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FIGURE 1: GISS-2 CMIP5 FORCINGS

 

FIGURE 2: NASA GISS-2 WMGHG & ALLFORCINGS 1851-2012

FORCINGS1851CHART

 

FIGURE 3: HADCRUT4 MOVING 30-YEAR CORRELATIONS 

HAD1851CHART

 

 

FIGURE 4: FULL SPAN CORRELATION ANALYSIS 

FULLSPANCORR

FULLSPANCORRCHART

30YRMOVINGWINDOWANALYSIS

MOVINGWINDOWCHART

 

FIGURE 5: FIRST HALF CORRELATION ANALYSIS

FIRSTHALFCORRTABLE

 

FIRSTHALFCORRCHARTS

FIRSTHALFMOVINGWINDOW

 

FIGURE 6: SECOND HALF CORRELATION ANALYSIS

2NDHALFCORRTABLE

2NDHALFCORRCHARTS

2NDHALFMOVINGWINDOW

The author acknowledges the kind assistance and encouragement of Ashley Francs of Salisbury, England in carrying out this work.

This work is a correlation analysis that evaluates proposed “forcings” that should determine surface temperature according to theory against  observed and predicted temperatures. The Coupled Model Intercomparison Project of 2008 (CMIP5) was a meeting of the IPCC Working Group for Coupled Modeling (WGCM) with Atmosphere-Ocean General Circulation Models (AOGCM). The meeting was held to prepare for the IPCC Fifth Assessment Report AR5 because it was expected that some of the scientific questions that arose during preparation of the IPCCAR4 would be addressed by CMIP5. These scientific questions arose because climate science acknowledged “gaps in the understanding” of how the climate system works particularly having to do with forcings, feedbacks, and ocean uptake.

The CMIP5 has reconciled differences among general circulation models and coupled ocea-atmosphere models to standardize climate forcings. These parameters have been estimated from theoretical considerations in conjunction with data on atmospheric composition, emissions, aerosols, and other relevant factors and tested with climate  models against historical data both paleo and reconstructions of the instrumental record (Taylor, 2012). It follows that historical temperature reconstructions by NASA-GISS and the Hadley Centre, both being participants in CMIP5, should be consistent with the CMIP5 forcings published by NASA-GISS and used by the Hadley Center.

This analysis uses the NASA GISS-2 forcings (Figure 1) against the NASA-GISTEMP. Additional temperature series studied include the HadCRUT4 global temperature reconstructions from the Hadley Climate Research Unit. In additon the RCP8.5 theoretical hindcast of temperatures under the “business as usual” scenario (where no climate action is taken) is also presented and the three series are compared.

The end year in this study is 2012. It is constrained by the availability of NASA GISS-2 CMIP5 forcings data. In addition to CO2-GHG forcing (WMGHG), eight additional forcings are published, They include ozone, land use, snow albedo, aerosols (both tropospheric and stratospheric) and solar. NASA-GISS also publishes the net total forcing from all sources both natural and human caused, as a separate parameter called “ALLFORCINGS”. Only the CO2 forcing series (WMGHG) and the total forcing series (ALLFORCINGS) 1851-2012 are used in this correlation analysis. The correlation between WMGHG and ALLFORCINGS is also presented.

The analysis considers not only the full span correlations in the source data but also its decomposition into contributions from shared trends and contributions from responsiveness at an annual time scale with the use of detrended fluctuation analysis. Discrepancies between source data and detrended correlations are examined for instability with split half tests and also with correlations in a moving 30-year window. These issues are discussed in greater detail in related posts on Spurious Correlations in Climate Science and ECS: Equilibrium Climate SensitivityIn short, unstable correlations are normally spurious and have no interpretation in terms of cause and effect in the study of field data.

The forcings are available for the time span 1851-2012 but global temperature data are available in three different spans that begin in 1851 (Hadcrut), 1861 (RCP 8.5), and 1880 (NASA-GISTEMP). Because differences in the span are known to change correlation value (Time Series Analysis by Box and Jenkins), the data with longer time spans are also studied at the shorter time spans. Thus, for the three temperature time series used, there are actually six different time series in the correlation analysis. They are Hadcrut 1851, HadCrut 1861, Hadcrut 1880, RCP8.5 1861, RCP8.5 1880, and GISTEMP 1880.

The full span correlations between the WMGHG /ALLFORCINGS data and HADCRUT4 NASA GISTEMP global temperature reconstructions, and RCP8.5 temperature hindcasts, as well as the correlation between the two forcing functions, are tabulated in Figure 4. With one exception, they show a strong and statistically significant correlation of temperature with both forcing measures as well as between the two forcing measures. Strong correlations in the source data between r=[0.74-0.94] survive into the detrended series as statistically significant responsiveness at an annual time scale with r=[0.33-0.79]. The critical values of correlation for statistical significance at alpha=0.001 are listed in the column marked CRITCOR. Rows labeled as FOR1851, FOR1861, and FOR1880 contain correlations between the two forcing functions WMGHG and ALLFORCINGS; and all of these correlations are strong with statistical significance surviving into the detrended series. The sole exception here is GISTEMP 1880-2012 global temperature reconstruction. It shows a strong correlation of r=0.74 with WMGHG but fails to show a statistically significant detrended correlation with ALLFORCINGS. As implied in (Lacis &Schmidt “Atmospheric CO2: Principal control knob governing Earth’s temperature.” Science 330.6002 (2010): 356-359.), it seems that CO2 alone is almost as good as if not better than the sum of all forcings in explaining temperatures at these time spans.

As strong as the full span correlations are, the table and chart of 30-year moving correlations in the lower portion of Figure 4 reveal a weakness in this result. In the chart we see that moving 30-year correlations between temperature and the two forcing measures vary over a large range above and below the horizontal statistical significance line and also above and below the zero-line such that both insignificant and negative correlations are seen in the table of 30-year correlations above the chart. The table of 30-year moving correlations also presents a comparison of the two forcing metrics. The correlations between the two forcings is presented in the rows labeled FOR1851, FOR1861, and FOR1880. They contain data for 30-year moving correlations between the two forcing measures WMGHG and ALLFORCINGS published by NASA-GISS. They show good evidence that the two forcing metrics are correlated in support of the strong full span correlations in the first table of Figure 4. In comparing the second and third charts of Figure 3, it appears that the correlation of warming with the two CMIP5 forcings is strong at high warming rates and weak at low warming rates. Periods of high 30-year warming rates (second chart of Figure 3) correspond with periods of strong 30-year correlation above the line demarcating statistical significance (third chart of Figure 3). In summary, the moving 30-year correlations show a large range of values with about half of them below the horizontal line of statistical significance. This pattern is indicative of an unstable correlation between forcings and temperature.

The stability of the correlation is therefore tested with a split half test in Figures 5&6. Each time span is cut in half and results for the first half of the time span are presented in Figure 5 and those for the second half in Figure 6. The comparison of the split half correlations and detrended correlations confirms the instability of correlations between temperature and the two forcings. The first half of the data show generally weak, statistically insignificant and more negative correlations whereas the second half of the time series show generally strong correlations as in the full span of the data.

 

FIGURE 7: COMPARATIVE ANALYSIS

COMPARETEMPS

  1. CORRELATION BETWEEN THE TWO MEASURES OF FORCING WMGHG & ALLFORCINGS: {FULL SPAN} Strong correlations between CO2 forcing and all forcings with supporting detrended correlations are seen in the full span of the data particularly so in the longer time spans. The observed correlations and detrended correlations between WMGHG & ALLFORCINGS are [corr, detcorr] = [0.844, 0.489], [0.841, 0.476], [0.838, 0.334] in the three time spans of 162, 152, and 133 years. All correlations are statistically significant. The averages for all three time spans are [corr, detcorr] = [0.841, 0.433] in the full span, [0.494, 0.078] in the first half, and [0.801, 0.420] in the second half. The two forcings are strongly correlated in the most recent portions of the time series that begin later than 1931 but that correlation is  not found in time series that end earlier than 1947. This behavior is anomalous.
  2. {MOVING WINDOW} More than 50% of the 30-year moving average correlations between WMGHG & ALLFORCINGS are found to be statistically significant in the 152-year and 133-year time spans. The significance percentage is just shy of 50% when the oldest decade is included in the 162-year time span 1851-2012.
  3. {SPLIT HALF} No statistically significant correlation between WMGHG & ALLFORCINGS is found in the first half of any of the three time spans studied. The second half of all three time spans shows statistically significant correlations between the two forcing measures.
  4. In conclusion, the two measures of climate forcing are found to be correlated but with some anomalous behavior in the oldest portions of the time series studied.
  5. COMPARISON OF THE EXPLANATORY POWER OF THE TWO FORCING MEASURES: ALLFORCINGS shows a higher average correlation of r=0.471 in the 30-year moving correlations across the full span of the data with a lower proportion of negative correlations at 5%. However, WMGHG shows a higher proportion of statistically significant moving correlations at 52% compared with 38% for ALLFORCINGS. Average correlations with temperature in the full span are [corr, detcorr] = [0.880, 0.544] for WMGHG against [0.824, 0.501] for ALLFORCINGS. In the first half of the data series, [corr, detcorr] = [0.407, 0.226] for WMGHG against [0.477, 0.370] for ALLFORCINGS. In the second half of the data series, [corr, detcorr] = [0.832, 0.413] for WMGHG against [0.787, 0.485] for ALLFORCINGS. The two measures appear to be comparable with no clear winner although ALLFORCINGS may be somewhat better in terms of detrended correlation.
  6. The comparison at the bottom of Figure 7 above is a confirmation of this conclusion as it shows that the averages of all full span and half span correlations with temperature are approximately the same for the two forcings.
  7. In conclusion, the two measures of forcing study appear to be similar in their ability to explain temperature. ALLFORCINGS does not show a greater correlation with temperature than WMGHG alone.
  8. COMPARISON OF CORRELATIONS OF THE THREE TEMPERATURE SERIES WITH FORCINGS. The comparison is presented in Figure 7. It shows that when all full span and half span correlations are averaged, the the strongest correlation is seen with the RCP8.5 global mean temperature projections. The average of all correlations of the RCP8.5 series are [corr, detcorr] = [0.857, 0.663] for with WMGHG forcing and [0.752, 0.739] with ALLFORCINGS. The corresponding correlations for the two global temperature reconstructions are HadCRUT4 [corr, detcorr] = [0.729, 0.553] with WMGHG and [0.605, 0.359] with ALLFORCINGS and for GISTEMP they are [corr, detcorr] = [0.460, -0.136] with WMGHG and [0.424, 0.074] with ALLFORCINGS.
  9. The close correspondence between temperature projections according to theory and forcings is simply verification that the theory was accurately applied in the construction of the RCP8.5 projection and their lower correlations with observations are indicative of the degree of departure of data from theory.

 

SUMMARY: A correlation analysis is carried out with NASA GISS-2 CMIP5 climate forcings against two global surface temperature reconstructions and the RCP8.5 “business as usual” temperature projection based on CMIP5. Two climate forcings are used. They are WMGHG, mostly a contribution of human action, and ALLFORCINGS, that includes natural factors. All three temperature series show anomalous differences in correlation with forcings according to location along the temperature time series. Among the temperature data, the RCP8.5 series shows the strongest correlation with forcings as expected since this series was derived from forcings in climate models. The observational data show weaker correlations and these differences may be interpreted in terms of departure from theory. No significant difference in correlation was found between the anthropogenic WMGHG forcing and the ALLFORCING series that includes natural forcing. This finding supports Andrew Lacis who had written that human emissions alone explain warming (Lacis &Schmidt “Atmospheric CO2: Principal control knob governing Earth’s temperature.” Science 330.6002 (2010): 356-359). This post was initiated by Ashley Francis of Salisbury, England who had kindly forwarded the information, encouragement, and data needed to carry out this work.

 

