Monthly Archives: November 2006

EOS Paper On The Hottest Spots on Earth Illustrates The Major Role of Landscape on Surface Temperatures

The October 24 2006 issue of EOS had an interesting article entitled “What Are the Hottest Spots on Earth?” (subscription required). The article by D. Mildrexler, M. Zhao and S.W. Running is summarized in EOS as follows,

“The location of the hottest spot on the Earth’s surface has long been a source of interest and curiosity. To identify the hottest places on Earth, this article presents a synthesis of remotely sensed radiometric land surface temperatures. Studying patterns of maximum land surface temperatures across the global land surface and the interaction with vegetation, or the absence of vegetation, can help develop an improved methodology for detecting land cover change and understanding the potential consequences of land cover change. “

The paper includes section headings of the “Influence of Vegetation on Maximum LST” and “Influence of Irrigation on Maximum LST” [LST=land surface temperature].

This paper, however, while quite interesting in its own right, has significance beyond the specific focus of the article. For instance, with the newly developed capability to assess maximum land surface temperatures, this data should be routinely compared with the site-based air temperature data that is used to construct values of the global average temperature trends.

Of even more importance in this paper, however, is the documentation of the very major role of the presence of vegetation or not at a location. The hottest temperatures were observed in the EOS study at the locations without vegetation. This means that if landscape change in a region results in less vegetation, the maximum surface temperatures are expected to be hotter. If an oasis is developed by irrigation from subsurface water in a desert, the maximum temperatures would be less. The difference in the surface temperatures between the Amazon and the Sahara desert seen in Figure 1 of the Mildrexler et al paper illustrates the dramatic differences that occur. Figure 3 in their paper documents that very large differences (over 25C!) occur between distances of just meters.

Thus, in terms of the diagnosis of climate system heat changes (“global warming”) through the use of 1.5m surface air temperatures, there is a clear confounding issue of what type of landscape occurs at each observing site, and if it has changed during the period of record. The paper “Land use/land cover change effects on temperature trends at U.S. Climateâ€? by R. C. Hale, K. P. Gallo, T. W. Owen, and T. R. Loveland June 3 2006 Geophysical Research Letters has shown that the observed temperatures almost always increase due to landscape change in the data they examined.

The third author of the EOS paper (S. Running) published a paper several years ago (which I was co-author on), that demonstrates the importance of landscape change on surface temperatures. The paper is

Nemani, R.R., S.W. Running, R.A. Pielke, and T.N. Chase, 1996: Global vegetation cover changes from coarse resolution satellite data. J. Geophys. Res., 101, 7157-7162, with the abstract

“Land cover plays a key role in various biophysical processes related to global climate and terrestrial biogeochemistry. Although global land cover has dramatically changed over the last few centuries, until now there has been no consistent way of quantifying the changes globally. In this study we used long-term climate and soils data along with coarse resolution satellite observations to quantify the magnitude and spatial extent of large-scale land cover changes attributable to anthropogenic processes. Differences between potential leaf area index (LAI), derived from climate-soil-leaf area equilibrium, and actual leaf area index obtained from satellite data are used to estimate changes in land cover. Further, changes in LAI between potential and actual conditions are linked to climate by expressing them as possible changes in radiometric surface temperatures (Tr) resulting from changes in surface energy partitioning. As expected, areas with high population densities, such as India, China, and western Europe showed large reductions in LAI. Changes in global land cover expressed as summer, midafternoon Tr, ranged from −8° to +16°C. Deforestation resulted in an increase in Tr, while irrigated agriculture reduced the Tr. Many of the current general circulation models (GCMs) use potential vegetation maps to represent global vegetation. Our results indicate that there are widespread changes in global land cover due to deforestation and agriculture below the resolution of many GCMs, and these changes could have a significant impact on climate. Potential and actual LAI data sets are available for climate modelers at 0.5°×0.5° resolution to study the possible impacts of land cover changes on global temperatures and circulation patterns.”

Clearly, the analysis in the Nemani et al paper should be revisited using the new satellite data.

