and, possibly, thermal dissociation of seafloor methane hydrate. Indirect evidence of an impact is the unusual abundance of magnetic nanoparticles in kaolinite-rich shelf sediments that closely coincide with the onset and nadir of the CIE at three drill sites on the Atlantic Coastal Plain. After considering various alternative mechanisms that could have produced the magnetic nanoparticle assemblage and by analogy with the reported detection of iron-rich nanophase material at the Cretaceous/Tertiary boundary, we suggest that the CIE occurrence was derived from an impact plume condensate. The sudden increase in kaolinite is thus thought to represent the redeposition on the marine shelf of a rapidly weathered impact ejecta dust blanket. Published reports of a small but significant iridium anomaly at or close to the Paleocene/Eocene boundary provide supportive evidence for an impact.
  7. 2003: Zachos, James C., et al. “A transient rise in tropical sea surface temperature during the Paleocene-Eocene thermal maximum.” Science 302.5650 (2003): 1551-1554. The Paleocene-Eocene Thermal Maximum (PETM) has been attributed to a rapid rise in greenhouse gas levels. If so, warming should have occurred at all latitudes, although amplified toward the poles. Existing records reveal an increase in high-latitude sea surface temperatures (SSTs) (8° to 10°C) and in bottom water temperatures (4° to 5°C). To date, however, the character of the tropical SST response during this event remains unconstrained. Here we address this deficiency by using paired oxygen isotope and minor element (magnesium/calcium) ratios of planktonic foraminifera from a tropical Pacific core to estimate changes in SST. Using mixed-layer foraminifera, we found that the combined proxies imply a 4° to 5°C rise in Pacific SST during the PETM. These results would necessitate a rise in atmospheric pCO2 to levels three to four times as high as those estimated for the late Paleocene.
  8. *2004: Svensen, Henrik, et al. “Release of methane from a volcanic basin as a mechanism for initial Eocene global warming.” Nature 429.6991 (2004): 542. A 200,000-yr interval of extreme global warming marked the start of the Eocene epoch about 55 million years ago. Negative carbon- and oxygen-isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid (10,000 yr) input of isotopically depleted carbon1,2. It has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source3,4 and has caused the global climate change. Large-scale hydrate melting, however, requires a hitherto unknown triggering mechanism. Here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the Vøring and Møre basins in the Norwegian Sea. We propose that intrusion of voluminous mantle-derived melts in carbon-rich sedimentary strata in the northeast Atlantic may have caused an explosive release of methane—transported to the ocean or atmosphere through the vent complexes—close to the Palaeocene/Eocene boundary. Similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the Siberian Traps (250 million years ago) and the Karoo Igneous Province (183 million years ago).
  9. 2004: Bowen, Gabriel J., et al. “A humid climate state during the Palaeocene/Eocene thermal maximum.” Nature 432.7016 (2004): 495. An abrupt climate warming of 5 to 10 °C during the Palaeocene/Eocene boundary thermal maximum (PETM) 55 Myr ago is linked to the catastrophic release of 1,050–2,100 Gt of carbon from sea-floor methane hydrate reservoirs1. Although atmospheric methane, and the carbon dioxide derived from its oxidation, probably contributed to PETM warming, neither the magnitude nor the timing of the climate change is consistent with direct greenhouse forcing by the carbon derived from methane hydrate. Here we demonstrate significant differences between marine2,3 and terrestrial4,5,6 carbon isotope records spanning the PETM. We use models of key carbon cycle processes7,8,9 to identify the cause of these differences. Our results provide evidence for a previously unrecognized discrete shift in the state of the climate system during the PETM, characterized by large increases in mid-latitude tropospheric humidity and enhanced cycling of carbon through terrestrial ecosystems. A more humid atmosphere helps to explain PETM temperatures, but the ultimate mechanisms underlying the shift remain unknown.
  10. 2005: Tripati, Aradhna, and Henry Elderfield. “Deep-sea temperature and circulation changes at the Paleocene-Eocene thermal maximum.” Science 308.5730 (2005): 1894-1898. A rapid increase in greenhouse gas levels is thought to have fueled global warming at the Paleocene-Eocene Thermal Maximum (PETM). Foraminiferal magnesium/calcium ratios indicate that bottom waters warmed by 4° to 5°C, similar to tropical and subtropical surface ocean waters, implying no amplification of warming in high-latitude regions of deep-water formation under ice-free conditions. Intermediate waters warmed before the carbon isotope excursion, in association with down-welling in the North Pacific and reduced Southern Ocean convection, supporting changing circulation as the trigger for methane hydrate release. A switch to deep convection in the North Pacific at the PETM onset could have amplified and sustained warming.
  11. 2005: Zachos, James C., et al. “Rapid acidification of the ocean during the Paleocene-Eocene thermal maximum.” Science308.5728 (2005): 1611-1615. The Paleocene-Eocene thermal maximum (PETM) has been attributed to the rapid release of ∼2000 × 109 metric tons of carbon in the form of methane. In theory, oxidation and ocean absorption of this carbon should have lowered deep-sea pH, thereby triggering a rapid (<10,000-year) shoaling of the calcite compensation depth (CCD), followed by gradual recovery. Here we present geochemical data from five new South Atlantic deep-sea sections that constrain the timing and extent of massive sea-floor carbonate dissolution coincident with the PETM. The sections, from between 2.7 and 4.8 kilometers water depth, are marked by a prominent clay layer, the character of which indicates that the CCD shoaled rapidly (<10,000 years) by more than 2 kilometers and recovered gradually (>100,000 years). These findings indicate that a large mass of carbon (»2000 × 109 metric tons of carbon) dissolved in the ocean at the Paleocene-Eocene boundary and that permanent sequestration of this carbon occurred through silicate weathering feedback.
  12. 2006: Higgins, John A., and Daniel P. Schrag. “Beyond methane: towards a theory for the Paleocene–Eocene thermal maximum.” Earth and Planetary Science Letters 245.3-4 (2006): 523-537. Extreme global warmth and an abrupt negative carbon isotope excursion during the Paleocene–Eocene Thermal Maximum (PETM) have been attributed to a massive release of methane hydrate from sediments on the continental slope [1]. However, the magnitude of the warming (5 to 6 °C [2],[3]) and rise in the depth of the CCD (> 2 km; [4]) indicate that the size of the carbon addition was larger than can be accounted for by the methane hydrate hypothesis. Additional carbon sources associated with methane hydrate release (e.g. pore-water venting and turbidite oxidation) are also insufficient. We find that the oxidation of at least 5000 Gt C of organic carbon is the most likely explanation for the observed geochemical and climatic changes during the PETM, for which there are several potential mechanisms. Production of thermogenic CH4 and CO2during contact metamorphism associated with the intrusion of a large igneous province into organic rich sediments [5] is capable of supplying large amounts of carbon, but is inconsistent with the lack of extensive carbon loss in metamorphosed sediments, as well as the abrupt onset and termination of carbon release during the PETM. A global conflagration of Paleocene peatlands [6] highlights a large terrestrial carbon source, but massive carbon release by fire seems unlikely as it would require that all peatlands burn at once and then for only 10 to 30 ky. In addition, this hypothesis requires an order of magnitude increase in the amount of carbon stored in peat. The isolation of a large epicontinental seaway by tectonic uplift associated with volcanism or continental collision, followed by desiccation and bacterial respiration of the aerated organic matter is another potential mechanism for the rapid release of large amounts of CO2. In addition to the oxidation of the underlying marine sediments, the desiccation of a major epicontinental seaway would remove a large source of moisture for the continental interior, resulting in the desiccation and bacterial oxidation of adjacent terrestrial wetlands.
  13. 2006: Zachos, James C., et al. “Extreme warming of mid-latitude coastal ocean during the Paleocene-Eocene Thermal Maximum: Inferences from TEX86 and isotope data.” Geology34.9 (2006): 737-740. Changes in sea surface temperature (SST) during the Paleocene-Eocene Thermal Maximum (PETM) have been estimated primarily from oxygen isotope and Mg/Ca records generated from deep-sea cores. Here we present a record of sea surface temperature change across the Paleocene-Eocene boundary for a nearshore, shallow marine section located on the eastern margin of North America. The SST record, as inferred from TEX86 data, indicates a minimum of 8 °C of warming, with peak temperatures in excess of 33 °C. Similar SSTs are estimated from planktonic foraminifer oxygen isotope records, although the excursion is slightly larger. The slight offset in the oxygen isotope record may reflect on seasonally higher runoff and lower salinity.
  14. 2006: Sluijs, Appy, et al. “Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum.” Nature441.7093 (2006): 610. The Palaeocene/Eocene thermal maximum, ∼55 million years ago, was a brief period of widespread, extreme climatic warming1,2,3, that was associated with massive atmospheric greenhouse gas input4. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition5. We show that sea surface temperatures near the North Pole increased from ∼18 °C to over 23 °C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean’s bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations6, but the absolute polar temperatures that we derive before, during and after the event are more than 10 °C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms—perhaps polar stratospheric clouds7 or hurricane-induced ocean mixing8—to amplify early Palaeogene polar temperatures.
  15. 2006: Gingerich, Philip D. “Environment and evolution through the Paleocene–Eocene thermal maximum.” Trends in ecology & evolution 21.5 (2006): 246-253. The modern orders of mammals, Artiodactyla, Perissodactyla and Primates (APP taxa), first appear in the fossil record at the Paleocene–Eocene boundary, c. 55 million years ago. Their appearance on all three northern continents has been linked to diversification and dispersal in response to rapid environmental change at the beginning of a worldwide 100 000–200 000-year Paleocene–Eocene thermal maximum (PETM) and carbon isotope excursion. As I discuss here, global environmental events such as the PETM have had profound effects on evolution in the geological past and must be considered when modeling the history of life. The PETM is also relevant when considering the causes and consequences of global greenhouse warming.
  16. 2007: Röhl, Ursula, et al. “On the duration of the PaleoceneEocene thermal maximum (PETM).” Geochemistry, Geophysics, Geosystems 8.12 (2007). The Paleocene‐Eocene thermal maximum (PETM) is one of the best known examples of a transient climate perturbation, associated with a brief, but intense, interval of global warming and a massive perturbation of the global carbon cycle from injection of isotopically light carbon into the ocean‐atmosphere system. One key to quantifying the mass of carbon released, identifying the source(s), and understanding the ultimate fate of this carbon is to develop high‐resolution age models. Two independent strategies have been employed, cycle stratigraphy and analysis of extraterrestrial helium (HeET), both of which were first tested on Ocean Drilling Program (ODP) Site 690. These two methods are in agreement for the onset of the PETM and initial recovery, or the clay layer (“main body”), but seem to differ in the final recovery phase of the event above the clay layer, where the carbonate contents rise and carbon isotope values return toward background values. Here we present a state‐of‐the‐art age model for the PETM derived from a new orbital chronology developed with cycle stratigraphic records from sites drilled during ODP Leg 208 (Walvis Ridge, Southeastern Atlantic) integrated with published records from Site 690 (Weddell Sea, Southern Ocean, ODP Leg 113). During Leg 208, five Paleocene‐Eocene (P‐E) boundary sections (Sites 1262 to 1267) were recovered in multiple holes over a depth transect of more than 2200 m at the Walvis Ridge, yielding the first stratigraphically complete P‐E deep‐sea sequence with moderate to relatively high sedimentation rates (1 to 3 cm/ka, where “a” is years). A detailed chronology was developed with nondestructive X‐ray fluorescence (XRF) core scanning records on the scale of precession cycles, with a total duration of the PETM now estimated to be ∼170 ka. The revised cycle stratigraphic record confirms original estimates for the duration of the onset and initial recovery but suggests a new duration for the final recovery that is intermediate to the previous estimates by cycle stratigraphy and HeET. The Paleocene Eocene thermal maximum (PETM) is one of the most abrupt and transient climatic events documented in the geologic record [e.g., Zachos et al., 2001, 2005]. This event was associated with pronounced warming of the oceans and atmosphere, changes in ocean chemistry, and reorganization of the global carbon cycle [Kennett and Stott, 1991; Koch et al., 1992; Thomas et al., 2002; Zachos et al., 2003, 2005; Tripati and Elderfield, 2005; Sluijs et al., 2006]. Warming of deep waters and subsequent oxygen deficiency may have been responsible for extinction of 30–50% of deep‐sea benthic foraminiferal species [Thomas and Shackleton, 1996] and planktonic biota were affected by changes in surface water habitats [e.g., Kelly et al., 1996; Bralower et al., 2002; Kelly, 2002; Raffi et al., 2005; Gibbs et al., 2006a, 2006b]; global warming also may have led to a pulse of speciation or migration among mammalian groups [e.g., Koch et al., 1992, Bowen et al., 2001; Gingerich, 2003]. The PETM corresponds to a significant (∼3.5–4.5‰) negative carbon isotope excursion (CIE) recorded in marine and terrestrial sections [e.g., Kennett and Stott, 1991; Koch et al., 1992; Bralower et al., 1997; Zachos et al., 2004, 2005; Schouten et al., 2007]. The source and triggering mechanism of this event are still the focus of much debate [e.g., Lourens et al., 2005; Sluijs et al., 2007; Storey et al., 2007]. An orbital trigger for the PETM and similar (but less severe) events has been suggested [Lourens et al., 2005], but the specific orbital parameter association is still not completely resolved [Westerhold et al., 2007]. Other mechanisms that might explain the abruptness of the CIE include the input of methane into the ocean and atmosphere from the dissociation of methane hydrates in continental margin sediments or from the cracking of coal during rifting of the northern North Atlantic Ocean [Dickens et al., 1995, 1997; Svensen et al., 2004]. Identifying potential triggering mechanisms for the PETM, as well as understanding the relationship between forcing and consequences requires a very precise and high‐resolution chronology. For example, quantifying the climate sensitivity requires robust estimates of the mass of carbon released, and hence the rate of the CIE. Until recently, however, estimates of the absolute age of the onset and the duration of the event were poorly constrained, varying between 54.88 and 55.50 Ma, and 100 and 250 ka, respectively [e.g., Kennett and Stott, 1991; Koch et al., 1992; Aubry et al., 1996; Röhl and Abrams, 2000; Röhl et al., 2000; Farley and Eltgroth, 2003; Giusberti et al., 2007]. By using an astronomically calibrated but floating timescale, the age of the onset (54.93 to 54.98 Ma) and the duration (150 to 220 ka) of the CIE were initially determined at Ocean Drilling Program (ODP) Site 1051 [Norris and Röhl, 1999] then refined using combined records from Sites 690 and 1051 [Röhl et al., 2000]. However, because the onset of the PETM in pelagic sequences is marked by a pronounced dissolution layer or condensed interval and the recovery by a lithologically uniform carbonate‐rich interval, an alternative constant flux age model was developed [Farley and Eltgroth, 2003]. This model is based on the concentrations of extraterrestrial He (3HeET) and the assumption that the flux of this isotope to the Earth remained constant during the PETM. Both age models are in agreement for the duration of the main body of the PETM (70–80 ka for the “core”, the onset, peak, and initial recovery phase (rapid rise in δ13C, but low carbonate; here termed phase 1)), but diverge for the final recovery phase of the CIE (slow rise in δ13C, high carbonate; here termed phase II), with orbital age models producing 140 ka for this interval and He age models 30 ka. Identification of cycles in the Ca (or Fe) records in the recovery interval of the Site 690 section is complicated due to the high and uniform carbonate content of the sediments. A new era in Cenozoic paleoceanography was launched with the recovery of Paleogene sediments in multisite depth transects during Ocean Drilling Program Legs 198 (Shatsky Rise, Pacific Ocean [Bralower et al., 2002; Westerhold and Röhl, 2006]) and 208 (Walvis Ridge, Southeast Atlantic Ocean [Zachos et al., 2004]). These expeditions yielded the first high‐quality, stratigraphically complete sedimentary sequences of the early Paleogene, recovered in offset, multiple‐hole sites. The lithologic and geochemical records generated from these cores exhibit the highly cyclic nature of early Paleogene climate, while also demonstrating that the early Eocene Greenhouse World was punctuated by multiple transient global warming events, or hyperthermals [Thomas et al., 2000; Zachos et al., 2004]. The occurrence of multiple hyperthermals within the late Paleocene–early Eocene suggests a repeated trigger as their cause. Recently, X‐ray fluorescence (XRF) core scanning records from ODP Leg 208 sites and from ODP Site 1051 spanning a ∼4.3 million year interval of the late Paleocene to early Eocene were used to establish a longer time series and to develop a robust and improved chronology of magnetochrons [Westerhold et al., 2007] which is consistent with records from the Bighorn Basin [Wing et al., 2000; Clyde et al., 2007]. One of the obstacles to developing age models for PETM sections is providing a exact definition of the termination of the CIE on a global scale, e.g., at Site 690, the location of the termination is somewhat subjective because of the asymptotic shape of the CIE. In addition, the low signal‐to‐noise ratio of the XRF Ca concentrations in this high‐carbonate interval has made cycle extraction difficult and somewhat subjective. Here we develop a revised chronology for the PETM using high‐resolution geochemical data from the ODP Leg 208 depth transect in combination with new Barium (Ba) XRF intensity data of the expanded section at ODP Site 690 from the Weddell Sea, Southern Ocean (Figure 1). The Barium (Ba) records, in combination with Fe, Ca, and carbon isotope data from the Leg 208 sites and Site 690, show similar patterns that allow for refinement of correlation and age calibrations. These new data provide much better constraints on the durations of each phase of the CIE, particularly the recovery phases (I and II). These records will also allow for a more accurate recalibration of the He isotope chronology from Site 690 [Farley and Eltgroth, 2003]. Moreover, we propose that the definition of the termination of the CIE be based on a combination of cyclostratigraphic proxies derived from XRF scanner and other methods rather than carbon isotopes which gradually become uniform, thus making it difficult to define a globally recognizable termination point for the recovery2009: Zeebe, Richard E., James C. Zachos, and Gerald R. Dickens. “Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming.” Nature Geoscience 2.8 (2009): 576.
  17. 2008: Panchuk, K., A. Ridgwell, and L. R. Kump. “Sedimentary response to Paleocene-Eocene Thermal Maximum carbon release: A model-data comparison.” Geology 36.4 (2008): 315-318. Possible sources of carbon that may have caused global warming at the Paleocene-Eocene boundary are constrained using an intermediate complexity Earth-system model configured with early Eocene paleogeography. We find that 6800 Pg C (δ13C of –22‰) is the smallest pulse modeled here to reasonably reproduce observations of the extent of seafloor CaCO3 dissolution. This pulse could not have been solely the result of methane hydrate destabilization, suggesting that additional sources of CO2 such as volcanic CO2, the oxidation of sedimentary organic carbon, or thermogenic methane must also have contributed. Observed contrasts in dissolution intensity between Atlantic and Pacific sites are reproduced in the model by reducing bioturbation in the Atlantic during the event, simulating a potential consequence of the spread of low-oxygen bottom waters.
  18. 2009: Zeebe, Richard E., James C. Zachos, and Gerald R. Dickens. “Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming.” Nature Geoscience 2.8 (2009): 576. The Palaeocene–Eocene Thermal Maximum (about 55 Myr ago) represents a possible analogue for the future and thus may provide insight into climate system sensitivity and feedbacks1,2. The key feature of this event is the release of a large mass of 13C-depleted carbon into the carbon reservoirs at the Earth’s surface, although the source remains an open issue3,4. Concurrently, global surface temperatures rose by 5–9 C within a few thousand years5,6,7,8,9. Here we use published palaeorecords of deep-sea carbonate dissolution10,11,12,13,14and stable carbon isotope composition10,15,16,17 along with a carbon cycle model to constrain the initial carbon pulse to a magnitude of 3,000 Pg C or less, with an isotopic composition lighter than −50‰. As a result, atmospheric carbon dioxide concentrations increased during the main event by less than about 70% compared with pre-event levels. At accepted values for the climate sensitivity to a doubling of the atmospheric CO2 concentration1, this rise in CO2 can explain only between 1 and 3.5 C of the warming inferred from proxy records. We conclude that in addition to direct CO2 forcing, other processes and/or feedbacks that are hitherto unknown must have caused a substantial portion of the warming during the Palaeocene–Eocene Thermal Maximum. Once these processes have been identified, their potential effect on future climate change needs to be taken into account.
  19. 2011: Dickens, Gerald R. “Down the rabbit hole: Toward appropriate discussion of methane release from gas hydrate systems during the Paleocene-Eocene thermal maximum and other past hyperthermal events.” Climate of the Past 7.3 (2011): 831-846. Enormous amounts of 13C-depleted carbon rapidly entered the exogenic carbon cycle during the onset of the Paleocene-Eocene thermal maximum (PETM), as attested to by a prominent negative carbon isotope (δ13C) excursion and deep-sea carbonate dissolution. A widely cited explanation for this carbon input has been thermal dissociation of gas hydrate on continental slopes, followed by release of CH4 from the seafloor and its subsequent oxidation to CO2 in the ocean or atmosphere. Increasingly, papers have argued against this mechanism, but without fully considering existing ideas and available data. Moreover, other explanations have been presented as plausible alternatives, even though they conflict with geological observations, they raise major conceptual problems, or both. Methane release from gas hydrates remains a congruous explanation for the δ13C excursion across the PETM, although it requires an unconventional framework for global carbon and sulfur cycling, and it lacks proof. These issues are addressed here in the hope that they will prompt appropriate discussions regarding the extraordinary carbon injection at the start of the PETM and during other events in Earth’s history.
  20. 2011: Cui, Ying, et al. “Slow release of fossil carbon during the Palaeocene–Eocene Thermal Maximum.” Nature Geoscience4.7 (2011): 481. The transient global warming event known as the Palaeocene–Eocene Thermal Maximum occurred about 55.9 Myr ago. The warming was accompanied by a rapid shift in the isotopic signature of sedimentary carbonates, suggesting that the event was triggered by a massive release of carbon to the ocean–atmosphere system. However, the source, rate of emission and total amount of carbon involved remain poorly constrained. Here we use an expanded marine sedimentary section from Spitsbergen to reconstruct the carbon isotope excursion as recorded in marine organic matter. We find that the total magnitude of the carbon isotope excursion in the ocean–atmosphere system was about 4‰. We then force an Earth system model of intermediate complexity to conform to our isotope record, allowing us to generate a continuous estimate of the rate of carbon emissions to the atmosphere. Our simulations show that the peak rate of carbon addition was probably in the range of 0.3–1.7 Pg C yr−1, much slower than the present rate of carbon emissions.
  21. 2011: McInerney, Francesca A., and Scott L. Wing. “The Paleocene-Eocene Thermal Maximum: A perturbation of carbon cycle, climate, and biosphere with implications for the future.” Annual Review of Earth and Planetary Sciences 39 (2011): 489-516. During the Paleocene-Eocene Thermal Maximum (PETM), ∼56 Mya, thousands of petagrams of carbon were released into the ocean-atmosphere system with attendant changes in the carbon cycle, climate, ocean chemistry, and marine and continental ecosystems. The period of carbon release is thought to have lasted <20 ka, the duration of the whole event was ∼200 ka, and the global temperature increase was 5–8°C. Terrestrial and marine organisms experienced large shifts in geographic ranges, rapid evolution, and changes in trophic ecology, but few groups suffered major extinctions with the exception of benthic foraminifera. The PETM provides valuable insights into the carbon cycle, climate system, and biotic responses to environmental change that are relevant to long-term future global changes.
  22. 2016: Gehler, Alexander, Philip D. Gingerich, and Andreas Pack. “Temperature and atmospheric CO2 concentration estimates through the PETM using triple oxygen isotope analysis of mammalian bioapatite.” Proceedings of the National Academy of Sciences 113.28 (2016): 7739-7744. The Paleocene–Eocene Thermal Maximum (PETM) is a remarkable climatic and environmental event that occurred 56 Ma ago and has importance for understanding possible future climate change. The Paleocene–Eocene transition is marked by a rapid temperature rise contemporaneous with a large negative carbon isotope excursion (CIE). Both the temperature and the isotopic excursion are well-documented by terrestrial and marine proxies. The CIE was the result of a massive release of carbon into the atmosphere. However, the carbon source and quantities of CO2 and CH4 greenhouse gases that contributed to global warming are poorly constrained and highly debated. Here we combine an established oxygen isotope paleothermometer with a newly developed triple oxygen isotope paleo-CO2 barometer. We attempt to quantify the source of greenhouse gases released during the Paleocene–Eocene transition by analyzing bioapatite of terrestrial mammals. Our results are consistent with previous estimates of PETM temperature change and suggest that not only CO2 but also massive release of seabed methane was the driver for CIE and PETM.