CMIP5 FORCINGS BIBLIOGRAPHY

  1. 2011: Bellouin, Nicolas, et al. “Aerosol forcing in the Climate Model Intercomparison Project (CMIP5) simulations by HadGEM2‐ES and the role of ammonium nitrate.” Journal of Geophysical Research: Atmospheres 116.D20 (2011). The latest Hadley Centre climate model, HadGEM2‐ES, includes Earth system components such as interactive chemistry and eight species of tropospheric aerosols. It has been run for the period 1860–2100 in support of the fifth phase of the Climate Model Intercomparison Project (CMIP5). Anthropogenic aerosol emissions peak between 1980 and 2020, resulting in a present‐day all‐sky top of the atmosphere aerosol forcing of −1.6 and −1.4 W m−2 with and without ammonium nitrate aerosols, respectively, for the sum of direct and first indirect aerosol forcings. Aerosol forcing becomes significantly weaker in the 21st century, being weaker than −0.5 W m−2 in 2100 without nitrate. However, nitrate aerosols become the dominant species in Europe and Asia and decelerate the decrease in global mean aerosol forcing. Considering nitrate aerosols makes aerosol radiative forcing 2–4 times stronger by 2100 depending on the representative concentration pathway, although this impact is lessened when changes in the oxidation properties of the atmosphere are accounted for. Anthropogenic aerosol residence times increase in the future in spite of increased precipitation, as cloud cover and aerosol‐cloud interactions decrease in tropical and midlatitude regions. Deposition of fossil fuel black carbon onto snow and ice surfaces peaks during the 20th century in the Arctic and Europe but keeps increasing in the Himalayas until the middle of the 21st century. Results presented here confirm the importance of aerosols in influencing the Earth’s climate, albeit with a reduced impact in the future, and suggest that nitrate aerosols will partially replace sulphate aerosols to become an important anthropogenic species in the remainder of the 21st century.
  2. 2012: Ahlström, Anders, et al. “Robustness and uncertainty in terrestrial ecosystem carbon response to CMIP5 climate change projections.” Environmental Research Letters 7.4 (2012): 044008. We have investigated the spatio-temporal carbon balance patterns resulting from forcing a dynamic global vegetation model with output from 18 climate models of the CMIP5 (Coupled Model Intercomparison Project Phase 5) ensemble. We found robust patterns in terms of an extra-tropical loss of carbon, except for a temperature induced shift in phenology, leading to an increased spring uptake of carbon. There are less robust patterns in the tropics, a result of disagreement in projections of precipitation and temperature. Although the simulations generally agree well in terms of the sign of the carbon balance change in the middle to high latitudes, there are large differences in the magnitude of the loss between simulations. Together with tropical uncertainties these discrepancies accumulate over time, resulting in large differences in total carbon uptake over the coming century (−0.97–2.27 Pg C yr−1 during 2006–2100). The terrestrial biosphere becomes a net source of carbon in ten of the 18 simulations adding to the atmospheric CO2 concentrations, while the remaining eight simulations indicate an increased sink of carbon.
  3. 2012: Andrews, Timothy, et al. “Forcing, feedbacks and climate sensitivity in CMIP5 coupled atmosphere‐ocean climate models.” Geophysical Research Letters 39.9 (2012). We quantify forcing and feedbacks across available CMIP5 coupled atmosphere‐ocean general circulation models (AOGCMs) by analysing simulations forced by an abrupt quadrupling of atmospheric carbon dioxide concentration. This is the first application of the linear forcing‐feedback regression analysis of Gregory et al. (2004) to an ensemble of AOGCMs. The range of equilibrium climate sensitivity is 2.1–4.7 K. Differences in cloud feedbacks continue to be important contributors to this range. Some models show small deviations from a linear dependence of top‐of‐atmosphere radiative fluxes on global surface temperature change. We show that this phenomenon largely arises from shortwave cloud radiative effects over the ocean and is consistent with independent estimates of forcing using fixed sea‐surface temperature methods. We suggest that future research should focus more on understanding transient climate change, including any time‐scale dependence of the forcing and/or feedback, rather than on the equilibrium response to large instantaneous forcing.
  4. 2012: Booth, Ben BB, et al. “Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability.” Nature484.7393 (2012): 228. Systematic climate shifts have been linked to multidecadal variability in observed sea surface temperatures in the North Atlantic Ocean1. These links are extensive, influencing a range of climate processes such as hurricane activity2 and African Sahel3,4,5 and Amazonian5 droughts. The variability is distinct from historical global-mean temperature changes and is commonly attributed to natural ocean oscillations6,7,8,9,10. A number of studies have provided evidence that aerosols can influence long-term changes in sea surface temperatures11,12, but climate models have so far failed to reproduce these interactions6,9 and the role of aerosols in decadal variability remains unclear. Here we use a state-of-the-art Earth system climate model to show that aerosol emissions and periods of volcanic activity explain 76 per cent of the simulated multidecadal variance in detrended 1860–2005 North Atlantic sea surface temperatures. After 1950, simulated variability is within observational estimates; our estimates for 1910–1940 capture twice the warming of previous generation models but do not explain the entire observed trend. Other processes, such as ocean circulation, may also have contributed to variability in the early twentieth century. Mechanistically, we find that inclusion of aerosol–cloud microphysical effects, which were included in few previous multimodel ensembles, dominates the magnitude (80 per cent) and the spatial pattern of the total surface aerosol forcing in the North Atlantic. Our findings suggest that anthropogenic aerosol emissions influenced a range of societally important historical climate events such as peaks in hurricane activity and Sahel drought. Decadal-scale model predictions of regional Atlantic climate will probably be improved by incorporating aerosol–cloud microphysical interactions and estimates of future concentrations of aerosols, emissions of which are directly addressable by policy actions.
  5. 2012: Taylor, Karl E., Ronald J. Stouffer, and Gerald A. Meehl. “An overview of CMIP5 and the experiment design.” Bulletin of the American Meteorological Society 93.4 (2012): 485-498. The fifth phase of the Coupled Model Intercomparison Project (CMIP5) will produce a state-of-the- art multimodel dataset designed to advance our knowledge of climate variability and climate change. Researchers worldwide are analyzing the model output and will produce results likely to underlie the forthcoming Fifth Assessment Report by the Intergovernmental Panel on Climate Change. Unprecedented in scale and attracting interest from all major climate modeling groups, CMIP5 includes “long term” simulations of twentieth-century climate and projections for the twenty-first century and beyond. Conventional atmosphere–ocean global climate models and Earth system models of intermediate complexity are for the first time being joined by more recently developed Earth system models under an experiment design that allows both types of models to be compared to observations on an equal footing. Besides the longterm experiments, CMIP5 calls for an entirely new suite of “near term” simulations focusing on recent decades and the future to year 2035. These “decadal predictions” are initialized based on observations and will be used to explore the predictability of climate and to assess the forecast system’s predictive skill. The CMIP5 experiment design also allows for participation of stand-alone atmospheric models and includes a variety of idealized experiments that will improve understanding of the range of model responses found in the more complex and realistic simulations. An exceptionally comprehensive set of model output is being collected and made freely available to researchers through an integrated but distributed data archive. For researchers unfamiliar with climate models, the limitations of the models and experiment design are described.
  6. 2012Morice, Colin P., et al. “Quantifying uncertainties in global and regional temperature change using an ensemble of observational estimates: The HadCRUT4 data set.” Journal of Geophysical Research: Atmospheres 117.D8 (2012). Recent developments in observational near‐surface air temperature and sea‐surface temperature analyses are combined to produce HadCRUT4, a new data set of global and regional temperature evolution from 1850 to the present. This includes the addition of newly digitized measurement data, both over land and sea, new sea‐surface temperature bias adjustments and a more comprehensive error model for describing uncertainties in sea‐surface temperature measurements. An ensemble approach has been adopted to better describe complex temporal and spatial interdependencies of measurement and bias uncertainties and to allow these correlated uncertainties to be taken into account in studies that are based upon HadCRUT4. Climate diagnostics computed from the gridded data set broadly agree with those of other global near‐surface temperature analyses. Fitted linear trends in temperature anomalies are approximately 0.07°C/decade from 1901 to 2010 and 0.17°C/decade from 1979 to 2010 globally. Northern/southern hemispheric trends are 0.08/0.07°C/decade over 1901 to 2010 and 0.24/0.10°C/decade over 1979 to 2010. Linear trends in other prominent near‐surface temperature analyses agree well with the range of trends computed from the HadCRUT4 ensemble members.
  7. 2013: Jones, Gareth S., Peter A. Stott, and Nikolaos Christidis. “Attribution of observed historical near‒surface temperature variations to anthropogenic and natural causes using CMIP5 simulations.” Journal of Geophysical Research: Atmospheres118.10 (2013): 4001-4024. We have carried out an investigation into the causes of changes in near‒surface temperatures from 1860 to 2010. We analyze the HadCRUT4 observational data set which has the most comprehensive set of adjustments available to date for systematic biases in sea surface temperatures and the CMIP5 ensemble of coupled models which represents the most sophisticated multi‒model climate modeling exercise yet carried out. Simulations that incorporate both anthropogenic and natural factors span changes in observed temperatures between 1860 and 2010, while simulations of natural factors do not warm as much as observed. As a result of sampling a much wider range of structural modeling uncertainty, we find a wider spread of historic temperature changes in CMIP5 than was simulated by the previous multi‒model ensemble, CMIP3. However, calculations of attributable temperature trends based on optimal detection support previous conclusions that human‒induced greenhouse gases dominate observed global warming since the mid‒20th century. With a much wider exploration of model uncertainty than previously carried out, we find that individually the models give a wide range of possible counteracting cooling from the direct and indirect effects of aerosols and other non‒greenhouse gas anthropogenic forcings. Analyzing the multi‒model mean over 1951–2010 (focusing on the most robust result), we estimate a range of possible contributions to the observed warming of approximately 0.6 K from greenhouse gases of between 0.6 and 1.2 K, balanced by a counteracting cooling from other anthropogenic forcings of between 0 and −0.5 K.
  8. 2013: Gillett, Nathan P., et al. “Constraining the ratio of global warming to cumulative CO2 emissions using CMIP5 simulations.” Journal of Climate 26.18 (2013): 6844-6858. The ratio of warming to cumulative emissions of carbon dioxide has been shown to be approximately independent of time and emissions scenarios and directly relates emissions to temperature. It is therefore a potentially important tool for climate mitigation policy. The transient climate response to cumulative carbon emissions (TCRE), defined as the ratio of global-mean warming to cumulative emissions at CO2doubling in a 1% yr−1 CO2 increase experiment, ranges from 0.8 to 2.4 K EgC−1 in 15 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5)—a somewhat broader range than that found in a previous generation of carbon–climate models. Using newly available simulations and a new observational temperature dataset to 2010, TCRE is estimated from observations by dividing an observationally constrained estimate of CO2-attributable warming by an estimate of cumulative carbon emissions to date, yielding an observationally constrained 5%–95% range of 0.7–2.0 K EgC−1.
  9. 2013: Forster, Piers M., et al. “Evaluating adjusted forcing and model spread for historical and future scenarios in the CMIP5 generation of climate models.” Journal of Geophysical Research: Atmospheres 118.3 (2013): 1139-1150. We utilize energy budget diagnostics from the Coupled Model Intercomparison Project phase 5 (CMIP5) to evaluate the models’ climate forcing since preindustrial times employing an established regression technique. The climate forcing evaluated this way, termed the adjusted forcing (AF), includes a rapid adjustment term associated with cloud changes and other tropospheric and land‐surface changes. We estimate a 2010 total anthropogenic and natural AF from CMIP5 models of 1.9 ± 0.9 W m−2 (5–95% range). The projected AF of the Representative Concentration Pathway simulations are lower than their expected radiative forcing (RF) in 2095 but agree well with efficacy weighted forcings from integrated assessment models. The smaller AF, compared to RF, is likely due to cloud adjustment. Multimodel time series of temperature change and AF from 1850 to 2100 have large intermodel spreads throughout the period. The intermodel spread of temperature change is principally driven by forcing differences in the present day and climate feedback differences in 2095, although forcing differences are still important for model spread at 2095. We find no significant relationship between the equilibrium climate sensitivity (ECS) of a model and its 2003 AF, in contrast to that found in older models where higher ECS models generally had less forcing. Given the large present‐day model spread, there is no indication of any tendency by modelling groups to adjust their aerosol forcing in order to produce observed trends. Instead, some CMIP5 models have a relatively large positive forcing and overestimate the observed temperature change.
  10. 2013: Knutti, Reto, and Jan Sedláček. “Robustness and uncertainties in the new CMIP5 climate model projections.” Nature Climate Change 3.4 (2013): 369. Estimates of impacts from anthropogenic climate change rely on projections from climate models. Uncertainties in those have often been a limiting factor, in particular on local scales. A new generation of more complex models running scenarios for the upcoming Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5) is widely, and perhaps naively, expected to provide more detailed and more certain projections. Here we show that projected global temperature change from the new models is remarkably similar to that from those used in IPCC AR4 after accounting for the different underlying scenarios. The spatial patterns of temperature and precipitation change are also very consistent. Interestingly, the local model spread has not changed much despite substantial model development and a massive increase in computational capacity. Part of this model spread is irreducible owing to internal variability in the climate system, yet there is also uncertainty from model differences that can potentially be eliminated. We argue that defining progress in climate modelling in terms of narrowing uncertainties is too limited. Models improve, representing more processes in greater detail. This implies greater confidence in their projections, but convergence may remain slow. The uncertainties should not stop decisions being made.
  11. 2013: Vial, Jessica, Jean-Louis Dufresne, and Sandrine Bony. “On the interpretation of inter-model spread in CMIP5 climate sensitivity estimates.” Climate Dynamics 41.11-12 (2013): 3339-3362. This study diagnoses the climate sensitivity, radiative forcing and climate feedback estimates from eleven general circulation models participating in the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5), and analyzes inter-model differences. This is done by taking into account the fact that the climate response to increased carbon dioxide (CO2) is not necessarily only mediated by surface temperature changes, but can also result from fast land warming and tropospheric adjustments to the CO2 radiative forcing. By considering tropospheric adjustments to CO2 as part of the forcing rather than as feedbacks, and by using the radiative kernels approach, we decompose climate sensitivity estimates in terms of feedbacks and adjustments associated with water vapor, temperature lapse rate, surface albedo and clouds. Cloud adjustment to CO2 is, with one exception, generally positive, and is associated with a reduced strength of the cloud feedback; the multi-model mean cloud feedback is about 33 % weaker. Non-cloud adjustments associated with temperature, water vapor and albedo seem, however, to be better understood as responses to land surface warming. Separating out the tropospheric adjustments does not significantly affect the spread in climate sensitivity estimates, which primarily results from differing climate feedbacks. About 70 % of the spread stems from the cloud feedback, which remains the major source of inter-model spread in climate sensitivity, with a large contribution from the tropics. Differences in tropical cloud feedbacks between low-sensitivity and high-sensitivity models occur over a large range of dynamical regimes, but primarily arise from the regimes associated with a predominance of shallow cumulus and stratocumulus clouds. The combined water vapor plus lapse rate feedback also contributes to the spread of climate sensitivity estimates, with inter-model differences arising primarily from the relative humidity responses throughout the troposphere. Finally, this study points to a substantial role of nonlinearities in the calculation of adjustments and feedbacks for the interpretation of inter-model spread in climate sensitivity estimates. We show that in climate model simulations with large forcing (e.g., 4 × CO2), nonlinearities cannot be assumed minor nor neglected. Having said that, most results presented here are consistent with a number of previous feedback studies, despite the very different nature of the methodologies and all the uncertainties associated with them.
  12. 2013: Kumar, Sanjiv, et al. “Evaluation of temperature and precipitation trends and long-term persistence in CMIP5 twentieth-century climate simulations.” Journal of Climate26.12 (2013): 4168-4185. The authors have analyzed twentieth-century temperature and precipitation trends and long-term persistence from 19 climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5). This study is focused on continental areas (60°S–60°N) during 1930–2004 to ensure higher reliability in the observations. A nonparametric trend detection method is employed, and long-term persistence is quantified using the Hurst coefficient, taken from the hydrology literature. The authors found that the multimodel ensemble–mean global land–average temperature trend (0.07°C decade−1) captures the corresponding observed trend well (0.08°C decade−1). Globally, precipitation trends are distributed (spatially) at about zero in both the models and in the observations. There are large uncertainties in the simulation of regional-/local-scale temperature and precipitation trends. The models’ relative performances are different for temperature and precipitation trends. The models capture the long-term persistence in temperature reasonably well. The areal coverage of observed long-term persistence in precipitation is 60% less (32% of land area) than that of temperature (78%). The models have limited capability to capture the long-term persistence in precipitation. Most climate models underestimate the spatial variability in temperature trends. The multimodel ensemble–average trend generally provides a conservative estimate of local/regional trends. The results of this study are generally not biased by the choice of observation datasets used, including Climatic Research Unit Time Series 3.1; temperature data from Hadley Centre/Climatic Research Unit, version 4; and precipitation data from Global Historical Climatology Network, version 2.