There is also the issue as to what locations is the hottest in terms of heat content. As shown in the paper

Pielke Sr., R.A., C. Davey, and J. Morgan, 2004: Assessing “global warming” with surface heat content. Eos, 85, No. 21, 210-211,

the diagnosis of heat content requires the measurement of moisture content in addition to the air temperature. In terms of heat content in Joules, the Amazon region, for example, may have hotter conditions than in Iran, Libya, Queensland or elsewhere in desert locations!

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Global and Planetary Change Special Issue: Land-use/land-cover Change And Its Impact On Climate

A special issue of Global and Planetary Change has appeared on the subject “Land-use/land-cover change and its impact on climate“.

The Preface to the issue (written by Rezaul Mahmood, Roger A. Pielke, Sr. and Kenneth G. Hubbard), reads

“Land use/land cover change and its impacts on climate has been recognized by the International Geosphere- Biosphere Programme (IGBP) as a key research item for better understanding of climate variability and change. Over the last two and half decades, the scientific community has made notable efforts in understanding land use/land cover change as part of the climate system. However, additional research is needed to observe, measure and model these complex interactions. This theme issue includes a number of papers presenting results from various aspects of land use change and its impacts on local, regional and global climates. These studies include both observation-based and modeling investigations that illustrate the role of land use/ land cover change on climate. For example, by using observed data, Ray et al. and Mahmood et al. demonstrate the impacts of land use change on precipitation, temperature and near-surface atmospheric moisture content. The modeling studies by Pitman et al. and Molen et al. show the multifaceted influences of changed landscape and climate. Davey et al. present a new metric that is needed to better interpret landscape effects on temperature trends. We expect that this focused issue will shed new light on the complex involvement of land use/land cover change on climate and further demonstrates the importance of this research theme in the context of climate variability and change.”

The titles in the Special Issue are

Impacts of irrigation on 20th century temperature in the northern Great Plains by Rezaul Mahmood, Stuart A. Foster, Travis Keeling, Kenneth G. Hubbard, Christy Carlson and Ronnie Leeper

Differences between near-surface equivalent temperature and temperature trends for the Eastern United States: Equivalent temperature as an alternative measure of heat content by Christopher A. Davey, Roger A. Pielke, Sr. and Kevin P. Gallo

Climate impacts of anthropogenic land use changes on the Tibetan Plateau by Xuefeng Cui, Hans-F. Graf, Baerbel Langmann, Wen Chen and Ronghui Huang

The impact of land cover change on storms in the Sydney Basin, Australia by A.F. Gero, A.J. Pitman, G.T. Narisma, C. Jacobson and R.A. Pielke

Feedbacks between agriculture and climate: An illustration of the potential unintended consequences of human land use activities by Navin Ramankutty, Christine Delire and Peter Snyder

Soil moisture regulates the biological response of elevated atmospheric CO2 concentrations in a coupled atmosphere biosphere model by Dev Niyogi and Yongkang Xue

The climate sensitivity to human appropriation of vegetation productivity and its thermodynamic characterization by Axel Kleidon

Climate is affected more by maritime than by continental land use change: A multiple scale analysis M.K. van der Molen, A.J. Dolman, M.J. Waterloo and L.A. Bruijnzeel

Dry season clouds and rainfall in northern Central America: Implications for the Mesoamerican Biological Corridor by Deepak K. Ray, Ronald M. Welch, Robert O. Lawton and Udaysankar S. Nair

Potential individual versus simultaneous climate change effects on soybean (C3) and maize (C4) crops: An agrotechnology model based study by Roberto J. Mera, Dev Niyogi, Gregory S. Buol, Gail G. Wilkerson and Fredrick H.M. Semazzi

Meteorological impact assessment of possible large scale irrigation in Southwest Saudi Arabia by H.W. Ter Maat, R.W.A. Hutjes, R. Ohba, H. Ueda, B. Bisselink and T. Bauer

Evidence for carbon dioxide and moisture interactions from the leaf cell up to global scales: Perspective on human-caused climate change by P. Alpert, D. Niyogi, R.A. Pielke, Sr., J.L. Eastman, Y.K. Xue and S. Raman

Upcoming weblogs will discuss several of these papers in more detail.

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Spatial Analyses of Climate Forcings And Their Influence on Atmospheric and Ocean Circulations – The IPCC Needs to Include This Subject In Their Upcoming Assessment

Gavin Schmidt in his Comment #1 on November 21 2006 introduced a link to very useful data that has been analyzed from the GISS model. The analyses are available under the heading “Datasets and Images – Efficacy of Climate Forcings”“.