 

 

FIGURE 1: HADCRUT4 GLOBAL TEMPERATURE ANOMALIES 1850-20171CWARMING1CWARMINGGIF

 

FIGURE 2: GISTEMP GLOBAL TEMPERATURE ANOMALIES 1880-2017GISSTABLEGISSGIF

 

FIGURE 3: BERKELEY1 GLOBAL TEMPERATURE ANOMALIES 1850-2017TABLEBERKELEY1GIF

 

FIGURE 4: BERKELEY2 GLOBAL TEMPERATURE ANOMALIES 1850-2017TABLEBERKELEY2GIF

 

 

FIGURE 5: RCP8.5 GLOBAL TEMPERATURES 1861-2017TABLERCP85GIF

 

FIGURE 6: CORRELATION ANALYSIS OF THE TOTAL WARMING CURVESCORRTABLECORRCHART

 

FIGURE 7: THE AVERAGE WARMING AMOUNT ACROSS DATASETSAVGWARMT1AVGWARMT2AVGWARMCHART

 

 

FIGURE 8: COMPARISON OF THE FIVE TEMPERATURE SERIESECPGIF

 

 

 

FIGURE 9: HUMAN CAUSE FINGERPRINT FROM CLIMATE MODELS

gavin

texas-sharpshooter

 

[LIST OF POSTS AT THIS SITE]

 

LIST OF FIGURES

  1. FIGURE 1: HADCRUT4 GLOBAL TEMPERATURE ANOMALIES 1850-2017
  2. FIGURE 2: GISTEMP GLOBAL TEMPERATURE ANOMALIES 1880-2017
  3. FIGURE 3: BERKELEY1 GLOBAL TEMPERATURE ANOMALIES 1850-2017
  4. FIGURE 4: BERKELEY2 GLOBAL TEMPERATURE ANOMALIES 1850-2017
  5. FIGURE 5: RCP8.5 GLOBAL TEMPERATURES 1861-2017
  6. FIGURE 6: CORRELATION ANALYSIS OF THE TOTAL WARMING CURVES
  7. FIGURE 7: THE AVERAGE WARMING AMOUNT ACROSS DATASETS
  8. FIGURE 8: COMPARISON OF THE FIVE TEMPERATURE SERIES
  9. FIGURE 9: HUMAN CAUSE FINGERPRINT FROM CLIMATE MODELS

 

 

  1. This work is a critical evaluation of the claim in the IPCC SR15 that by the year 2017 human activity in the form of fossil fuel emissions had caused a warming of 1ºC since pre-Industrial times. Five different global temperature series including four reconstructions and the RCP8.5 theoretical series are used to frame the context of this claim and to test its validity.
  2. The RCP8.5 is a temperature series predicted by climate models with CMIP5 forcings for the “business as usual” emission scenario (no climate action taken).  The four temperature anomaly reconstructions are the HadCRUT4 anomalies 1850-2017 from the Hadley Centre of the Climate Research Unit of the UK Met Office, the GISTEMP anomalies 1880-2017 from NASA-GISS, and the B.E.S.T reconstruction from Berkeley Earth 1850-2017. There are two versions of the Berkeley Earth reconstruction depending on how sea ice temperatures are estimated. Both are used and labeled as Berkeley1 and Berkeley2.
  3. The temperature datasets are studied one calendar month at a time separately as it has been shown that the warming trend behaviors of the months differ significantly and that their combination into an annual temperature risks losing a great deal of trend behavior information [RELATED POST] . For each of five  temperature datasets and for each of twelve calendar months we compute the total amount of warming from all possible start years separated by ten-year increments. The amount of warming is computed as the linear OLS regression trend in ºC/year for each time span, times the length of the time span in years. The analysis consists of a study of these warming amounts in the context of the claim by the IPCC that human emissions of carbon dioxide in the industrial economy generated a warming “since pre-industrial times” of 1ºC.
  4. The HadCRUT4, GISTEMP, Berkeley1, Berkeley2, and RCP8.5 data are presented in Figure 1, Figure 2, Figure 3, Figure 4, and Figure 5 respectively. Each presentation consists of a tabulation of the computed warming amounts in degrees Celsius and their graphical display. The end of the time span for each starting year from 1850 to 1970 is fixed at 2017. Below the tabulated total warming values for each calendar month, is a chart that shows the plot of these values for each calendar month (in red) compared with the average of all twelve calendar months (in blue).
  5. It is noted that as the number of years in the warming period decreases linearly from 168 years for start year 1850 to 48 years for start year 1970, the amount of warming does not show a corresponding linear decrease but rather a complex non-linear pattern of both rising and falling amounts of warming as the time span decreases linearly. This behavior is driven by extreme short term changes in the rate of warming that include both warming and cooling periods with a greater influence of cooling in the earlier part of the time series as seen in the 30-year trend profile shown in Figure 7. As a result the greatest amount of arming is seen for start years around the year 1900, thereafter falling until 1940 and then rising again until the end of the time series likely driven by higher rates of warming. This is an example of the kind of complexity in temperature trend information that becomes lost when seasonal temperatures are combined into annual means as shown in the chart below. Here, the red curve shows the amount of warming computed for each calendar month separately and then averaged. The blue curve shows the result of the more conventional procedure of averaging monthly temperatures into annual means prior to trend analysis. The trend behavior of the calendar months are very different and this information becomes lost when monthly mean temperatures are combined into annual mean temperatures as shown in a related post.  [LINK]  AVERAGING-ANOMALY
  6. Figure 6 is a correlation analysis of the total warming amounts presented in Figure 1 to Figure 5. It shows fairly good agreement among the observational data series  but little or no correlation between the observational data and the theoretical temperature series created by climate models with CMIP5 forcings.  Underneath the tabulation of these correlations are two charts. The one on the left shows correlation between warming amounts in the observational series with the RCP8.5 climate model generated theoretical series. The black horizontal line marks the zero correlation location. Most of the correlations are negative and the few positive correlations found (with the GISS temperature reconstructions) are not statistically significant. The chart on the right shows correlations among the observational data. Mostly strong correlations are seen except where the GISS data are involved. All low correlations seen in this chart involve GISS and all correlations that do not involve GISS show strong statistically significant correlations. The correlation behavior of GISS is anomalous in ways that imply that its construction may have been influenced by climate models.
  7. A direct comparison of the five temperature time series is shown graphically in Figure 8. The four observational data series are shown in thin lines of various colors while the RCP8.5 climate model series appears as a thick black line. The left frame compares temperatures directly. It appear to show good agreement among all five temperatures with the RCP8.5 theoretical series tracking the middle of the distribution. The right frame of the chart compares the the “trend profiles” of the five temperature series computed as trends in a moving 30-year window as ºC/century equivalent (the period of 30-years is recognized as the appropriate span for study of short term trends. See references below). Here we find that in terms of short term trends, the homogeneity seen among the source temperatures is not found. Significant differences between the RCP8.5 and the observational data and also among the observational data are seen. The charts cycle through the twelve calendar months in a GIF animation demonstrating differences in the comparison among calendar months. This comparison implies that short term trends cannot be generalized across the full span of the data or across calendar months; and that the homogeneity among the source temperature data seen in the left frame is illusory.
  8. The “total warming” data in Figure 1 to Figure 5 contain 61 average values (averaged across all twelve calendar months). Of these warming of 1ºC or greater is found in 16 cases for an overall rate of 26%. The highest rate of warming found is 1.11ºC in the RCP8.5 theoretical series and the highest value in the observational data is 1.08ºC in the Berkeley1 series.
  9. A more extensive analysis of the overall assessment of the amount of warming across datasets is presented in Figure 7 where the warming amounts seen in the five datasets are summarized as averages across datasets. There are two tables in Figure 7, one atop the other. The top table contains averages among the four observational data series while the averages in the bottom table also include the RCP8.5 climate model series. The chart below the two tables show the average of the averages across calendar months for the four observational datasets (in blue) and the corresponding averages that include the theoretical RCP8.5 climate model series (in red). The horizontal purple line delineates the grand average as the average of averages as approximately 0.91ºC of warming across all calendar months, all time spans and locations, and all datasets. The dark horizontal line at the top of the cart marks location of the 1ºC warming mark claimed by the IPCC. We conclude from this analysis that although the claimed 1ºC warming (or greater) can be found in specific instances of the data, it is not representative since most of the data show lower warming rates. Thus the most generous assessment possible is that the IPCC’s claim to 1ºC warming since pre-industrial times is an exaggeration possibly motivated by the needs of advocacy for pushing climate action.
  10. However, a more serious issue is the the reference to pre-industrial times as the baseline from which the anthropogenic effect of fossil fuel emissions should be measured. In the AR5 and other publications, the IPCC states that “Human-induced warming reached approximately 1°C (±0.2°C likely range) above pre-industrial levels in 2017. Warming is expressed relative to the period 1850-1900, used as an approximation of pre-industrial temperatures in AR5″. Yet, in the matter of identifying human cause, the IPCC writes that “The current warming trend is of particular significance because most of it is extremely likely (greater than 95 percent probability) to be the result of human activity since the mid-20thcentury” (citations below). In other words, the whole of the 1°C warming from pre-industrial times cannot be shown to be human caused because only the warming since the “mid-20th-century” is human caused. That raises the question with regard to the amount of warming that can be shown to be human caused in this context.
  11. That only the warming since the mid-20th century contains a “fingerprint” of human cause is found elsewhere in climate science. Figure 9 contains a graphic from that “human drivers of climate” are detectable at some time after 1960 using a fingerprinting method climate models are run with and without the human forcings. A demonstration of this fingerprinting methodology by climate scientist Peter Cox of the University of Exeter is shown in the video that appears in the bottom panel of Figure 9. Here, the Hadcrut temperatures since 1850 are plotted in red and then overlaid with two sets of climate model runs one after the other in the video sequence. The first climate model run contains only natural factors and the output is plotted in green. It shows good agreement with the observational data until at some point after 1960 where the green curve and the red curve begin to diverge. A second climate model run is made but this time with human factors included and the output of this run is plotted in yellow and now with human factors included the model output and the data do not diverge proving that “from about 1970 onwards” the climate model and the data show excellent agreement. This analysis and its conclusions are consistent with the IPCC’s identification of the “mid-20th century” when a human hand is detectable in the climate.
  12. The analysis presented above implies that only the amount of warming since 1970 can be ascribed to human cause. The average of the warming amounts in the observational data found in Figure 7 for start-year=1970 is 0.847°C. This is the best unbiased estimate of the total amount of warming caused by human activity. The standard error is 0.02 which yields a 90% confidence interval of [0.814-0.880).
  13. We conclude that the IPCC claims to human caused warming of 1°C or greater “since pre-industrial times” is not an unbiased assessment and that it is inconsistent with the data.