  13. 2014: Santer, Benjamin D., et al. “Volcanic contribution to decadal changes in tropospheric temperature.” Nature Geoscience 7.3 (2014): 185. Despite continued growth in atmospheric levels of greenhouse gases, global mean surface and tropospheric temperatures have shown slower warming since 1998 than previously1,2,3,4,5. Possible explanations for the slow-down include internal climate variability3,4,6,7, external cooling influences1,2,4,8,9,10,11 and observational errors12,13. Several recent modelling studies have examined the contribution of early twenty-first-century volcanic eruptions1,2,4,8 to the muted surface warming. Here we present a detailed analysis of the impact of recent volcanic forcing on tropospheric temperature, based on observations as well as climate model simulations. We identify statistically significant correlations between observations of stratospheric aerosol optical depth and satellite-based estimates of both tropospheric temperature and short-wave fluxes at the top of the atmosphere. We show that climate model simulations without the effects of early twenty-first-century volcanic eruptions overestimate the tropospheric warming observed since 1998. In two simulations with more realistic volcanic influences following the 1991 Pinatubo eruption, differences between simulated and observed tropospheric temperature trends over the period 1998 to 2012 are up to 15% smaller, with large uncertainties in the magnitude of the effect. To reduce these uncertainties, better observations of eruption-specific properties of volcanic aerosols are needed, as well as improved representation of these eruption-specific properties in climate model simulations.
  14. 2014: Wuebbles, Donald, et al. “CMIP5 climate model analyses: climate extremes in the United States.” Bulletin of the American Meteorological Society 95.4 (2014): 571-583. This is the fourth in a series of four articles on historical and projected climate extremes in the United States. Here, we examine the results of historical and future climate model experiments from the phase 5 of the Coupled Model Intercomparison Project (CMIP5) based on work presented at the World Climate Research Programme (WCRP) Workshop on CMIP5 Climate Model Analyses held in March 2012. Our analyses assess the ability of CMIP5 models to capture observed trends, and we also evaluate the projected future changes in extreme events over the contiguous Unites States. Consistent with the previous articles, here we focus on model-simulated historical trends and projections for temperature extremes, heavy precipitation, large-scale drivers of precipitation variability and drought, and extratropical storms. Comparing new CMIP5 model results with earlier CMIP3 simulations shows that in general CMIP5 simulations give similar patterns and magnitudes of future temperature and precipitation extremes in the United States relative to the projections from the earlier phase 3 of the Coupled Model Intercomparison Project (CMIP3) models. Specifically, projections presented here show significant changes in hot and cold temperature extremes, heavy precipitation, droughts, atmospheric patterns such as the North American monsoon and the North Atlantic subtropical high that affect interannual precipitation, and in extratropical storms over the twenty-first century. Most of these trends are consistent with, although in some cases (such as heavy precipitation) underestimate, observed trends
  15. 2014: Friedlingstein, Pierre, et al. “Uncertainties in CMIP5 climate projections due to carbon cycle feedbacks.” Journal of Climate27.2 (2014): 511-526. In the context of phase 5 of the Coupled Model Intercomparison Project, most climate simulations use prescribed atmospheric CO2 concentration and therefore do not interactively include the effect of carbon cycle feedbacks. However, the representative concentration pathway 8.5 (RCP8.5) scenario has additionally been run by earth system models with prescribed CO2 emissions. This paper analyzes the climate projections of 11 earth system models (ESMs) that performed both emission-driven and concentration-driven RCP8.5 simulations. When forced by RCP8.5 CO2 emissions, models simulate a large spread in atmospheric CO2; the simulated 2100 concentrations range between 795 and 1145 ppm. Seven out of the 11 ESMs simulate a larger CO2 (on average by 44 ppm, 985 ± 97 ppm by 2100) and hence higher radiative forcing (by 0.25 W m−2) when driven by CO2 emissions than for the concentration-driven scenarios (941 ppm). However, most of these models already overestimate the present-day CO2, with the present-day biases reasonably well correlated with future atmospheric concentrations’ departure from the prescribed concentration. The uncertainty in CO2 projections is mainly attributable to uncertainties in the response of the land carbon cycle. As a result of simulated higher CO2 concentrations than in the concentration-driven simulations, temperature projections are generally higher when ESMs are driven with CO2 emissions. Global surface temperature change by 2100 (relative to present day) increased by 3.9° ± 0.9°C for the emission-driven simulations compared to 3.7° ± 0.7°C in the concentration-driven simulations. Although the lower ends are comparable in both sets of simulations, the highest climate projections are significantly warmer in the emission-driven simulations because of stronger carbon cycle feedbacks.
  16. 2014: Huber, Markus, and Reto Knutti. “Natural variability, radiative forcing and climate response in the recent hiatus reconciled.” Nature Geoscience 7.9 (2014): 651. Global mean surface warming over the past 15 years or so has been less than in earlier decades and less than simulated by most climate models1. Natural variability2,3,4, a reduced radiative forcing5,6,7, a smaller warming response to atmospheric carbon dioxide concentrations8,9 and coverage bias in the observations10 have been identified as potential causes. However, the explanations of the so-called ‘warming hiatus’ remain fragmented and the implications for long-term temperature projections are unclear. Here we estimate the contribution of internal variability associated with the El Niño/Southern Oscillation (ENSO) using segments of unforced climate model control simulations that match the observed climate variability. We find that ENSO variability analogous to that between 1997 or 1998 and 2012 leads to a cooling trend of about −0.06 °C. In addition, updated solar and stratospheric aerosol forcings from observations explain a cooling trend of similar magnitude (−0.07 °C). Accounting for these adjusted trends we show that a climate model of reduced complexity with a transient climate response of about 1.8 °C is consistent with the temperature record of the past 15 years, as is the ensemble mean of the models in the Coupled Model Intercomparison Project Phase 5 (CMIP5). We conclude that there is little evidence for a systematic overestimation of the temperature response to increasing atmospheric CO2 concentrations in the CMIP5 ensemble.
  17. 2015: Sharmila, S., et al. “Future projection of Indian summer monsoon variability under climate change scenario: An assessment from CMIP5 climate models.” Global and Planetary Change 124 (2015): 62-78. In this study, the impact of enhanced anthropogenic greenhouse gas emissionson the possible future changes in different aspects of daily-to-interannual variability of Indian summer monsoon (ISM) is systematically assessed using 20 coupled models participated in the Coupled Model Inter-comparison ProjectPhase 5. The historical (1951–1999) and future (2051–2099) simulations under the strongest Representative Concentration Pathway have been analyzed for this purpose. A few reliable models are selected based on their competence in simulating the basic features of present-climate ISM variability. The robust and consistent projections across the selected models suggest substantial changes in the ISM variability by the end of 21st century indicating strong sensitivity of ISM to global warming. On the seasonal scale, the all-India summer monsoon mean rainfall is likely to increase moderately in future, primarily governed by enhanced thermodynamic conditions due to atmospheric warming, but slightly offset by weakened large scale monsoon circulation. It is projected that the rainfall magnitude will increase over core monsoon zone in future climate, along with lengthening of the season due to late withdrawal. On interannual timescales, it is speculated that severity and frequency of both strong monsoon (SM) and weak monsoon (WM) might increase noticeably in future climate. Substantial changes in the daily variability of ISM are also projected, which are largely associated with the increase in heavy rainfall events and decrease in both low rain-rate and number of wet days during future monsoon. On the subseasonal scale, the model projections depict considerable amplification of higher frequency (below 30 day mode) components; although the dominant northward propagating 30–70 day mode of monsoon intraseasonal oscillationsmay not change appreciably in a warmer climate. It is speculated that the enhanced high frequency mode of monsoon ISOs due to increased GHG induced warming may notably modulate the ISM rainfall in future climate. Both extreme wet and dry episodes are likely to intensify and regionally extend in future climate with enhanced propensity of short active and long break spells. The SM (WM) could also be more wet (dry) in future due to the increment in longer active (break) spells. However, future changes in the spatial pattern during active/break phase of SM and WM are geographically inconsistent among the models. The results point out the growing climate-related vulnerability over Indian subcontinent, and further suggest the requisite of profound adaptation measures and better policy making in future.
  18. 2015: Slangen, Aimée BA, et al. “The sea level response to external forcings in historical simulations of CMIP5 climate models.” Journal of Climate 28.21 (2015): 8521-8539. Changes in Earth’s climate are influenced by internal climate variability and external forcings, such as changes in solar radiation, volcanic eruptions, anthropogenic greenhouse gases (GHG), and aerosols. Although the response of surface temperature to external forcings has been studied extensively, this has not been done for sea level. Here, a range of climate model experiments for the twentieth century is used to study the response of global and regional sea level change to external climate forcings. Both the global mean thermosteric sea level and the regional dynamic sea level patterns show clear responses to anthropogenic forcings that are significantly different from internal climate variability and larger than the difference between models driven by the same external forcing. The regional sea level patterns are directly related to changes in surface winds in response to the external forcings. The spread between different realizations of the same model experiment is consistent with internal climate variability derived from preindustrial control simulations. The spread between the different models is larger than the internal variability, mainly in regions with large sea level responses. Although the sea level responses to GHG and anthropogenic aerosol forcing oppose each other in the global mean, there are differences on a regional scale, offering opportunities for distinguishing between these two forcings in observed sea level change.
  19. 2016: Atwood, A. R., et al. “Quantifying climate forcings and feedbacks over the last millennium in the CMIP5–PMIP3 models.” Journal of Climate 29.3 (2016): The role of radiative forcings and climate feedbacks on global cooling over the last millennium is quantified in the CMIP5–PMIP3 transient climate model simulations. Changes in the global energy budget over the last millennium are decomposed into contributions from radiative forcings and climate feedbacks through the use of the approximate partial radiative perturbation method and radiative kernels. Global cooling occurs circa 1200–1850 CE in the multimodel ensemble mean with pronounced minima corresponding with volcanically active periods that are outside the range of natural variability. Analysis of the global energy budget during the last millennium indicates that Little Ice Age (LIA; 1600–1850 CE) cooling is largely driven by volcanic forcing (comprising an average of 65% of the total forcing among models), while contributions due to changes in land use (13%), greenhouse gas concentrations (12%), and insolation (10%) are substantially lower. The combination of these forcings directly contributes to 47% of the global cooling during the LIA, while the remainder of the cooling arises from the sum of the climate feedbacks. The dominant positive feedback is the water vapor feedback, which contributes 29% of the global cooling. Additional positive feedbacks include the surface albedo feedback (which contributes 7% of the global cooling and arises owing to high-latitude sea ice expansion and increased snow cover) and the lapse rate feedback (which contributes an additional 7% of the global cooling and arises owing to greater cooling near the surface than aloft in the middle and high latitudes).1161-1178.
  20. 2017: Stouffer, Ronald J., et al. “CMIP5 scientific gaps and recommendations for CMIP6.” Bulletin of the American Meteorological Society 98.1 (2017): 95-105.The Coupled Model Intercomparison Project (CMIP) is an ongoing coordinated international activity of numerical experimentation of unprecedented scope and impact on climate science. Its most recent phase, the fifth phase (CMIP5), has created nearly 2 PB of output from dozens of experiments performed by dozens of comprehensive climate models available to the climate science research community. In so doing, it has greatly advanced climate science. While CMIP5 has given answers to important science questions, with the help of a community survey we identify and motivate three broad topics here that guided the scientific framework of the next phase of CMIP, that is, CMIP6: How does the Earth system respond to changes in forcing? What are the origins and consequences of systematic model biases? How can we assess future climate changes given internal climate variability, predictability, and uncertainties in scenarios? CMIP has demonstrated the power of idealized experiments to better understand how the climate system works. We expect that these idealized approaches will continue to contribute to CMIP6. The quantification of radiative forcings and responses was poor, and thus it requires new methods and experiments to address this gap. There are a number of systematic model biases that appear in all phases of CMIP that remain a major climate modeling challenge. These biases need increased attention to better understand their origins and consequences through targeted experiments. Improving understanding of the mechanisms’ underlying internal climate variability for more skillful decadal climate predictions and long-term projections remains another challenge for CMIP6.
  21. 2017: Power, Scott, et al. “Apparent limitations in the ability of CMIP5 climate models to simulate recent multi-decadal change in surface temperature: implications for global temperature projections.” Climate Dynamics 49.1-2 (2017): 53-69. Observed surface temperature trends over the period 1998–2012/2014 have attracted a great deal of interest because of an apparent slowdown in the rate of global warming, and contrasts between climate model simulations and observations of such trends. Many studies have addressed the statistical significance of these relatively short-trends, whether they indicate a possible bias in the model values and the implications for global warming generally. Here we re-examine these issues, but as they relate to changes over much longer-term changes. We find that on multidecadal time scales there is little evidence for any change in the observed global warming rate, but some evidence for a recent temporary slowdown in the warming rate in the Pacific. This multi-decadal slowdown can be partly explained by a cool phase of the Interdecadal Pacific Oscillation and a short-term excess of La Niña events. We also analyse historical and projected changes in 38 CMIP climate models. All of the model simulations examined simulate multi-decadal warming in the Pacific over the past half-century that exceeds observed values. This difference cannot be fully explained by observed internal multi-decadal climate variability, even if allowance is made for an apparent tendency for models to underestimate internal multi-decadal variability in the Pacific. Models which simulate the greatest global warming over the past half-century also project warming that is among the highest of all models by the end of the twenty-first century, under both low and high greenhouse gas emission scenarios. Given that the same models are poorest in representing observed multi-decadal temperature change, confidence in the highest projections is reduced.
  22. 2018: Hao, Mingju, et al. “Narrowing the surface temperature range in CMIP5 simulations over the Arctic.” Theoretical and Applied Climatology 132.3-4 (2018): 1073-1088. Much uncertainty exists in reproducing Arctic temperature using different general circulation models (GCMs). Therefore, evaluating the performance of GCMs in reproducing Arctic temperature is critically important. In our study, 32 GCMs in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) during the period 1900–2005 are used, and several metrics, i.e., bias, correlation coefficient (R), and root mean square error (RMSE), are applied. The Cowtan data set is adopted as the reference data. The results suggest that the GCMs used can reasonably reproduce the Arctic warming trend during the period 1900–2005, as observed in the observational data, whereas a large variation of inter-model differences exists in modeling the Arctic warming magnitude. With respect to the reference data, most GCMs have large cold biases, whereas others have weak warm biases. Additionally, based on statistical thresholds, the models MIROC-ESM, CSIRO-Mk3-6-0, HadGEM2-AO, and MIROC-ESM-CHEM (bias ≤ ±0.10 °C, R ≥ 0.50, and RMSE ≤ 0.60 °C) are identified as well-performingGCMs. The ensemble of the four best-performing GCMs (ES4), with bias, R, and RMSE values of −0.03 °C, 0.72, and 0.39 °C, respectively, performs better than the ensemble with all 32 members, with bias, R, and RMSE values of −0.04 °C, 0.64, and 0.43 °C, respectively. Finally, ES4 is used to produce projections for the next century under the scenarios of RCP2.6, RCP4.5, and RCP8.0. The uncertainty in the projected temperature is greater in the higher emissions scenarios. Additionally, the projected temperature in the cold half year has larger variations than that in the warm half year.
  23. 2018: Palmer, Matthew D., Glen R. Harris, and Jonathan M. Gregory. “Extending CMIP5 projections of global mean temperature change and sea level rise due to thermal expansion using a physically-based emulator.” Environmental Research Letters13.8 (2018): 084003. We present a physically-based emulator approach to extending 21st century CMIP5 model simulations of global mean surface temperature (GMST) and global thermal expansion (TE) to 2300. A two-layer energy balance model that has been tuned to emulate the CO2 response of individual CMIP5 models is combined with model-specific radiative forcings to generate an emulated ensemble to 2300 for RCP2.6, RCP4.5 and RCP8.5. Errors in the emulated time series are quantified using a subset of CMIP5 models with data available to 2300 and factored into the ensemble uncertainty. The resulting projections show good agreement with 21st century ensemble projections reported in IPCC AR5 and also compare favourably with individual CMIP5 model simulations post-2100. There is a tendency for the two-layer model simulations to overestimate both GMST rise and TE under RCP2.6, which is suggestive of a systematic error in the applied radiative forcings. Overall, the framework shows promise as a basis for extending process-based projections of global sea level rise beyond the 21st century time horizon that typifies CMIP5 simulations. The results also serve to illustrate the differing responses of GMST and Earth’s energy imbalance (EEI) to reductions in greenhouse gas emissions. GMST responds relatively quickly to changes in emissions, leading to a negative trend post-2100 for RCP2.6, although temperature remains substantially elevated compared to present day at 2300. In contrast, EEI remains positive under all RCPs, and results in ongoing sea level rise from TE.