Their summary illustrates the spatial structure of the climate forcings from their model simulations. The forcing Fa ["’Fa’, the adjusted forcing, is the flux change at the top of the atmosphere (and throughout the stratosphere) after the stratosphere is allowed to adjust radiatively to the presence of the forcing agentâ€?], can be used to illustrate the need to incorporate the spatial structure of climate forcings in any assessment of the role of humans in altering the climate system.

Spatial maps of Fa from the GISS model include, for example, the forcings due to:

1. 2 X CO2

2. methane 837ppb to 1752 ppb

3. combinations of tropospheric aerosols 1850 to 2000 (direct effects)

A critically important research question is

How important is the spatial gradient of the diabatic heating and cooling from such climate forcings on climate patterns including atmospheric and ocean circulations?

In the paper

Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974

we proposed a metric to assess the relative importance of different climate forcings. We concluded that

“This paper diagnoses the spatial mean and the spatial gradient of the aerosol radiative forcing in comparison with those of well-mixed green-house gases (GHG). Unlike GHG, aerosols have much greater spatial heterogeneity in their radiative forcing. The heterogeneous diabatic heating can modulate the gradient in horizontal pressure field and atmospheric circulations, thus altering the regional climate. For this, we diagnose the Normalized Gradient of Radiative Forcing (NGoRF), as a fraction of the present global heterogeneous insolation attributed to human activity.”

Figure 1 in the Matsui and Pielke article presents a spatial map of shortwave aerosol direct radiative forcing in the atmosphere equatorward of 37 degrees, with Figure 5 comparing the aerosol forcings to that of the GHG in this latitude band.

The GISS analyses can and should be analyzed using this diagnostic metric of climate change.

An important conclusion with respect to the evidence of such significant spatial structure in the diabatic heating from human climate forcings is that the IPCC assessment needs to include this climate system analysis. Such an approach, as presented in the Matsui and Pielke paper, was recommended by the 2005 National Research Council Report “Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties“.

We look forward to seeing the IPCC discussion of relative importance of the spatial structure of climate forcings. They would be derelict in their responsibility to present the spectrum of information on climate change if they do not include this analysis in their upcoming report.

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A New Paper On the Complexity Of The Climate System

A new paper (alerted to me by Dev Niyogi of Purdue University) has appeared which documents the complexity of the climate system, and our limited understanding of consequences due to deliberate or inadvertent human climate intervention.

The paper published by Science on November 17, 2006 by Randerson et al in Science is entitled “The Impact of Boreal Forest Fire on Climate Warming” (subscription required) has the abstract,

“We report measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black carbon deposition on snow and sea ice, and postfire changes in surface albedo. The net effect of all agents was to increase radiative forcing during the first year (34 ± Watts per square meter of burned area), but to decrease radiative forcing when averaged over 80-year fire cycle (−2.3 ± 2.2 Watts per square meter) because multidecadal increases in surface albedo had a larger impact than fire-emitted greenhouse gases. This result implies that future increases in boreal fire may not accelerate climate warming.”

The conclusion of the paper has the very important conclusion that.

“Future interactions between the land surface and climate in northern regions may involve both negative feedbacks within the boreal interior (via mechanisms outlined here) and positive feedbacks involving shrub and forest expansion in arctic tundra ecosystems and loss of snow cover. Our analysis illustrates how ecosystem processes that generate carbon sources and sinks have inseparable consequences for other forcing agents. To the extent that the contemporary Northern Hemisphere carbon sink originates from changes in northern forest cover and age, its value from a climate perspective requires a more nuanced view that encompasses all agents of radiative forcing. Important next steps include reducing uncertainties associated with direct and indirect aerosol effects and disturbance-linked changes in albedo, exploring the combined impacts of feedbacks of the forcing agents estimated here within climate models, and extending this approach to assess the radiative forcing associated with land-cover transitions in temperate and tropical ecosystems.”

The Randerson et al paper also has significant relevance in terms of the sequestration of carbon within vegetation and soils as a component of deliberate human climate intervention.

