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The Eemian Interglacial

Posted on: December 21, 2018

 

 

 

 

FIGURE 1: JAMES HANSEN ON EEMIAN SEA LEVEL RISE

 

 

FIGURE 1: LANDSCAPE, ANIMALS, AND HUMANS OF THE EEMIAN

 

FIGURE 2: SINCE THE EEMIAN: THE LAST GLACIAL AND THE HOLOCENE

 

 

FIGURE 3: THE GLACIATION AND INTER-GLACIALS IN THE LAST 400,000 YEARS

 

 

 

 

 

 

[LIST OF POSTS ON THIS SITE]

 

 

 

  1. A principal feature of the effort by climate science and the UN to motivate an overhaul of the world’s energy infrastructure away from hydrocarbon fuels has been a repeated invocation of the collapse of the Greenland and Antarctic ice sheets and of the devastation by sea level rise that the melting ice sheets would cause. Some examples of the obsession of climate science with the collapse of the Greenland and Antarctic ice sheets, even when the details in the data are at odds with this assessment, are listed in paragraph#7 to paragraph#28 belowJames Hansen, a high profile climate scientist and activist, has been the primary spokesman for the ice sheet collapse and sea level rise scenarios and of the necessity of attenuating these changes by cutting emissions. Figure 1 is a clip from a Youtube video [LINK]  in which Hansen describes his sea level rise fears. His reference to the Eemian Interglacial period to describe the horror of ice sheet collapse and sea level rise is noteworthy. The fear of “extreme weather” and of “abrupt climate change” also plays a significant role in the case for “climate action” to curtain the current warming trend; and we show here that they too may have their roots in the EemianIn this post we present the case that much of the most dramatic and catastrophic fears of human caused global warming and climate change “since pre-industrial times” ostensibly by way of fossil fuel emissions from the industrial economy, derives from prior natural events. In a related post, a case was presented that the fear of ocean acidification by carbon dioxide from fossil fuels and its species extinction possibilities derive from an ocean acidification and extinction devastation in the Paleocene-Eocene Thermal Maximum (PETM[LINK] . Other oft repeated alarms about the current warming, that of rising ocean heat content and a runaway positive feedback of methane hydrate decomposition may also have been inspired by the PETM
  2. We live in an ice age in which the world is mostly an ice planet during glacial periods (about 90% of the time) but with brief balmy interglacial periods between them (about 10% of the time). We are currently in one of these brief balmy interglacials but strangely fearful of the warmth as an unwanted and dangerous impact of a misalignment between human activity and nature. Our interglacial is  called the Holocene. It evolved about 11,700 years ago (YA) when the Last Glacial Period (115,000YA – 12000YA) receded. The interglacial prior to the Last Glacial Period is called the Eemian. These transitions are depicted in a video clip in Figure 2 taken from a Youtube video [LINK] . It shows transitions in the degree of glaciation from the Eemian interglacial through the glaciation of the Last Glacial Period to its end in the balmy warmth of the Holocene interglacial where we are now. Figure 3 is a video clip of three glaciation-interglacial cycles over a period of 400,000 years. This post is a description of the Eemian interglacial and its relevance to the widespread fear of anthropogenic global warming since the 1980s apparently sparked by rising temperatures since the brief glaciation of the Little Ice Age (LIA) described in a related post [LINK] .
  3. The Eemian interglacial started 130,000 years ago and ended about 115,000 years ago when the Last Glacial Period got started. Paleo climate research on the Eemian interglacial is presented below as a bibliography. The data are mostly from Greenland ice cores and pollen and the geographical areas most studied are Europe and the Arctic. An interesting feature of this line of research, missing in the study of AGW is that winter and summer temperatures are studied separately as their trend behavior can be very different. Despite the usual claim that the intensity of “post industrial anthropogenic global warming” is unprecedented  [LINK] , it is generally agreed that the Eemian, at times, was warmer than the the present by as much as 5ºC (an opposing view in (Hansen 2015) is that it was never more than 1ºC warmer). In general, the Eemian is described as hotter than today with January (boreal winter) temperatures 3ºC to 5ºC higher and July (boreal summer) temperatures 2ºC to 4ºC higher but with large fluctuations in temperature between conditions hotter than today and colder than today. However, three stages of the Eemian are described by most authors as warmer than today, colder than today, and about the same as today over decades and centuries. Rapid fluctuations between warm and cold periods in multi-decadal time scales are found. Fluctuations in winter temperatures correlate with rise and fall of sea level. These changes can be described as abrupt climate change over decades with great regional variability but with an ability of nature for rapid recovery from abrupt changes. It is generally agreed that Eemian climate was more unstable than the Holocene with multiple cold periods lasting from decades to centuries. A remarkable shift occurred about 5,000 years into the Eemian when it cooled by 6ºC to 10ºC before rising again to warm conditions. There is some disagreement in this regard with some authors presenting evidence of a more stable Eemian (Kukla 2000).
  4. A significant feature of the Eemian is sea level rise and fluctuations in sea level caused by fluctuations in temperature. Sea level rise of 3 to 6 meters are reported by some authors and 5 to 9 meters by others and is generally attributed to a complete disintegration of the West Antarctic Ice Sheet. (It is noted that global mean sea level would rise by 6 to 7 meters today if either of the two ice sheets melted completely but it is generally agreed that the Greenland ice sheet was smaller at that time and its complete melt could not have contributed more than 5 meters of sea level rise. The West Antarctic Ice Sheet was likely the main source of the dramatic sea level rise found in the data. Some authors cite sudden warming of 5ºC to 10ºC and “massive surges of icebergs into the North Atlantic” as a perturbation of ocean circulation that was responsible for abrupt climate change in the Eemian. Details of these findings may be found in the Eemian Bibliography presented below.
  5. CONCLUSION: We propose in this post that the fear of ice sheet collapse and devastating sea level rise in the current warming episode described by James Hansen and by other climate scientists  (see “AGW COLLAPSE OF ICE SHEETS” bibliography below) can be related to events in the Eemian but not to the post LIA period of the Holocene. However, the concern we raise in this post is that there is not a sufficient correspondence between these two events, i.e., the Eemian and the post Little Ice Age warming usually attributed to the use of hydrocarbon fuels by humans, to draw conclusions about one from the details of the other.
  6. EXAMPLES OF EEMIAN NIGHTMARES IN THE HOLOCENE
  7. 1999An article in the Journal Science says that the melting of the West Antarctic Ice Sheet is a natural event not related to global warming contrary to claims by climate scientists. The WAIS is indeed melting quite rapidly receding at the rate of 400 feet per year but it has been doing so for thousands of years long before human activity and greenhouse gas emissions, having receded 800 miles since the last ice age. If the process continues unchecked it will melt completely in another 7000 years.Therefore it seems unlikely that the event is linked to human activity or that the time frame of a collapse of the ice shelf could fall within 100 years.
  8. 2001 ABRUPT CLIMATE CHANGE: A report by the National Research Council (USA) says that global warming may trigger climate changes so abrupt that ecosystems will not be able to adapt. Look for local or short term cooling, floods, droughts, and other unexpected changes. A growing CO2 concentration in the atmosphere due to the use of fossil fuels is to blame. Some regional climates have changed by as much as 10C in 10 years. Antarctica’s largest glaciers are rapidly thinning, and in the last 10 years have lost up to 150 feet of thickness in some places, enough to raise global sea levels by 0.4 mm. Global warming is a real problem and it is getting worse.