 

 

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FIGURE 1: ORW SHAPE: Optimal Regular Wave Function

solarcycleorwf

 

FIGURE 2: ORW RESIDUAL ANALYSIS AND THE HURST EXPONENT

solarcycle-hurst-exponents

FULL TEXT DOWNLOAD: SSRN.COM  ACADEMIA.EDU

 

  1. Sunspots are evanescent dark spots on the sun ranging in size from megameters to gigameters in diameter. Their life span varies from two days to two weeks and their number at any given time from a few to more than a hundred. The total number of sunspots is known to serve as a measure of the level of solar activity (Rogers, 2006) (Yan, 2013). The time series of the number of sunspots appears to form a cyclical pattern with a period of about eleven-years. However, both the period and the amplitude of this cycle are variable and irregular apparently containing long run and irregular cycles of their own (Hathaway, 1994) (Rogers, 2006) (Miletsky, 2014).
  2. Sunspot cycles have presented researchers with an enigmatic and vexing quandary for centuries because their irregular nature is not well understood (Hathaway, The Solar Cycle, 2010). Sunspot counts have been recorded and studied since 1610 and all aspects of the patterns in the time series have been subjected to intense scrutiny and interpretation in terms of solar phenomena and their effects on earth (Usoskin, A solar cycle lost, 2009) (Usoskin, Grand minima and maxima of solar activity, 2007) (Hathaway, The Solar Cycle, 2010).
  3. The interest in sunspot numbers has grown in the climate change era due to advances in satellite measurements of solar activity and also because of the possible effects of changes in solar irradiance on climate (Weart, 2003) (Haigh, 2007) (Fox, 2004). However, certain issues in the utility of sunspot count time series data remain unresolved, the most prominent being the irregular nature of both the short term solar cycle and the long wave of its amplitude.
  4. In this short post we show that these issues may be addressed by separating the regular cyclical components of the solar cycle from the irregular and by describing the system as a sum of two independent phenomena – one cyclical and the other random and chaotic. The random component is shown to be a non-Gaussian Hurst process with dependence and persistence, properties known to create irregular patterns from randomness (Hurst, 1951) (Koutsoyiannis D. , 2002) (Mandelbrot B. , 1972) (Kim, 2006) (Watari, 1995) (Zhou, 2014).
  5. A hurdle to the analysis and understanding of the cyclical behavior of sunspot counts has been the irregular nature of these cycles. We therefore propose that the phenomenon is best described as the sum of two components – one regular and cyclical and the other irregular and random. For mean monthly sunspot counts in the sample period 1/1818-11/2015 we show that the regular and cyclical component of the phenomenon consists of two superimposed wave functions, one a short wave and the other a long wave. FIGURE 1.
  6. The short wave is identified as a 131-month asymmetric and triangular cycle of sunspot counts with a 50-month rising leg and an 81-month falling leg. The long wave is found to be a 100-year symmetric triangular wave in which the amplitude of the short wave fluctuates between 100 and 230 sunspots (FIGURE 1).  This optimal regular component of sunspot number behavior is constructed by minimizing the residuals of the compound wave function.
  7. It is shown that these residuals are not random Gaussian but that they tend to form patterns (FIGURE 2). Rescaled range analysis of the residuals shows that they contain the Hurst effect of memory and persistence and it is proposed that the patterns in the residuals may be explained in terms of the non-linear dynamics and chaos. It is proposed therefore that the behavior of sunspot cycles may be understood in terms of its regular and cyclical components overlaid with a chaotic process.

 

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Climate scientist Peter Cox wrote a climate model computer program with the assumptions that (1) human fossil fuel emissions cause atmospheric CO2 concentration to rise, (2) surface temperature is responsive to atmospheric CO2 concentration according to the theory of the greenhouse effect of CO2.

When he ran this program he was amazed to find that his climate model proves that (1) human fossil fuel emissions cause atmospheric CO2 concentration to rise, (2) surface temperature is responsive to atmospheric CO2 concentration according to the theory of the greenhouse effect of CO2.

There you have it ladies and gentlemen – absolute proof presented by a scientist with a computer program – that our fossil fuel emissions cause climate change and that therefore we can control the climate by reducing our emissions.

 

controlknob

 

Statistical tests of these assumptions are provided in a related post.

Human Caused Climate Change?

 

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stratos4

 

FIGURE 1: GLOBAL TEMP: WARMING TROPOSPHERE, COOLING STRATOSPHERE

TROP-STRAT-CORR

 

FIGURE 2: GLOBAL TEMP: CORRELATION WITH LN(CO2)

TROP-STRAT-CO2-CORR

 

FIGURE 3: TYLER VIGEN SPURIOUS CORRELATION DEMONSTRATION

Spurious_Correlation

 

FIGURE 4: THE RATIONALE FOR DETRENDED CORRELATION ANALYSIS

 

 

FIGURE 5: DETRENDED ANALYSIS: RESPONSIVENESS OF STRATOSPHERIC COOLING TO TROPOSPHERIC WARMING AT AN ANNUAL TIME SCALE

DET-TROP-STRAT

 

FIGURE 6: DETRENDED CORRELATION: LN(ATMOS-CO2) AND TROPOSPHERIC AND STRATOSPHERIC TEMPERATURE 1979-2017

DETCORRP-TEMP-CO2

 

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The literature review presented below describes results of a large number of climate model simulations of atmospheric conditions under an artificial increase in carbon dioxide concentration. Their unanimous conclusion is that such artificial forcing will cause warming of the troposphere, popularly known as global warming and climate change by way of the heat trapping effect of carbon dioxide. Less well known is that the model simulations also describe the effect of these changes on the stratosphere. In particular, the models show a cooling of the lower stratosphere. It is thought that the partial shielding of the stratosphere from long wave surface radiation due to CO2 absorption causes the stratosphere to cool.

These trends are found in the observational data. Since 1979 microwave sounding units (MSUs) on National Oceanic and Atmospheric Administration polar orbiting satellites have been recording accurate measures of zonal atmospheric temperatures at various elevations in both the troposphere and the stratosphere. Figure 1 above contains three panels that depict satellite temperature anomaly data for the sample period 1979-2017 supplied by the University of Alabama, Huntsville (UAH) available online at Christy/Spencer 2018The left panel shows the lower troposphere is warming. OLS linear regression shows a very high average warming rate 1.29C/century. The middle panel shows that the corresponding temperature anomalies in the lower stratosphere are in a downward trend with a high average OLS cooling rate of -2.96C/century. This pattern of warming troposphere and cooling stratosphere is exactly what the model simulations listed below have predicted. The right panel of Figure 1 appears to indicate that these two opposing trends are synchronized by way of a statistically significant negative correlation r=-0.60.

The theoretical causal connection between synchronized tropospheric warming and stratospheric cooling seen in the climate models is rising atmospheric carbon dioxide. The theoretical relationship and rationale for these changes built into the climate models is that the temperature in both of these layers of the atmosphere is driven by atmospheric carbon dioxide concentration in terms of a theoretical linear relationship between the logarithm of carbon dioxide concentration and temperature. These relationships are shown in Figure 2.

The middle panel of Figure 2 shows a strong positive correlation between log(CO2) and tropospheric temperature in terms of a strong correlation of r=0.72. The positive sign of the correlation is consistent with the theoretical relationship in which CO2 causes troposphere temperature to rise. The right panel of Figure 2 shows a strong negative correlation between log(CO2) and lower stratospheric temperature in terms of a strong correlation of r=-0.76. The negative sign of the correlation is consistent with the theoretical relationship in which CO2 causes lower stratospheric temperature to fall.

However, there are some statistical considerations that require caution in the interpretation of time series data, particularly field data taken as given and not under a controlled experiment. This issue is discussed at length in a related post on SPURIOUS CORRELATIONS IN CLIMATE SCIENCE

In short, correlations between time series of field data require extreme caution to separate out and remove the effect of long term trends so that the theoretical responsiveness at a given time scale may be assessed. Failure to do so results in the kind of comical conclusions demonstrated by Tyler Vigen in his excellent statistics site  TYLERVIGEN SPURIOUS CORRELATION DEMONSTRATIONS An example from the large Tyler Vigen collection is shown in Figure 3. These spurious correlations demonstrate that shared trends can create a faux correlation that is unrelated to responsiveness at the time scale of interest. Long term trends have a time scale equal to the full span with a sample size of one, no degrees of freedom, and no statistical power. his issue is discussed in a Youtube video lecture by Alex Tolley (Link:  ALEX TOLLEY’S LECTURE  . A small portion of the video appears above in Figure 4.

The inverse correlation of r=-0.60 between tropospheric warming and stratospheric cooling shown in Figure 1 is tested with detrended correlation analysis for responsiveness at an annual time scale in Figure 5. No statistically significant correlation is found. The observed correlation has dropped from r=-0.60 in the source data to r=-0.08 in the detrended data indicating that the high source data correlation is an artifact of shared trends and not an indication of responsiveness at an annual time scale.

Figure 6 displays the results of detrended correlation analysis for the responsiveness of of the two atmospheric temperature series to changes in LN(CO2) at an annual time scale net of long term trends. Here we find that the strong correlation seen in the source data of r = +0.72 in tropospheric temperature and r = -0.76 in lower stratospheric temperature do not survive into the detrended data and are therefore spurious artifacts of long term trends and do not indicators of responsiveness at an annual time scale. For the tropospheric temperature series, the correlation drops to a near zero and statistically insignificant value of r = +0.15 and for the lower stratosphere the correlation flips sign over to a positive value of r = +0.385. Since these are one-sided hypothesis tests where we expect r>0 for tropospheric temperatures and r<0 for stratospheric temperatures, we are unable to reject the null hypothesis in either case.

We conclude that no evidence is found in the observational data to indicate that either tropospheric warming or lower stratospheric cooling is responsive to changes in LN(CO2) or that stratospheric cooling is responsive to tropospheric warming, at an annual time scale. These data do not support the theory of causation that links tropospheric warming or stratospheric cooling to atmospheric CO2.