 

 

[LIST OF POSTS AT THIS SITE]

 

 

HUMAN CAUSE IN GLOBAL WARMING: BIBLIOGRAPHY

  1. [2018: IPCC SR15 SPECIAL REPORT] Human-induced warming reached approximately 1°C (±0.2°C likely range) above pre-industrial levels in 2017, increasing at 0.2°C (±0.1°C) per decade (high confidence). Global warming is defined in this report as an increase in combined surface air and sea surface temperatures averaged over the globe and a 30-year period. Unless otherwise specified, warming is expressed relative to the period 1850-1900, used as an approximation of pre-industrial temperatures in AR5. For periods shorter than 30 years, warming refers to the estimated average temperature over the 30 years centered on that shorter period, accounting for the impact of any temperature fluctuations or trend within those 30 years. Accordingly, warming up to the decade 2006-2015 is assessed at 0.87°C (±0.12°C likely range). Since 2000, the estimated level of human-induced warming has been equal to the level of observed warming with a likely range of ±20% accounting for uncertainty due to contributions from solar and volcanic activity over the historical period (high confidence). {1.2.1} Warming greater than the global average has already been experienced in many regions and seasons, with average warming over land higher than over the ocean?? (high confidence). Most land regions are experiencing greater warming than the global average, while most ocean regions are warming at a slower rate. Depending on the temperature dataset considered, 20-40% of the global human population live in regions that, by the decade 2006-2015, had already experienced warming of more than 1.5°C above pre-industrial in at least one season ?? (medium confidence). {1.2.1 & 1.2.2}
  2. 2018: NASA, Global climate change, vital signs of the planet,  [SOURCE DOCUMENT]The Earth’s climate has changed throughout history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives. The current warming trend is of particular significance because most of it is extremely likely (greater than 95 percent probability) to be the result of human activity since the mid-20thcentury and proceeding at a rate that is unprecedented over decades to millennia. Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. This body of data, collected over many years, reveals the signals of a changing climate. The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century. Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many instruments flown by NASA. There is no question that increased levels of greenhouse gases must cause the Earth to warm in response. Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that the Earth’s climate responds to changes in greenhouse gas levels. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly ten times faster than the average rate of ice-age-recovery warming.
  3. 2015: Trenberth, Kevin E., John T. Fasullo, and Theodore G. Shepherd. “Attribution of climate extreme events.” Nature Climate Change 5.8 (2015): 725. There is a tremendous desire to attribute causes to weather and climate events that is often challenging from a physical standpoint. Headlines attributing an event solely to either human-induced climate change or natural variability can be misleading when both are invariably in play. The conventional attribution framework struggles with dynamically driven extremes because of the small signal-to-noise ratios and often uncertain nature of the forced changes. Here, we suggest that a different framing is desirable, which asks why such extremes unfold the way they do. Specifically, we suggest that it is more useful to regard the extreme circulation regime or weather event as being largely unaffected by climate change, and question whether known changes in the climate system’s thermodynamic state affected the impact of the particular event. Some examples briefly illustrated include ‘snowmaggedon’ in February 2010, superstorm Sandy in October 2012 and supertyphoon Haiyan in November 2013, and, in more detail, the Boulder floods of September 2013, all of which were influenced by high sea surface temperatures that had a discernible human component.
  4. [2014: IPCC AR5] Scientific evidence for warming of the climate system is unequivocal according to the IPCC. The current warming trend is of particular significance because most of it is extremely likely (greater than 95 percent probability) to be the result of human activity since the mid-20th century and proceeding at a rate that is unprecedented over decades to millennia. [Source: IPCC Fifth Assessment Report, Summary for Policymakers]
  5. 2011: Hegerl, Gabriele, and Francis Zwiers. “Use of models in detection and attribution of climate change.” Wiley interdisciplinary reviews: climate change 2.4 (2011): 570-591. Most detection and attribution studies use climate models to determine both the expected ‘fingerprint’ of climate change and the uncertainty in the estimated magnitude of this fingerprint in observations, given the climate variability. This review discusses the role of models in detection and attribution, the associated uncertainties, and the robustness of results. Studies that use observations only make substantial assumptions to separate the components of observed changes due to radiative forcing from those due to internal climate variability. Results from observation‐only studies are broadly consistent with those from fingerprint studies. Fingerprint studies evaluate the extent to which patterns of response to external forcing (fingerprints) from climate model simulations explain observed climate change in observations. Fingerprints are based on climate models of various complexities, from energy balance models to full earth system models. Statistical approaches range from simple comparisons of observations with model simulations to multi‐regression methods that estimate the contribution of several forcings to observed change using a noise‐reducing metric. Multi‐model methods can address model uncertainties to some extent and we discuss how remaining uncertainties can be overcome. The increasing focus on detecting and attributing regional climate change and impacts presents both opportunities and challenges. Challenges arise because internal variability is larger on smaller scales, and regionally important forcings, such as from aerosols or land‐use change, are often uncertain. Nevertheless, if regional climate change can be linked to external forcing, the results can be used to provide constraints on regional climate projections
  6. 2010: Stott, Peter A., et al. “Detection and attribution of climate change: a regional perspective.” Wiley Interdisciplinary Reviews: Climate Change 1.2 (2010): 192-211. The Intergovernmental Panel on Climate Change fourth assessment report, published in 2007 came to a more confident assessment of the causes of global temperature change than previous reports and concluded that ‘it is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent except Antarctica.’ Since then, warming over Antarctica has also been attributed to human influence, and further evidence has accumulated attributing a much wider range of climate changes to human activities. Such changes are broadly consistent with theoretical understanding, and climate model simulations, of how the planet is expected to respond. This paper reviews this evidence from a regional perspective to reflect a growing interest in understanding the regional effects of climate change, which can differ markedly across the globe. We set out the methodological basis for detection and attribution and discuss the spatial scales on which it is possible to make robust attribution statements. We review the evidence showing significant human‐induced changes in regional temperatures, and for the effects of external forcings on changes in the hydrological cycle, the cryosphere, circulation changes, oceanic changes, and changes in extremes. We then discuss future challenges for the science of attribution. To better assess the pace of change, and to understand more about the regional changes to which societies need to adapt, we will need to refine our understanding of the effects of external forcing and internal variability
  7. 2010: Gleick, Peter H., et al. “Climate change and the integrity of science.” Science 328.5979 (2010): 689-690. Climate change falls into the category of undeniable science along with the big bang theory, the theory of the earth, and the theory of evolution. There is compelling, comprehensive, and consistent objective evidence that humans are changing the climate in ways that threaten our societies and the ecosystems on which we depend. The planet is warming due to increased concentrations of heat-trapping gases in our atmosphere. A snowy winter in Washington does not alter this fact. Most of the increase in the concentration of these gases over the last century is due to human activities, especially the burning of fossil fuels and deforestation. Natural causes always play a role in changing Earth’s climate, but are now being overwhelmed by human-induced changes.(iv) Warming the planet will cause many other climatic patterns to change at speeds unprecedented in modern times, including increasing rates of sea-level rise and alterations in the hydrological cycle. Rising concentrations of carbon dioxide are making the oceans more acidic. The combination of these complex climate changes threatens coastal communities and cities, our food and water supplies, marine and freshwater ecosystems, forests, high mountain environments, and far more. Much more can be, and has been, said by the world’s scientific societies, national academies, and individuals, but these conclusions should be enough to indicate why scientists are concerned about what future generations will face from business-as-usual practices. We urge our policy-makers and the public to move forward immediately to address the causes of climate change, including the unrestrained burning of fossil fuels.
  8. 2009: Shindell, Drew T., et al. “Improved attribution of climate forcing to emissions.” Science 326.5953 (2009): 716-718. Evaluating multicomponent climate change mitigation strategies requires knowledge of the diverse direct and indirect effects of emissions. Methane, ozone, and aerosols are linked throughatmospheric chemistry so that emissions of a single pollutant can affect several species. We calculated atmospheric composition changes, historical radiative forcing, and forcing per unit of emission due to aerosol and tropospheric ozone precursor emissions in a coupled compositionclimate model. We found that gas-aerosol interactions substantially alter the relative importance of the various emissions. In particular, methane emissions have a larger impact than that used in current carbon-trading schemes or in the Kyoto Protocol. Thus, assessments of multigas mitigation policies, as well as any separate efforts to mitigate warming from short-lived pollutants, should include gas-aerosol interactions.
  9. 2003: Parmesan, Camille, and Gary Yohe. “A globally coherent fingerprint of climate change impacts across natural systems.” Nature 421.6918 (2003): 37. Causal attribution of recent biological trends to climate change is complicated because non-climatic influences dominate local, short-term biological changes. Any underlying signal from climate change is likely to be revealed by analyses that seek systematic trends across diverse species and geographic regions; however, debates within the Intergovernmental Panel on Climate Change (IPCC) reveal several definitions of a ‘systematic trend’. Here, we explore these differences, apply diverse analyses to more than 1,700 species, and show that recent biological trends match climate change predictions. Global meta-analyses documented significant range shifts averaging 6.1 km per decade towards the poles (or metres per decade upward), and significant mean advancement of spring events by 2.3 days per decade. We define a diagnostic fingerprint of temporal and spatial ‘sign-switching’ responses uniquely predicted by twentieth century climate trends. Among appropriate long-term/large-scale/multi-species data sets, this diagnostic fingerprint was found for 279 species. This suite of analyses generates ‘very high confidence’ (as laid down by the IPCC) that climate change is already affecting living systems.
  10. 1999: Allen, Myles R., and Simon FB Tett. “Checking for model consistency in optimal fingerprinting.” Climate Dynamics 15.6 (1999): 419-434. Current approaches to the detection and attribution of an anthropogenic influence on climate involve quantifying the level of agreement between model-predicted patterns of externally forced change and observed changes in the recent climate record. Analyses of uncertainty rely on simulated variability from a climate model. Any numerical representation of the climate is likely to display too little variance on small spatial scales, leading to a risk of spurious detection results. The risk is particularly severe if the detection strategy involves optimisation of signal-to-noise because unrealistic aspects of model variability may automatically be given high weight through the optimisation. The solution is to confine attention to aspects of the model and of the real climate system in which the model simulation of internal climate variability is adequate, or, more accurately, cannot be shown to be deficient. We propose a simple consistency check based on standard linear regression which can be applied to both the space-time and frequency domain approaches to optimal detection and demonstrate the application of this check to the problem of detection and attribution of anthropogenic signals in the radiosonde-based record of recent trends in atmospheric vertical temperature structure. The influence of anthropogenic greenhouse gases can be detected at a high confidence level in this diagnostic, while the combined influence of anthropogenic sulphates and stratospheric ozone depletion is less clearly evident. Assuming the time-scales of the model response are correct, and neglecting the possibility of non-linear feedbacks, the amplitude of the observed signal suggests a climate sensitivity range of 1.2–3.4 K, although the upper end of this range may be underestimated by up to 25% due to uncertainty in model-predicted response patterns
  11. 1998: North, Gerald R., and Mark J. Stevens. “Detecting climate signals in the surface temperature record.” Journal of climate11.4 (1998): 563-577. Optimal signal detection theory has been applied in a search through 100 yr of surface temperature data for the climate response to four specific radiative forcings. The data used comes from 36 boxes on the earth and was restricted to the frequency band 0.06–0.13 cycles yr−1 (16.67–7.69 yr) in the analysis. Estimates were sought of the strengths of the climate response to solar variability, volcanic aerosols, greenhouse gases, and anthropogenic aerosols. The optimal filter was constructed with a signal waveform computed from a two-dimensional energy balance model (EBM). The optimal weights were computed from a 10000-yr control run of a noise-forced EBM and from 1000-yr control runs from coupled ocean–atmosphere models at Geophysical Fluid Dynamics Laboratory (GFDL) and Max-Planck Institute; the authors also used a 1000-yr run using the GFDL mixed layer model. Results are reasonably consistent across these four separate model formulations. It was found that the component of the volcanic response perpendicular to the other signals was very robust and highly significant. Similarly, the component of the greenhouse gas response perpendicular to the others was very robust and highly significant. When the sum of all four climate forcings was used, the climate response was more than three standard deviations above the noise level. These findings are considered to be powerful evidence of anthropogenically induced climate change.
  12. 1997: Hegerl, Gabriele C., et al. “Multi-fingerprint detection and attribution analysis of greenhouse gas, greenhouse gas-plus-aerosol and solar forced climate change.” Climate Dynamics13.9 (1997): 613-634. A multi-fingerprint analysis is applied to the detection and attribution of anthropogenic climate change. While a single fingerprint is optimal for the detection of climate change, further tests of the statistical consistency of the detected climate change signal with model predictions for different candidate forcing mechanisms require the simultaneous application of several fingerprints. Model-predicted climate change signals are derived from three anthropogenic global warming simulations for the period 1880 to 2049 and two simulations forced by estimated changes in solar radiation from 1700 to 1992. In the first global warming simulation, the forcing is by greenhouse gas only, while in the remaining two simulations the direct influence of sulfate aerosols is also included. From the climate change signals of the greenhouse gas only and the average of the two greenhouse gas-plus-aerosol simulations, two optimized fingerprint patterns are derived by weighting the model-predicted climate change patterns towards low-noise directions. The optimized fingerprint patterns are then applied as a filter to the observed near-surface temperature trend patterns, yielding several detection variables. The space-time structure of natural climate variability needed to determine the optimal fingerprint pattern and the resultant signal-to-noise ratio of the detection variable is estimated from several multi-century control simulations with different CGCMs and from instrumental data over the last 136 y. Applying the combined greenhouse gas-plus-aerosol fingerprint in the same way as the greenhouse gas only fingerprint in a previous work, the recent 30-y trends (1966–1995) of annual mean near surface temperature are again found to represent a significant climate change at the 97.5% confidence level. However, using both the greenhouse gas and the combined forcing fingerprints in a two-pattern analysis, a substantially better agreement between observations and the climate model prediction is found for the combined forcing simulation. Anticipating that the influence of the aerosol forcing is strongest for longer term temperature trends in summer, application of the detection and attribution test to the latest observed 50-y trend pattern of summer temperature yielded statistical consistency with the greenhouse gas-plus-aerosol simulation with respect to both the pattern and amplitude of the signal. In contrast, the observations are inconsistent with the greenhouse-gas only climate change signal at a 95% confidence level for all estimates of climate variability. The observed trend 1943–1992 is furthermore inconsistent with a hypothesized solar radiation change alone at an estimated 90% confidence level. Thus, in contrast to the single pattern analysis, the two pattern analysis is able to discriminate between different forcing hypotheses in the observed climate change signal. The results are subject to uncertainties associated with the forcing history, which is poorly known for the solar and aerosol forcing, the possible omission of other important forcings, and inevitable model errors in the computation of the response to the forcing. Further uncertainties in the estimated significance levels arise from the use of model internal variability simulations and relatively short instrumental observations (after subtraction of an estimated greenhouse gas signal) to estimate the natural climate variability. The resulting confidence limits accordingly vary for different estimates using different variability data. Despite these uncertainties, however, we consider our results sufficiently robust to have some confidence in our finding that the observed climate change is consistent with a combined greenhouse gas and aerosol forcing, but inconsistent with greenhouse gas or solar forcing alone.
  13. 1996: Santer, Benjamin D., et al. “A search for human influences on the thermal structure of the atmosphere.” Nature 382.6586 (1996): 39. The observed spatial patterns of temperature change in the free atmosphere from [1963 to 1987] are similar to those predicted by state-of-the-art climate models incorporating various combinations of changes in carbon dioxide, anthropogenic sulphate aerosol and stratospheric ozone concentrations. The degree of pattern similarity between models and observations increases through this period. It is likely that this trend is partially due to human activities, although many uncertainties remain, particularly relating to estimates of natural variability.
  14. 1996: Hegerl, Gabriele C., et al. “Detecting greenhouse-gas-induced climate change with an optimal fingerprint method.” Journal of Climate 9.10 (1996): 2281-2306. A strategy using statistically optimal fingerprints to detect anthropogenic climate change is outlined and applied to near-surface temperature trends. The components of this strategy include observations, information about natural climate variability, and a “guess pattern” representing the expected time–space pattern of anthropogenic climate change. The expected anthropogenic climate change is identified through projection of the observations onto an appropriate optimal fingerprint, yielding a scalar-detection variable. The statistically optimal fingerprint is obtained by weighting the components of the guess pattern (truncated to some small-dimensional space) toward low-noise directions. The null hypothesis that the observed climate change is part of natural climate variability is then tested. This strategy is applied to detecting a greenhouse-gas-induced climate change in the spatial pattern of near-surface temperature trends defined for time intervals of 15–30 years. The expected pattern of climate change is derived from a transient simulation with a coupled ocean-atmosphere general circulation model. Global gridded near-surface temperature observations are used to represent the observed climate change. Information on the natural variability needed to establish the statistics of the detection variable is extracted from long control simulations of coupled ocean-atmosphere models and, additionally, from the observations themselves (from which an estimated greenhouse warming signal has been removed). While the model control simulations contain only variability caused by the internal dynamics of the atmosphere-ocean system, the observations additionally contain the response to various external forcings (e.g., volcanic eruptions, changes in solar radiation, and residual anthropogenic forcing). The resulting estimate of climate noise has large uncertainties but is qualitatively the best the authors can presently offer. The null hypothesis that the latest observed 20-yr and 30-yr trend of near-surface temperature (ending in 1994) is part of natural variability is rejected with a risk of less than 2.5% to 5% (the 5% level is derived from the variability of one model control simulation dominated by a questionable extreme event). In other words, the probability that the warming is due to our estimated natural variability is less than 2.5% to 5%. The increase in the signal-to-noise ratio by optimization of the fingerprint is of the order of 10%–30% in most cases. The predicted signals are dominated by the global mean component; the pattern correlation excluding the global mean is positive but not very high. Both the evolution of the detection variable and also the pattern correlation results are consistent with the model prediction for greenhouse-gas-induced climate change. However, in order to attribute the observed warming uniquely to anthropogenic greenhouse gas forcing, more information on the climate’s response to other forcing mechanisms (e.g., changes in solar radiation, volcanic, or anthropogenic sulfate aerosols) and their interaction is needed. It is concluded that a statistically significant externally induced warming has been observed, but our caveat that the estimate of the internal climate variability is still uncertain is emphasized.
  15. 1995: Santer, B. D., K. E. Taylor, and J. E. Penner. A search for human influences on the thermal structure of the atmosphere. No. UCRL-ID-121956. Lawrence Livermore National Lab., CA (United States), 1995. Several recent studies have compared observed changes in near-surface temperature with patterns of temperature change predicted by climate models in response to combined forcing by carbon dioxide and anthropogenic sulphate aerosols. These results suggest that a combined carbon dioxide + sulphate aerosol signal is easier to identify in the observations than a pattern of temperature change due to carbon dioxide alone. This work compares modelled and observed patterns of vertical temperature change in the atmosphere. Results show that the observed and model-predicted changes in the mid- to low troposphere are in better accord with greenhouse warming predictions when the likely effects of anthropogenic sulphate aerosols and stratospheric ozone reduction are incorporated in model calculations, and that the level of agreement increases with time. This improved correspondence is primarily due to hemispheric-scale temperature contrasts. If current model-based estimates of natural internal variability are realistic, it is likely that the level of time-increasing similarity between modelled and predicted patterns of vertical temperature change is partially due to human activities.
  16. 1995: North, Gerald R., et al. “Detection of forced climate signals. Part 1: Filter theory.” Journal of Climate 8.3 (1995): 401-408. This paper considers the construction of a linear smoothing filter for estimation of the forced part of a change in a climatological field such as the surface temperature. The filter is optimal in the sense that it suppresses the natural variability or “noise” relative to the forced part or “signal” to the maximum extent possible. The technique is adapted from standard signal processing theory. The present treatment takes into account the spatial as well as the temporal variability of both the signal and the noise. In this paper we take the signal’s waveform in space-time to be a given deterministic field in space and lime. Formulation of the expression for the minimum mean-squared error for the problem together with a no-bias constraint leads to an integral equation whose solution is the filter. The problem can be solved analytically in terms of the space-time empirical orthogonal function basis set and its eigenvalue spectrum for the natural fluctuations and the projection amplitudes of the signal onto these eigenfunctions. The optimal filter does not depend on the strength of the assumed waveform used in its construction. A lesser mean-square error in estimating the signal occurs when the space-time spectral characteristics of the signal and the noise are highly dissimilar; for example, if the signal is concentrated in a very narrow spectral band and the noise in a very broad band. A few pedagogical exercises suggest that these techniques might be useful in practical situations.
  17. 1993: Hasselmann, Klaus. “Optimal fingerprints for the detection of time-dependent climate change.” Journal of Climate 6.10 (1993): 1957-1971. An optimal linear filter (fingerprint) is derived for the detection of a given time-dependent, multivariate climate change signal in the presence of natural climate variability noise. Application of the fingerprint to the observed (or model simulated) climate data yields a climate change detection variable (detector) with maximal signal-to-noise ratio. The optimal fingerprint is given by the product of the assumed signal pattern and the inverse of the climate variability covariance matrix. The data can consist of any, not necessarily dynamically complete, climate dataset for which estimates of the natural variability covariance matrix exist. The single-pattern analysis readily generalizes to the multipattern case of a climate change signal lying in a prescribed (in practice relatively low dimensional) signal pattern space: the single-pattern result is simply applied separately to each individual base pattern spanning the signal pattern space. Multipattern detection methods can be applied either to test the statistical significance of individual components of a predicted multicomponent climate change response, using separate single-pattern detection tests, or to determine the statistical significance of the complete signal, using a multivariate test. Both detection modes make use of the same set of detectors. The difference in direction of the assumed signal pattern and computed optimal fingerprint vector allows alternative interpretations of the estimated signal associated with the set of optimal detectors. The present analysis yields an estimated signal lying in the assumed signal space, whereas an earlier analysis of the time-independent detection problem by Hasselmann yielded an estimated signal in the computed fingerprint space. The different interpretations can be explained by different choices of the metric used to relate the signal space to the fingerprint space (inverse covariance matrix versus standard Euclidean metric, respectively). Two simple natural variability models are considered: a space-time separability model, and an expansion in terms of P0Ps (principal oscillation patterns). For each model the application of the optimal fingerprint method is illustrated by an example.