  9. 2002, ICE SHELF COLLAPSE: A piece of ice the size of Rhode island broke off the Larsen ice shelf in Antarctica and within a month it dissipated sending a huge flotsam of ice into the sea. At about the same time an iceberg the size of Delaware broke off the Thwaites Glacier. A few months ago parts of the Ross ice shelf had broken off in a similar way. These events serve as a dramatic reminders that global warming is real and its effects are potentially catastrophic and underscores the urgent need for a binding international agreement to cut greenhouse gas emissions.
  10. 2004: An unprecedented 4-year study of the Arctic shows that polar bears, walruses, and some seals are becoming extinct. Arctic summer sea ice may disappear entirely. Combined with a rapidly melting Greenland ice sheet, it will raise the sea level 3 feet by 2100 inundating lowlands from Florida to Bangladesh. Average winter temperatures in Alaska and the rest of the Arctic are projected to rise an additional 7 to 13 degrees over the next 100 years because of increasing emissions of greenhouse gases from human activities. The area is warming twice as fast as anywhere else because of global air circulation patterns and natural feedback loops, such as less ice reflecting sunlight, leading to increased warming at ground level and more ice melt. Native peoples’ ways of life are threatened. Animal migration patterns have changed, and the thin sea ice and thawing tundra make it too dangerous for humans to hunt and travel.
  11. 2004: A meltdown of the massive Greenland ice sheet, which is more than 3km-thick would raise sea levels by an average seven meters, threatening countries such as Bangladesh, certain islands in the Pacific and some parts of Florida. Greenland’s huge ice sheet could melt within the next thousand years if emissions of carbon dioxide (CO2) and global warming are not reduced.
  12. 2004: The Arctic Climate Impact Assessment (ACIA) report says: increasing greenhouse gases from human activities is causing the Arctic to warm twice as fast as the rest of the planet; in Alaska, western Canada, and eastern Russia winter temperatures have risen by 2C to 4C in the last 50 years; the Arctic will warm by 4C to 7C by 2100. A portion of Greenland’s ice sheet will melt; global sea levels will rise; global warming will intensify. Greenland contains enough melting ice to raise sea levels by 7 meters; Bangkok, Manila, Dhaka, Florida, Louisiana, and New Jersey are at risk of inundation; thawing permafrost and rising seas threaten Arctic coastal regions; climate change will accelerate and bring about profound ecological and social changes; the Arctic is experiencing the most rapid and severe climate change on earth and it’s going to get a lot worse; Arctic summer sea ice will decline by 50% to 100%; polar bears will be driven towards extinction; this report is an urgent SOS for the Arctic; forest fires and insect infestations will increase in frequency and intensity; changing vegetation and rising sea levels will shrink the tundra to its lowest level in 21000 years; vanishing breeding areas for birds and grazing areas for animals will cause extinctions of many species; “if we limit emission of heat trapping carbon dioxide we can still help protect the Arctic and slow global warming”.
  13. 2007: A comparison of Landsat photos taken on 8/11/1985 and 9/5/2002 shows that global warming caused by our use of fossil fuels is melting the massive Greenland ice sheet and exposing the rocky peninsula beneath the ice previously covered by ice.
  14. 2007: Climate scientists say that the current rate of increase in the use of fossil fuels will melt the Greenland ice sheet and cause sea levels to rise by 7 meters in 100 years and devastate low-lying countries like Bangladesh. When these estimates were challenged and their internal inconsistencies exposed, the forecast was quietly revised downward 100-fold from 7 meters to 7 centimeters on their website but the news media alarm about 7 meters continued unabated with “thousands of years” inserted in place of “100 years. 
  15. 2008: IMMINENT COLLAPSE OF PETERMANN GLACIER IN GREENLAND
    Climate scientists looking through satellite pictures found a crack in the Petermann glacier in Greenland and concluded that it could speed up sea level rise because huge chunks of ice the size of Manhattan were hemorrhaging off. Yet, scientists who has been travelling to Greenland for years to study glaciers say that the crack in the glacier is normal and not different from other cracks seen in the 1990s.
  16. 2008: When there was a greater focus on Antarctica climate scientists said that global warming was melting the West Antarctic Ice Shelf; but the melting was found to be localized and with an active volcano underneath the melting and the attention of “melt forecast” climate science shifted to Arctic sea ice after the an extensive summer melt was observed in September 2007.
  17. 2008: Climate scientists have determined that Adelie penguins in Antarctica are threatened because climate change is melting Antarctic glaciers although it is not clear whether the melting is caused greenhouse gas emissions or by volcanic activity underneath the ice.
  18. 2008: Mt. Erebus along with most of the mountains in Antarctica are volcanic mountains and it is now known with certainty that volcanic activity under the ice there is causing great amounts of ice to melt and to cause glaciers to flow faster. The attempt by climate scientists to represent these events as climate change phenomena is inconsistent with this reality.
  19. 2008: THE FIRE BELOW: A volcano under the West Antarctic Ice Sheet, that last erupted 2000 years ago, is now active and responsible for melting ice and for retreating glaciers in that part of the continent (The fire below, Bangkok Post, April 28, 2008). Yet, climate scientists claim that these changes are man-made and that they are caused by carbon dioxide emissions from fossil fuels as predicted by their computer model of the earth’s climate.
  20. 2009: Carbon dioxide emissions from fossil fuels have caused the Wilkins Ice Shelf to break up. If all of the land based ice in Antarctica melted it would raise the sea level by 80 meters. 
  21. 2009: Human caused global warming is causing havoc in Antarctica with potentially incalculable results. Over one hundred icebergs broke off and a huge flotilla of them are floating up to New Zealand. 
  22. 2009: Our carbon dioxide emissions are causing the East Antarctic ice shelf to lose 57 billion tonnes of ice per year and that if CO2 emissions are not reduced this process could raise sea levels by 5 meters.
  23. 2009: Temperature data 1957-2008 show that the whole of Antarctica including Western Antarctica, the Antarctic Peninsula, and Eastern Antarctica, is warming due to CO2 emissions from fossil fuels.
  24. 2009: Man-made global warming is causing Greenland’s glaciers to melt at an alarming rate. By the year 2100 all the ice there will have melted causing a calamitous rise in the sea level that will inundate Bangladesh, the Maldives, Bangkok, New Orleans, and atolls in the Pacific. 
  25. 2009: Climate scientists say that the melting of Antarctica is more severe than “previously thought” because the melt is not limited to the Antarctic Peninsula but extends to West Antarctica as well. The melt could cause devastating sea level rise. (although new data show that the West Antarctic ice shelf collapses every 40,000 years or so and that this cyclical process has been regular feature of this ice shelf for millions of years (Antarctica ice collapses were regular, Bangkok Post, March 19, 2009). These melting episodes can raise the sea level by as much as 5 meters but the process takes a thousand years or more.
  26. 2009: Climate scientists say that the Wilkins Ice Shelf collapse is caused by warming of the Antarctic Peninsula due to man-made “global climate change”.
  27. 2009: In 2005 two glaciers in Greenland were found to be moving faster than they were in 2001. Scientists concluded from these data that the difference observed was a a long term trend of glacial melt in Greenland and that carbon dioxide was the cause of this trend. The assumed trend was then extrapolated forward and we were told that carbon dioxide would cause the land based ice mass of Greenland to be discharged to the sea and raise the sea level by six meters. They said that the only way out of the devastation was to drastically reduce carbon dioxide emissions from fossil fuels. However, in 2009, just before a meeting in Copenhagen where these deep cuts in emissions were to be negotiated, it was found that the glaciers had returned to their normal rate of discharge.
  28. 2009: Some glaciers on north and northeast Greenland terminate in fiords with long glacier tongues that extend into the sea. It is found that the warming of the oceans caused by our use of fossil fuels is melting these tongues and raising the specter of devastation by sea level rise.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EEMIAN BIBLIOGRAPHY