  1. 1975: Manabe, Syukuro, and Richard T. Wetherald. “The effects of doubling the CO2 concentration on the climate of a general circulation model.” Journal of the Atmospheric Sciences 32.1 (1975): 3-15. An attempt is made to estimate the temperature changes resulting from doubling the present CO2concentration by the use of a simplified three-dimensional general circulation model. This model contains the following simplications: a limited computational domain, an idealized topography, no beat transport by ocean currents, and fixed cloudiness. Despite these limitations, the results from this computation yield some indication of how the increase of CO2 concentration may affect the distribution of temperature in the atmosphere. It is shown that the CO2 increase raises the temperature of the model troposphere, whereas it lowers that of the model stratosphere. The tropospheric warming is somewhat larger than that expected from a radiative-convective equilibrium model. In particular, the increase of surface temperature in higher latitudes is magnified due to the recession of the snow boundary and the thermal stability of the lower troposphere which limits convective heating to the lowest layer. It is also shown that the doubling of carbon dioxide significantly increases the intensity of the hydrologic cycle of the model.
  2. 1988: Ramanathan, Veerabhachan. “The greenhouse theory of climate change: a test by an inadvertent global experiment.” Science 240.4850 (1988): 293-299. Since the dawn of the industrial era, the atmospheric concentrations of several radiatively active gases have been increasing as a result of human activities. The radiative heating from this inadvertent experiment has driven the climate system out of equilibrium with the incoming solar energy. According to the greenhouse theory of climate change, the climate system will be restored to equilibrium by a warming of the surfacetroposphere system and a cooling of the stratosphere. The predicted changes, during the next few decades, could far exceed natural climate variations in historical times. Hence, the greenhouse theory of climate change has reached the crucial stage of verification. Surface warming as large as that predicted by models would be unprecedented during an interglacial period such as the present. The theory, its scope for verification, and the emerging complexities of the climate feedback mechanisms are discussed.
  3. 1989: Washington, Warren M., and Gerald A. Meehl. “Climate sensitivity due to increased CO 2: experiments with a coupled atmosphere and ocean general circulation model.” Climate dynamics 4.1 (1989): 1-38. A version of the National Center for Atmospheric Research community climate model — a global, spectral (R15) general circulation model — is coupled to a coarse-grid (5° latitude-] longitude, four-layer) ocean general circulation model to study the response of the climate system to increases of atmospheric carbon dioxide (CO2). Three simulations are run: one with an instantaneous doubling of atmospheric CO2 (from 330 to 660 ppm), another with the CO2concentration starting at 330 ppm and increasing linearly at a rate of 1% per year, and a third with CO2 held constant at 330 pm. Results at the end of 30 years of simulation indicate a globally averaged surface air temperature increase of 1.6° C for the instantaneous doubling case and 0.7°C for the transient forcing case. Inherent characteristics of the coarse-grid ocean model flow sea-surface temperatures (SSTs) in the tropics and higher-than-observed SSTs and reduced sea-ice extent at higher latitudes] produce lower sensitivity in this model after 30 years than in earlier simulations with the same atmosphere coupled to a 50-m, slab-ocean mixed layer. Within the limitations of the simulated meridional overturning, the thermohaline circulation weakens in the coupled model with doubled CO2 as the high-latitude ocean-surface layer warms and freshens and westerly wind stress is decreased. In the transient forcing case with slowly increasing CO2 (30% increase after 30 years), the zonal mean warming of the ocean is most evident in the surface layer near 30°–50° S. Geographical plots of surface air temperature change in the transient case show patterns of regional climate anomalies that differ from those in the instantaneous CO2 doubling case, particularly in the North Atlantic and northern European regions. This suggests that differences in CO2 forcing in the climate system are important in CO2 response in regard to time-dependent climate anomaly regimes. This confirms earlier studies with simple climate models that instantaneous CO2 doubling simulations may not be analogous in all respects to simulations with slowly increasing CO2
  4. 1990: Rind, D., et al. “Climate change and the middle atmosphere. Part I: The doubled CO2 climate.” Journal of the Atmospheric Sciences 47.4 (1990): 475-494.The impact of doubled atmospheric CO2 on the climate of the middle atmosphere is investigated using the GISS global climate/middle atmosphere model. In the standard experiment, the CO2 concentration is doubled both in the stratosphere and troposphere, and the sea surface temperatures are increased to match those of the doubled CO2 run of the GISS 9 level climate model. Additional experiments are run to determine how the middle atmospheric effects are influenced by tropospheric changes, and to separate the dynamic and radiative influences. These include the use of the greater high latitude/low latitude surface warming ratio generated by the Geophysical Fluid Dynamics Laboratory doubled CO2experiments, doubling the CO2 only in either the troposphere or stratosphere, and allowing the middle atmosphere to react only radiatively. As expected, doubled CO2 produces warmer temperatures in the troposphere, and generally cooler temperatures in the stratosphere. The net result is a decrease of static stability for the atmosphere as a whole. In addition, the 100 mb warming maximizes in the tropics, leading to improved propagation conditions for planetary waves, and increased potential energy in the lower stratosphere. These processes generate increased eddy energy in the middle atmosphere in most seasons. With greater eddy energy comes greater eddy forcing of the mean flow and an increase in the intensity of the residual circulation from the equator to the pole, which tends to warm high latitudes. Increased gravity wave drag in some of the experiments also helps to intensify the circulation. The middle atmosphere dynamical differences are on the order of 10%–20% of the model values for the current climate, and, along with the calculated temperature differences of up to some 10°C, may have a significant impact on the chemistry of the future atmosphere including that of stratospheric ozone, the polar ozone “hole,” and basic atmospheric composition.
  5. 1992: Pitari, G., et al. “Ozone response to a CO2 doubling: Results from a stratospheric circulation model with heterogeneous chemistry.” Journal of Geophysical Research: Atmospheres97.D5 (1992): 5953-5962. A spectral three‐dimensional model of the stratosphere has been used to study the sensitivity of polar ozone with respect to a carbon dioxide increase. The lower stratospheric cooling associated with an imposed CO2 doubling may increase the probability of polar stratospheric cloud (PSC) formation and thus affect ozone. We compare the ozone perturbation obtained with the inclusion of a simple parameterization for heterogeneous chemistry on PSCs to that relative to a pure homogeneous chemistry. In both cases the temperature perturbation is determined by a CO2 doubling, while the total chlorine content is kept at the present level. It is shown that the lower temperature may increase the depth and the extension of the ozone hole by extending the area amenable to PSC formation. It may be argued that this effect, coupled with an increasing amount of chlorine, may produce a positive feedback on the ozone destruction.
  6. 1998: Danilin, Michael Y., et al. “Stratospheric cooling and Arctic ozone recovery.” Geophysical research letters 25.12 (1998): 2141-2144. We present sensitivity studies using the AER box model for an idealized parcel in the lower stratosphere at 70°N during winter/spring with different assumed stratospheric coolings and chlorine loadings. Our calculations show that stratospheric cooling could further deplete ozone via increased polar stratospheric cloud (PSC) formation and retard its expected recovery even with the projected chlorine loading decrease. We introduce the concept of chlorine‐cooling equivalent and show that a 1 K cooling could provide the same local ozone depletion as an increase of chlorine by 0.4–0.7 ppbv for the scenarios considered. Thus, sustained stratospheric cooling could further reduce Arctic ozone content and delay the anticipated ozone recovery in the Northern Hemisphere even with the realization of the Montreal Protocol and its Amendments.
  7. 1998: Rosenfield, Joan E., and Anne R. Douglass. “Doubled CO2 effects on NOy in a coupled 2D model.” Geophysical research letters 25.23 (1998): 4381-4384. Stratospheric NOy fields calculated using a zonally averaged interactive chemistry‐radiation‐dynamics model show significant sensitivity to the model CO2. Modeled upper stratospheric NOy decreases by about 15% in response to CO2 doubling, mainly due to the temperature decrease calculated to result from increased CO2 cooling. The abundance of atomic nitrogen, N, increases because the rate of the strongly temperature dependent reaction N + O2 → NO + O decreases at lower temperatures. Increased N leads to an increase in the loss of NOy which is controlled by the reaction N + NO → N2 + O. The decrease in NOy due to the lowered temperatures is partially compensated by changes in the residual circulation. In addition, the NOy reduction is shown to be sensitive to the NO photolysis rate.
  8. 1998: Rind, D., et al. “Climate change and the middle atmosphere. Part III: The doubled CO2 climate revisited.” Journal of Climate 11.5 (1998): 876-894. The response of the troposphere–stratosphere system to doubled atmospheric CO2 is investigated in a series of experiments in which sea surface temperatures are allowed to adjust to radiation imbalances. The Goddard Institute for Space Studies (GISS) Global Climate Middle Atmosphere Model (GCMAM) warms by 5.1°C at the surface while the stratosphere cools by up to 10°C. When ozone is allowed to respond photochemically, the stratospheric cooling is reduced by 20%, with little effect in the troposphere. Planetary wave energy increases in the stratosphere, producing dynamical warming at high latitudes, in agreement with previous GCMAM doubled CO2 simulations; the effect is due to increased tropospheric generation and altered refraction, both strongly influenced by the magnitude of warming in the model’s tropical upper troposphere. This warming also results in stronger zonal winds in the lower stratosphere, which appears to reduce stratospheric planetary wave 2 energy and stratospheric warming events. The dynamical changes in the lower stratosphere are weakened when O3 chemistry on polar stratospheric cloud effects are included at current stratospheric chlorine levels. Comparison with the nine-level version of the GISS GCM with a top at 10 mb shows that both the stratospheric and tropospheric dynamical responses are different. The tropospheric effect is mostly a function of the vertical resolution in the troposphere; finer vertical resolution leads to increased latent heat release in the warmer climate, greater zonal available potential energy increase, and greater planetary longwave energy and energy transports. The increase in planetary longwave energy and residual circulation in the stratosphere is reproduced when the model top is lifted from 30 to 50 km, which also affects upper-tropospheric stability, convection and cloud cover, and climate sensitivity.
  9. 1998: Dameris, M., et al. “Assessment of the future development of the ozone layer.” Geophysical Research Letters 25.19 (1998): 3579-3582.
  10. 1999: de F. Forster, Piers M., and Keith P. Shine. “Stratospheric water vapour changes as a possible contributor to observed stratospheric cooling.” Geophysical research letters 26.21 (1999): 3309-3312. The observed cooling of the lower stratosphere over the last two decades has been attributed, in previous studies, largely to a combination of stratospheric ozone loss and carbon dioxide increase, and as such it is meant to provide one of the best pieces of evidence for an anthropogenic cause to climate change. This study shows how increases in stratospheric water vapour, inferred from available observations, may be capable of causing as much of the observed cooling as ozone loss does; as the reasons for the stratospheric water vapour increase are neither fully understood nor well characterized, it shows that it remains uncertain whether the cooling of the lower stratosphere can yet be fully attributable to human influences. In addition, the changes in stratospheric water vapour may have contributed, since 1980, a radiative forcing which enhances that due to carbon dioxide alone by 40%.
  11. 2003: Gillett, N. P., M. R. Allen, and K. D. Williams. “Modelling the atmospheric response to doubled CO2 and depleted stratospheric ozone using a stratosphere‐resolving coupled GCM.” Quarterly Journal of the Royal Meteorological Society129.589 (2003): 947-966. We investigate the atmospheric response to doubled CO2 and stratospheric ozone depletion in three versions of a general‐circulation model with differing vertical resolution and upper‐boundary heights. We find that an approximate doubling of the vertical resolution below 10 hPa reduces the temperature response to a doubling of CO2from 3.4 K to 2.5 K. Much of this difference is associated with changes in the cloud response. All model versions show an increase in the Arctic Oscillation index in response to a doubling of CO2, but the increase is no larger in the model with an upper boundary at 0.01 hPa than in the standard model with a top level at 5 hPa. All models also show general stratospheric cooling in response to doubling CO2. However, unlike some other authors, we find no cooling in the Arctic winter vortex below around 10 hPa in the stratosphere‐resolving model, and a weakening of the zonal winds throughout this region. This effect is due to enhanced upward propagation of planetary waves from the troposphere, and is an effect found only in the northern hemisphere, probably because of its larger zonal asymmetries. All models show a small but significant surface cooling in response to a reconstruction of 1998 stratospheric ozone depletion, and an increase in the Antarctic Oscillation index in the southern summer. The cooling extends through most of the atmosphere, and reaches a maximum in the region of the Antarctic ozone hole in November and December. © Royal Meteorological Society, 2003. K. D. Williams’s contribution is Crown copyright.
  12. 2003: Langematz, Ulrike, et al. “Thermal and dynamical changes of the stratosphere since 1979 and their link to ozone and CO2 changes.” Journal of Geophysical Research: Atmospheres108.D1 (2003): ACL-9.  This study examines which part of the observed stratospheric thermal and dynamical changes since 1979 can be attributed to the observed stratospheric ozone (O3) losses and CO2 increases. Further, the processes are studied that lead to temperature and circulation changes when stratospheric O3 and CO2 are modified. We compared results from simulations of the Freie Universität Berlin Climate Middle Atmosphere Model (FUB CMAM) using observed O3 and CO2 changes with observed trends of stratospheric temperature and circulation for the period 1979–2000 from FUB data and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses. The observed O3 decrease leads in the FUB CMAM to a global mean stratospheric cooling, which is enhanced in the upper stratosphere by the imposed CO2 increase. While the model is able to reproduce the observed stratospheric cooling in the upper stratosphere, it underestimates the observed trends in the lower stratosphere, particularly in middle latitudes and during Northern Hemisphere (NH) spring. The observed intensification and increased lifetimes of the polar vortices in spring are captured by the model but with smaller magnitude than observed. It is suggested that the observed upper stratospheric temperature trends during the past two decades in low to middle latitudes are caused by radiative effects due to the O3 and CO2 changes, while the cooling of the polar stratosphere in winter is enhanced by changes in dynamical heating. However, in northern midlatitudes and in Arctic spring, other effects than O3 and CO2 changes must be considered to fully explain the observed changes in the lower stratosphere.
  13. 2004: Sigmond, M., et al. “A simulation of the separate climate effects of middle-atmospheric and tropospheric CO2 doubling.” Journal of Climate 17.12 (2004): 2352-2367. The separate climate effects of middle-atmospheric and tropospheric CO2 doubling have been simulated and analyzed with the ECHAM middle-atmosphere climate model. To this end, the CO2 concentration has been separately doubled in the middle-atmosphere, the troposphere, and the entire atmosphere, and the results have been compared to a control run. During NH winter, the simulated uniformly doubled CO2 climate shows an increase of the stratospheric residual circulation, a small warming in the Arctic lower stratosphere, a weakening of the zonal winds in the Arctic middle-atmosphere, an increase of the NH midlatitude tropospheric westerlies, and a poleward shift of the SH tropospheric westerlies. The uniformly doubled CO2 response in most regions is approximately equal to the sum of the separate responses to tropospheric and middle-atmospheric CO2 doubling. The increase of the stratospheric residual circulation can be attributed for about two-thirds to the tropospheric CO2 doubling and one-third to the middle-atmospheric CO2 doubling. This increase contributes to the Arctic lower-stratospheric warming and, through the thermal wind relationship, to the weakening of the Arctic middle-atmospheric zonal wind. The increase of the tropospheric NH midlatitude westerlies can be attributed mainly to the middle-atmospheric CO2 doubling, indicating the crucial importance of the middle-atmospheric CO2 doubling for the tropospheric climate change. Results from an additional experiment show that the CO2 doubling above 10 hPa, which is above the top of many current GCMs, also causes significant changes in the tropospheric climate.
  14. 2006: Schmidt, H., et al. “The HAMMONIA chemistry climate model: Sensitivity of the mesopause region to the 11-year solar cycle and CO2 doubling.” Journal of Climate 19.16 (2006): 3903-3931. This paper introduces the three-dimensional Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), which treats atmospheric dynamics, radiation, and chemistry interactively for the height range from the earth’s surface to the thermosphere (approximately 250 km). It is based on the latest version of the ECHAM atmospheric general circulation model of the Max Planck Institute for Meteorology in Hamburg, Germany, which is extended to include important radiative and dynamical processes of the upper atmosphere and is coupled to a chemistry module containing 48 compounds. The model is applied to study the effects of natural and anthropogenic climate forcing on the atmosphere, represented, on the one hand, by the 11-yr solar cycle and, on the other hand, by a doubling of the present-day concentration of carbon dioxide. The numerical experiments are analyzed with the focus on the effects on temperature and chemical composition in the mesopause region. Results include a temperature response to the solar cycle by 2 to 10 K in the mesopause region with the largest values occurring slightly above the summer mesopause. Ozone in the secondary maximum increases by up to 20% for solar maximum conditions. Changes in winds are in general small. In the case of a doubling of carbon dioxide the simulation indicates a cooling of the atmosphere everywhere above the tropopause but by the smallest values around the mesopause. It is shown that the temperature response up to the mesopause is strongly influenced by changes in dynamics. During Northern Hemisphere summer, dynamical processes alone would lead to an almost global warming of up to 3 K in the uppermost mesosphere.
  15. 2007: Fomichev, V. I., et al. “Response of the middle atmosphere to CO2 doubling: Results from the Canadian Middle Atmosphere Model.” Journal of Climate 20.7 (2007): 1121-1144. The Canadian Middle Atmosphere Model (CMAM) has been used to examine the middle atmosphere response to CO2 doubling. The radiative-photochemical response induced by doubling CO2 alone and the response produced by changes in prescribed SSTs are found to be approximately additive, with the former effect dominating throughout the middle atmosphere. The paper discusses the overall response, with emphasis on the effects of SST changes, which allow a tropospheric response to the CO2 forcing. The overall response is a cooling of the middle atmosphere accompanied by significant increases in the ozone and water vapor abundances. The ozone radiative feedback occurs through both an increase in solar heating and a decrease in infrared cooling, with the latter accounting for up to 15% of the total effect. Changes in global mean water vapor cooling are negligible above ∼30 hPa. Near the polar summer mesopause, the temperature response is weak and not statistically significant. The main effects of SST changes are a warmer troposphere, a warmer and higher tropopause, cell-like structures of heating and cooling at low and middlelatitudes in the middle atmosphere, warming in the summer mesosphere, water vapor increase throughout the domain, and O3 decrease in the lower tropical stratosphere. No noticeable change in upward-propagating planetary wave activity in the extratropical winter–spring stratosphere and no significant temperature response in the polar winter–spring stratosphere have been detected. Increased upwelling in the tropical stratosphere has been found to be linked to changed wave driving at low latitudes.
  16. 2018: Smith, Karen L., et al. “No Surface Cooling over Antarctica from the Negative Greenhouse Effect Associated with Instantaneous Quadrupling of CO2 Concentrations.” Journal of Climate 31.1 (2018): 317-323. Over the highest elevations of Antarctica, during many months of the year, air near the surface is colder than in much of the overlying atmosphere. This unique feature of the Antarctic atmosphere has been shown to result in a negative greenhouse effect and a negative instantaneous radiative forcing at the top of the atmosphere , when carbon dioxide (CO2) concentrations are increased, and it has been suggested that this effect might play some role in the recent cooling trends observed over East Antarctica. Here, using fully coupled global climate model integrations, in addition to radiative transfer model calculations, the authors confirm the existence of such a negative  over parts of Antarctica in response to an instantaneous quadrupling of CO2. However, it is also shown that the instantaneous radiative forcing at the tropopause  is positive. Further, the negative  lasts only a few days following the imposed perturbation, and rapidly disappears as the stratosphere cools in response to increased CO2. As a consequence, like the , the stratosphere-adjusted radiative forcing at the TOA is positive over all of Antarctica and, in the model presented herein, surface temperatures increase everywhere over that continent in response to quadrupled CO2. The results, therefore, clearly demonstrate that the curious negative instantaneous radiative forcing plays no role in the recently observed East Antarctic cooling.