This new paper supports the perspective in a short essay that I wrote for the Bulletin of the American Meteorological Society in 2001. It is entitled “Carbon sequestration — The need for an integrated climate system approach“.

The essay reads as follows,

“The concern with respect to the anthropogenic input of carbon dioxide into the atmosphere (Houghton et al. 1995) has resulted in proposals for long-term removal programs of this gas based on forestation and agricultural procedures. Referred to as “carbon sequestration,â€? the value of this effort is defined by the amount of CO2 removal and the length of time before it would be reemitted into the atmosphere. The extraction of the CO2 from the atmosphere reduces its contribution as a radiatively active greenhouse gas. Landscapes that would be modified for this purpose have been referred to as “biomass farms.â€?

However, the alteration of the land surface is likely to result in other effects on the heat energy of the atmosphere. Any additional water vapor evaporated or transpired into the atmosphere, for instance, would increase the greenhouse gas warming effect and at least partially offset the benefit of carbon sequestration. Alternatively, a net reduction in water vapor input might enhance the benefit of carbon sequestration with respect to a reduction in greenhouse gas concentrations.

Since, in the atmosphere, however, a water vapor molecule has a much shorter lifetime than a carbon dioxide molecule, the evaluation of changes in transpiration or evaporation would have to consider its net effect over multiyear timescales. Changes in water vapor flux into the atmosphere can also alter cloud and precipitation, so that its net effect on the radiation budget is quite complex.

It is, therefore, somewhat more straightforward to evaluate the change in the long-term surface energy budget due to the landscape change associated with carbon sequestration. A darkening of the land surface, for example, would result in a lower albedo, which would contribute to atmospheric heating (Cotton and Pielke 1995) an effort contrary to the goals of carbon sequestration. Elevating the albedo would add to the goal of carbon sequestration. Just changing the surface albedo from 0.2 to 0.15, for example, can reduce the annual averaged insolation reflected back into space by 5 W m−2 or more!

There has, unfortunately, been no attempt to evaluate the benefit of carbon sequestration as a means of reducing the concentrations of the radiatively active gas CO2 in the atmosphere, while at the same time, assessing the influence of this sequestration on the radiatively active gas H2O, and on the surface heat energy budget. Until these effects are factored in as part of an integrated climate assessment, a policy based on carbon sequestration as a means to reduce the radiative warming effect of increased atmospheric concentrations of CO2 could actually enhance this warming.

References

Cotton, W. R., and R. A. Pielke, 1995: Human Impacts on Weather
and Climate. Cambridge University Press, 288 pp.

Houghton, J. T., L. G. Meira Filho, B. A. Callendar, N. Harris,
A. Kattenberg, and K. Maskell, Eds., 1995: Climate Change”

Clearly, the issue of carbon sequestration, and the climate system in general, are not as well understood as claimed in climate assessments such as presented in the previous IPCC reports, nor in the draft AMS Statement on climate change (see). We will see soon if this complexity is reported on in the new IPCC assessment and in the revised version of the AMS draft Statement..

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Should Scientific Societies Issue Position Statements? by Ross McKitrick

The American Meteorological Society has released a draft statement on climate change for comment over the next few weeks. As an economist I find it strange that scientific societies show such a propensity to issue position statements. One of the reasons economists have maintained relatively free collegiality while debating issues with controversial policy implications is that our major associations do not issue position statements.

I am a member of the American Economic Association. Its 3 objectives are listed at http://www.vanderbilt.edu/AEA/gen_info.htm:

1. The encouragement of economic research, especially the historical and statistical study of the actual conditions of industrial life.

2. The issue of publications on economic subjects.

3. The encouragement of perfect freedom of economic discussion. The Association as such will take no partisan attitude, nor will it commit its members to any position on practical economic questions.

I am also a member of the Canadian Economics Association. Its policies are at http://economics.ca/en/information.php. Its position is like that of the AEA:

The Association has for its object the advancement of economic knowledge through the encouragement of study and research, the issuing of publications, and the furtherance of free and informed discussion of economic questions. The Association as such will not assume a partisan position upon any question of practical politics nor commit its members to any position thereupon.

In both cases the promotion of free discussion is coupled to the refusal to issue position statements.