Featured Authors

Katrine Andersen, Michael Field, Eugene Karabonov, Willem Vandeberg, Andrew Weaver, Waldo Zagwijn

  1. 1993: Dansgaard, Willi, et al. “Evidence for general instability of past climate from a 250-kyr ice-core record.” Nature 364.6434 (1993): 218.  RECENT results1,2 from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent during the late stages of the last glaciation, suggesting that climate in the North Atlantic region is able to reorganize itself rapidly, perhaps even within a few decades. Here we present a detailed stable-isotope record for the full length of the Greenland Ice-core Project Summit ice core, extending over the past 250 kyr according to a calculated timescale. We find that climate instability was not confined to the last glaciation, but appears also to have been marked during the last interglacial (as explored more fully in a companion paper3) and during the previous Saale–Holstein glacial cycle. This is in contrast with the extreme stability of the Holocene, suggesting that recent climate stability may be the exception rather than the rule. The last interglacial seems to have lasted longer than is implied by the deep-sea SPECMAP record4, in agreement with other land-based observations5,6. We suggest that climate instability in the early part of the last interglacial may have delayed the melting of the Saalean ice sheets in America and Eurasia, perhaps accounting for this discrepancy.
  2. 1994: Field, Michael H., Brian Huntley, and Helmut Müller. “Eemian climate fluctuations observed in a European pollen record.” Nature 371.6500 (1994): 779. Recent ice-core data from Greenland1,2 suggest that the climate during the last interglacial period the Eemian was more unstable than that of the Holocene (about 10,000 years ago to the present), being characterized in particular by a series of cold episodes each lasting about 70 to 750 years. Subsequent analysis of a second Greenland ice core3,4, however, failed to corroborate the details of these Eemian climate fluctuations, a result that may be attributable to the effects of ice flow4. To resolve this discrepancy, it is imperative to seek alternative sources of information about the Eemian climate. Here we present climate reconstructions from pollen data from the annually laminated Eemian lake-sediment record at Bispingen5 and from the Eemian and Holocene peat records at La Grande Pile6. The former record indicates that an initially warm period of 2,900 yr was followed by cooling and a series of colder episodes, one of which had winter temperatures comparable to those at the end of the preceding cold stage. The latter records show greater climate instability during the Eemian than the Holocene. These results are in broad agreement with those from the GRIP ice core, but contrast both with the GISP2 core3,4 and with recent high-resolution marine records from the North Atlantic7,8.
  3. 1994: Weaver, Andrew J., and Tertia MC Hughes. “Rapid interglacial climate fluctuations driven by North Atlantic ocean circulation.” Nature 367.6462 (1994): 447. RECENT data from the GRIP ice core1–3 in Greenland suggest that the climate of the last Eemian interglacial period was much less stable than that of the present interglacial. Rapid transitions between warm and cold periods were found to occur on timescales of just a few decades. The North Atlantic climate during the Eemian period was also shown to be characterized by three states, respectively warmer than, similar to and colder than today1,2. Recent data from the nearby GISP2 ice core have revealed some discrepancies with these findings, which remain to be resolved4,5. Here we present simulations using an idealized global ocean model, which suggest that the North Atlantic ocean has three distinct circulation modes, each of which corresponds to a distinct climate state. We find that adding a simple random component to the mean freshwater flux (which forces circulation) can induce rapid transitions between these three modes. We suggest that increased variability in the hydrological cycle associated with the warmer Eemian climate could have caused transition between these distinct modes in the North Atlantic circulation, which may in turn account for the apparent rapid variability of the Eemian climate.
  4. 1994: Keigwin, Lloyd D., et al. “The role of the deep ocean in North Atlantic climate change between 70 and 130 kyr ago.” Nature371.6495 (1994): 323.  THE suggestion1 that changes in North Atlantic Deep Water (NADW) production are linked through surface heat flux to the atmospheric temperature over Greenland is supported by earlier indications2,3 that NADW production decreased during glacial times, and by the subsequent finding4–6 that it declined during the Younger Dryas cool period at the end of the last glaciation. Changes in North Atlantic surface temperatures have been found7 to mirror high-frequency temperature changes recorded in Greenland ice cores over the past 80 kyr, but the connection to abyssal circulation has yet to be established, except for one or two isolated oscillations8,9. Here we present carbon and oxygen isotope analyses of benthic foraminifera in a high-resolution North Atlantic deep-sea sediment core for the period 70–130kyr ago. These data allow us to reconstruct the history of NADW production, which shows a close correlation with Greenland climate variability for much of this time interval, suggesting that the climate influence of NADW variability was widespread. We see no evidence, however, for changes in NADW production during substage 5e (the Eemian interglacial period), in contrast with recent ice-core data10which suggest severe climate instability in Greenland during this time period. Our results may support suggestions, based on data from a second ice core, that this apparent instability is an artefact caused by ice flow11. Alternatively, the Eemian climate instability may have had a different origin from the subsequent climate events.
  5. 1995: Blanchon, Paul, and John Shaw. “Reef drowning during the last deglaciation: evidence for catastrophic sea-level rise and ice-sheet collapse.” Geology 23.1 (1995): 4-8.  Elevations and ages of drowned Acropora palmata reefs from the Caribbean-Atlantic region document three catastrophic, metre-scale sea-level–rise events during the last deglaciation. These catastrophic rises were synchronous with (1) collapse of the Laurentide and Antarctic ice sheets, (2) dramatic reorganization of ocean-atmosphere circulation, and (3) releases of huge volumes of subglacial and proglacial meltwater. This correlation suggests that release of stored meltwater periodically destabilized ice sheets, causing them to collapse and send huge fleets of icebergs into the Atlantic. Massive inputs of ice not only produced catastrophic sea-level rise, drowning reefs and destabilizing other ice sheets, but also rapidly reduced the elevation of the Laurentide ice sheet, flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid North Atlantic. Such dramatic evidence of catastrophic climate and sea-level change during deglaciation has potentially disastrous implications for the future, especially as the stability of remaining ice sheets—such as in West Antarctica—is in question
  6. 1996: Zagwijn, W. H. “An analysis of Eemian climate in western and central Europe.” Quaternary Science Reviews 15.5-6 (1996): 451-469. On the basis of 31 pollen diagrams and additional data for botanical macrofossils an analysis is made of the Last Interglacial Eemian climatic history in Western and Central Europe. The main tool for this analysis is the climatic indicator species method. Only selected woody species are used for the quantification of data. Partial climatic range diagrams are presented for: Abies alba, Acer monspessulanum, Acer tataricum, Buxus sempervirens, Tilia tomentosa. The problem of time correlation and pollen zonation of the Eemian is discussed. The climatic analysis itself is based on an improved version of the indicator species method. In this version not every site is analysed for its climatic values. Instead maps and tables on the migrational history of Hedera, Ilex, Buxus, Abies and species of Acer, Tilia and Abies are the basis for climatic maps showing respectively January and July isotherms for the periods of the Corylus zone (E4a) and the Carpinus zone (E5). It is concluded that mean January temperatures were as much as 3°C higher at Amsterdam (The Netherlands), than at present, and mean temperatures in July were 2°C higher. However, the thermal maximum in winter was later (zone E5) than the summer thermal maximum (zone E4a). Winter temperatures changed parallel to rise and fall of global sea-level. Precipitation changes are more difficult to estimate. In the first part of the Eemian precipitation must have been relatively low, but from zone E4b onward it increased to higher values, reaching 800 mm and probably substantially more in zones E5 and E6. Hence the Eemian climate was in its beginning relatively more contintental, and later (from E4b onward) more oceanic. However, as compared with the Holocene, the Eemian climate was, generally speaking, more oceanic.