 

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Climate-Optimum

The ice of the last ice age began to melt about 20 KYBP (thousand years before the present) but that process was interrupted by the Younger Dryas about 12 KYBP with a return to icy conditions. After the end of the Younger Dryas, it returned to a warming trend. This warming trend got us to the fine weather conditions that made the Neolithic Revolution possible in which the hunter-gatherer humans settled and started farming, building homes, and forming communities. This period, usually marked as between 9 and 5 KYBP is known as the Holocene Climate Optimum (HCO). An extensive body of research exists on the study of climate during this period. Some surprising details are found in these papers, particularly the older ones prior to the time when all climate research had to relate to AGW one way or another. Presented below are a selection of papers on the HCO. The early papers, prior to 2004, are mostly European and are about the HCO in Europe. I found the Weidick, Ciais, and Hjort papers particularly noteworthy for their study of Greenland, the Arctic, and Antarctica. The later papers, particularly since 2004, are mostly Chinese and are about the HCO experience in different parts of China. If you have a paper or if you yourself have done work in this area that should be included in this list but is not, kindly leave the info in a comment.

  1. 1978: Sarnthein, Michael. “Sand deserts during glacial maximum and climatic optimum.” Nature 272.5648 (1978): 43. The past 20,000 yr have witnessed tremendous climatic changes, a glacial maximum at about 18,000 yr BP and a climatic optimum centred on about 6,000 yr BP, both of which mark extreme situations for the Quaternary. This paper attempts to show that active sand dunes were extensive 18,000 yr ago. Conversely, it seems that sand dunes were generally dormant 6,000 yr ago. Thus the former textbook concept1,2 of an arid climatic optimum and a pluvially active glacial maximum is reversed.
  2. 1979: Eronen, Matti. “The retreat of pine forest in Finnish Lapland since the Holocene climatic optimum: a general discussion with radiocarbon evidence from subfossil pines.” Fennia-International Journal of Geography 157.2 (1979): 93-114. Literature data on the retreat of the pine forest in Northern Fennoscandia are presented to cover the period from the early 19th century onwards, i.e. since the first reliable observations were made. These data are compared with radiocarbon datings of 44 samples from subfossil pines found at or beyond the present limit of pine forest. The trees had usually been preserved best in moist surroundings, the majority of the trunks and stumps having been recovered from small lakes or wet paludified depressions. Although the dates are scattered over a wide period of time, from about 7000 B.P. up to recent times, there is a concentration around 4000‑6000 B.P. sufficient to suggest that pine forest grew beyond the present limit during the Holocene climatic optimum. The most pronounced retreat in the forest limit since that time is recorded in Enontekiö, in the western part of Finnish Lapland. The results fit well with existing pollen records, which indicate that pine spread to Lapland around 8500‑7500 B.P. and achieved its maximum distribution in the period 7500‑5000 B.P., gradually retreating since then, due to the deteriorating climate.
  3. 1990: Weidick, Anker, et al. “The recession of the Inland Ice margin during the Holocene climatic optimum in the Jakobshavn Isfjord area of West Greenland.” Palaeogeography, Palaeoclimatology, Palaeoecology 82.3-4 (1990): 389-399. Recent subsurface mapping of parts of the Greenland Inland Ice margin in the region of Jakobshavn Isbræ indicates that the fjord system in the period of at least 2700–4700 calendar yr B.P. was more ice free than at present, and that the front of the glacier was at least 15 km behind the present position. The 14C-datings of subfossils brought to the present ice margin fit with the climatic records from ice cores and confirm the favourable conditions for Greenland’s first settlers, the Sarqaq people, who arrived in the region about 4000 yr ago to find hunting grounds 10–20% larger than the present.
  4. 1992: Ciais, P., et al. “Evidence for an early Holocene climatic optimum in the Antarctic deep ice-core record.” Climate Dynamics 6.3-4 (1992): 169-177. In the interpretation of the Antarctic deep ice-core data, little attention has been given to the Holocene part of the records. As far as translation of the stable isotope content in terms of temperature is concerned, this can be understood because expected temperature changes may be obscured by isotopic noise of various origins and because no 14C dating has yet been available for this type of sequence. In this article, we focus on the Dome C and Vostok cores and on a new 850-m long ice core drilled out at Komsomolskaïa by the Soviet Antarctic Expeditions. These three sites are located in East Antarctica, on the Antarctic plateau, in a region essentially undisturbed by ice-flow conditions, so that their detailed intercomparison may allow us to identify the climatically significant isotopic signal. Our results compare well with the proximal records of Southern Hemisphere high latitudes and support the existence of a warmer “climatic optimum” between 10 and 6 ka y BP. Maximum temperatures are reached just at the end of the last deglaciation, which confirms previous observations at high latitudes, in contrast with later dates for the Atlantic and hypsithermal optima in Europe and North America.
  5. 1995: Hjort, Christian, et al. “Radiocarbon dated common mussels Mytilus edulis from eastern Svalbard and the Holocene marine climatic optimum.” Polar Research 14.2 (1995): 239-243. The common mussel Mytilus edulis is an indicator of milder marine conditions in the Arctic, with stronger Atlantic Water influx, during the Holocene and earlier interglacials. Twelve Holocene radiocarbon dates of mytilus from eastern Svalbard fall between ca 8800 and 5000 BP and roughly delimit the marine climatic optimum period there. The beginning of this period in the east coincides with the immigration of boreal extralimital molluscs to western Svalbard, indicating the culmination of Holocene Atlantic influence.
  6. 1996: Gingele, Franz X. “Holocene climatic optimum in Southwest Africa—evidence from the marine clay mineral record.” Palaeogeography, Palaeoclimatology, Palaeoecology 122.1-4 (1996): 77-87. Sediment composition, grain size and clay mineral record of a high-resolution sediment core from the continental slope off Namibia was investigated to gain information on the deposition of terrigenous matter in this part of the Southwest African continental margin during the last 18 k.y. The depositional processes involved are fluvial input by the Kunene River and eolian input from the Namib and Kalahari deserts, each supplying characteristic mineral suites. During low sea level, erosion of the exposed shelf yields additional material. The amount of eolian or fluvial matter depends on the strength of the transport process, which is a function of aridity or humidity of the source area, thus allowing paleoclimatic interpretations. Arid conditions prevailed during a low sea level from 18 to 15 ka and unconsolidated shelf sediment was mobilized and supplied to the slope by short-distance transport by southerly winds. A dramatic increase in the accumulation of terrigenous sediment is recorded from 15 to 10 ka without major changes in sediment composition, which is attributed to increased runoff of the Kunene River and fluvial erosion of shelf sediments. This period coincides with a strengthening of the monsoonal system during a precessional minimum, which is observed in numerous sites in Central Africa and indicates an intensified influence of the monsoon at the Kunene headwaters. A distinct shift in clay mineralogy towards river-derived material marks a second period of increased river runoff—during high sea level—from 9 to 5 ka, indicating maximum humidity in the source area from 6 to 5 ka. This corresponds to the Holocene climatic optimum observed in the arid belts of Northern Africa. The present balance between fluvial and eolian input was reached approximately at 4 ka.
  7. 1999: Rossignol-Strick, Martine. “The Holocene climatic optimum and pollen records of sapropel 1 in the eastern Mediterranean, 9000–6000 BP.” Quaternary Science Reviews 18.4-5 (1999): 515-530. The most recent sapropel in the deep eastern Mediterranean Sea has been deposited between 9 and 6 ka bp. Climate conditions, as revealed by the pollen records of this sapropel in marine cores, were most favorable for temperate deciduous trees, which is in agreement with the inferences from records of peripheral land pollen sites. The abundance of deciduous oak pollen is much higher than that of Artemisia (sage-brush), indicating that annual precipitation in the mid-elevation borderlands was at least 550 mm without summer drought, but more probably in the range 800–1300 mm. The pollen of Pistacia, which formed a savanna at low elevations, is also at its highest abundance and signals the absence of frost in winter, while being capable of withstanding summer drought. The early Holocene therefore appears as the post-glacial climatic optimum with the highest moisture and mildest winters. In southwest Asia, this is also the time of the Neolithic population explosion with incipient domestication of cereals, possibly following natural selection of the ‘tough rachis’ mutation in wheat and barley by the extreme aridity of the preceding Younger Dryas.
  8. 2000: An, Zhisheng, et al. “Asynchronous Holocene optimum of the East Asian monsoon.” Quaternary Science Reviews 19.8 (2000): 743-762. The spatial and temporal distribution of summer monsoon precipitation (or effective moisture) during the Holocene has been reconstructed on the basis of geological data, including lake levels, pollen profiles, and loess/paleosol records. In addition, the summer (July) precipitation increment, effective precipitation, and monsoon strength index have been obtained from numerical modeling experiments. Both geological data and numerical modeling indicate that the Holocene optimum, as defined by peak East Asian summer monsoon precipitation, was asynchronous in central and eastern China, reaching a maximum at different times in different regions, e.g., ca. 10,000–8000 yr ago in northeastern China, 10,000–7000 yr ago in north-central and northern east-central China, ca. 7000–5000 yr ago in the middle and lower reaches of the Yangtze River, and ca. 3000 yr ago in southern China. In southwestern China the maximum appeared ca. 11,000 yr ago, but probably was related to the maximum landward extension of the Indian summer monsoon. The regional shift in the maximum precipitation belt from northwest to southeast over the past 10,000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate. The southeastward shift of the East Asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the Holocene and the East Asian monsoon index declined, while the early maximum in southwestern China matches the maximum of the Indian monsoon index.
  9. 2003: Kalis, Arie J., Josef Merkt, and Jürgen Wunderlich. “Environmental changes during the Holocene climatic optimum in central Europe-human impact and natural causes.” Quaternary Science Reviews 22.1 (2003): 33-79. The priority programme “Changes of the Geo-Biosphere” aimed to reconstruct the environmental history of central Europe with emphasis on the time interval from 9000 to 5500 cal BP (time-slice II), coinciding with the Holocene climatic optimum. During this period, the onset of human activities such as settlement, agriculture and animal husbandry caused environmental changes. Studies of different landscape units in Germany were carried out to identify these anthropogenically induced changes and to distinguish them from natural effects on the environmental system. The investigated archives included laminated lake sediments, fluvial sediments, colluvia and soils, speleothems, peat and coastal sediments. The different archives were examined using refined research methods including a variety of sedimentary and geochemical analyses, together with pollen analysis and dating methods for the establishment of a reliable chronology. The results of the various research groups are summarised and critically discussed. Based on these results, the climatic optimum can be subdivided into three periods: (1) the Early Atlantic from 9000 to 7500 cal BP with negligible human impact and stable environmental conditions; (2) the Late Atlantic during Early and Middle Neolithic from 7500 to 6300 cal BP with pollen evidence for vegetation changes but only negligible changes detectable in other proxy records; and (3) the Late Atlantic during the Younger Neolithic (Jungneolithikum), after 6300 cal BP, with human impact observed in many archives and proxy records especially in the pollen record but also in lacustrine and fluvial sediments. During the whole climatic optimum natural causes, such as minor shifts of temperature, did not induce substantial environmental changes, though some changes, such as temporary droughts, may have facilitated and amplified the observed human impact.
  10. 2004: Andersen, Christine, Nalan Koc, and M. Moros. “A highly unstable Holocene climate in the subpolar North Atlantic: evidence from diatoms.” Quaternary Science Reviews 23.20 (2004): 2155-2166. A composite record (LO09-14) of three sediment cores from the subpolar North Atlantic (Reykjanes Ridge) was investigated in order to assess surface ocean variability during the last 11 kyr. The core site is today partly under the influence of the Irminger Current (IC), a branch of the North Atlantic Drift continuing northwestward around Iceland. However, it is also proximal to the Sub-Arctic Front (SAF) that may cause extra dynamic hydrographic conditions. We used statistical methods applied to the fossil assemblages of diatoms to reconstruct quantitative sea surface temperatures (SSTs). Our investigations give evidence for different regional signatures of Holocene surface oceanographic changes in the North Atlantic. Core LO09-14 reveal relatively low and highly variable SSTs during the early Holocene, indicating a weak IC and increased advection of subpolar water over the site. A mid-Holocene thermal optimum with a strong IC occurs from 7.5 to 5 kyr and is followed by cooler and more stable late Holocene surface conditions. Several intervals throughout the Holocene are dominated by the diatom species Rhizosolenia borealis, which we suggest indicates proximity to a strongly defined convergence front, most likely the SAF. Several coolings, reflecting southeastward advection of cold and ice-bearing waters, occur at 10.4, 9.8, 8.3, 7.9, 6.4, 4.7, 4.3 and 2.8 kyr. The cooling events recorded in the LO09-14 SSTs correlate well with both other surface records from the area and the NADW reductions observed at ODP Site 980 indicating a surface-deepwater linkage through the Holocene.
  11. 2004: He, Y., et al. “Asynchronous Holocene climatic change across China.” Quaternary Research 61.1 (2004): 52-63. A review of Holocene climatic variations in different parts of China shows that they were asynchronous. Proxy data from ice cores, pollen, loess, lacustrine sediments, and changes of sea and lake levels demonstrate that many warm and cold oscillations have occurred in China during the Holocene, including a most important climatic event known as the “Holocene optimum,” a milder and wetter period, and that the duration and amplitude of the optimum period, as well as its start and end times, differed in different parts of China. Uplift of the Tibetan plateau over the past millions of years led to the development of the monsoon climate and to complex atmospheric circulation over continental China during the Holocene. As a result, the Holocene optimum began and terminated earlier in high-altitude regions of western China than at lower elevations in eastern China, and the amplitude of the variations was lower in the east. This suggests that the western higher-altitude areas were more sensitive to climatic change than were the eastern lower-altitude areas. Holocene climatic records in the Dunde and Guliya ice cores do not correspond. Inverse δ18O variations between the two cores indicate that the effects of climate and atmospheric processes on the stable isotopes at the two sites differed. The correlation between the isotopic composition of carbonates in lake deposits in western China and climatic variations is similar to that in the ice cores. The climatic resolution in ice cores and lake sediments is higher than that in other media. The lack of precise correspondence of climatic records constructed on the basis of proxy data from different parts of China is a result of the different locations and elevations of the sampling sites, the different resolutions of the source material, and the varied climatic conditions within China. Further work is needed to confirm both the conclusions and the inferences presented here.
  12. 2004: Zhou, Weijian, et al. “High-resolution evidence from southern China of an early Holocene optimum and a mid-Holocene dry event during the past 18,000 years.” Quaternary Research62.1 (2004): 39-48. Computer models suggest that the Holocene Optimum for East Asian summer monsoon precipitation occurred at different times in different regions of China. Previous studies indicate that this time-transgressive Holocene Optimum should have been experienced about 3000 yr ago in southern China. In this study we describe a section which allows us to test this timing directly. We have closely examined high-resolution eutrophic peat/mud sequences covering the past 18,000 cal yr at Dahu, Jiangxi, on the southern boundary of the mid subtropical zone in China. Late Pleistocene successions in the Dahu record indicate cooler and much wetter conditions relative to synchronous events in north-central China. Our results indicate that the Holocene Optimum occurred between ca. 10,000 and 6000 cal yr ago in southern China, consistent with the global pattern. Conditions were relatively dry and cold from 6000 to 4000 cal yr ago. Our data also support the conclusion that the last deglaciation to early Holocene in the south was much wetter, resulting in the formation of dense broad-leaved forests, which could have acted to moderate land temperature ∼10,000 to 6000 cal yr ago, yielding a stable early-Holocene climate. After 6000 cal yr, forest reduction led to unstable land temperatures, and possibly to a northerly shift of the subtropical high-pressure system. Whatever the mechanism, these changes resulted in decreased precipitation between 6000 and 4000 cal yr B.P. in southern China
  13. 2004: Yu, Ke-Fu, et al. “High-frequency winter cooling and reef coral mortality during the Holocene climatic optimum.” Earth and Planetary Science Letters 224.1-2 (2004): 143-155. A detailed ecological, micro-structural and skeletal Sr/Ca study of a 3.42 m thick Goniopora reef profile from an emerged Holocene reef terrace at the northern South China Sea reveals at least nine abrupt massive Goniopora stress and mortality events occurred in winter during the 7.0–7.5 thousand calendar years before present (cal. ka BP) (within the Holocene climatic optimum). Whilst calculated Sr/Ca-SST (sea surface temperature) maxima during this period are comparable to those in the 1990s, Sr/Ca-SST minima are significantly lower, probably due to stronger winter monsoons. Such generally cooler winters, superimposed by further exceptional winter cooling on inter-annual to decadal scales, may have caused stress and mortality of the corals about every 50 years. Sea level rose by ∼3.42 m during this period, with present sea-level reached at ∼7.3 ka BP and a sea-level highstand of at least ∼1.8 m occurred at ∼7.0 ka. The results show that it took about 20–25 years for a killed Gonioporacoral reef to recover.
  14. 2004: Xiao, Jule, et al. “Holocene vegetation variation in the Daihai Lake region of north-central China: a direct indication of the Asian monsoon climatic history.” Quaternary Science Reviews23.14-15 (2004): 1669-1679. DH99a sediment core recovered at the center of Daihai Lake in north-central China was analyzed at 4-cm intervals for pollen assemblage and concentration. The pollen record spanning the last ca 10,000yr revealed a detailed history of vegetation and climate changes over the Daihai Lake region during the Holocene. From ca 10,250 to 7900calyr BP, arid herbs and shrubs dominated the lake basin in company with patches of mixed pine and broadleaved forests, indicating a mild and dry climatic condition. Over this period, the woody plants displayed an increasing trend, which may suggest a gradual increase in warmth and humidity. The period between ca 7900 and 4450calyr BP exhibits large-scale covers of mixed coniferous and broadleaved forests, marking a warm and humid climate. Changes in the composition of the forests indicate that both temperature and precipitation displayed obvious fluctuations during this period, i.e., cool and humid ca 7900–7250calyr BP, warm and slightly humid ca 7250–6050calyr BP, warm and humid between ca 6050 and 5100calyr BP, mild and slightly humid ca 5100–4800calyr BP, and mild and humid ca 4800–4450calyrBP. The period can be viewed as the Holocene optimum (characterized by a warm and moist climate) of north-central China, with the maximum (dominated both by warmest temperatures and by richest precipitations) occurring from ca 6050 to 5100calyr BP. During the period of ca 4450–2900calyr BP, the woody plants declined, and the climate generally became cooler and drier than the preceding period. This period is characterized by a cold, dry episode from ca 4450 to 3950calyr BP, a warm, slightly humid interval between ca 3950 and 3500calyr BP and a mild, slightly dry episode from ca 3500 to 2900calyr BP, and appears to be a transition from warm and humid to cold and dry climatic conditions. Since ca 2900calyr ago, the forests disappeared and the vegetation density decreased, reflecting a cool and dry climate. However, a relative recovery of the woody plants occurring between ca 1700 and 1350calyr BP may denote an increase both in temperature and in precipitation. Fluctuations in the climatic condition of the Daihai Lake region were not only related to changes in the seasonal distribution of solar insolation and in the axis and intensity of the ocean current in the western North Pacific but were also closely linked to variations in the position and strength of polar high-pressure systems and in the pattern and intensity of the Westerly winds.
  15. 2007: Wang, ShuYun, et al. “The early Holocene optimum inferred from a high-resolution pollen record of Huguangyan Maar Lake in southern China.” Chinese Science Bulletin 52.20 (2007): 2829-2836. A high-resolution pollen record of the past 13000 a from Huguangyan Maar Lake reveals the vegetation and environment changes in southern China during the Holocene. It shows that (i) pollen percentage of trees and shrubs reached 56% during the early Holocene (11600–7800 cal a BP), of which the pollen percentage of tropical trees reached a maximum at 9500-8000 cal a BP, reflecting a hot and wet environment; (ii) during the mid-Holocene (7800–4200 cal a BP), the pollen percentage of montane coniferous trees and herbs increased, while the percentage of tropical-subtropical trees decreased, indicating lower temperature and humidity; (iii) in the late Holocene spanning from 4200 to 350 cal a BP, the pollen percentage of herbs and montane conifer increased significantly, indicating a marked decrease of temperature and humidity. Our pollen data reveal that the time period 9500–8000 cal a BP in southern China represents a climatic optimum for the Holocene characterized by hot and wet conditions. This is consistent with the Holocene optimum found in lower latitude regions globally. We speculate that strong insolation might cause the northward migration of the ITCZ and subtropical summer monsoon front, which resulted in an early Holocene optimum in the Huguangyan area. The dry tendency and climate fluctuations of the middle and late Holocene could be associated with a decrease in solar insolation and frequent ENSO event.
  16. 2008: Joerin, U. E., et al. “Holocene optimum events inferred from subglacial sediments at Tschierva Glacier, Eastern Swiss Alps.” Quaternary Science Reviews 27.3-4 (2008): 337-350. This study investigates the subglacial sedimentary archive at Tschierva Glacier, Eastern Swiss Alps. Subfossil wood remains found at the retreating glacier tongue indicate that their emergence results from recent transport from an upvalley basin. A confluence-basin-like structure was found to exist by georadar measurements underneath the present glacier. In combination with high resolution age determinations based on dendrochronology and radiocarbon dating it is implied that a retreated Tschierva Glacier allowed vegetation growth and sediment accumulation in that basin. Three periods of glacier recession were detected, which occurred around 9200 cal yr BP, from 7450 to 6650 cal yr BP and from 6200 to 5650 cal yr BP. These periods are called Holocene optimum events (HOE). Accordingly, an equilibrium line rise >220 m compared to the reference period from 1960 to 1985 was inferred from digital elevation models of former glacier extents. Since glacier mass balance depends on summer (June–July–August) temperature and precipitation, an equilibrium line altitude (ELA) rise of 220 m implies a summer temperature increase of about 1.8 °C assuming unchanged precipitation during the dated HOE. Alternative calculations point to probable temperature increase in a broad interval between +1.0 °C taking into account a precipitation change of −250 mm/a to +2.5 °C with +250 mm/a precipitation change, supporting earlier paleotemperature estimates. It is proposed that higher mean summer insolation caused a stronger seasonality during the mid-Holocene as compared to late Holocene conditions.