Official statements celebrate group think and conformity. They effectively demote members who disagree with some or all of the statement to second-class status within their profession, regardless of the quality of their own individual work or their reasons for disagreement. And they create divisions and alienation within the profession. Having issued a party line, it cannot be a surprise that partisanship emerges, with all its potential for polarization and resentment.

Official statements also legitimate the appeal to authority as a form of argumentation. By issuing a position statement, they encourage outside commentators to buttress their position by appeal to the “Expert Statement”, rather than by appeal to evidence. The official statement thereby supplies a fallacious rhetorical device to one side in a political debate.

Perhaps some climate scientists think the benefits of issuing official statements outweigh the loss of collegiality, and the discouragement of free and informed discussion. For my part I prefer the official neutrality of economic societies.

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A New Paper On The Need To Assess The Importance Of Ocean Heat Content Changes In The Assessment of Global Warming

An important new paper on climate system heat content has appeared. It is Shin H.-J., I.-U. Chung, H.-J. Kim, J.-W. Kim (2006), Global energy cycle between land and ocean in the simulated 20th century climate systems, Geophys. Res. Lett., 33, L14702, doi:10.1029/2006GL025977.

The abstract of the paper reads,

“The global energy cycle between the land and the ocean has been studied with simulations of the 20th century performed with coupled ocean-atmosphere climate models. The energy cycle consists of the net energy fluxes at the top-of-the-atmosphere (TOA) and the surface, the atmospheric energy storage rates over the global land and ocean, and the atmospheric energy transport between the land and ocean. The energy cycle was investigated using a multi-model ensemble for its centennial mean, climatological annual variation and long-term trend. Some distinctive features of the cycle were revealed: (1) the ocean-to-land atmospheric energy transport plays a key role in partitioning the global net TOA flux between the ocean and land, (2) the annual variation of the global net TOA flux is primarily attributed by the ocean surface flux, and (3) it is ascertained that the planetary energy imbalance on the long-term period is induced by the ocean’s heat uptake. “

Excerpts from the Conclusion and Remarks state,

“…….the annual mean ocean-to-land energy transport can be largely explained by the global water cycle (characterized as the water vapor transport from the ocean to the land and its compensating run-off from the land to the ocean [Shin et al., 2002]). In conclusion, the authors believe that the global energy cycle between land and ocean is important to understand the climate system and climate change.”

“Through the analysis with the long-term time series of the TOA and the surface fluxes, the importance of the ocean’s role for the planetary energy imbalance was illuminated.”

This last conclusion further substantiated the conclusions in Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335 that

“The earth’s heat budget observations, within the limits of their representativeness and accuracy, provide an observational constraint on the radiative forcing imposed in retrospective climate modeling.

A snapshot at any time documents the accumulated heat content and its change since the last assessment. Unlike temperature, at some specific level of the ocean, land, or the atmosphere, in which there is a time lag in its response to radiative forcing, there are no time lags associated with heat changes.

Since the surface temperature is a two-dimensional global field, while heat content involves volume integrals ……the utilization of surface temperature as a monitor of the earth system climate change is not particularly useful in evaluating the heat storage changes to the earth system. The heat storage changes, rather than surface temperatures, should be used to determine what fraction of the radiative fluxes at the top of the atmosphere are in radiative equilibrium….”.

The recognition of the importance of ocean heat content changes is a reason that the paper

Lyman J. M., J. K. Willis, G. C. Johnson (2006), Recent cooling of the upper ocean, Geophys. Res. Lett., 33, L18604, doi:10.1029/2006GL027033

should receive a lot of attention. This paper represents another challenge to the IPCC perspective on the use of global average surface air temperature trends as the primary global warming metric.

The new Shin et al paper is an excellent new contribution which provides further evidence as to why a change to the assessment of global average ocean heat content variability and trends is needed.

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How Well Do Multi-Decadal Global Climate Models Represent The Radiative Effect of Well-Mixed Greenhouse Gases? Part II

Gavin’s comment in the weblog Draft American Meterological Society Statement on Climate Change [comment #7] made the important statement that,

“As to how the forcings are calculated, it is essential that you do the analysis over the globe and over the seasonal cycleâ€?,

I agree.