  7. 1996: Litt, Thomas, Frank W. Junge, and Tanja Böttger. “Climate during the Eemian in north-central Europe—a critical review of the palaeobotanical and stable isotope data from central Germany.” Vegetation History and Archaeobotany 5.3 (1996): 247-256.  This paper reviews the evidence from terrestrial palaeoenvironmental records in north-central Europe and, in particular, central Germany, which relates to the controversial proposition that there were strong climate oscillations during the last interglacial (oxygen isotope substage 5e). In contrast to the evidence from the GRIP ice core at Summit, Greenland, and a recent palaeoclimate reconstruction based on the pollen profile from Bispingen, Germany, the evaluation of the palaeobotanical and the stable isotope data presented here strongly suggests relatively stable temperature for most of the Eemian and with instability confined to the beginning and end of the interglacial. High amplitude temperature variations can be seen in both the Early Weichselian pollen and isotope records. It is argued that this pattern of climate development is applicable to most of continental north-central Europe.
  8. 1997: Johnsen, Sigfús J., et al. “The δ18O record along the Greenland Ice Core Project deep ice core and the problem of possible Eemian climatic instability.” Journal of Geophysical Research: Oceans 102.C12 (1997): 26397-26410.  Over 70,000 samples from the 3029‐m‐long Greenland Ice Core Project (GRIP) ice core drilled on the top of the Greenland Ice Sheet (Summit) have been analyzed for δ8O. A highly detailed and continuous δ8O profile has thus been obtained and is discussed in terms of past temperatures in Greenland. We also discuss a three‐core stacked annual δ8O profile for the past 917 years. The short‐term (<50 years) variability of the annual δ8O signal is found to be 1‰ in the Holocene, and estimates for the coldest parts of the last glacial are 3‰ or higher. These data also provide insights into possible disturbances of the stratigraphic layering in the core which seems to be sound down to the onset of the Eemian. Spectral analysis of highly detailed sequences of the profile helps determine the smoothing of the δ8O signal, which for the Holocene ice is found to be considerably stronger than expected. We suggest this is due to a process involving diffusion of water molecules along crystal boundaries in the recrystallizing ice matrix. Deconvolution techniques were employed for restoring with great confidence the highly attenuated annual δ8O signal in the Holocene. We confirm earlier findings of dramatic temperature changes in Greenland during the last glacial cycle. Abrupt and strong climatic shifts are also found within the Eem/Sangamon Interglaciation, which is normally recorded as a period of warm and stable climate in lower latitudes. The stratigraphic continuity of the Eemian layers is consequently discussed in section 3 of this paper in terms of all pertinent data which we are not able to reconcile
  9. 1998: Cheddadi, R., et al. “Was the climate of the Eemian stable? A quantitative climate reconstruction from seven European pollen records.” Palaeogeography, Palaeoclimatology, Palaeoecology 143.1-3 (1998): 73-85. The aim of the present study is to estimate the range of the climatic variability during the Eemian interglacial, which lasted about 10,000 years (marine isotopic stage 5e). The modern pollen analogue technique is applied to seven high resolution pollen records from France and Poland to infer the annual precipitation and the mean temperature of the coldest month. The succession of pollen taxa and the reconstructed climate can be interpreted coherently. The warmest winter temperatures are centred in the first three millennia of the Eemian interglacial, during the mixed oak forest phase with Quercus and Corylus as dominant trees. A rapid shift to cooler winter temperatures of about 6° to 10°C occurred between 4000 and 5000 years after the beginning of the Eemian, related to the spread of the Carpinus forest. This shift is more obvious for the reconstructed temperatures than for precipitation and is unique and irreversible for the whole Eemian period. Following this climatic shift of the Eemian, variations of temperature and precipitation during the last 5000 years were only slight with an amplitude of about 2° to 4°C and 200 to 400 mm/yr. The estimated temperature changes were certainly not as strong as those reconstructed for the stage 6/5e termination or the transition 5e/5d. This is consistent with the constantly high ratio of tree pollen throughout the Eemian, indicative of a succession of temperate forest types. This gradual transition between different forest landscapes can be related to intrinsic competition between the species rather than to a drastic climatic change.
  10. 1998: Aalbersberg, Gerard, and Thomas Litt. “Multiproxy climate reconstructions for the Eemian and Early Weichselian.” Journal of Quaternary Science: Published for the Quaternary Research Association 13.5 (1998): 367-390. Palaeobotanical, coleopteran and periglacial data from 106 sites across northwestern Europe have been analysed in order to reconstruct palaeoclimatic conditions during the Eemian and Early Weichselian. Three time slices in the Eemian and four in the Early Weichselian have been considered. In the Pinus–Quercetum mixtum–Corylus phase of the Eemian, summer temperatures were probably at their highest and the botanic evidence suggests a southeast to northwest gradient for both the warmest and coldest month. Coleoptera indicate that the summers in southern England were several degrees warmer than those of present day. The climate during theCarpinus–Picea phase was uniform and oceanic without obvious gradients. In the final time slice of the Eemian, the Pinus–Picea–Abies phase, temperatures of the warmest month seem to drop slightly with some indication of a shift towards a more boreal and suboceanic climate. The reconstruction of the palaeoclimate in the Herning Stadial and Rederstall Stadial is hampered by the limited number of sites, but botanical evidence suggests a gradient in temperature of the coldest month from east to west. Coleoptera from the Herning Stadial in central England and eastern Germany suggest similarly cold and continental climates. During the Brørup Interstadial and the Odderade Interstadial the botanical evidence suggests that the minimum mean July temperatures rose to 15–16°C but during the coldest month these temperatures show a gradient between −13°C in the east and −5°C in the west. © 1998 John Wiley & Sons, Ltd.
  11. 2000: Cuffey, Kurt M., and Shawn J. Marshall. “Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet.” Nature 404.6778 (2000): 591.  During the last interglacial period (the Eemian), global sea level was at least three metres, and probably more than five metres, higher than at present1,2. Complete melting of either the West Antarctic ice sheet or the Greenland ice sheet would today raise sea levels by 6–7 metres. But the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the West Antarctic ice sheet3, with model studies attributing only 1–2 m of sea-level rise to meltwater from Greenland4,5. This result was considered consistent with ice core evidence4, although earlier work had suggested a much reduced Greenland ice sheet during the last interglacial period6. Here we reconsider the Eemian evolution of the Greenland ice sheet by combining numerical modelling with insights obtained from recent central Greenland ice-core analyses. Our results suggest that the Greenland ice sheet was considerably smaller and steeper during the Eemian, and plausibly contributed 4–5.5 m to the sea-level highstand during that period. We conclude that the high sea level during the last interglacial period most probably included a large contribution from Greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the West Antarctic ice sheet. [FULL TEXT PDF]  
  12. 2000: Karabanov, Eugene B., et al. “Evidence for mid-Eemian cooling in continental climatic record from Lake Baikal.” Journal of Paleolimnology 23.4 (2000): 365-371. The discussion on climatic instability observed in Greenland ice cores during the Eemian period (substage 5e) resulted in discovery of a pronounced mid-Eemian cooling event. We report that the mid-Eemian cooling is found for the first time in the biogenic silica climatic record and microfossil abundance record of Lake Baikal. Timing of this event in Lake Baikal correlates well with timing of the European pollen records and marine sedimentary records. The presence of the mid-Eemian cooling signal in the Lake Baikal record suggests a much closer link between Asian climate influenced by strong pressure fields over the vast land masses and the climate-controlling processes in the North Atlantic during interglacial periods, than what was generally believed. Furthermore, the Lake Baikal record suggests that after the mid-Eemian cooling, the climatic conditions returned close to the warmth of the 5e optimum and thus argues that the warm conditions of the last interglacial persisted in Siberia throughout 5e, and did not end with the mid-Eemian cooling as suggested by several published marine records.