 

THE COLLE GNIFETTI

 

 

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  1. Conventional wisdom about the abrupt glacial melt in the Alps at the end the Little Ice Age   [LIA Bibliography] holds that it was caused by black carbon soot deposition on the glaciers. “At the end of the Little Ice Age in the European Alps glaciers began to retreat abruptly in the mid-19th century, but reconstructions of temperature and precipitation indicate that glaciers should have instead advanced into the 20th century. We observe that industrial black carbon in snow began to increase markedly in the mid-19th century and show with simulations that the associated increases in absorbed sunlight by black carbon in snow and snowmelt were of sufficient magnitude to cause this scale of glacier retreat. This hypothesis offers a physically based explanation for the glacier retreat that maintains consistency with the temperature and precipitation reconstructions.” [Painter, Thomas H., et al. “End of the Little Ice Age in the Alps forced by industrial black carbon.” Proceedings of the national academy of sciences (2013): 201302570.[FULL TEXT PDF DOWNLOAD]
  2. A more recent paper has pointed out a temporal anomaly in the reasoning in the (Painter etal 2013) paper. It says that “Starting around 1860, many glaciers in the European Alps began to retreat from their maximum mid-19th century terminus positions marking the end of the Little Ice Age in Europe. Radiative forcing by increasing deposition of industrial black carbon to snow has been suggested as the main driver of the abrupt glacier retreats in the Alps. The basis for this hypothesis was model simulations using elemental carbon concentrations at low temporal resolution from two ice cores in the Alps. Here we present sub-annually resolved concentration records of refractory black carbon (rBC; using soot photometry) as well as distinctive tracers for mineral dust, biomass burning and industrial pollution from the Colle Gnifetti ice core in the Alps from 1741 to 2015. These records allow precise assessment of a potential relation between the timing of observed acceleration of glacier melt in the mid-19th century with an increase of rBC deposition on the glacier caused by the industrialization of Western Europe. Our study reveals that in 1875, the time when rBC ice-core concentrations started to significantly increase, the majority of Alpine glaciers had already experienced more than 80% of their total 19th century length reduction, casting doubt on a leading role for soot in terminating of the Little Ice Age. Attribution of glacial retreat requires expansion of the spatial network and sampling density of high alpine ice cores to balance potential biasing effects arising from transport, deposition, and snow conservation in individual ice-core records.  [ Sigl, M., Abram, N. J., Gabrieli, J., Jenk, T. M., Osmont, D., and Schwikowski, M.: 19th century glacier retreat in the Alps preceded the emergence of industrial black carbon deposition on high-alpine glaciers, The Cryosphere, 12, 3311-3331, https://doi.org/10.5194/tc-12-3311-2018, 2018.[FULL TEXT PDF DOWNLOAD]
  3. In other words, by the time the (Painter etal 2013) causation is observed most of the glacial melt had already occurred. These data therefore do not serve as evidence that the end of the Little Ice Age was initiated by the Industrial Economy by way of black carbon soot emissions and later exacerbated by CO2  emissions from the combustion of fossil fuels. This temporal anomaly weakens the AGW argument that the Little Ice Age was ended by the Industrial Revolution and not by nature and that the current warming trend is therefore human caused by way of fossil fuel emissions from the Industrial Economy. The results suggest that if AGW science had studied the same data in the absence of advocacy against fossil fuels, a greater attention may have been paid to natural climate change.
  4. The usual argument that the current rate of warming is unprecedented and therefore too high to be natural is inconsistent with the data as has been shown in a related post here  [Unprecedented Warming of the Arctic] .
  5. With thanks to the Lubos Motl blog for bringing the 2018 paper to public attention.  [LUBOS MOTL BLOG]

 

 

COLLE GNIFETTI BIBLIOGRAPHY

  1. 1988: Wagenbach, D., et al. “The anthropogenic impact on snow chemistry at Colle Gnifetti, Swiss Alps.” Annals of Glaciology10 (1988): 183-187. By chemical analysis of the upper 40 m of a 124 m ice core from a high-altitude Alpine glacier (Colle Gnifetti, Swiss Alps; 4450 m a.s.l.), records of mineral dust, pH, melt-water conductivity, nitrate and sulfate are obtained. The characteristics of the drilling site are discussed, as derived from glacio-meteorological and chemical analysis. As a consequence of high snow-erosion rates (usually during the winter months), annual snow accumulation is dominated by summer precipitation. Clean-air conditions prevail even during summer; however, they are frequently interrupted by polluted air masses or by air masses which are heavily loaded with desert dust.Absolutely dated reference horizons for Saharan dust, together with the position of the broad nuclear-weapon tritium peak, provide the time-scale for the following statements: (1) Since at least the turn of the century the background melt-water conductivity has been rising steadily, as has the mean snow acidity. The trend of increasing background conductivity at Colle Gnifetti (1.9μS/cm around the beginning of this century, and at present 3.4 μS/cm) is found to be comparable with the records of mean melt-water conductivity reported from ice cores from the Canadian High Arctic. (2) Sulfate and nitrate concentrations are higher by a factor of 4–5 than they were at the beginning of the century. This is to be compared with the two- to three-fold rise in the concentrations in south Greenland during about the same time span.
  2. 1989: Wagenbach, Dietmar, and Klaus Geis. “The mineral dust record in a high altitude Alpine glacier (Colle Gnifetti, Swiss Alps).” Paleoclimatology and paleometeorology: modern and past patterns of global atmospheric transport. Springer, Dordrecht, 1989. 543-564. Ice-core and snow-pit samples from a non-temperated glacier in the summit range of Monte Rosa, Swiss Alps (4450 m.a.s.l.) has been analyzed for total mineral dust and the size distribution of insoluble particulate matter in the size range 0.63–20 microns. Based on a 50 years-record Saharan dust accounts for two third of the mean mineral dust flux of 60 μgcm-2yr-1. Both, background and Saharan dust influenced samples show a distinct mode in the volume size distribution of insoluble particles over the optical active size range with a typical volume mean diameter of 2.5 and 4.5 μm, respectively. These two size distribution categories are attributed to the insoluble fraction of the long lived background aerosol and to the relatively short lived aerosol dominated by soil derived dust (i.e. ground-level aerosol in aride areas).
  3. 1999: Lavanchy, V. M. H., et al. “Historical record of carbonaceous particle concentrations from a European high‐alpine glacier (Colle Gnifetti, Switzerland).” Journal of Geophysical Research: Atmospheres 104.D17 (1999): 21227-21236. Historical records of the concentrations of black carbon (BC) and elemental carbon (EC), as well as of water insoluble organic carbon (OC) and total carbon (TC) covering the time period ∼1755–1975 are presented. Concentrations were obtained from an ice core of a European high‐alpine glacier, using an optical and a thermal method. Concentrations were found to vary between 7 and 128 μg L−1 for BC, between 5 and 130 μg L−1 for EC, between 53 and 484 μg L−1 for OC, and between 66 and 614 μg L−1 for TC. From preindustrial (1755–1890) to modern times (1950–1975) BC, EC, OC, and TC concentrations increased by a factor of 3.7, 3.0, 2.5, and 2.6, respectively. The sum of BC emissions of Germany, France, Switzerland, and Italy, calculated from fossil fuel consumption, and the EC concentration record correlate well (R2 = 0.56) for the time period from 1890 to 1975; this indicates that the ice core record reflects the emissions of western Europe. High pre‐1860 concentrations indicate that by that time BC emissions to the atmosphere were already significant.
  4. 1999: Schwikowski, M., et al. “Anthropogenic versus natural sources of atmospheric sulphate from an Alpine ice core.” Tellus B: Chemical and Physical Meteorology 51.5 (1999): 938-951. Opposite to greenhouse gases, sulphate aerosol particles are expected to cause climate cooling, but uncertainties exist about source variability and strength. We analysed an ice core from a European glacier to quantify source strengths of aerosol-borne sulphate over a 200-year period. Sulphate from emissions of SO2increased by more than an order of magnitude during this century. This anthropogenic source is responsible for about 80% of total sulphate in the industrial period, and reflects emissions of west European countries. In the pre-industrial period mineral dust was the dominant contributor, followed by sulphate from SO2 emissions with volcanoes or biomass burning as possible sources.
  5. 1999: Schwikowski, M., et al. “A high‐resolution air chemistry record from an Alpine ice core: Fiescherhorn glacier, Swiss Alps.” Journal of Geophysical Research: Atmospheres 104.D11 (1999): 13709-13719. Glaciochemical studies at midlatitudes promise to contribute significantly to the understanding of the atmospheric cycling of species with short atmospheric lifetimes. Here we present results of chemical analyses of environmentally relevant species performed on an ice core from Fiescherhorn glacier, Swiss Alps (3890 m above sea level). This glacier site is unique since it is located near the high‐alpine research station Jungfraujoch. There long‐term meteorological and air quality measurements exist, which were used to calibrate the paleodata. The 77‐m‐long ice core was dated by annual layer counting using the seasonally varying signals of tritium and δ18O. It covers the time period 1946–1988 and shows a high net accumulation of water of 1.4 m yr−1 allowing for the reconstruction of high‐resolution environmental records. Chemical composition was dominated by secondary aerosol constituents as well as mineral dust components, characterizing the Fiescherhorn site as a relatively unpolluted continental site. Concentrations of species like ammonium, nitrate, and sulfate showed an increasing trend from 1946 until about 1975, reflecting anthropogenic emission trends in western Europe. For mineral dust tracers, no trends were obvious, whereas chloride and sodium showed slightly higher levels from 1965 until 1988, indicating a change in the strength of sea‐salt transport. Good agreement between the sulfate paleorecord with direct atmospheric measurements was found (correlation coefficient r2 = 0.41). Thus a “calibration” of the paleorecord over a significant period of time could be conducted, revealing an average scavenging ratio of 180 for sulfate.
  6. 2009: Thevenon, Florian, et al. “Mineral dust and elemental black carbon records from an Alpine ice core (Colle Gnifetti glacier) over the last millennium.” Journal of Geophysical Research: Atmospheres 114.D17 (2009). Black carbon (BC) and mineral dust aerosols were analyzed in an ice core from the Colle Gnifetti glacier (Monte Rosa, Swiss‐Italian Alps, 45°55′N, 7°52′E, 4455 m above sea level) using chemical and optical methods. The resulting time series obtained from this summer ice record indicate that BC transport was primarily constrained by regional anthropogenic activities, i.e., biomass and fossil fuel combustion. More precisely, the δ13C composition of BC suggests that wood combustion was the main source of preindustrial atmospheric BC emissions (C3:C4 ratio of burnt biomass of 75:25). Despite relatively high BC emissions prior to 1570, biomass burning activity and especially C4 grassland burning abruptly dropped between 1570 and 1750 (C3:C4 ratio of burnt biomass of 90:10), suggesting that agricultural practices strongly decreased in Europe during this cold period of the “Little Ice Age” (LIA). On the other hand, optical analysis revealed that the main source for atmospheric dust transport to the southern parts of the Alps during summer months was driven by large‐scale atmospheric circulation control on the dust export from the northern Saharan desert. This southern aerosol source was probably associated with global‐scale hydrologic changes, at least partially forced by variability in solar irradiance. In fact, periods of enhanced Saharan dust deposition in the ice core (around 1200–1300, 1430–1520, 1570–1690, 1780–1800, and after 1870) likely reflect drier winters in North Africa, stronger North Atlantic southwesterlies, and increased spring/summer precipitation in west‐central Europe. These results, therefore, suggest that the climatic pejorations and the resulting socioeconomic crises, which occurred in Europe during periods of the LIA, could have been indirectly triggered by large‐scale meridional advection of air masses and wetter summer climatic conditions.

 

 

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jpteam1970SCOOLING

 

 

FIGURE 1: NEWS MEDIA FEAR OF A COMING ICE AGE

 

 

FIGURE 2: NORTHERNHEMISPHERE LANDlandnhgif

FIGURE 3: SOUTHERNHEMISPHERE LANDlandshgif

 

FIGURE 4: NORTHERNHEMISPHERE OCEANseanhgif

 

FIGURE 5:  SOUTHERNHEMISPHERE OCEANseashgif

 

[LIST OF POSTS ON THIS SITE]

 