The Collins et al 2006 paper that I weblogged on yesterday did not do this analysis. Thus where does the conclusion that the current radiative forcing is around “1.5W/m2″ [Gavin's Comment #1] come from?

The most complete paper that does summarize how radiative forcings are defined (as communicated to me by Gavin Schmidt) is

Hansen, J., Mki. Sato, R. Ruedy, L. Nazarenko, A. Lacis, G.A. Schmidt, G. Russell, I. Aleinov, M. Bauer, S. Bauer, N. Bell, B. Cairns, V. Canuto, M. Chandler, Y. Cheng, A. Del Genio, G. Faluvegi, E. Fleming, A. Friend, T. Hall, C. Jackman, M. Kelley, N. Kiang, D. Koch, J. Lean, J. Lerner, K. Lo, S. Menon, R. Miller, P. Minnis, T. Novakov, V. Oinas, Ja. Perlwitz, Ju. Perlwitz, D. Rind, A. Romanou, D. Shindell, P. Stone, S. Sun, N. Tausnev, D. Thresher, B. Wielicki, T. Wong, M. Yao, and S. Zhang 2005. Efficacy of climate forcings. J. Geophys. Res. 110, D18104, doi:10.1029/2005JD005776.
.
This is the paper where they concluded that

“Attempts to slow global warming must focus primarily on restricting CO2 emissions.”

With respect to the climate forcing from CO2, or other forcings, they provide the following definition,

“The simplest forcing, and the only pure forcing, is the instantaneous forcing, Fi. Fi is the radiative flux change at the tropopause after the forcing agent is introduced with the climate held fixed.”

The Hansen et al paper, unfortunately, does not provide the vertical variation of this forcing (i.e. the radiative flux divergence), nor its spatial structure. These are also “pure forcingsâ€?. The need to report on the vertical and regional variation of the radiative forcings was one of the main recommendations in the 2005 NRC Report “Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties” (see page 5).

Moreover they state,

“The climate forcing by CO2 in the present GISS model III is at the high end of the range estimated by IPCC [Ramaswamy et al., 2001]. Specifically, doubled CO2 in our current model, from the 1880 value of 291 ppm to 582 ppm, yields Fi = 4.52 W/m2.”

What was the specific procedure used to obtain this value of Fi? Did they run the model’s radiation parameterization off-line for each grid point in the model over a long time period? They are also silent on what is their current estimate of Fi, since the climate presumably has equilibrated to some fraction of the CO2 added after 1880.

As admitted by Hansen et al, the other forcings that they consider in their paper include feedbacks.

The summation globally and over long averaging times of Fi and its vertical divergence in the models should be a priority and would be a valuable addition to the quantification of CO2 radiative forcing. Regional maps of this forcing would also be valuable to address the issue that was raised in

Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974.

http://blue.atmos.colostate.edu/publications/pdf/R-312.pdf

where we compared the climate forcings of CO2 and aerosols in terms of the horizontal gradients of diabatic heating that these forcings produce.

To better quantify radiative forcing, including its vertical and horizontal structure, I propose an experiment, following what we report on with respect to the analysis by Norm Woods in the second Edition of Cotton, W.R. and R.A. Pielke, 2007: Human impacts on weather and climate, Cambridge University Press, New York (to be available late January 2007) and building on the Hansen et al paper.

The radiation codes that are used in each AOGCM should be applied to vertical profiles extracted from the NCAR-NCEP and ECMWF global reanalyses (e.g. at 6 hour intervals for a year globally) in order to diagnose the instantaneous long and short radiative flux divergences associated with each well-mixed greenhouse gas. This includes their vertical and horizontal structure. Then rerun these diagnoses but increment the well-mixed greenhouse concentrations to selected different values (e.g. adding 100 ppm to the current concentration of CO2; adding 100 ppb to CH4, etc).

Once this experiment is completed, the same framework can be used with the non-well mixed climate forcings.

This framework would provide a clear signal of the relative and absolute radiative forcings of each well-mixed greenhouse gases (and when completed, the other climate forcings) without involving climate feedbacks in the assessment. These would be “pure forcings” using the terminology given in the Hansen et al paper. These “pure forcings” are what should be presented when comparing the relative contribution of each radiative forcing to climate system heat changes.

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