  13. 2000: Kukla, George J. “The last interglacial.” Science 287.5455 (2000): 987-988.  Climate during the last 10,000 years, the Holocene, has been relatively mild and stable. In contrast, the climate during the last interglacial is often portrayed as more variable. But, as Kukla discusses in this Perspective, evidence for a more stable last interglacial is emerging. Furthermore, the transition to the next glacial proceeded in stages and was not uniform across Europe.
  14. 2002: Rahmstorf, Stefan. “Ocean circulation and climate during the past 120,000 years.” Nature 419.6903 (2002): 207. Oceans cover more than two-thirds of our blue planet. The waters move in a global circulation system, driven by subtle density differences and transporting huge amounts of heat. Ocean circulation is thus an active and highly nonlinear player in the global climate game. Increasingly clear evidence implicates ocean circulation in abrupt and dramatic climate shifts, such as sudden temperature changes in Greenland on the order of 5–10 °C and massive surges of icebergs into the North Atlantic Ocean — events that have occurred repeatedly during the last glacial cycle.
  15. 2002: Cane, Tim, et al. “High-resolution stratigraphic framework for Mediterranean sapropel S5: defining temporal relationships between records of Eemian climate variability.” Palaeogeography, Palaeoclimatology, Palaeoecology 183.1 (2002): 87-101. A high-resolution stratigraphic framework is presented for sapropel S5, which represents the low-mid latitude climate optimum of the previous interglacialperiod (Eemian). The framework is based on three sites along a transect from west to east through the eastern Mediterranean, and is further validated using a fourth site. This method allows expression of S5-based proxy records of Eemianclimate variability along a standardised depth scale that offers unprecedented possibilities for assessment of spatial gradients and signal leads and lags in an interval where high-resolution (radiocarbon-style) dating cannot be performed. Our lateral comparison of S5 sapropels suggests that the onset of S5 in ODPsite 967C (Eratosthenes seamount) was 1–6 centuries delayed relative to the onsets in more westerly sites.  [FULL TEXT PDF]
  16. 2003: Klotz, Stefan, Joel Guiot, and Volker Mosbrugger. “Continental European Eemian and early Würmian climate evolution: comparing signals using different quantitative reconstruction approaches based on pollen.” Global and Planetary Change36.4 (2003): 277-294. Analyses of Eemian climate dynamics based on different reconstruction methods were conducted for several pollen sequences in the northern alpine foreland. The modern analogue and mutual climate sphere techniques used, which are briefly presented, complement one another with respect to comparable results. The reconstructions reveal the occurrence of at least two similar thermal periods, representing temperate oceanic conditions warmer and with a higher humidity than today. Intense changes of climate processes become obvious with a shift of winter temperatures of about 15 °C from the late Rissian to the first thermal optimum of the Eemian. The transition shows a pattern of summer temperatures and precipitation increasing more rapidly than winter temperatures. With the first optimum during the PinusQuercetum mixtumCorylus phase (PQC) at an early stage of the Eemian and a second optimum period at a later stage, which is characterised by widespread Carpinus, climate gradients across the study area were less intense than today. Average winter temperatures vary between −1.9 and 0.4 °C (present-day −3.6 to 1.4 °C), summer temperatures between 17.8 and 19.6 °C (present-day 14 to 18.9 °C). The timberline expanded about 350 m when compared to the present-day limit represented by Pinus mugo. Whereas the maximum of temperature parameters is related to the first optimum, precipitation above 1100 mm is higher during the second warm period concomitant to somewhat reduced temperatures. Intermediate, smaller climate oscillations and a cooling becomes obvious, which admittedly represent moderate deterioration but not extreme chills. During the boreal semicontinental Eemian PinusPiceaAbies phase, another less distinct fluctuation occurs, initiating the oscillating shift from temperate to cold conditions.
  17. 2004: Andersen, Katrine K., et al. “High-resolution record of Northern Hemisphere climate extending into the last interglacial period.” Nature 431.7005 (2004): 147. Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from a North Greenland ice core, which extends back to 123,000 years before the present, within the last interglacial period. The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5 °C warmer than today. We find unexpectedly large temperature differences between our new record from northern Greenland and the undisturbed sections of the cores from central Greenland, suggesting that the extent of ice in the Northern Hemisphere modulated the latitudinal temperature gradients in Greenland. This record shows a slow decline in temperatures that marked the initiation of the last glacial period. Our record reveals a hitherto unrecognized warm period initiated by an abrupt climate warming about 115,000 years ago, before glacial conditions were fully developed. This event does not appear to have an immediate Antarctic counterpart, suggesting that the climate see-saw between the hemispheres (which dominated the last glacial period) was not operating at this time.  [FULL TEXT PDF] 
  18. 2006: Peltier, W. R., and Richard G. Fairbanks. “Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record.” Quaternary Science Reviews25.23-24 (2006): 3322-3337.  Fundamental characteristics of the climate system during the most recent precessional cycle of the Earth’s orbit around the Sun consist of the final expansion of land ice to its maximum extent, the subsequent episode of deglaciation, and the variations of global sea level that accompanied these events. In order to address the important issue of the variation of continental ice volume and related changes in global sea level through the late glacial period, we employ an extended set of observations of the pre-glacial and postglacial history of sea-level rise at the island of Barbados, together with a refined model of continental deglaciation and an accurate methodology for the prediction of postglacial sea-level change. Although our results provide unambiguous evidence that the post LGM rise of eustatic sea-level was very close to the widely supported estimate of 120 m, the data also provide evidence that LGM must have occurred 26,000 years ago, approximately 5000 yr earlier than the usually assumed age.
  19. 2007: Tarasov, Pavel, et al. “Vegetation and climate dynamics during the Holocene and Eemian interglacials derived from Lake Baikal pollen records.” Palaeogeography, Palaeoclimatology, Palaeoecology 252.3-4 (2007): 440-457. The last interglacial (LI) and Holocene changes in annual precipitation (Pann), the mean temperature of the warmest (Tw) and coldest (Tc) month and the moisture index (α) were reconstructed from continuous pollen records from Lake Baikal. The Holocene core (52°31′N, 106°09′E) presented in this study was recovered from a depth of 355 m in the 25-km wide underwater Buguldeika saddle separating the southern sub-basin of Lake Baikal from its central sub-basin. The biome reconstruction shows that tundra and steppe biomes have highest scores during ca. 15,000–13,300 cal. years B.P. and that taiga becomes a dominant vegetation type after ca. 13,300 cal. years B.P. Our quantitative reconstruction indicates an onset of relatively warm and wet conditions soon after ca. 10,000 cal. years B.P. The warmest and wettest climate with Tw ∼ 16 °C, Pann ∼ 480 mm and α ∼ 0.9–1 has been reconstructed for ca. 9000–7000 cal. years B.P. In the Lake Baikal region this interval is characterized by the appearance and spread of hunter communities (Kitoi culture). Consistently a hiatus in the regional archaeological record (4900–4200 years B.C. or 6850–6150 cal. years B.P.) coincides with the interval of a major climate deterioration which followed the ‘climatic optimum’. An attempt to find a relationship between the archaeological record and a spread of steppe and meadow communities in the Lake Baikal region demonstrates that despite a long habitation of the area the human impact on vegetation was local rather than regional and likely did not affect the pollen record from Lake Baikal. The reconstructed peaks in the steppe biome scores during the last 9000 years are consistent with short (one to five hundred year) episodes of weak Pacific (summer) monsoon supporting our interpretation that the Holocene vegetation changes around Lake Baikal are associated with large-scale circulation processes controlling regional water balance rather than with human activities. Thus, our study proves the suitability of Lake Baikal pollen data for the reconstruction of natural vegetation and climate dynamics through the whole period from the onset of the LI to the present. Comparison of the recent and the last interglacial suggests that the Holocene ‘climatic optimum’ was less pronounced (e.g. lower summer and winter temperatures and annual precipitation sums) than that of the LI. On the other hand, pollen records demonstrate that the Holocene ‘forest phase’ already lasts some thousand years longer than that of the LI. The interglacial vegetation dynamics derived from the Lake Baikal pollen records can be satisfactorily explained by reconstructed changes in summer and winter temperatures and in available moisture. The interglacial vegetation around Lake Baikal is dominated by the boreal forests, which are associated with a generally warm and wet climate. The high sea level associated with decreased ice volume appears to have had a greater impact on the Siberian environments during the last and the recent interglacial than the direct effect of lower-than-present winter insolation. Reconstructed changes in the winter temperature correlate well with changes in the sea level and global ice volume, while the summer temperatures derived from the Lake Baikal pollen records track changes in the summer insolation.  [FULL TEXT PDF]