  1. The warming trend that began since the Industrial Revolution (coincidental with the end of the Little Ice Age or LIA) after the year 1850 has been attributed to rising atmospheric carbon dioxide concentration in terms of its theoretical heat trapping effect. In turn, rising atmospheric CO2 is attributed to emissions from fossil fuel combustion in the industrial economy. The carbon from fossil fuels is considered an thought of as a perturbation of the carbon cycle and climate system with external carbon dug up from deep under the ground where it had been sequestered for millions of years. The warming trend is thus attributed to the industrial economy and described as artificial (Callendar 1938), human caused(Hansen 1981), anthropogenic (IPCC 2007).
  2. Yet, it is generally recognized that CO2 driven Anthropogenic Global Warming (AGW) was interrupted with significant cooling for a period of 30 years or more at some time after the 1930s and before the 1980s with the period generally described as 1940s to 1970s. The cooling trend in this period is recorded in the instrumental temperature record and in global and regional temperature reconstructions. News media archives from that period show a global fear of a return to the Little Ice Age (Figure 1) even though the recovery from the LIA is also feared as catastrophic human caused global warming.
  3. This cooling period is considered to be anomalous and contentious because it appears to be incompatible with the theory of AGW. Skeptics often use this cooling period to argue against AGW theory. Proponents of AGW have either minimized its importance in terms of climate change theory and consensus among climate scientists (Peterson 2008) or have offered explanations for the cooling within the context of global warming. It is argued that the cooling may be explained in terms that are not inconsistent with AGW. For example, it is possible that climate instability is an effect of AGW and the brief period of cooling is an outcome of such instability (Asakura 1981) (Allen 1982) (Suckling 1984).
  4. It is also proposed that an artificial effect of the industrial economy,in addition to the generation of artificial carbon dioxide, is an increase in atmospheric aerosols. It is known that aerosols can cause cooling. Here we examine the aerosol argument in some detail as it is the generally accepted theory of the anomalous 1940s-1970s cooling period in the era of AGW. References to the literature are listed in the AEROSOL BIBLIOGRAPHY below.
  5. Empirical evidence of cooling in a period of approximately 30 to 40 years at some time between 1940 and 1980 is presented in Figure 2 to Figure 5 using regional temperature reconstructions provided by the Hadley Centre Climate Research Unit of the Met Office of the Government of the UK. Four distinct regions, that together encompass the globe, are studied separately. These are LAND areas of the Northern (Figure 2) and Southern (Figure 3) hemispheres and OCEAN areas of the Northern (Figure 4) and Southern (Figure 5) hemispheres. Each figure is a GIF animation that shows a trend profile for each of the twelve calendar months, one month at a time and cycles through all twelve calendar months. Each graphic is a display of the temperature trend in a moving 15-year window. A horizontal line is drawn at the zero trend position. Warming trends (above the zero line) are colored Red and Coolingtrends (below the zero line) are colored Blue. Although the data are provided from 1850, only the portion after 1918 is shown for greater clarity of the study period of 1940 to 1980.
  6. We find in these charts that all four regions and all twelve calendar months show 15yr cooling periods of various degrees of persistence and intensity at somewhat different locations within the study period of 1940-1980 within a global warming context. The period 1918-2017 is dominated by more intense and more persistent episodes of warming. Some cooling periods are found outside the study period particularly so in the 1920s when cooling was more intense and after the year 2000 when cooling is less intense but consistent with the so called “warming hiatus” hypothesis that has been explained in terms of changes in ocean heat content (Related post [Ocean Heat Content] ). The ocean heat content argument is not used for the 1940s-1970s cooling because the cooling is also found in ocean heat content.
  7. The location, duration, and intensity of the 1940s-1970s cooling period vary among calendar months, between land and ocean in each hemisphere, and between the two hemispheres for each surface type. However, some kind of a cooling trend is found somewhere within this period. In some cases both short term cooling and warming periods are found. Although cooling dominates, the cooling is not found to be sustained in all cases. It should be noted that a significant and deep blue patch of cooling is seen in the Northern Hemisphere Oceans. This observations is consistent with the cooling in the North Atlantic and Arctic in the 1960s and 1970s described in (Read 1992) & (Hodson 2014).
  8. A great deal of aerosols are created in the industrial economy as can be seen in the current problem with haze in rapidly industrializing countries such as China and India. Aerosol was also created in testing of atomic bombs. One way that aerosols can affect surface temperature is their backscatter property in which they reflect solar radiation back into space high up in the stratosphere thus shielding to some extent the lower atmosphere from solar radiation. In 1971, Stephen Schneider (with co-author Rasool) published the defining paper for the explanation of the 1940s-1970s cooling in the context of a longer period of global warming driven by rising atmospheric CO2. He argued that the warming effect of carbon dioxide is logarithmic so that the greater the CO2 concentration the less the effect on the rate of warming of increasing CO2 concentration. However, that relationship is exactly in reverse for aerosol backscatter cooling – the greater the aerosol concentration, the greater is the effect of additional aerosol. Based on these rate considerations, he concluded that in the long term, CO2 warming will be saturated and more easily overcome by aerosol backscatter cooling so that in the limit, at high atmospheric CO2 levels, the principal determinant of surface temperature will be aerosols. The aerosol backscatter cooling hypothesis was widely held and a number of papers were published in support of this explanation of the 1940s-1070s cooling. Notable are the McCormick 1967 paper postulating a relationship between atmospheric turbidity and cooling (turbidity to the non-transparency or haziness of the atmosphere usually caused by aerosols).
  9. However, the impact of aerosols on surface temperature is more complex than simple backscatter and its other effects are addressed many of the papers listed below. Aerosols can warm the atmosphere by absorbing solar radiation and retaining that heat. They can also seed high altitude cloud formation thereby increasing cloud albedo and cause cooling. The general case for cloud albedo as an explanation for the anomalous cooling period is presented by Schneider in his 1972 paper which says in effect that since warming increases cloud formation and therefore cloud albedo, warming can lead to periods of cooling.
  10. A specific instance of the warming effect of aerosols relevant to the period under study is found in the so called “Gottschalk curve” attributed to Bernard Gottschalk, Professor of Physics at Harvard University. He found a brief period of warming in global temperature reconstructions towards the end of World War II. A study of the Gottschalk curve is presented in (Herndon 2018). It is argued (by both Gottsschalk and Herndon) that the Gottschalk curve is result of aerosol warming by the large amount of aerosols generated by war activities including for example the carpet bombing of Dresden and the nuclear bombs in Hiroshima. The Gottschalk curve appears in many of the frames of the HadCRU temperature data displayed in Figure 2 to Figure 5 as a brief triangular warming period just prior to 1959 (the war ended in 1945). The brief red warming peak is seen in some but not all months for land surfaces. (Herndon 218) uses the Gottschalk curve to highlight the warming effect of aerosols and to propose an alternate theory of AGW in terms of aerosol warming.
  11. A special consideration is that of sulfate aerosols as their ultrafine aerosol cooling effect is well known and well documented as seen in (Junge 1961, Wiedensohler 1996) below. In terms of sulfate aerosols, the 1940s-1970s cooling effect can be explained by rapid increase in hydrogen sulfide (H2S) emissions from the combustion of hydrocarbon fuels before H2S emissions were regulated and eventually almost eliminated. The rapid increase in sulfate aerosol emissions is recorded in environmental history as the age of acid rain. By the end of the 1970s, tight regulation of sulfate emissions by acid rain programs worldwide, had significantly reduced sulfate aerosol emissions . The 1940s-1970s cooling can be understood in that context as well as the resurgent global warming since the 1980s. Yet another causal connection between the acid rain program and global warming is proposed by NASA-GISS. It holds that acid rain kills bacteria in wetlands and reduces the biological production of methane which in turn causes global warming  [LINK]
  12. IN SUMMARY: The data provided above shows conclusive evidence of anomalous period of cooling in an overall era of global warming. The cooling anomaly is seen in all four regions of the world defined according to hemisphere and surface (land vs ocean). Significant research references exist that have described the cooling and explained it in terms of aerosol backscatter. The attempt by some climate scientists to minimize the importance of the 1940s-1970s cooling to climate science seems incongruous in the context of the data and research papers presented. The end of the cooling period and the return to warming may be explained by the Schneider hypothesis relating cloud albedo to warming in a negative feedback loop but that necessarily implies that another 1940s-1970s type cooling period is forthcoming particularly in light of increasing atmospheric turbidity from rapid industrialization in China and India.

 

 

 

 

STEPHEN SCHNEIDERschneider

 