 

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FIGURE 1: MEAN DECADAL SEASONAL CYCLE IN THE CET 1722-2016

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FIGURE 2: TRENDS IN THE DIFFERENCE BETWEEN SUMMER AND WINTER

 

 

 

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FIGURE 3: FULL SPAN OLS TREND FOR EACH CALENDAR MONTH

 

 

 

FIGURE 4: TREND PROFILE FOR EACH CALENDAR MONTH

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FIGURE 5: RELATIONSHIP BETWEEN FULL SPAN TREND & THE TREND PROFILE

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  1. Temperature data taken at weather stations contain a diurnal cycle, a seasonal cycle, and random natural variations. Along with these they may also contain a long term trend over a period of many years. Typically, the diurnal and seasonal cycles represent more than 80-90% of the total variance in the actual temperature measurements. The remaining 10-20% or so consists mostly of unexplained random variations. In cases where a statistically significant trend is found with OLS linear regression, no more than a small portion of the variance, around 3% or so, can be ascribed to a long term warming or cooling trend.
  2. It is for these reasons that the study of global warming over many decades, regression coefficients for long term trends are relatively a very weak feature of the time series that must be teased out of the data net of the greater diurnal, seasonal, and random variations. The large seasonal cycle is removed from monthly mean temperature data by subtracting the corresponding temperature in a reference period. The temperature data thus deseasonalized are published as “temperature anomalies”. Global warming research is carried out with these data sets. This procedure contains the assumption that the seasonal cycle is constant and unchanging across the full span of the time series being studied.
  3. This study is an investigation of the validity of this assumption. Figure 1 is a graphical representation of the seasonal cycle. The seasonal cycle is represented as a plot of the decadal mean temperature for each calendar month from January (labeled as “1”) to December (labeled as “12”). The GIF image cycles through 25 decades of decadal mean seasonal cycles in the CET from 1772 to 2016. The display clearly shows that the shape of the seasonal cycle graphic changes over time and implies that the seasonal cycle is not constant across time. The changes may seem small and insignificant but they should be understood in relation to long term trends in temperature which are typically less than 5% of the diurnal range per century.
  4. The inconstancy of the seasonal cycle is confirmed in Figure 2 where long term trends in the differences in temperature among calendar months is presented. The results show that there are statistically significant long term trends in the temperature differences between summer months and winter months. This difference confirms that the seasonal cycle is changing as the climate warms and that the constancy of the seasonal cycle assumed in the construction of temperature anomalies is not valid.
  5. The reason for the differences in seasonal cycles seen in Figures 1&2 is presented in Figure 3.  It shows that when the long term trends are computed separately for each calendar month we find that the warming trend is stronger in the winter months than in the summer months. These differential trends imply a gradual narrowing of the the their temperature differences as for example between January and July as shown in Figure 2.
  6. Figure 4 is a GIF image that cycles through the twelve calendar months displaying the full span OLS linear trend for that calendar month as well as a graphic for a different approach to the study of temperature trends proposed in this work that we shall refer to as a Trend Profile. Rather than one full span OLS trend over the full sample of N observations, the Trend Profile tracks changes in temperature through the full span of the time series as a time series of temperature trends in a moving 30-year window. The window moves through the temperature time series one year at a time computing 30-year trends.
  7. The trend profiles in the GIF image of Figure 4 show that an observed full span warming trend is the net result of multiple 30-year warming and cooling trends with magnitudes that are more than an order of magnitude larger than the full span trends.
  8. A great variety of shapes are seen in the Trend Profiles of the twelve calendar months. We can also see in these images that the differences among the calendar months are much more intense and complex than just differences in the numerical values of the full span trend seen in Figure 3. The Trend Profile procedure provides a a great deal of more information. More insight is thus gained into the trend behavior of the time series into the differences among the calendar months.
  9. The relationship between the full span OLS trend and the Trend Profile is displayed in Figure 5. It shows that the mean of thee moving 30-year trends is a good and possibly more robust estimate for the overall full span trend and that this estimate is related the the ratio of warming and cooling trends as well as their magnitudes in the Trend Profile. In short, the argument is presented that the trend profile provides more information than a single OLS full span trend line.
  10. The temperature trend information presented and understood in terms of trend profiles for each calendar month contains more information and offers greater statistical validity and reliability than a single OLS trend line drawn through the deseasonalized temperatures for all twelve calendar months.
  11. In conclusion we find that the use of temperature anomalies that facilitates the combination of the deseasonalized temperatures for the twelve calendar months is an inadequate, erroneous, and unnecessary innovation and that temperature trends are best understood in terms of the twelve Trend Profiles for the twelve calendar months.

 

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Climate Change: Late Bronze Age Collapse

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The Late Bronze Age (LBA) was the ultimate expression of the settled agricultural civilization that got started in the Neolithic Revolution. The macro economy of agricultural wealth creation and its control had evolved such that the farmers themselves became pawns (peasants) in a power game among individuals who could raise armies to control agricultural lands. With further developments such as language both spoken and written and artisan and engineering innovations such as copper mining, metal works, making of tools for agriculture and warfare, and pottery, the controlled agricultural lands evolved into large and powerful kingdoms ruled by the king with his army in a palatial sub-economy and worked by peasants and artisans in a rural agricultural sub-economy. It is important in this context to understand the kingdoms as a bifurcation because these distinct sub-economies were differently impacted by the Late Bronze Age Collapse (LBAC). The distinction is similar to that between urban and rural societies in our time. High end artisans and engineers who worked for the palace were part of the palatial culture.