    • 2007: Schurgers, Guy, et al. “The effect of land surface changes on Eemian climate.” Climate dynamics 29.4 (2007): 357-373. Transient experiments for the Eemian (128–113 ky BP) were performed with a complex, coupled earth system model, including atmosphere, ocean, terrestrial biosphere and marine biogeochemistry. In order to investigate the effect of land surface parameters (background albedo, vegetation and tree fraction and roughness length) on the simulated changes during the Eemian, simulations with interactive coupling between climate and vegetation were compared with additional experiments in which these feedbacks were suppressed. The experiments show that the influence of land surface on climate is mainly caused by changes in the albedo. For the northern hemisphere high latitudes, land surface albedo is changed partially due to the direct albedo effect of the conversion of grasses into forest, but the indirect effect of forests on snow albedo appears to be the major factor influencing the total absorption of solar radiation. The Western Sahara region experiences large changes in land surface albedo due to the appearance of vegetation between 128 and 120 ky BP. These local land surface albedo changes can be as much as 20%, thereby affecting the local as well as the global energy balance. On a global scale, latent heat loss over land increases more than 10% for 126 ky BP compared to present-day.  [FULL TEXT PDF]
    • 2008: Brewer, S., et al. “The climate in Europe during the Eemian: a multi-method approach using pollen data.” Quaternary Science Reviews 27.25-26 (2008): 2303-2315. The Last Interglacial period, the Eemian, offers a testbed for comparing climate evolution throughout an interglacial with the current warm period. We present here results from climatic reconstructions from 17 sites distributed across the European continent, allowing an assessment of trends and regional averages of climate changes during this period. We use a multi-method approach to allow for an improved assessment of the uncertainties involved in the reconstruction. In addition, the method takes into account the errors associated with the age model. The resulting uncertainties are large, but allow a more robust assessment of the reconstructed climatic variations than in previous studies. The results show a traditional three-part Eemian, with an early optimum, followed by slight cooling and eventually a sharp drop in both temperatures and precipitation. This sequence is however, restricted to the north, as this latter change is not observed in the south where temperatures remain stable for longer. These variations led to marked variation in the latitudinal temperature gradient during the Eemian. The difference between the two regions is also noticeable in the magnitude of changes, with greater variations in the north than the south. Some evidence is found for changes in lapse rates, however, a greater number of sites is needed to confirm this.  [FULL TEXT PDF]
    • 2009: Kopp, Robert E., et al. “Probabilistic assessment of sea level during the last interglacial stage.” Nature 462.7275 (2009): 863.  With polar temperatures 3–5 °C warmer than today, the last interglacial stage (125 kyr ago) serves as a partial analogue for 1–2 °C global warming scenarios. Geological records from several sites indicate that local sea levels during the last interglacial were higher than today, but because local sea levels differ from global sea level, accurately reconstructing past global sea level requires an integrated analysis of globally distributed data sets. Here we present an extensive compilation of local sea level indicators and a statistical approach for estimating global sea level, local sea levels, ice sheet volumes and their associated uncertainties. We find a 95% probability that global sea level peaked at least 6.6 m higher than today during the last interglacial; it is likely (67% probability) to have exceeded 8.0 m but is unlikely (33% probability) to have exceeded 9.4 m. When global sea level was close to its current level (≥-10 m), the millennial average rate of global sea level rise is very likely to have exceeded 5.6 m kyr-1 but is unlikely to have exceeded 9.2 m kyr-1. Our analysis extends previous last interglacial sea level studies by integrating literature observations within a probabilistic framework that accounts for the physics of sea level change. The results highlight the long-term vulnerability of ice sheets to even relatively low levels of sustained global warming.
    • 2010: Fischer, N., and J. H. Jungclaus. “Effects of orbital forcing on atmosphere and ocean heat transports in Holocene and Eemian climate simulations with a comprehensive Earth system model.” Climate of the Past 6 (2010): 155-168. Orbital forcing not only exerts direct insolation effects, but also alters climate indirectly through feedback mechanisms that modify atmosphere and ocean dynamics and meridional heat and moisture transfers. We investigate the regional effects of these changes by detailed analysis of atmosphere and ocean circulation and heat transports in a coupled atmosphere-ocean-sea ice-biosphere general circulation model (ECHAM5/JSBACH/MPI-OM). We perform long term quasi equilibrium simulations under pre-industrial, mid-Holocene (6000 years before present – yBP), and Eemian (125 000 yBP) orbital boundary conditions. Compared to pre-industrial climate, Eemian and Holocene temperatures show generally warmer conditions at higher and cooler conditions at lower latitudes. Changes in sea-ice cover, ocean heat transports, and atmospheric circulation patterns lead to pronounced regional heterogeneity. Over Europe, the warming is most pronounced over the north-eastern part in accordance with recent reconstructions for the Holocene. We attribute this warming to enhanced ocean circulation in the Nordic Seas and enhanced ocean-atmosphere heat flux over the Barents Shelf in conduction with retreat of sea ice and intensified winter storm tracks over northern Europe. [FULL TEXT PDF]
    • 2011: Nicholls, Robert J., et al. “Sea-level rise and its possible impacts given a ‘beyond 4 C world’in the twenty-first century.” Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 369.1934 (2011): 161-181.  The range of future climate-induced sea-level rise remains highly uncertain with continued concern that large increases in the twenty-first century cannot be ruled out. The biggest source of uncertainty is the response of the large ice sheets of Greenland and west Antarctica. Based on our analysis, a pragmatic estimate of sea-level rise by 2100, for a temperature rise of 4°C or more over the same time frame, is between 0.5 m and 2 m—the probability of rises at the high end is judged to be very low, but of unquantifiable probability. However, if realized, an indicative analysis shows that the impact potential is severe, with the real risk of the forced displacement of up to 187 million people over the century (up to 2.4% of global population). This is potentially avoidable by widespread upgrade of protection, albeit rather costly with up to 0.02 per cent of global domestic product needed, and much higher in certain nations. The likelihood of protection being successfully implemented varies between regions, and is lowest in small islands, Africa and parts of Asia, and hence these regions are the most likely to see coastal abandonment. To respond to these challenges, a multi-track approach is required, which would also be appropriate if a temperature rise of less than 4°C was expected. Firstly, we should monitor sea level to detect any significant accelerations in the rate of rise in a timely manner. Secondly, we need to improve our understanding of the climate-induced processes that could contribute to rapid sea-level rise, especially the role of the two major ice sheets, to produce better models that quantify the likely future rise more precisely. Finally, responses need to be carefully considered via a combination of climate mitigation to reduce the rise and adaptation for the residual rise in sea level. In particular, long-term strategic adaptation plans for the full range of possible sea-level rise (and other change) need to be widely developed.  [FULL TEXT PDF]