AEROSOLS AND CLIMATE: BIBLIOGRAPHY

  1. 1961: Junge, Christian E., and James E. Manson. “Stratospheric aerosol studies.” Journal of Geophysical Research 66.7 (1961): 2163-2182. The stratospheric aerosol layer previously identified by balloon measurements has been studied extensively by means of recovered rod impactor samples obtained during aircraft flights at the 20‐km level from 63°S to 72°N during March–November 1960. From a variety of physical and chemical measurements, which are presented in detail, the conclusion is drawn that this layer is stable, constant in time and space, and composed mainly of sulfate particles. The various questions raised by this result, particularly with respect to collection of micrometeorites, are presented and discussed.</p>
  2. 1967: McCormick, Robert A., and John H. Ludwig. “Climate modification by atmospheric aerosols.” Science 156.3780 (1967): 1358-1359. Theoretical considerations and empirical evidence indicate that atmospheric turbidity, a function of aerosol loading, is an important factor in the heat balance of the earth-atmosphere system. Turbidity increase over the past few decades may be primarily responsible for the decrease in worldwide air temperatures since the 1940’s.
  3. 1971: Rasool, S. Ichtiaque, and Stephen H. Schneider. “Atmospheric carbon dioxide and aerosols: Effects of large increases on global climate.” Science 173.3992 (1971): 138-141. Effects on the global temperature of large increases in carbon dioxide and aerosol densities in the atmosphere of Earth have been computed. It is found that, although the addition of carbon dioxide in the atmosphere does increase the surface temperature, the rate of temperature increase diminishes with increasing carbon dioxide in the atmosphere. For aerosols, however, the net effect of increase in density is to reduce the surface temperature of Earth. Because of the exponential dependence of the backscattering, the rate of temperature decrease is augmented with increasing aerosol content. An increase by only a factor of 4 in global aerosol background concentration may be sufficient to reduce the surface temperature by as much as 3.5 ° K. If sustained over a period of several years, such a temperature decrease over the whole globe is believed to be sufficient to trigger an ice age.
  4. 1971: Mitchell Jr, J. Murray. “The effect of atmospheric aerosols on climate with special reference to temperature near the earth’s surface.” Journal of Applied Meteorology 10.4 (1971): 703-714. A generalized model of the effect of an optically thin atmospheric aerosol on the terrestrial heat budget is proposed, and applied to the problem of estimating the impact of the aerosol on temperatures near the earth’s surface. The distinction between warming and cooling near the surface attributable to the aerosol is found on the basis of this model to depend on whether the ratio of absorption a to backscatter b of incoming solar radiation by the aerosol is greater or less than the critical ratio            (a/b)O = C(1−A)(1−Ak)/[D(1+A)−C(1−A)], where A is the surface albedo, C the fraction of sensible to total (sensible plus latent) solar heating of the surface, D the fraction of aerosol that is in convective contact with the surface, and k a multiple of b that measures the relative aerosol backscattering efficiency with respect to solar radiation reflected upward from the surface.A distinction is drawn between a stratospheric aerosol (D=0) which generally cools the atmosphere near the surface, and a tropospheric aerosol (D→1) which may either cool or warm the atmosphere near the surface depending on various properties of the aerosol and of the surface itself. Over moist surfaces, such as vegetated areas and oceans, the critical ratio (a/b)o is of order 0.1. Over drier surfaces, such as deserts and urban areas, (a/b)o is of order unity. If the actual ratio a/b of most tropospheric aerosols is of order unity, as inferred by previous authors, then the dominant effect of such aerosols is warming except over deserts and urban arms where the effect is somewhat marginal between warming and cooling.Further aerosol climatic effects are found likely to include a slight decrease of cloudiness and precipitation, and an increase of “planetary” albedo above the oceans, although not necessarily above the continents. Suggestions by several previous authors to the effect that the apparent worldwide cooling of climate in recent decades is attributable to large-scale increases of particulate pollution of the atmosphere by human activities are not supported by this analysis.
  5. 1972: Schneider, Stephen H. “Cloudiness as a global climatic feedback mechanism: The effects on the radiation balance and surface temperature of variations in cloudiness.” Journal of the Atmospheric Sciences 29.8 (1972): 1413-1422. The effect of variation in cloudiness on the climate is considered in terms of 1) a relation between the radiation balance of the earth-atmosphere system and variations in the amount of cloud cover or effective cloud top height, 2) the effect on the surface temperature of variations in cloudiness, and 3) the dynamic coupling or “feedback” effects relating changes in surface temperature to the formation of clouds. The first two points are studied by numerical integration of a simple radiation flux model, and the third point is discussed qualitatively. Global-average radiation balance calculations show that an increase in the amount of low and middle level cloud cover (with cloud top height and cloud albedo fixed) decreases the surface temperature. But, this result for the global-average case does not hold near polar regions, where the albedo of the cloudy areas can he comparable to (or even smaller than) the albedo of the snow-covered cloudless areas, and where, especially in the winter season, the amount of incoming solar radiation at high latitudes is much less than the global-average value of insolation. The exact latitude at which surface cooling changes to surface warming from a given increase in cloud cover amount depends critically upon the local values of the cloud albedo and the albedo of the cloudless areas that are used in the calculation. However, an increase in effective cloud top height (with cloud cover and cloud albedo fixed) increases the surface temperature at all latitudes.
  6. 1974: Chýlek, Petr, and James A. Coakley. “Aerosols and climate.” Science 183.4120 (1974): 75-77. To determine the effects of atmospheric aerosols on the radiative heating of the earth-atmosphere system, the radiative transfer equation is solved analytically in the two-stream approximation. It is found that the sign of the heating is independent of optical thickness of an aerosol layer and the amount of heating approaches a finite limit with increasing thickness of a layer. Limitations of the two-stream approximation are discussed.
  7. 1976: Cess, Robert D. “Climate change: An appraisal of atmospheric feedback mechanisms employing zonal climatology.” Journal of the Atmospheric Sciences 33.10 (1976): 1831-1843. The sensitivity of the earth’s surface temperature to factors which can induce long-term climate change, such as a variation in solar constant, is estimated by employing two readily observable climate changes. One is the latitudinal change in annual mean climate, for which an interpretation of climatological data suggests that cloud amount is not a significant climate feedback mechanism, irrespective of how cloud amount might depend upon surface temperature, since there are compensating changes in both the solar and infrared optical properties of the atmosphere. It is further indicated that all other atmospheric feedback mechanisms, resulting, for example, from temperature-induced changes in water vapor amount, cloud altitude and lapse rate, collectively double the sensitivity of global surface temperature to a change in solar constant. The same conclusion is reached by considering a second type of climate change, that associated with seasonal variations for a given latitude zone. The seasonal interpretation further suggests that cloud amount feedback is unimportant zonally as well as globally. Application of the seasonal data required a correction for what appears to be an important seasonal feedback mechanism. This is attributed to a variability in cloud albedo due to seasonal changes in solar zenith angle. No attempt was made to individually interpret the collective feedback mechanisms which contribute to the doubling in surface temperature sensitivity. It is suggested, however, that the conventional assumption of fixed relative humidity for describing feedback due to water vapor amount might not be as applicable as is generally believed. Climate models which additionally include ice-albedo feedback are discussed within the framework of the present results.
  8. 1983: Coakley Jr, James A., Robert D. Cess, and Franz B. Yurevich. “The effect of tropospheric aerosols on the Earth’s radiation budget: A parameterization for climate models.” Journal of the Atmospheric Sciences 40.1 (1983): 116-138. Guided by the results of doubling-adding solutions to the equation of radiative transfer, we develop a simple technique for incorporating in climate models the effect of the background tropospheric aerosol on solar radiation. Because the atmosphere is practically nonabsorbing for much of the solar spectrum the effects of the tropospheric aerosol on the reflectivity, transmissivity and absorptivity of the atmosphere are adequately accounted for by the properties of a two-layered system with the atmosphere placed above the aerosol layer. The two-stream and delta-Eddington approximations to the radiative transfer equation then provide reasonably accurate estimates of the changes brought about by the aerosol. Furthermore, results of the doubling-adding calculations lead to a simple parameterization for the distribution of absorption by the aerosol within the atmosphere. Using these simple techniques, we calculate the changes caused by models for the naturally occurring tropospheric aerosol in a zonal mean energy balance climate model. The 2–30°C surface cooling caused by the background aerosol is comparable in magnitude but opposite in sign to the temperature changes brought about by the current atmospheric concentrations of N20 and CH4 and by a doubling of CO2. The model results also indicate that even though the background aerosol may decrease the planetary albedo at high latitudes, it causes cooling at all latitudes. We also use the simple techniques to calculate the influence of dust on the planetary albedo of a desert. Here we demonstrate that the interaction of the aerosol scattering with the angular dependence of the surface reflectivity strongly influences the planetary albedo.
  9. 1987: Charlson, Robert J., et al. “Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate.” Nature326.6114 (1987): 655. The major source of cloud-condensation nuclei (CCN) over the oceans appears to be dimethylsulphide, which is produced by planktonic algae in sea water and oxidizes in the atmosphere to form a sulphate aerosol Because the reflectance (albedo) of clouds (and thus the Earth’s radiation budget) is sensitive to CCN density, biological regulation of the climate is possible through the effects of temperature and sunlight on phytoplankton population and dimethylsulphide production. To counteract the warming due to doubling of atmospheric CO2, an approximate doubling of CCN would be needed.
  10. 1989: Blanchet, Jean-Pierre. “Toward estimation of climatic effects due to Arctic aerosols.” Atmospheric Environment (1967)23.11 (1989): 2609-2625. During the last decade, the estimation of the climatic implications of principal anthropogenic aerosols (soot and sulphates) has been investigated by observation and modeling efforts at three scales of dimension:(1) the aerosol scale where the optical properties are determined; (2) the kilometer scale where the radiative fluxes and diabatic heating are felt, and finally, (3) the regional and hemispheric scales where the climate questions pertain. This paper reviews the current results on these three scales, with an emphasis on the comparisons between observations and model results.
  11. 1990: Hansen, James E., and Andrew A. Lacis. “Sun and dust versus greenhouse gases: An assessment of their relative roles in global climate change.” Nature 346.6286 (1990): 713. Many mechanisms, including variations in solar radiation and atmospheric aerosol concentrations, compete with anthropogenic greenhouse gases as causes of global climate change. Comparisons of available data show that solar variability will not counteract greenhouse warming and that future observations will need to be made to quantify the role of tropospheric aerosols, for example.
  12. 1992: Clarke, Antomy D. “Atmospheric nuclei in the remote free-troposphere.” Journal of atmospheric chemistry 14.1-4 (1992): 479-488. During May-June of 1990 an extensive flight series to survey aerosol present in the upper-troposphere was undertaken aboard the NASA DC-8 as part of the CLObal Backscatter Experiment (GLOBE). About 50,000 km were characterized between 8–12 km altitude and between 70°N and 58°S. Aerosol with diameters greater than 3nm were counted and sized with a combination of condensation nuclei counters and optical particle counters. Aerosol number and mass concentrations were separately identified with regard to both refractory and volatile components. Regions of the free-troposphere with the lowest mass concentrations were generally found to have the highest number concentrations and appeared to be effective regions for new particle production. These new particle concentrations appear inversely related to available aerosol surface area and their volatility suggests a sulfuric acid composition. The long lifetime of these new particles aloft can result in their growth to sizes effective as CN and CCN that can be mixed throughout the troposphere.
  13. 1992: Charlson, Robert J., et al. “Climate forcing by anthropogenic aerosols.” Science 255.5043 (1992): 423-430. Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol in particular has imposed a major perturbation to this forcing. Both the direct scattering of shortwave solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be –1 to –2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.
  14. 1993: Kiehl, J. T., and B. P. Briegleb. “The relative roles of sulfate aerosols and greenhouse gases in climate forcing.” Science260.5106 (1993): 311-314. Calculations of the effects of both natural and anthropogenic tropospheric sulfate aerosols indicate that the aerosol climate forcing is sufficiently large in a number of regions of the Northern Hemisphere to reduce significantly the positive forcing from increased greenhouse gases. Summer sulfate aerosol forcing in the Northern Hemisphere completely offsets the greenhouse forcing over the eastern United States and central Europe. Anthropogenic sulfate aerosols contribute a globally averaged annual forcing of –0.3 watt per square meter as compared with +2.1 watts per square meter for greenhouse gases. Sources of the difference in magnitude with the previous estimate of Charlson et al. are discussed.
  15. 1994: Schneider, Stephen H. “Detecting climatic change signals: are there any” fingerprints“?.” Science 263.5145 (1994): 341-347. Projected changes in the Earth’s climate can be driven from a combined set of forcing factors consisting of regionally heterogeneous anthropogenic and natural aerosols and land use changes, as well as global-scale influences from solar variability and transient increases in human-produced greenhouse gases. Thus, validation of climate model projections that are driven only by increases in greenhouse gases can be inconsistent when one attempts the validation by looking for a regional or time-evolving “fingerprint” of such projected changes in real climatic data. Until climate models are driven by time-evolving, combined, multiple, and heterogeneous forcing factors, the best global climatic change “fingerprint” will probably remain a many-decades average of hemispheric-scale to global-scale trends in surface air temperatures. Century-long global warming (or cooling) trends of 0.5°C appear to have occurred infrequently over the past several thousand years—perhaps only once or twice a millennium, as proxy records suggest. This implies an 80 to 90 percent heuristic likelihood that the 20th-century 0.5 ± 0.2°C warming trend is not a wholly natural climatic fluctuation.
  16. 1995: Pilinis, Christodoulos, Spyros N. Pandis, and John H. Seinfeld. “Sensitivity of direct climate forcing by atmospheric aerosols to aerosol size and composition.” Journal of Geophysical Research: Atmospheres 100.D9 (1995): 18739-18754. We evaluate, using a box model, the sensitivity of direct climate forcing by atmospheric aerosols for a “global mean” aerosol that consists of fine and coarse modes to aerosol composition, aerosol size distribution, relative humidity (RH), aerosol mixing state (internal versus external mixture), deliquescence/crystallization hysteresis, and solar zenith angle. We also examine the dependence of aerosol upscatter fraction on aerosol size, solar zenith angle, and wavelength and the dependence of single scatter albedo on wavelength and aerosol composition. The single most important parameter in determining direct aerosol forcing is relative humidity, and the most important process is the increase of the aerosol mass as a result of water uptake. An increase of the relative humidity from 40 to 80% is estimated for the global mean aerosol considered to result in an increase of the radiative forcing by a factor of 2.1. Forcing is relatively insensitive to the fine mode diameter increase due to hygroscopic growth, as long as this mode remains inside the efficient scattering size region. The hysteresis/deliquescence region introduces additional uncertainty but, in general, errors less than 20% result by the use of the average of the two curves to predict forcing. For fine aerosol mode mean diameters in the 0.2–0.5 μm range direct aerosol forcing is relatively insensitive (errors less than 20%) to variations of the mean diameter. Estimation of the coarse mode diameter within a factor of 2 is generally sufficient for the estimation of the total aerosol radiative forcing within 20%. Moreover, the coarse mode, which represents the nonanthropogenic fraction of the aerosol, is estimated to contribute less than 10% of the total radiative forcing for all RHs of interest. Aerosol chemical composition is important to direct radiative forcing as it determines (1) water uptake with RH, and (2) optical properties. The effect of absorption by aerosol components on forcing is found to be significant even for single scatter albedo values of ω=0.93–0.97. The absorbing aerosol component reduces the aerosol forcing from that in its absence by roughly 30% at 60% RH and 20% at 90% RH. The mixing state of the aerosol (internal versus external) for the particular aerosol considered here is found to be of secondary importance. While sulfate mass scattering efficiency (m2 (g SO42−)−1) and the normalized sulfate forcing (W (g SO42−)−1) increase strongly with RH, total mass scattering efficiency (m2 g−1) and normalized forcing (W g−1) are relatively insensitive to RH, wherein the mass of all species, including water, are accounted for. Following S. Nemesure et al. (Direct shortwave forcing of climate by anthropogenic sulfate aerosol: sensitivity to particle size, composition, and relative humidity, submitted to Journal of Geophysical Research, 1995), we find that aerosol feeing achieves a maximum at a particular solar zenith angle, reflecting a balance between increasing upscatter fraction with increasing solar zenith angle and decreasing solar flux (from Rayleigh scattering) with increasing solar zenith angle.
  17. 1996: Wiedensohler, Alfred, et al. “Occurrence of an ultrafine particle mode less than 20 nm in diameter in the marine boundary layer during Arctic summer and autumn.” Tellus B 48.2 (1996): 213-222. The International Arctic Ocean Expedition 1991 (IAOE‐91) provided a platform to study the occurrence and size distributions of ultrafine particles in the marine boundary layer (MBL) during Arctic summer and autumn. Measurements of both aerosol physics, and gas/particulate chemistry were taken aboard the Swedish icebreaker Oden. Three separate submicron aerosol modes were found: an ultrafine mode (Dp < 20 nm), the Aitken mode (20 < Dp < 100 nm), and the accumulation mode (Dp > 100 nm). We evaluated correlations between ultrafine particle number concentrations and mean diameter with the entire measured physical, chemical, and meteorological data set. Multivariate statistical methods were then used to make these comparisons. A principal component (PC) analysis indicated that the observed variation in the data could be explained by the influence from several types of air masses. These were characterised by contributions from the open sea or sources from the surrounding continents and islands. A partial least square (PLS) regression of the ultrafine particle concentration was also used. These results implied that the ultrafine particles were produced above or in upper layers of the MBL and mixed downwards. There were also indications that the open sea acted as a source of the precursors for ultrafine particle production. No anti‐correlation was found between the ultrafine and accumulation particle number concentrations, thus indicating that the sources were in separate air masses.
  18. 1995: Andreae, Meinrat O. “Climatic effects of changing atmospheric aerosol levels.” World survey of climatology 16 (1995): 347-398. bandicam 2018-10-18 10-15-51-596
  19. 1997: Raes, Frank, et al. “Observations of aerosols in the free troposphere and marine boundary layer of the subtropical Northeast Atlantic: Discussion of processes determining their size distribution.” Journal of Geophysical Research: Atmospheres 102.D17 (1997): 21315-21328. During July 1994, submicron aerosol size distributions were measured at two sites on Tenerife, Canary Islands. One station was located in the free troposphere (FT), the other in the marine boundary layer (MBL). Transport toward these two sites was strongly decoupled: the FT was first affected by dust and sulfate‐laden air masses advecting from North Africa and later by clean air masses originating over the North Atlantic, whereas the MBL was always subject to the northeasterly trade wind circulation. In the FT the submicron aerosol distribution was predominantly monomodal with a geometric mean diameter of 120 nm and 55 nm during dusty and clean conditions, respectively. The relatively small diameter during the clean conditions indicates that the aerosol originated in the upper troposphere rather than over continental areas or in the lower stratosphere. During dusty conditions the physical and chemical properties of the submicron aerosol suggest that it has an anthropogenic origin over southern Europe and that it remains largely externally mixed with the supermicron mineral dust particles during its transport over North Africa to Tenerife. Apart from synoptic variations, a strong diurnal variation in the aerosol size distribution is observed at the FT site, characterized by a strong daytime mode of ultrafine particles. This is interpreted as being the result of photoinduced nucleation in the upslope winds, which are perturbed by anthropogenic and biogenic emissions on the island. No evidence was found for nucleation occurring in the undisturbed FT. The MBL site was not strongly affected by European pollution during the period of the measurements. The MBL aerosol size distribution was bimodal, but the relative concentration of Aitken and accumulation mode varied strongly. The accumulation mode can be related to cloud processing of the Aitken mode but also to pollution aerosol which was advected within the MBL or entrained from the FT. No bursts of nucleation were observed within the MBL.
  20. 1997: Andreae, Meinrat O., and Paul J. Crutzen. “Atmospheric aerosols: Biogeochemical sources and role in atmospheric chemistry.” Science 276.5315 (1997): 1052-1058. Atmospheric aerosols play important roles in climate and atmospheric chemistry: They scatter sunlight, provide condensation nuclei for cloud droplets, and participate in heterogeneous chemical reactions. Two important aerosol species, sulfate and organic particles, have large natural biogenic sources that depend in a highly complex fashion on environmental and ecological parameters and therefore are prone to influence by global change. Reactions in and on sea-salt aerosol particles may have a strong influence on oxidation processes in the marine boundary layer through the production of halogen radicals, and reactions on mineral aerosols may significantly affect the cycles of nitrogen, sulfur, and atmospheric oxidants.
  21. 1997: Hansen, J., Mki Sato, and R. Ruedy. “Radiative forcing and climate response.” Journal of Geophysical Research: Atmospheres 102.D6 (1997): 6831-6864. We examine the sensitivity of a climate model to a wide range of radiative forcings, including changes of solar irradiance, atmospheric CO2, O3, CFCs, clouds, aerosols, surface albedo, and a “ghost” forcing introduced at arbitrary heights, latitudes, longitudes, seasons, and times of day. We show that, in general, the climate response, specifically the global mean temperature change, is sensitive to the altitude, latitude, and nature of the forcing; that is, the response to a given forcing can vary by 50% or more depending upon characteristics of the forcing other than its magnitude measured in watts per square meter. The consistency of the response among different forcings is higher, within 20% or better, for most of the globally distributed forcings suspected of influencing global mean temperature in the past century, but exceptions occur for certain changes of ozone or absorbing aerosols, for which the climate response is less well behaved. In all cases the physical basis for the variations of the response can be understood. The principal mechanisms involve alterations of lapse rate and decrease (increase) of large‐scale cloud cover in layers that are preferentially heated (cooled). Although the magnitude of these effects must be model‐dependent, the existence and sense of the mechanisms appear to be reasonable. Overall, we reaffirm the value of the radiative forcing concept for predicting climate response and for comparative studies of different forcings; indeed, the present results can help improve the accuracy of such analyses and define error estimates. Our results also emphasize the need for measurements having the specificity and precision needed to define poorly known forcings such as absorbing aerosols and ozone change. Available data on aerosol single scatter albedo imply that anthropogenic aerosols cause less cooling than has commonly been assumed. However, negative forcing due to the net ozone change since 1979 appears to have counterbalanced 30–50% of the positive forcing due to the increase of well‐mixed greenhouse gases in the same period. As the net ozone change includes halogen‐driven ozone depletion with negative radiative forcing and a tropospheric ozone increase with positive radiative forcing, it is possible that the halogen‐driven ozone depletion has counterbalanced more than half of the radiative forcing due to well‐mixed greenhouse gases since 1979.
  22. 2000: Robock, Alan. “Volcanic eruptions and climate.” Reviews of Geophysics 38.2 (2000): 191-219. Volcanic eruptions are an important natural cause of climate change on many timescales. A new capability to predict the climatic response to a large tropical eruption for the succeeding 2 years will prove valuable to society. In addition, to detect and attribute anthropogenic influences on climate, including effects of greenhouse gases, aerosols, and ozone‐depleting chemicals, it is crucial to quantify the natural fluctuations so as to separate them from anthropogenic fluctuations in the climate record. Studying the responses of climate to volcanic eruptions also helps us to better understand important radiative and dynamical processes that respond in the climate system to both natural and anthropogenic forcings. Furthermore, modeling the effects of volcanic eruptions helps us to improve climate models that are needed to study anthropogenic effects. Large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with an e‐folding residence time of about 1 year. Large ash particles fall out much quicker. The radiative and chemical effects of this aerosol cloud produce responses in the climate system. By scattering some solar radiation back to space, the aerosols cool the surface, but by absorbing both solar and terrestrial radiation, the aerosol layer heats the stratosphere. For a tropical eruption this heating is larger in the tropics than in the high latitudes, producing an enhanced pole‐to‐equator temperature gradient, especially in winter. In the Northern Hemisphere winter this enhanced gradient produces a stronger polar vortex, and this stronger jet stream produces a characteristic stationary wave pattern of tropospheric circulation, resulting in winter warming of Northern Hemisphere continents. This indirect advective effect on temperature is stronger than the radiative cooling effect that dominates at lower latitudes and in the summer. The volcanic aerosols also serve as surfaces for heterogeneous chemical reactions that destroy stratospheric ozone, which lowers ultraviolet absorption and reduces the radiative heating in the lower stratosphere, but the net effect is still heating. Because this chemical effect depends on the presence of anthropogenic chlorine, it has only become important in recent decades. For a few days after an eruption the amplitude of the diurnal cycle of surface air temperature is reduced under the cloud. On a much longer timescale, volcanic effects played a large role in interdecadal climate change of the Little Ice Age. There is no perfect index of past volcanism, but more ice cores from Greenland and Antarctica will improve the record. There is no evidence that volcanic eruptions produce El Niño events, but the climatic effects of El Niño and volcanic eruptions must be separated to understand the climatic response to each.
  23. 2001: Jacobson, Mark Z. “Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols.” Nature409.6821 (2001): 695. Aerosols affect the Earth’s temperature and climate by altering the radiative properties of the atmosphere. A large positive component of this radiative forcing from aerosols is due to black carbon—soot—that is released from the burning of fossil fuel and biomass, and, to a lesser extent, natural fires, but the exact forcing is affected by how black carbon is mixed with other aerosol constituents. From studies of aerosol radiative forcing, it is known that black carbon can exist in one of several possible mixing states; distinct from other aerosol particles (externally mixed1,2,3,4,5,6,7) or incorporated within them (internally mixed1,3,7), or a black-carbon core could be surrounded by a well mixed shell7. But so far it has been assumed that aerosols exist predominantly as an external mixture. Here I simulate the evolution of the chemical composition of aerosols, finding that the mixing state and direct forcing of the black-carbon component approach those of an internal mixture, largely due to coagulation and growth of aerosol particles. This finding implies a higher positive forcing from black carbon than previously thought, suggesting that the warming effect from black carbon may nearly balance the net cooling effect of other anthropogenic aerosol constituents. The magnitude of the direct radiative forcing from black carbon itself exceeds that due to CH4, suggesting that black carbon may be the second most important component of global warming after CO2in terms of direct forcing.
  24. 2002: Kaufman, Yoram J., Didier Tanré, and Olivier Boucher. “A satellite view of aerosols in the climate system.” Nature419.6903 (2002): 215. Anthropogenic aerosols are intricately linked to the climate system and to the hydrologic cycle. The net effect of aerosols is to cool the climate system by reflecting sunlight. Depending on their composition, aerosols can also absorb sunlight in the atmosphere, further cooling the surface but warming the atmosphere in the process. These effects of aerosols on the temperature profile, along with the role of aerosols as cloud condensation nuclei, impact the hydrologic cycle, through changes in cloud cover, cloud properties and precipitation. Unravelling these feedbacks is particularly difficult because aerosols take a multitude of shapes and forms, ranging from desert dust to urban pollution, and because aerosol concentrations vary strongly over time and space. To accurately study aerosol distribution and composition therefore requires continuous observations from satellites, networks of ground-based instruments and dedicated field experiments. Increases in aerosol concentration and changes in their composition, driven by industrializationand an expanding population, may adversely affect the Earth’s climate and water supply.
  25. 2002: Menon, Surabi, et al. “Climate effects of black carbon aerosols in China and India.” Science 297.5590 (2002): 2250-2253. In recent decades, there has been a tendency toward increased summer floods in south China, increased drought in north China, and moderate cooling in China and India while most of the world has been warming. We used a global climate model to investigate possible aerosol contributions to these trends. We found precipitation and temperature changes in the model that were comparable to those observed if the aerosols included a large proportion of absorbing black carbon (“soot”), similar to observed amounts. Absorbing aerosols heat the air, alter regional atmospheric stability and vertical motions, and affect the large-scale circulation and hydrologic cycle with significant regional climate effects.
  26. 2005: Andreae, Meinrat O., Chris D. Jones, and Peter M. Cox. “Strong present-day aerosol cooling implies a hot future.” Nature 435.7046 (2005): 1187. Atmospheric aerosols counteract the warming effects of anthropogenic greenhouse gases by an uncertain, but potentially large, amount. This in turn leads to large uncertainties in the sensitivity of climate to human perturbations, and therefore also in carbon cycle feedbacks and projections of climate change. In the future, aerosol cooling is expected to decline relative to greenhouse gas forcing, because of the aerosols’ much shorter lifetime and the pursuit of a cleaner atmosphere. Strong aerosol cooling in the past and present would then imply that future global warming may proceed at or even above the upper extreme of the range projected by the Intergovernmental Panel on Climate Change.
  27. 2005: Pöschl, Ulrich. “Atmospheric aerosols: composition, transformation, climate and health effects.” Angewandte Chemie International Edition 44.46 (2005): 7520-7540. Aerosols are of central importance for atmospheric chemistry and physics, the biosphere, climate, and public health. The airborne solid and liquid particles in the nanometer to micrometer size range influence the energy balance of the Earth, the hydrological cycle, atmospheric circulation, and the abundance of greenhouse and reactive trace gases. Moreover, they play important roles in the reproduction of biological organisms and can cause or enhance diseases. The primary parameters that determine the environmental and health effects of aerosol particles are their concentration, size, structure, and chemical composition. These parameters, however, are spatially and temporally highly variable. The quantification and identification of biological particles and carbonaceous components of fine particulate matter in the air (organic compounds and black or elemental carbon, respectively) represent demanding analytical challenges. This Review outlines the current state of knowledge, major open questions, and research perspectives on the properties and interactions of atmospheric aerosols and their effects on climate and human health.
  28. 2005: Jickells, T. D., et al. “Global iron connections between desert dust, ocean biogeochemistry, and climate.” science 308.5718 (2005): 67-71. The environmental conditions of Earth, including the climate, are determined by physical, chemical, biological, and human interactions that transform and transport materials and energy. This is the “Earth system”: a highly complex entity characterized by multiple nonlinear responses and thresholds, with linkages between disparate components. One important part of this system is the iron cycle, in which iron-containing soil dust is transported from land through the atmosphere to the oceans, affecting ocean biogeochemistry and hence having feedback effects on climate and dust production. Here we review the key components of this cycle, identifying critical uncertainties and priorities for future research.
  29. 2005: Lohmann, Ulrike, and Johann Feichter. “Global indirect aerosol effects: a review.” Atmospheric Chemistry and Physics5.3 (2005): 715-737.  Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei, they may inhibit freezing and they could have an influence on the hydrological cycle. While the cloud albedo enhancement (Twomey effect) of warm clouds received most attention so far and traditionally is the only indirect aerosol forcing considered in transient climate simulations, here we discuss the multitude of effects. Different approaches how the climatic implications of these aerosol effects can be estimated globally as well as improvements that are needed in global climate models in order to better represent indirect aerosol effects are discussed in this paper.
  30. 2009: Ramanathan, Veerabhadran, and Yan Feng. “Air pollution, greenhouse gases and climate change: Global and regional perspectives.” Atmospheric environment 43.1 (2009): 37-50. Greenhouse gases (GHGs) warm the surface and the atmosphere with significant implications for rainfall, retreat of glaciers and sea ice, sea level, among other factors. About 30 years ago, it was recognized that the increase in tropospheric ozone from air pollution (NOx, CO and others) is an important greenhouse forcing term. In addition, the recognition of chlorofluorocarbons (CFCs) on stratospheric ozone and its climate effects linked chemistry and climate strongly. What is less recognized, however, is a comparably major global problem dealing with air pollution. Until about ten years ago, air pollution was thought to be just an urban or a local problem. But new data have revealed that air pollution is transported across continents and ocean basins due to fast long-range transport, resulting in trans-oceanic and trans-continental plumes of atmospheric brown clouds (ABCs) containing sub micron size particles, i.e., aerosols. ABCs intercept sunlight by absorbing as well as reflecting it, both of which lead to a large surface dimming. The dimming effect is enhanced further because aerosols may nucleate more cloud droplets, which makes the clouds reflect more solar radiation. The dimming has a surface cooling effect and decreases evaporation of moisture from the surface, thus slows down the hydrological cycle. On the other hand, absorption of solar radiation by black carbon and some organics increase atmospheric heating and tend to amplify greenhouse warming of the atmosphere. ABCs are concentrated in regional and mega-city hot spots. Long-range transport from these hot spots causes widespread plumes over the adjacent oceans. Such a pattern of regionally concentrated surface dimming and atmospheric solar heating, accompanied by widespread dimming over the oceans, gives rise to large regional effects. Only during the last decade, we have begun to comprehend the surprisingly large regional impacts. In S. Asia and N. Africa, the large north-south gradient in the ABC dimming has altered both the north-south gradients in sea surface temperatures and land–ocean contrast in surface temperatures, which in turn slow down the monsoon circulation and decrease rainfall over the continents. On the other hand, heating by black carbon warms the atmosphere at elevated levels from 2 to 6 km, where most tropical glaciers are located, thus strengthening the effect of GHGs on retreat of snow packs and glaciers in the Hindu Kush-Himalaya-Tibetan glaciers. Globally, the surface cooling effect of ABCs may have masked as much 47% of the global warming by greenhouse gases, with an uncertainty range of 20–80%. This presents a dilemma since efforts to curb air pollution may unmask the ABC cooling effect and enhance the surface warming. Thus efforts to reduce GHGs and air pollution should be done under one common framework. The uncertainties in our understanding of the ABC effects are large, but we are discovering new ways in which human activities are changing the climate and the environment.
  31. 2009: Jimenez, Jose L., et al. “Evolution of organic aerosols in the atmosphere.” science 326.5959 (2009): 1525-1529. Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high–time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.
  32. 2017: Stanley, S. (2017), Satellite data reveal effects of aerosols in Earth’s atmosphere, Eos, 98,https://doi.org/10.1029/2017EO069945. Published on 24 March 2017.  Earth’s atmosphere is dusted with tiny particles known as aerosols, which include windblown ash, sea salt, pollution, and other natural and human-produced materials. Aerosols can absorb or scatter sunlight, affecting how much light reflects back into space or stays trapped in the atmosphere. Despite aerosols’ known impact on Earth’s temperature, major uncertainties plague current estimates of their overall effects, which in turn limit the certainty of climate change models. In an effort to reduce this uncertainty, Lacagnina et al. have combined new satellite data, providing, for the first time, data on aerosols’ ability to absorb or reflect light globally, through model simulations In this new study, the team focused on the direct effects of aerosols on shortwave radiation in 2006. These effects depended on the particles’ vertical location with respect to clouds, the reflective properties of the underlying land or water, and the optical properties of the aerosol particles themselves, including how much light they are prone to scatter or absorb.The researchers used instruments aboard the French Polarization and Anisotropy of Reflectances for Atmospheric Science coupled with Observations from a Lidar (PARASOL) satellite and NASA’s Aura spacecraft to measure aerosol optical properties around the world. Data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) satellite instrument provided measurements of cloud characteristics and land reflectance, and an aerosol climate model known as ECHAM5-HAM2 helped fill in any gaps in the observations. Using these data, calculations of the global average radiative effect for 2006 revealed an overall cooling effect due to aerosols. At regional scales, however, different mixtures of aerosols led to widely varying effects. For example, the cooling effects of aerosols were larger in the Northern Hemisphere because of higher pollution emissions and infiltration by desert dust. Overall, the heat transfer measurements in this study were consistent with past measurements using other methods. The authors call for additional studies that also integrate data from multiple sources and for improved global measurements of aerosol absorption to better understand and predict the future effects of aerosols on climate change.
  33. 2017: Lacagnina, Carlo, Otto P. Hasekamp, and Omar Torres. “Direct radiative effect of aerosols based on PARASOL and OMI satellite observations.” Journal of Geophysical Research: Atmospheres 122.4 (2017): 2366-2388. Accurate portrayal of the aerosol characteristics is crucial to determine aerosol contribution to the Earth’s radiation budget. We employ novel satellite retrievals to make a new measurement‐based estimate of the shortwave direct radiative effect of aerosols (DREA), both over land and ocean. Global satellite measurements of aerosol optical depth, single‐scattering albedo (SSA), and phase function from PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) are used in synergy with OMI (Ozone Monitoring Instrument) SSA. Aerosol information is combined with land‐surface bidirectional reflectance distribution function and cloud characteristics from MODIS (Moderate Resolution Imaging Spectroradiometer) satellite products. Eventual gaps in observations are filled with the state‐of‐the‐art global aerosol model ECHAM5‐HAM2. It is found that our estimate of DREA is largely insensitive to model choice. Radiative transfer calculations show that DREA at top‐of‐atmosphere is −4.6 ± 1.5 W/m2 for cloud‐free and −2.1 ± 0.7 W/m2 for all‐sky conditions, during year 2006. These fluxes are consistent with, albeit generally less negative over ocean than, former assessments. Unlike previous studies, our estimate is constrained by retrievals of global coverage SSA, which may justify different DREA values. Remarkable consistency is found in comparison with DREA based on CERES (Clouds and the Earth’s Radiant Energy System) and MODIS observations.
  34. 2018: Ralph Kahn, NASAAerosol Remote Sensing and Modeling, 2018. [FULL TEXT] The global scope of aerosol environmental influences makes satellite remote sensing a key tool for the study of these particles. Desert dust storms, wildfire smoke and volcanic ash plumes, and urban pollution palls on hot, cloud-free summer days are among the most dramatic manifestations of aerosol particles visible in satellite imagery [LINK] .  Our group includes the core aerosol science team for the NASA Earth Observing System’s MODerate resolution Imaging Spectroradiometer (MODIS)instruments, and the aerosol scientist for the Multi-angle Imaging SpectroRadiometer (MISR).The MODIS Dark Target, Deep Blue, and MAIAC aerosol algorithms are developed and maintained here, along with the MISR Research Aerosol Retrieval algorithm. We also contribute to the Total Ozone Mapping Spectrometer (TOMS) the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Suomi National Polar-orbiting Partnership’s Visible Infrared Imaging Radiometer Suite (SNPP-VIIRS) aerosol retrieval algorithms. We perform validation studies on all these satellite aerosol products using ground-based remote-sensing aerosol measurements, such as those provided by the global Aerosol Robotic Network (AERONET) of Sun- and sky-scanning photometers and the Micro-Pulse Lidar Network (MPLNet). And through the Goddard Interactive Online Visualization ANd aNalysis Infrastructure (GIOVANNI), we have participated in the development of web-based tools to collocate multiple satellite and AERONET products and to analyze them statistically. In addition, we have developed and maintain a state-of-the-art, ground-based mobile facility for measuring the physical and chemical properties of aerosol and clouds, along with the ambient radiation fields (SMART-COMMIT-ACHIEVE), and the Cloud Absorption Radiometer (CAR) deployed in an aircraft nosecone, that can obtain radiance measurements over the entire sphere in 14 spectral bands. The aerosol applications which we lead, and to which we contribute, range from the fundamental radiative transfer used in satellite aerosol retrieval algorithms, to detailed studies of wildfire smoke and volcanic ash plumes, aerosol pollution events and long-term exposure, as well as large-scale aerosol transports, global energy balance assessments, and climate change studies.
  35. 2018: Herndon, J. Marvin. “Air Pollution, Not Greenhouse Gases: The Principal Cause of Global Warming.” 2018: Time series of global surface temperature presentations often exhibit a bump coincident with World War II (WW2) as did one such image on the front page of the January 19, 2017 New York Times. Intrigued by the front-page New York Times graph, Bernie Gottschalk of Harvard University applied sophisticated curve-fitting techniques and demonstrated that the bump, which shows a global burst in Earth temperature during WW2, is a robust feature showing up in eight independent NOAA databases, four land and four oceans. The broader activities of WW2, especially those capable of altering Earth’s delicate energy balance by particulate aerosols can be generalized to post-WW2 global warming. Increases in aerosolized particulates over time is principally responsible for the concomitant global warming increases. Proxies for global particulate pollution – increasing global coal and crude oil production, as well as aviation fuel consumption – rise in strikingly parallel fashion to the rise in global temperature as shown in the accompanying figure. The World War II wartime particulate-pollution had the same global-warming consequence as the subsequent ever-increasing global aerosol particulate-pollution from (1) increases in aircraft and vehicular traffic, and the industrialization of China and India with their smoke stacks spewing out smoke and coal fly ash, as well as from recently documented studies that show (2) coal fly ash [is being] covertly jet-sprayed into the region where clouds form on a near-daily, near-global basis. It is further noted that the integrity of [IPCC] models and assessments is compromised, because of their failure to take into account the aerosolized pollution particulates that have been intentionally and covertly sprayed into the atmosphere for decades in the region where clouds form. Instead of cooling Earth, as many scientists still believed it would, covert military geoengineering activity increases global warming.
    [FULL TEXT]