In the LBA, this agricultural macro-system had grown into a large, sophisticated, and interconnected global economy similar to what we have today. The major kingdom nation states in this global economy were The Egyptian New Kingdom (where Egypt is today), the Assyrian Empire (where Syria is today), the Hittite Empire (where Turkey is today), and the Mycenaeans (where Greece is today). Trade, travel, shipping, cooperation, global policy making, and warfare among these states were common much like things are today but without those big fat good-for-nothing UN bureaucrats. The America of the day was Egypt, in economic, diplomatic, and military power as well as in terms of attracting the best and brightest writers, philosophers, and artisans from around world shown in the video. Many smaller kingdoms existed such the Biblical states in the Levant but they were vassals of the large and powerful kingdoms. This global economy was extremely successful and the powerful kingdoms and empires enjoyed enormous wealth and advancements in technology, transportation, infrastructure, the arts, and in learning and knowledge. The pyramids of Egypt are a product of this civilization.

Then, around 1200 BC or so give or take 50 years, the archaeological and textual data show that the lights went out on the LBA. A long gap of more than a 200 years of a Dark Age followed with no evidence of the great LBA global economy until the Early Iron Age-1 when an entirely new kind of global economy grew from the ashes of the LBAC.

The big question is “what happened?”. The honest answer is that we don’t know and we will likely never know. But it is possible to construct theories that are consistent with the available archaeological, textual, and paleo-climate data. The two most popular theories are the Sea Peoples theory (see Drews 1993 below) and the climate change theory (Finkelstein, Weiss, Kaniewski, Drake, and others). Yet another possibility is class warfare between the palace and rural cultures. We don’t know. It’s a mystery. This bibliography is an exploration of this line of research in the context of the climate change alarm in our time.

In the context of the current alarm about catastrophic climate change that may end this civilization (“Alien apocalypse: Can any civilization make it through climate change?, University of Rochester, 2018, in Science Daily, LINK TO FULL TEXT ), it is interesting to note that religions prior to the LBAC do not contain a Judgement Day “end of the world” but religions that got started in the early Iron Age right after the Dark Ages of the LBAC do contain an end of the world of some kind. It is likely that our obsession with the end of the world scenario, now in the form of human caused climate change with fossil fuel emissions, is a distant genetic memory of the LBAC.

 

  1. 1982: Weiss, Barry. “The decline of Late Bronze Age civilization as a possible response to climatic change.” Climatic Change 4.2 (1982): 173-198. The disintegration of Eastern Mediterranean civilization at the end of the late Bronze Age (late thirteenth and twelfth centuries B.C.) has traditionally been attributed to the irruption of new peoples into this area. However, the nearly contemporaneous decline of highly organized and powerful states in Greece, Anatolia, Egypt, and Mesopotamia warrants consideration of possible environmental causes likely to operate over sizable areas, especially since archaeological research has not succeeded in establishing the presence of newcomers at the onset of the Bronze Age disturbances. Climatic change is a particularly attractive candidate since temperature and precipitation variations persisting over relatively short times can adversely affect agricultural output. Carpenter (1966) argued that the Mycenaean decline and migrations in and from Greece in the late thirteenth century were caused by prolonged drought and not the incursion of less civilized Dorian tribes. Donley (1971) and Bryson et al. (1974) have presented evidence of a spatial drought pattern which occurred in January 1955 that might be invoked to support this thesis. Population movements in Anatolia at the same time, though not as well established, can be delimited to some degree by the distribution of Hitto-Luwian peoples in the late ninth century B.C. It is hypothesized here that a drought induced migration of Luwian peoples from Western Antolia occurred early in the twelfth century B.C., that it was associated in some fashion with the invasion of Egypt by the ‘Sea Peoples’ in the reign of Ramesses III, and that the defeated remnants of these peoples settled along the Levantine coast and filtered into North Syria and the upper Euphrates valley. It has been suggested that past climatic patterns recur in the present epoch but with a possibly different frequency. To establish that a spatial drought analogue to the above hypothesized migration can occur, temperature and precipitation records from 35 Greek, Turkish, Cypriot, and Syrian weather stations for the period 1951–1976 were examined. The Palmer drought index, an empirical method of measuring drought severity, was computed for each of these stations for the period of record. Since wheat yields tend to be highly correlated with winter precipitation for the area in question, the drought indices for the winter months were subjected to an empirical eigenvector analysis. An eigenvector (drought pattern) consistent with the postulated population movements in Anatolia occurred within the modern climatological record and was found to have been the dominant pattern in January 1972. The potential problems of eigenvector analysis in investigating problems of this type are discussed.
  2. 1993: Drews, Robert. BOOK: “The end of the Bronze Age.” Changes in Warfare and the Catastrophe ca 1200 (1993): 113-129. BOOK REVIEW: {Note: this is the older sea people’s theory that is now challenged by the climate change theory}. A seafaring sword and shield armed infantry defeated and destroyed cities, armies and civilizations based on chariots. Stopped only in the marshes of Egypt, where they were assimilated into the Egyptian army and settled along the coasts of The Levant (the Biblical reference to the Philistines). The author doesn’t comment on how this parallels very similar events in 800 AD, where the sword and shield armed troops are the Vikings; and the mounted opponents are the Carolingians.The weakness in the book is that it doesn’t exactly explain how a loose order infantry could defeat chariots in the open. Most men run away when someone on a horse threatens to ride them down. And how does a man with a sword actually kill a man on a chariot? I also felt that the issue of whether the Sea Peoples weapons, iron versus bronze, was poorly addressed. If the Sea Peoples were not using iron weapons, then who did bring iron weapons to global prominence in this period?Also, an alternative theory on the end of the Bronze Age is that the Trojan war was real; the Sea Peoples were the Greeks who sacked Troy, who then went on a Med wide rampage and eventually settled as the Philistines. Would like to have seen this theory addressed…..Stimulating work, may need an update.4 of 4 people found the following review helpful. Notewory by Peter G. TsourasThis is one of those books that brings light to a distant but formative stage in history when the seemingly stable world of the late near eastern bronze age collapsed suddenly. The author makes good sense of the fragments of information that have survived. He pieces together the systemic collapse of the Mycenaean world and the forces that it unleashed against the already weakened Hititte Empire and sent like a growing storm to devastate the region from Anatolia to Canaan only to dash itself against the last might of Egypt. I highly recommend this book to anyone interested in the Greek Bronze Age as well as the other contemporary cultures of the eastern Mediterranean as well as to anyone interested in the evolution of the art of war. FULL TEXT
  3. 1997: Weiss, Harvey. “Late third millennium abrupt climate change and social collapse in West Asia and Egypt.” Third millennium BC climate change and Old World collapse. Springer, Berlin, Heidelberg, 1997. 711-723. The palaeoenvironmental record for the 2200 BC abrupt climate change is synthesized. Alternative explanations for synchronous and extended Old World social collapse are examined and rejected. Quantification of the abrupt climate change is necessary if we are to understand its social consequences. FULL TEXT
  4. 2010: Kaniewski, David, et al. “Late second–early first millennium BC abrupt climate changes in coastal Syria and their possible significance for the history of the Eastern Mediterranean.” Quaternary Research 74.2 (2010): 207-215. The alluvial deposits near Gibala-Tell Tweini provide a unique record of environmental history and food availability estimates covering the Late Bronze Age and the Early Iron Age. The refined pollen-derived climatic proxy suggests that drier climatic conditions occurred in the Mediterranean belt of Syria from the late 13th/early 12th centuries BC to the 9th century BC. This period corresponds with the time frame of the Late Bronze Age collapse and the subsequent Dark Age. The abrupt climate change at the end of the Late Bronze Age caused region-wide crop failures, leading towards socio-economic crises and unsustainability, forcing regional habitat-tracking. Archaeological data show that the first conflagration of Gibala occurred simultaneously with the destruction of the capital city Ugarit currently dated between 1194 and 1175 BC. Gibala redeveloped shortly after this destruction, with large-scale urbanization visible in two main architectural phases during the Early Iron Age I. The later Iron Age I city was destroyed during a second conflagration, which is radiocarbon-dated at circa 2950 cal yr BP. The data from Gibala-Tell Tweini provide evidence in support of the drought hypothesis as a triggering factor behind the Late Bronze Age collapse in the Eastern Mediterranean.
  5. 2011: Kaniewski, David, et al. “The Sea Peoples, from cuneiform tablets to carbon dating.” PloS one 6.6 (2011): e20232. The 13th century BC witnessed the zenith of the Aegean and Eastern Mediterranean civilizations which declined at the end of the Bronze Age, ∼3200 years ago. Weakening of this ancient flourishing Mediterranean world shifted the political and economic centres of gravity away from the Levant towards Classical Greece and Rome, and led, in the long term, to the emergence of the modern western civilizations. Textual evidence from cuneiform tablets and Egyptian reliefs from the New Kingdom relate that seafaring tribes, the Sea Peoples, were the final catalyst that put the fall of cities and states in motion. However, the lack of a stratified radiocarbon-based archaeology for the Sea People event has led to a floating historical chronology derived from a variety of sources spanning dispersed areas. Here, we report a stratified radiocarbon-based archaeology with anchor points in ancient epigraphic-literary sources, Hittite-Levantine-Egyptian kings and astronomical observations to precisely date the Sea People event. By confronting historical and science-based archaeology, we establish an absolute age range of 1192–1190 BC for terminal destructions and cultural collapse in the northern Levant. This radiocarbon-based archaeology has far-reaching implications for the wider Mediterranean, where an elaborate network of international relations and commercial activities are intertwined with the history of civilizations.
  6. 2012: Drake, Brandon L. “The influence of climatic change on the Late Bronze Age Collapse and the Greek Dark Ages.” Journal of Archaeological Science 39.6 (2012): 1862-1870. Between the 13th and 11th centuries BCE, most Greek Bronze Age Palatial centers were destroyed and/or abandoned. The following centuries were typified by low population levels. Data from oxygen-isotope speleothems, stable carbon isotopes, alkenone-derived sea surface temperatures, and changes in warm-species dinocysts and formanifera in the Mediterranean indicate that the Early Iron Age was more arid than the preceding Bronze Age. A sharp increase in Northern Hemisphere temperatures preceded the collapse of Palatial centers, a sharp decrease occurred during their abandonment. Mediterranean Sea surface temperatures cooled rapidly during the Late Bronze Age, limiting freshwater flux into the atmosphere and thus reducing precipitation over land. These climatic changes could have affected Palatial centers that were dependent upon high levels of agricultural productivity. Declines in agricultural production would have made higher-density populations in Palatial centers unsustainable. The ‘Greek Dark Ages’ that followed occurred during prolonged arid conditions that lasted until the Roman Warm Period. {Notes: Stable carbon isotopes from radiocarbon-dated pollen can indicate paleoclimate, Mediterranean sea surface temperatures (SST) indicate precipitation patterns, The Bronze Age Collapse is contemporaneous with a sharp drop in temperatures (GISP2), The Bronze Age Collapse and Greek Dark Ages may result from the same arid period.
  7. 2013: Langgut, Dafna, Israel Finkelstein, and Thomas Litt. “Climate and the Late Bronze Collapse: new evidence from the Southern Levant.” Tel Aviv 40.2 (2013): 149-175. A core drilled from the Sea of Galilee was subjected to high resolution pollen analysis for the Bronze and Iron Ages. The detailed pollen diagram (sample/~40 yrs) was used to reconstruct past climate changes and human impact on the vegetation of the Mediterranean zone of the southern Levant. The chronology is based on radiocarbon dating of short-lived terrestrial organic material. The results indicate that the driest event throughout the Bronze and Iron Ages occurred ~1250–1100 BCE—at the end of the Late Bronze Age. This arid phase was identified based on a significant decrease in Mediterranean tree values, denoting a reduction in precipitation and the shrinkage of the Mediterranean forest/maquis. The Late Bronze dry event was followed by dramatic recovery in the Iron I, evident in the increased percentages of both Mediterranean trees and cultivated olive trees. Archaeology indicates that the crisis in the eastern Mediterranean at the end of the Late Bronze Age took place during the same period—from the mid- 13th century to ca. 1100 BCE. In the Levant the crisis years are represented by destruction of a large number of urban centres, shrinkage of other major sites, hoarding activities and changes in settlement patterns. Textual evidence from several places in the Ancient Near East attests to drought and famine starting in the mid-13th and continuing until the second half of the 12th century. All this helps to better understand the ‘Crisis Years’ in the eastern Mediterranean at the end of the Late Bronze Age and the quick settlement recovery in the Iron I, especially in the highlands of the Levant.
  8. 2013: Kaniewski, David, et al. “Environmental roots of the Late Bronze Age crisis.” PLoS One 8.8 (2013): e71004. The Late Bronze Age world of the Eastern Mediterranean, a rich linkage of Aegean, Egyptian, Syro-Palestinian, and Hittite civilizations, collapsed famously 3200 years ago and has remained one of the mysteries of the ancient world since the event’s retrieval began in the late 19thcentury AD/CE. Iconic Egyptian bas-reliefs and graphic hieroglyphic and cuneiform texts portray the proximate cause of the collapse as the invasions of the “Peoples-of-the-Sea” at the Nile Delta, the Turkish coast, and down into the heartlands of Syria and Palestine where armies clashed, famine-ravaged cities abandoned, and countrysides depopulated. Here we report palaeoclimate data from Cyprus for the Late Bronze Age crisis, alongside a radiocarbon-based chronology integrating both archaeological and palaeoclimate proxies, which reveal the effects of abrupt climate change-driven famine and causal linkage with the Sea People invasions in Cyprus and Syria. The statistical analysis of proximate and ultimate features of the sequential collapse reveals the relationships of climate-driven famine, sea-borne-invasion, region-wide warfare, and politico-economic collapse, in whose wake new societies and new ideologies were created.
  9. 2014: Armit, Ian, et al. “Rapid climate change did not cause population collapse at the end of the European Bronze Age.” Proceedings of the National Academy of Sciences 111.48 (2014): 17045-17049. The impact of rapid climate change on humans is of contemporary global interest. Present-day debates are necessarily informed by paleoclimate studies in which climate is often assumed, without sufficient critical attention, to be the primary driver of societal change. Using new methods to analyze paleoclimatic and archeological datasets, we overturn the deterministic idea that population collapse at the end of the northwestern European Bronze Age was caused by rapid climate change. Our work demonstrates the necessity of high-precision chronologies in evaluating human responses to rapid climate change. It will be significant for geoscientists, climate change scientists, and archeologists. The impact of rapid climate change on contemporary human populations is of global concern. To contextualize our understanding of human responses to rapid climate change it is necessary to examine the archeological record during past climate transitions. One episode of abrupt climate change has been correlated with societal collapse at the end of the northwestern European Bronze Age. We apply new methods to interrogate archeological and paleoclimate data for this transition in Ireland at a higher level of precision than has previously been possible. We analyze archeological 14C dates to demonstrate dramatic population collapse and present high-precision proxy climate data, analyzed through Bayesian methods, to provide evidence for a rapid climatic transition at ca. 750 calibrated years B.C. Our results demonstrate that this climatic downturn did not initiate population collapse and highlight the non-deterministic nature of human responses to past climate change.

 

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