    • 2011: Krzysztof, Bińka, and Nitychoruk Jerzy. “Cyclicity in the Eemian climate? A case study of the Eemian site at Czaple, Eastern Poland.” Review of palaeobotany and palynology164.1-2 (2011): 39-44. The newly discovered lacustrine deposits from Czaple, Eastern Poland, examined by means of pollen analysis, revealed an undisturbed, continuous sequence of vegetational development of the Eemian/Early Vistulian age. We tried to trace the secondary climatic trends, cyclic in part on the basis of plant taxa — representing the second league in the spectra, as to frequency, but forming an important group of the index plants. Their appearance becomes more pronounced and reliable when extraordinarily high numbers of pollen are analyzed. The oscillations of curves of these taxa are more clearly expressed than by traditional counts, revealing the hidden picture in the palynological background. It is interesting that some taxa – e.g. Hedera – form a distinctive intermittent pattern reflecting cyclicity of climatic condition or additional factors which are responsible for it. Pollen curves of other index plants do not show such regular variation. This cyclicity can be traced in many European Eemian diagrams. Especially interesting is the sudden decline of ivy as well as of other indicator plants in the subzone E4b such as the Corylus which marks some increase in a continentality of climate. We can also trace this trend in other sequences. In addition, extra counts allow us to estimate the exact timing of the migration of rarely noted exotic taxa and their range of distribution in the sequence. BuxusOsmunda cinnamomea and Lycopodium lucidulum types are the best examples illustrating this.
    • 2011: Van de Berg, Willem Jan, et al. “Significant contribution of insolation to Eemian melting of the Greenland ice sheet.” Nature Geoscience 4.10 (2011): 679.  During the Eemian interglacial period, 130,000 to 114,000 years ago, the volume of the Greenland ice sheet was about 30–60% smaller than the present-day volume1,2. Summer temperatures in the Arctic region were about 2–4 K higher than today3,4,5, leading to the suggestion that Eemian conditions could be considered an analogue for future warming6, particularly for the future stability of the Greenland ice sheet. However, Northern Hemisphere insolation was much higher during the Eemian than today, which could affect the reliability of this analogy. Here we use a high-resolution regional climate model with a realistic ice-sheet surface representation to assess the surface mass balance of the Greenland ice sheet during the Eemian. Our simulations show that Eemian climate led to an 83% lower surface mass balance, compared with the preindustrial simulation. Our sensitivity experiments show that only about 55% of this change in surface mass balance can be attributed to higher ambient temperatures, with the remaining 45% caused by higher insolation and associated nonlinear feedbacks. We show that temperature–melt relations are dependent on changes in insolation. Hence, we suggest that projections of future Greenland ice loss on the basis of Eemian temperature–melt relations may overestimate the future vulnerability of the ice sheet[FULL TEXT PDF]
    • 2013: Nikolova, Irina, et al. “The last interglacial (Eemian) climate simulated by LOVECLIM and CCSM3.” Climate of the Past 9.4 (2013): 1789-1806. This paper presents a detailed analysis of the climate of the last interglacial simulated by two climate models of different complexities, CCSM3 (Community Climate System Model 3) and LOVECLIM (LOch-Vecode-Ecbilt-CLio-agIsm Model). The simulated surface temperature, hydrological cycle, vegetation and ENSO variability during the last interglacial are analyzed through the comparison with the simulated pre-industrial (PI) climate. In both models, the last interglacial period is characterized by a significant warming (cooling) over almost all the continents during boreal summer (winter) leading to a largely increased (reduced) seasonal contrast in the Northern (Southern) Hemisphere. This is mainly due to the much higher (lower) insolation received by the whole Earth in boreal summer (winter) during this interglacial. The Arctic is warmer than PI through the whole year, resulting from its much higher summer insolation, its remnant effect in the following fall-winter through the interactions between atmosphere, ocean and sea ice and feedbacks from sea ice and snow cover. Discrepancies exist in the sea-ice formation zones between the two models. Cooling is simulated by CCSM3 in the Greenland and Norwegian seas and near the shelves of Antarctica during DJF but not in LOVECLIM as a result of excessive sea-ice formation. Intensified African monsoon is responsible for the cooling during summer in northern Africa and on the Arabian Peninsula. Over India, the precipitation maximum is found further west, while in Africa the precipitation maximum migrates further north. Trees and grassland expand north in Sahel/Sahara, more clearly seen in LOVECLIM than in CCSM3 results. A mix of forest and grassland occupies continents and expands deep into the high northern latitudes. Desert areas reduce significantly in the Northern Hemisphere, but increase in northern Australia. The interannual SST variability of the tropical Pacific (El-Niño Southern Oscillation) of the last interglacial simulated by CCSM3 shows slightly larger variability and magnitude compared to the PI. However, the SST variability in our LOVECLIM simulations is particularly small due to the overestimated thermocline’s depth.  [FULL TEXT PDF]
    • 2015: Dutton, A., et al. “Sea-level rise due to polar ice-sheet mass loss during past warm periods.” science 349.6244 (2015): aaa4019.  We know that the sea level will rise as climate warms. Nevertheless, accurate projections of how much sea-level rise will occur are difficult to make based solely on modern observations. Determining how ice sheets and sea level have varied in past warm periods can help us better understand how sensitive ice sheets are to higher temperatures. Dutton et al. review recent interdisciplinary progress in understanding this issue, based on data from four different warm intervals over the past 3 million years. Their synthesis provides a clear picture of the progress we have made and the hurdles that still exist.  [FULL TEXT PDF]
    • 2015: Hansen, James, et al. “Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2° C global warming is highly dangerous.” Atmospheric Chemistry & Physics Discussions 15.14 (2015).  There is evidence of ice melt, sea level rise to +5–9 m, and extreme storms in the prior interglacial period that was less than 1C warmer than today. Human-made climate forcing is stronger and more rapid than paleo forcings, but much can be learned by 5 combining insights from paleoclimate, climate modeling, and on-going observations. We argue that ice sheets in contact with the ocean are vulnerable to non-linear disintegration in response to ocean warming, and we posit that ice sheet mass loss can be approximated by a doubling time up to sea level rise of at least several meters. Doubling times of 10, 20 or 40 years yield sea level rise of several meters in 50, 100 or 200 years. Paleoclimate data reveal that subsurface ocean warming causes ice shelf melt and ice sheet discharge. Our climate model exposes amplifying feedbacks in the Southern Ocean that slow Antarctic bottom water formation and increase ocean temperature near ice shelf grounding lines, while cooling the surface ocean and increasing sea ice cover and water column stability. Ocean surface cooling, in the North Atlantic 15 as well as the Southern Ocean, increases tropospheric horizontal temperature gradients, eddy kinetic energy and baroclinicity, which drive more powerful storms. We focus attention on the Southern Ocean’s role in affecting atmospheric CO2 amount, which in turn is a tight control knob on global climate. The millennial (500–2000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change, thus the time 20 scale for paleo global climate, ice sheet and sea level changes. This millennial carbon cycle time scale should not be misinterpreted as the ice sheet time scale for response to a rapid human-made climate forcing. Recent ice sheet melt rates have a doubling time near the lower end of the 10–40 year range. We conclude that 2C global warming above the preindustrial level, which would spur more ice shelf melt, is highly dangerous. Earth’s energy imbalance, which must be eliminated to stabilize climate, provides a crucial metric.  [FULL TEXT PDF]
    • 2016: DeConto, Robert M., and David Pollard. “Contribution of Antarctica to past and future sea-level rise.” Nature 531.7596 (2016): 591.  Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6–9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics—including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs—that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years.  [FULL TEXT PDF]