 

 

 

ATMOSPHERIC TURBIDITY BIBLIOGRAPHY

  1. 1964: Ångström, Anders. “The parameters of atmospheric turbidity.” Tellus 16.1 (1964): 64-75. The methods for evaluating the atmospheric turbidity parameters, introduced by the present author in 1929–30, are subjected to a critical examination. A method first suggested by M. Herovanu (1959) is here simplified and expanded, and used for deriving the named parameters in adherence to a procedure described by the present author in a previous paper in this journal (1961). The procedure is applied to the pyrheliometric observations at Potsdam in 1932–36, published by Hoelper (1939) A comparison between the frequency distribution of the coefficient of wave‐length dependence α at the high level station Davos and the low level station Potsdam gives results which are discussed in detail. In all the figures of the present paper, where the turbidity coefficients occur, they are multiplied by 103.
  2. 1967: McCormick, Robert A., and John H. Ludwig. “Climate modification by atmospheric aerosols.” Science 156.3780 (1967): 1358-1359. Theoretical considerations and empirical evidence indicate that atmospheric turbidity, a function of aerosol loading, is an important factor in the heat balance of the earth-atmosphere system. Turbidity increase over the past few decades may be primarily responsible for the decrease in worldwide air temperatures since the 1940′s.
  3. 1969: Flowers, E. C., R. A. McCormick, and K. R. Kurfis. “Atmospheric turbidity over the United States, 1961–1966.” Journal of Applied Meteorology 8.6 (1969): 955-962. Five years of turbidity measurements from a network of stations in the United States are analyzed. Measurements are made with the Volz sunphotometer; the instrument, its calibration, and its use are described. The relationship of these measurements to those of Linke and Ångström is briefly discussed. Analysis of the data indicates the following: 1) an annual mean pattern of low turbidity (near 0.05) over the western plains and Rocky Mountains and high turbidity (near 0.14) in the east; 2) observed minimum turbidity near 0.02; 3) an annual cycle of low turbidity in winter and high in summer; 4) lowest turbidity in continental polar air masses and highest in maritime tropical; and 5) no noticeable lowering of turbidity following precipitation.
  4. 1972: Lovelock, James E. “Atmospheric turbidity and CCl3F concentrations in rural southern England and southern Ireland.” Atmospheric Environment (1967) 6.12 (1972): 917-925. The seasonal changes in atmospheric turbidity in rural Southern England and Southern Ireland have been observed and are compared with wind direction and with the concentration of CCl3F a material whose origins are unequivocally anthropogenic. The observations suggest that the dense summertime aerosol is probably an end product of the atmospheric photochemistry of air pollutants and that Continental Europe is the principal source.
  5. 1979: Carlson, Toby N. “Atmospheric turbidity in Saharan dust outbreaks as determined by analyses of satellite brightness data.” Monthly Weather Review 107.3 (1979): 322-335. Using VHRR brightness data obtained from the NOAA 3 satellite, isopleths of aerosol Optical depth for Saharan dust have been drawn for seven days during summer 1974 over a portion of the eastern equatorial North Atlantic. The large-scale patterns reveal an elongated dust plume which emerges from a narrow region along the African coast. Thereafter, the plume moves westward and spreads laterally though maintaining rather discrete boundaries associated with sharp gradients of turbidity, especially along the southern border. Exceptionally large values of optical depth (>2.0) are found near the centers of some dust outbreaks but these high values contribute Little to the total dust loading, which, in typical episodes, are estimated to represent a loss of topsoil from Africa of ∼8 million metric tons of material in a period of 4–5 days. There appeared to be no direct intrusion of the dust plume into the ITCZ or north of 25°N in that region. Outbreaks of dust appear often to be in the rear of a well-developed easterly wave disturbance and inverted V-shaped cloud pattern. This paper demonstrates the feasibility of using satellite brightness data to quantitatively map dust outbreaks.
  6. 1981: Peterson, James T., et al. “Atmospheric turbidity over central North Carolina.” Journal of Applied Meteorology 20.3 (1981): 229-241. Some 8500 observations of atmospheric turbidity, taken at Raleigh, North Carolina from July 1969 to July 1975 are analyzed for within-day and day-to-day variations and their dependence on meteorological parameters. The annual average turbidity of 0.147 (0.336 aerosol optical thickness) is near the highest non-urban turbidity in the United States. A distinct diurnal turbidity cycle was evident with a maximum in early afternoon. Annually, highest turbidity and day-to-day variation occurred during summer with lowest values and variation during winter. Daily averages revealed an asymmetric annual cycle, with a minimum on 1 January and a maximum on 1 August. Turbidity showed a slight inverse dependence on surface wind speed. Aside from winter, highest turbidities occurred with southeast surface winds. Turbidity was directly proportional to both humidity and dew point. Correlations between turbidity and local visibility were best for visibilities <7 mi. Air mass trajectories arriving at Raleigh were used to study the dependence of turbidity on synoptic air mass. Air masses with a southern origin had greatest turbidities. Turbidity of an air mass significantly increased as the residence time of that air mass over the continental United States increased, with the most rapid changes during summer. A combination of Raleigh (1969–present) and Greensboro, North Carolina (1965–76) records showed a distinct summer increase through 1976, but no change during winter. A linear regression of annual averages for the complete record gave an 18% per decade turbidity increase.
  7. 1982: Shaw, Glenn E. “Atmospheric turbidity in the polar regions.” Journal of Applied meteorology 21.8 (1982): 1080-1088. Analysis is presented of 800 measurements of atmospheric monochromatic aerosol optical depth made poleward of ∼65° latitude. The atmosphere of the southern polar region appears to be uncontaminated but is charged with a background aerosol having a mean size of 0.1 μm radius, an almost constant mixing ratio throughout the troposphere, a sea level optical depth (λ = 500 nm) of ∼0.025 and an inferred columnar mass loading of 4-15 × 10−7 g cm−2.At around the time of spring equinox the northern polar region (all longitudes) is invaded with Arctic Haze, an aerosol showing a strong anthropogenic chemical fingerprint. The optical depth anomaly introduced by this man-caused haze is τ0 ≈ 0.110 and the associated columnar mass loading is ∼1.5 × 10−6 g cm−2. Turbidity measured seven decades ago at the solar observatory at Uppsala (60°N), suggests that Arctic optical depth has been rising at a rate of dτ/dt ≈ 0.01 ± 0.005 per decade.
  8. 1994: Jacovides, C. P., et al. “Atmospheric turbidity parameters in the highly polluted site of Athens basin.” Renewable Energy4.5 (1994): 465-470. Data on atmospheric turbidity coefficients, i.e. Linke factor TL and Angstrom coefficient β, calculated from measurements of broad-band filter at Athens Observatory (NOA), are reported. A linear model fitted to β vs TL for Athens is similar to the models reported for Avignon (France) and Dhahran (Saudi Arabia). The variation in the monthly average values of β and TL is of similar trend to that of Avignon and Dhahran. However, Athens has shown higher values of atmospheric turbidity coefficients than Avignon and similar turbidity levels to Dhahran. Finally, the long-term variation of the monthly mean values of the mid-day turbidity parameters and the broad-band direct and diffuse irradiances under cloudless skies are evaluated for the same period. The turbidity trends in conjunction with the trends of solar radiation components reflect the rapid urbanization and industrialization of the Athens basin.
  9. 1994: Gueymard, Christian. “Analysis of monthly average atmospheric precipitable water and turbidity in Canada and northern United States.” Solar Energy 53.1 (1994): 57-71. Atmospheric turbidity and precipitable water data are necessary as inputs to solar radiation or daylight availability models, and to daylighting simulation programs. A new model is presented to obtain precipitable water from long-term averages of temperature and humidity. Precipitable water data derived from this model are tabulated for some Canadian and northern U.S. sites. A discussion on the available turbidity data is presented. An analysis of the datasets from the WMO turbidity network is detailed. The effect of volcanic eruptions is discussed, as well as the possible comparisons with indirect determinations of turbidity from radiation data. A tabulation of the monthly average turbidity coefficients for ten Canadian stations and seven northern U.S. stations of the WMO network is presented.