     

     

     

     

     

    AGW COLLAPSE OF ICE SHEETS:  BIBLIOGRAPHY

    1. 1983: Zwally, H. Jay, et al. “Surface elevation contours of Greenland and Antarctic ice sheets.” Journal of Geophysical Research: Oceans 88.C3 (1983): 1589-1596. Surface elevations of the ice sheets are contoured at 50‐m intervals for the region of Greenland covered by SEASAT radar altimetry south of 72°N and at 100‐m intervals for a region of East Antarctica north of 72°S. The surface elevations were obtained from computer retracking of the radar altimeter waveforms, which were recorded at 0.1‐s intervals corresponding to 662‐m spacings on the surface. The precision of the elevation measurements before adjustment for radial orbit errors is 1.9 m as shown by analysis of elevation differences at orbital crossover points. This precision is partly determined by radial errors of approximately 1.0 m in orbit determination and partly by noise due to ice surface irregularities. Adjustment of the radial components of the orbits to minimize the differences in elevations at crossovers over a small, relatively flat region reduces the rms difference to 0.25 m, which is indicative of the optimum precision obtainable over the ice sheets. However, the precision degrades as the slope of the surface or amplitude of the undulations increases, yielding an overall precision of ±1.6 m. The preliminary contour maps are not corrected for slope‐induced displacements. A 2‐m contour map in a region of highest data density illustrates the three‐dimensional characteristics of some surface undulations.
    2. 1999: Huybrechts, Philippe, and Jan de Wolde. “The dynamic response of the Greenland and Antarctic ice sheets to multiple-century climatic warming.” Journal of Climate 12.8 (1999): 2169-2188.  New calculations were performed to investigate the combined response of the Greenland and Antarctic ice sheets to a range of climatic warming scenarios over the next millennium. Use was made of fully dynamic 3D thermomechanic ice sheet models, which were coupled to a two-dimensional climate model. The experiments were initialized with simulations over the last two glacial cycles to estimate the present evolution and were subsequently forced with temperature scenarios resulting from greenhouse emission scenarios which assume equivalent CO2 increases of two, four, and eight times the present (1990 a.d.) value by the year 2130 a.d. and a stabilization after that. The calculations brought to light that during the next century (short-term effect), the background evolution trend would dominate the response of the Antarctic ice sheet but would be negligible for the Greenland ice sheet. On that timescale, the Greenland and Antarctic ice sheets would roughly balance one another for the middle scenario (similar to the IPCC96 IS92a scenario), with respective contributions to the worldwide sea level stand on the order of about ±10 cm. On the longer term, however, both ice sheets would contribute positively to the worldwide sea level stand and the most important effect would come from melting on the Greenland ice sheet. Sensitivity experiments highlighted the role of ice dynamics and the height–mass-balance feedback on the results. It was found that ice dynamics cannot be neglected for the Greenland ice sheet, not even on a century timescale, but becomes only important for Antarctica on the longer term. The latter is related to an increased outflow of ice into the ice shelves and to the grounding-line retreat of the west Antarctic ice sheet, which are both found to be sensitive to basal melting below ice shelves and the effective viscosity of the ice shelves. Stretching parameters to their limits yielded a combined maximum rate of sea level rise of 85 cm century−1, of which 60 cm would originate from the Greenland ice sheet alone.
    3. 2005: Zwally, H. Jay, et al. “Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992–2002.” Journal of Glaciology 51.175 (2005): 509-527.  Changes in ice mass are estimated from elevation changes derived from 10.5 years (Greenland) and 9 years (Antarctica) of satellite radar altimetry data from the European Remote-sensing Satellites ERS-1 and -2. For the first time, the dH/dt values are adjusted for changes in surface elevation resulting from temperature-driven variations in the rate of firn compaction. The Greenland ice sheet is thinning at the margins (–42 ± 2Gta¯1 below the equilibrium-line altitude (ELA)) and growing inland (+53 ± 2Gta-1 above the ELA) with a small overall mass gain (+11 ± 3Gta–1; –0.03 mma–1 SLE (sea-level equivalent)). The ice sheet in West Antarctica (WA) is losing mass (–47 ± 4Gta–1) and the ice sheet in East Antarctica (EA) shows a small mass gain (+16 ± 11 Gta–1) for a combined net change of –31 ± 12 Gta–1(+0.08mma–1 SLE). The contribution of the three ice sheets to sea level is +0.05±0.03mma–1. The Antarctic ice shelves show corresponding mass changes of –95 ± 11 Gta–1 in WA and +142 ± 10Gta–1 in EA. Thinning at the margins of the Greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate. The marked thinnings in the Pine Island and Thwaites Glacier basins of WA and the Totten Glacier basin in EA are probably ice- dynamic responses to long-term climate change and perhaps past removal of their adjacent ice shelves. The ice growth in the southern Antarctic Peninsula and parts of EA may be due to increasing precipitation during the last century.
    4. 2009: Pollard, David, and Robert M. DeConto. “Modelling West Antarctic ice sheet growth and collapse through the past five million years.” Nature 458.7236 (2009): 329.  The West Antarctic ice sheet (WAIS), with ice volume equivalent to 5 m of sea level1, has long been considered capable of past and future catastrophic collapse2,3,4. Today, the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams. Grounding lines are several hundred metres below sea level and the bed deepens upstream, raising the prospect of runaway retreat3,5. Projections of future WAIS behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6,7. Its variation since the Last Glacial Maximum is best known, with grounding lines advancing to the continental-shelf edges around 15 kyr ago before retreating to near-modern locations by 3 kyr ago8. Prior collapses during the warmth of the early Pliocene epoch9and some Pleistocene interglacials have been suggested indirectly from records of sea level and deep-sea-core isotopes, and by the discovery of open-ocean diatoms in subglacial sediments10. Until now11, however, little direct evidence of such behaviour has been available. Here we use a combined ice sheet/ice shelf model12 capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing5 to simulate Antarctic ice sheet variations over the past five million years. Modelled WAIS variations range from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands. Transitions between glacial, intermediate and collapsed states are relatively rapid, taking one to several thousand years. Our simulation is in good agreement with a new sediment record (ANDRILL AND-1B) recovered from the western Ross Sea11, indicating a long-term trend from more frequently collapsed to more glaciated states, dominant 40-kyr cyclicity in the Pliocene, and major retreats at marine isotope stage 31 (1.07 Myr ago) and other super-interglacials.
    5. 2009: Pritchard, Hamish D., et al. “Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets.” Nature 461.7266 (2009): 971.  Many glaciers along the margins of the Greenland and Antarctic ice sheets are accelerating and, for this reason, contribute increasingly to global sea-level rise1,2,3,4,5,6,7. Globally, ice losses contribute 1.8 mm yr-1(ref. 8), but this could increase if the retreat of ice shelves and tidewater glaciers further enhances the loss of grounded ice9 or initiates the large-scale collapse of vulnerable parts of the ice sheets10. Ice loss as a result of accelerated flow, known as dynamic thinning, is so poorly understood that its potential contribution to sea level over the twenty-first century remains unpredictable11. Thinning on the ice-sheet scale has been monitored by using repeat satellite altimetry observations to track small changes in surface elevation, but previous sensors could not resolve most fast-flowing coastal glaciers12. Here we report the use of high-resolution ICESat (Ice, Cloud and land Elevation Satellite) laser altimetry to map change along the entire grounded margins of the Greenland and Antarctic ice sheets. To isolate the dynamic signal, we compare rates of elevation change from both fast-flowing and slow-flowing ice with those expected from surface mass-balance fluctuations. We find that dynamic thinning of glaciers now reaches all latitudes in Greenland, has intensified on key Antarctic grounding lines, has endured for decades after ice-shelf collapse, penetrates far into the interior of each ice sheet and is spreading as ice shelves thin by ocean-driven melt. In Greenland, glaciers flowing faster than 100 m yr-1thinned at an average rate of 0.84 m yr-1, and in the Amundsen Sea embayment of Antarctica, thinning exceeded 9.0 m yr-1 for some glaciers. Our results show that the most profound changes in the ice sheets currently result from glacier dynamics at ocean margins.
    6. 2009: Velicogna, Isabella. “Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE.” Geophysical Research Letters 36.19 (2009).  We use monthly measurements of time‐variable gravity from the GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission to determine the ice mass‐loss for the Greenland and Antarctic Ice Sheets during the period between April 2002 and February 2009. We find that during this time period the mass loss of the ice sheets is not a constant, but accelerating with time, i.e., that the GRACE observations are better represented by a quadratic trend than by a linear one, implying that the ice sheets contribution to sea level becomes larger with time. In Greenland, the mass loss increased from 137 Gt/yr in 2002–2003 to 286 Gt/yr in 2007–2009, i.e., an acceleration of −30 ± 11 Gt/yr2 in 2002–2009. In Antarctica the mass loss increased from 104 Gt/yr in 2002–2006 to 246 Gt/yr in 2006–2009, i.e., an acceleration of −26 ± 14 Gt/yr2 in 2002–2009. The observed acceleration in ice sheet mass loss helps reconcile GRACE ice mass estimates obtained for different time periods.
    7. 2011: Rignot, Eric, et al. “Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise.” Geophysical Research Letters 38.5 (2011). Ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques, over different time periods, and at various levels of spatial detail. Considerable disparity remains between these estimates due to the inherent uncertainties of each method, the lack of detailed comparison between independent estimates, and the effect of temporal modulations in ice sheet surface mass balance. Here, we present a consistent record of mass balance for the Greenland and Antarctic ice sheets over the past two decades, validated by the comparison of two independent techniques over the last 8 years: one differencing perimeter loss from net accumulation, and one using a dense time series of time‐variable gravity. We find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss. In 2006, the Greenland and Antarctic ice sheets experienced a combined mass loss of 475 ± 158 Gt/yr, equivalent to 1.3 ± 0.4 mm/yr sea level rise. Notably, the acceleration in ice sheet loss over the last 18 years was 21.9 ± 1 Gt/yr2 for Greenland and 14.5 ± 2 Gt/yr2 for Antarctica, for a combined total of 36.3 ± 2 Gt/yr2. This acceleration is 3 times larger than for mountain glaciers and ice caps (12 ± 6 Gt/yr2). If this trend continues, ice sheets will be the dominant contributor to sea level rise in the 21st century.
    8. 2012: Pritchard, HDx, et al. “Antarctic ice-sheet loss driven by basal melting of ice shelves.” Nature 484.7395 (2012): 502.  Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying1,2 glacier acceleration along Antarctic ice-sheet coastal margins3. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves, potentially limiting their ability to buttress the flow of grounded tributary glaciers4. Indeed, recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula5. But the extent and magnitude of ice-shelf thickness change, the underlying causes of such change, and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted3. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary control of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow2. The highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen6 and Bellingshausen7 seas, and atmospheric warming on the Antarctic Peninsula8. This implies that climate forcing through changing winds influences Antarctic ice-sheet mass balance, and hence global sea level, on annual to decadal timescales.
    9. 2014: Joughin, Ian, Benjamin E. Smith, and Brooke Medley. “Marine ice sheet collapse potentially under way for the Thwaites Glacier Basin, West Antarctica.” Science 344.6185 (2014): 735-738.  Resting atop a deep marine basin, the West Antarctic Ice Sheet has long been considered prone to instability. Using a numerical model, we investigated the sensitivity of Thwaites Glacier to ocean melt and whether its unstable retreat is already under way. Our model reproduces observed losses when forced with ocean melt comparable to estimates. Simulated losses are moderate (<0.25 mm per year at sea level) over the 21st century but generally increase thereafter. Except possibly for the lowest-melt scenario, the simulations indicate that early-stage collapse has begun. Less certain is the time scale, with the onset of rapid (>1 mm per year of sea-level rise) collapse in the different simulations within the range of 200 to 900 years.

     

     

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