 

 

 

 

OTHER THEORIES OF COOLING DURING AGW: BIBLIOGRAPHY

  1. 1961: Budyko, Mikhail Ivanovich. “The heat balance of the earth’s surface.” Soviet Geography 2.4 (1961): 3-13. The article discusses the present state of knowledge of the basic components of the heat balance of the earth’s surface (radiation balance, loss of heat to evaporation, turbulent heat exchange) and the distribution of these components in time and space. Soviet research is concerned with applying heat-balance data to the study of physical-geographical processes (hydrologic regime, plant and soil cover), to the study of integrated geographic problems (geographic zonality) and practical problems (weather and hydrologic forecasting, the use of solar energy for productive purposes, and the use of heat-balance data for planning reclamation projects and other nature-transforming measures
  2. 1969: Budyko, Mikhail I. “The effect of solar radiation variations on the climate of the earth.” tellus 21.5 (1969): 611-619. It follows from the analysis of observation data that the secular variation of the mean temperature of the Earth can be explained by the variation of short-wave radiation, arriving at the surface of the Earth. In connection with this, the influence of long-term changes of radiation, caused by variations of atmospheric transparency on the thermal regime is being studied. Taking into account the influence of changes of planetary albedo of the Earth under the development of glaciations on the thermal regime, it is found that comparatively small variations of atmospheric transparency could be sufficient for the development of quaternary glaciations.  [FULL TEXT]
  3. 1978: Angell, J. K., and J. Korshover. “Global temperature variation, surface-100 mb: An update into 1977.” Monthly Weather Review 106.6 (1978): 755-770. Based on a network of 63 well-spaced radiosonde stations around the world, the global temperature within the surface to 100 mb layer was lower in 1976 than in any year since commencement of the record in 1958, and the 1976 surface temperature equated the global record for the lowest temperature set in 1964; but even so the trend in global temperature since 1965 has been small compared to the 0.5°C decrease during 1960–65. Between 1958 and 1976 the surface to 100 mb temperature in north extratropics decreased by about 1°C, with the decrease twice as great in winter as in summer, and in 1976 this region was 0.2°C lower than in any previous year of record. During the northern winter of 1976–77, both temperate zones were very cold but the polar and tropical zones were quite warm, so that in the hemispheric or global average the season was not anomalous. In the Eastern Hemisphere of the northern extratropics there has been considerable surface warming during the past decade (although a cooling aloft), and this may explain the Soviet concern with warming related to carbon dioxide emissions. There has been a slight overall increase in temperature in the tropics since 1965, mostly in the Western Hemisphere, on which have been superimposed large and significant temperature variations of about a three-year period. These variations, probably related to the Southern Oscillation (and recently not so pronounced), extend in obvious fashion also into north extratropics, and should be taken into account for diagnoses and prognoses in northern latitudes. The rate of increase of carbon dioxide at Mauna Loa and the South Pole is augmented in the warm phase of the tropical oscillation, presumably because of a relation between atmospheric and oceanic temperature. There is evidence for a consistent quasi-biennial variation in temperature at all latitudes, with the temperature approximately 0.1°C higher than average about six months prior to the quasi-biennial west wind maximum at 50 mb in the tropics. The spatial and temporal variability in temperature have tended to increase over the period of record, in accord with the increase in meridional temperature gradient in both hemispheres and the indicated increase in lapse rate in the Northern Hemisphere.  [FULL TEXT]
  4. 1981: Asakura, T., and S. Ikeda. “Recent climatic change and unusual weather in the northern hemisphere.” GeoJournal 5.2 (1981): 113-116. Occurrence frequency of unusual weather caused by anomalous synoptic patterns has its peaks in the middle latitude regions and the subtropical regions. Height anomaly patterns at the 500 mb level for the last three decades show the expansion of negative area in the northern hemisphere, resulting in increase of variability in space and time.
  5. 1982: Perry, Allen. “Is the climate becoming more variable?.” Progress in Physical Geography 6.1 (1982): 108-114. bandicam 2018-10-21 16-28-58-252
  6. 1984: Suckling, Philip W. “TRENDS IN MONTHLY TEMPERATURE DEPARTURES FOR THE CONTINGUOUS UNITED STATES, 1940-1983.” Physical Geography 5.2 (1984): 150-163. A temperature departure index is calculated for each month of the year for 10 regions within the contiguous United States utilizing a total of 193 sites for the 44-year period 1940 to 1983. Five-year moving averages of the index values are plotted on graphs for each region by month in an attempt to detect trends toward an increase or decrease in the occurrence of well above or well below normal monthly temperatures in recent years. Considerable regional differences are found with respect to the size and temporal trend of monthly temperature departures. For example, the Northwest and Southwest regions are often exceptions to the average national trend supporting the concept of considerable east-west differences in temperature variation patterns. Only April, June and December show increases in temperature departure index values in the most recent years for a majority of regions while the summer months of July and August do not exhibit a clear national trend. For a majority of months (January, February, March, May, September, October, November), there has been a decrease in the occurrence of unusually above or below normal monthly temperatures for most regions during the late 1970s/early 1980s.
  7. 1984: Suckling, Philip W. “Temperature variability in Georgia in recent years.” Southeastern Geographer 24.1 (1984): 30-41. Southeastern Geographer Vol. 24, No. 1, May 1984,  In recent years several examples of temperature extremes have occurred in Georgia and across the southeast. These include extreme cold in the winter of 1976—77, above normal summer temperatures in 1980 and 1981, and the exceptionally warm Christmas season of 1982. Do these occurrences indicate that temperature variability has increased? Some writers have suggested that there has been an increase in climatic variability in recent years. The following are some relevant quotes: “droughts, floods, heat waves and cold spells unprecedented in living memory “; “record low temperatures reported with increasing frequency in many parts of the United States”; and “the range of short-term variations has widened since the middle of the century.” (J) Studies have addressed the issue of whether the climatic trend is towards cooling or warming. (2) Although the issue of climatic trends of cooling versus warming is important, it is the frequency of extremes (i.e., climatic variability) that may be of more significance to man and his activities, especially in agriculture. (3) In the past, it has been suggested that overall climatic cooling should cause increased temperature variability. However, a study by Van Loon and Williams indicated this concept to be wrong. (4) Previous studies on temperature variability have supported the contention that in recent years an increase in the frequency of extremes has occurred. Asakura and Ikeda concluded that an increase in temperature extremes for the northern hemisphere has occurred in the last two decades compared to the mid-twentieth century . (5) Similarly, Jones, Wigley and Kelly found increased year-toyear variability during the 1970s in a study of northern hemisphere temperature variations over the last century. (6) By contrast, Ratcliffe, Weiler and Collison in a study covering parts of Britain found no trend toward increased climatic variability in the last century. (7) In an assessment of interannual temperature variability for the United States * The technical assistance of Jeon Lee is gratefully acknowledged. Dr. Suckling is Associate Professor of Geography at the University of Georgia in Athens, GA 30602. Vol. XXIV, No. 1 31 since 1896, Chico and Sellers found a decrease in variability for the 1930s to the 1970s. (S) Boer and Higuchi found no evidence to support the contention that the climate has generally become more variable in the northern hemisphere for the last 25 years although, in a later article, they did find evidence suggesting increased summertime temperature variability. (9) Hoyt has shown that the popular opinion that more weather “records” have been set in recent years in the United States is mistaken. If anything, less “records” are being established than statistically expected. (JO) Regional differences in climatic change and variability are to be expected. (JJ) Using a limited number of sites, the study by Van Loon and Williams found decreasing temperature variability for U.S. locations in the midwest and northeast but increasing variability in the south and west. (J2) It is the purpose of the present study to assess temperature variability for the southern state of Georgia. Has there been an increase in the occurrence of unusually above or below normal monthly temperatures in recent years? METHODOLOGY. Mean monthly temperatures for the period 19401982 for seven sites in Georgia plus the nearby locations ofChattanooga, TN, Tallahassee, FL, and Jacksonville, FL, were used for study (Fig. 1). The three non-Georgia stations were included to provide surrogate data for the far northern and southern regions ofthe state in the absence ofappropriate in-state sites. Monthly average temperature and standard deviation values for the 43-year period are given in Table 1. It is notable that winter months have much more temperature variability than summer months as indicated by consistently higher standard deviation values at all sites. In order to assess interannual changes in temperature variability, it is therefore appropriate to conduct the analysis on a month by month basis.
  8. 1987: Suckling, Philip W. “A climate departure index for the study of climatic variability.” Physical Geography 8.2 (1987): 179-188. Three versions of a Climate Departure Index (CDI) are presented for studying how “normal” or “unusual” a particular year or event is compared to the long-term average for the region under consideration. Comparisons of a Simple CDI, Absolute Value CDI and Least-Squares CDI are made through the use of hypothetical examples and two case studies involving seasonal snowfall variations in northern New England and last spring-freeze date variations in the southeastern United States. Results clearly show that the Simple CDI is the inferior formulation owing to a compensation problem whereby above and below average sites within a region for a particular year cancel each other when computing the index value. Little difference in identifying extreme years was found between use of the Absolute Value CDI and Least-Squares CDI in the case studies examined. Nevertheless, a hypothetical example suggests that the least-squares approach for closeness of fit is the more appropriate method, thus making the Least-Squares CDI the preferred version.
  9. 1992: Read, J. F., and W. J. Gould. “Cooling and freshening of the subpolar North Atlantic Ocean since the 1960s.” Nature360.6399 (1992): 55. LITTLE is known of the interdecadal variability in the thermohaline circulation of the world’s oceans, yet such knowledge is essential as a background to studies of the effects of natural and anthropogenic climate change. The subpolar North Atlantic is an area of extensive water mass modification by heat loss to the atmosphere. Lying as it does at the northern limit of the global thermohaline “conveyor belt”12, changes in this region may ultimately have global consequences. Here we report that in August 1991 the waters between Greenland and the United Kingdom were on average 0.08 °C and 0.15 °C colder than in 1962 and 1981, respectively, and slightly less saline than in 1962. The cause appears to be renewed formation of intermediate water in the Labrador Sea from cooler and fresher source waters, and the spreading of this water mass from the west. Variations in the source characteristics of Labrador Sea Water can be traced across the North Atlantic, with a circulation time of 18–19 years between the Labrador Sea and Rockall Trough. More recently formed Labrador Sea Water, with even lower temperature and salinity, should cool and freshen the North Atlantic still further as it circulates around the ocean in the coming decade.
  10. 2000: Andronova, Natalia G., and Michael E. Schlesinger. “Causes of global temperature changes during the 19th and 20th centuries.” Geophysical Research Letters 27.14 (2000): 2137-2140. During the past two decades there has been considerable discussion about the relative contribution of different factors to the temperature changes observed now over the past 142 years. Among these factors are the “external’ factors of human (anthropogenic) activity, volcanoes and putative variations in the irradiance of the sun, and the “internal” factor of natural variability. Here, by using a simple climate/ocean model to simulate the observed temperature changes for different state‐of‐the‐art radiative‐forcing models, we present strong evidence that while the anthropogenic effect has steadily increased in size during the entire 20th century such that it presently is the dominant external forcing of the climate system, there is a residual factor at work within the climate system, whether a natural oscillation or something else as yet unknown. This has an important implication for our expectation of future temperature changes.
  11. 2008: Peterson, Thomas C., William M. Connolley, and John Fleck. “The myth of the 1970s global cooling scientific consensus.” Bulletin of the American Meteorological Society 89.9 (2008): 1325-1338. Climate science as we know it today did not exist in the 1960s and 1970s. The integrated enterprise embodied in the Nobel Prize winning work of the IPCC existed then as separate threads of research pursued by isolated groups of scientists. Atmospheric chemists and modelers grappled with the measurement of changes in carbon dioxide and atmospheric gases, and the changes in climate that might result. Meanwhile, geologists and paleoclimate researchers tried to understand when Earth slipped into and out of ice ages, and why. An enduring popular myth suggests that in the 1970s the climate science community was predicting “global cooling” and an “imminent” ice age, an observation frequently used by those who would undermine what climate scientists say today about the prospect of global warming. A review of the literature suggests that, on the contrary, greenhouse warming even then dominated scientists’ thinking as being one of the most important forces shaping Earth’s climate on human time scales. More importantly than showing the falsehood of the myth, this review describes how scientists of the time built the foundation on which the cohesive enterprise of modern climate science now rests. NOAA/National Climatic Data Center, Asheville
  12. 2014: Hodson, Daniel LR, Jon I. Robson, and Rowan T. Sutton. “An anatomy of the cooling of the North Atlantic Ocean in the 1960s and 1970s.” Journal of Climate 27.21 (2014): 8229-8243. In the 1960s and early 1970s, sea surface temperatures in the North Atlantic Ocean cooled rapidly. There is still considerable uncertainty about the causes of this event, although various mechanisms have been proposed. In this observational study, it is demonstrated that the cooling proceeded in several distinct stages. Cool anomalies initially appeared in the mid-1960s in the Nordic Seas and Gulf Stream extension, before spreading to cover most of the subpolar gyre. Subsequently, cool anomalies spread into the tropical North Atlantic before retreating, in the late 1970s, back to the subpolar gyre. There is strong evidence that changes in atmospheric circulation, linked to a southward shift of the Atlantic ITCZ, played an important role in the event, particularly in the period 1972–76. Theories for the cooling event must account for its distinctive space–time evolution. The authors’ analysis suggests that the most likely drivers were 1) the “Great Salinity Anomaly” of the late 1960s; 2) an earlier warming of the subpolar North Atlantic, which may have led to a slowdown in the Atlantic meridional overturning circulation; and 3) an increase in anthropogenic sulfur dioxide emissions. Determining the relative importance of these factors is a key area for future work.

 

[LIST OF POSTS ON THIS SITE]

 

 

  1. PETM Overview & Bibliography
  2. Climate Change Refugees
  3. Spurious Correlations in Time Series Data
  4. 1C AGW Since Pre-Industrial Times
  5. A Natural Recovery from the LIA?
  6. Aerosols and Climate Change
  7. Ocean Heat Content
  8. Unprecedented Warming of the Arctic
  9. Ocean Acidification by Fossil Fuel Emissions
  10. Hurst Persistence in UAH Temperature?
  11. A Test for ECS Climate Sensitivity in Observational Data
  12. HadCRUT4 Empirical ECS 1850-2017
  13. Climate Change and Hurricanes
  14. HadCRUT4 Mean Global Temperature Reconstruction Uncertainty
  15. Total Hurricane Energy & Fossil Fuel Emissions
  16. Correlation Between Cumulative Emissions and Cumulative Sea Level Rise
  17. A CO2 Radiative Forcing Seasonal Cycle?
  18. Climate Change: Theory vs Data
  19. Correlation of CMIP5 Forcings with Temperature
  20. Is the Solar Cycle Chaotic?
  21. Climate Scientist Proves Human Cause
  22. Stratospheric Cooling
  23. The Holocene Climate Optimum: A Bibliography
  24. Temperature Trend Profiles & the Seasonal Cycle
  25. Climate Change: Late Bronze Age Collapse
  26. Climate Sensitivity Research: 2014-2018
  27. Brewer-Dobson Circulation Bibliography
  28. Empirical Test of Ozone Depletion
  29. History of the Ozone Depletion Scare
  30. The Answer is Blowing in the Wind
  31. Antarctic Sea Ice: 1979-2018
  32. Tidal Cycles: A Bibliography
  33. Does Global Warming Drive Changes in Arctic Sea Ice?
  34. Superstition, Confirmation Bias, and Climate Change
  35. Climate Impact of the Kuwait Oil Fires: A Bibliography
  36. NASA: Evidence of Human Caused Climate Change #4
  37. NASA: Evidence of Human Caused Climate Change #3
  38. NASA: Evidence of Human Caused Climate Change #2
  39. NASA: Evidence of Human Caused Climate Change #1
  40. Global Warming and Arctic Sea Ice: A Bibliography
  41. Carl Wunsch 2010
  42. Little Ice Age Climatology: A Bibliography
  43. Noctilucent Clouds: A Bibliography
  44. The Anthropocene
  45. Event Attribution Case Study Citations
  46. Event Attribution Science: A Case Study
  47. Gerald Marsh, A Theory of Ice Ages
  48. Peer Review Comments on Callendar 1938
  49. The Greenhouse Effect of Atmospheric CO2
  50. Carl Sagan on Climate Change 1980
  51. Climate Change Denial Research: 2001-2018
  52. Climate Change Impacts Research
  53. Anti Fossil Fuel Activists wary of Climate Change Denialists
  54. HISTORY OF THE GLOBAL WARMING SCARE 1980-2010
  55. History of the Global Warming Scare Chapter 6: 2005-2010
  56. History of the Global Warming Scare Chapter 5: 2000-2005
  57. History of the Global Warming Scare Chapter 4: 1995-2000
  58. History of the Global Warming Movement: Chapter 3: 1990-1995
  59. The history of the global warming scare Chapter 2: 1985-1990
  60. History of the global warming scare Chapter 1: 1980-1985
  61. A Nobel Prize for Service to Humanity
  62. Carbon Cycle Measurement Problems Solved with Circular Reasoning
  63. Spurious Correlations in Climate Science
  64. Nonlinear Dynamics: Is Climate Chaotic?
  65. Elevated CO2 and Crop Chemistry
  66. Fishing for climate calamity?
  67. Climate Science 2007: “Dearth of scientific knowledge only adds to the alarm”
  68. Climate Science versus the FangZhi: 2005
  69. The Population Bomb Update: 2010
  70. Global Warming Causes Volcanic Eruption: 2010
  71. The Eve of Destruction by Climate Change
  72. Peer Review in a 97% Consensus Science
  73. ECS: Equilibrium Climate Sensitivity
  74. TCRE: Transient Climate Response to Cumulative Emissions
  75. Demonstration of Spurious Correlations in Climate Science
  76. AGW: Trends in Daily Station Data
  77. Ozone Depletion Chemistry
  78. Human Caused Global Warming