Review of the Congressional Budget Office “The Expected Impacts of Climate Change in the United States” by Roger A. Pielke Sr. January 14 2009

The Congessional Budget Office release a report yesterday (May 4 2009) titled “Potential Impacts of Climate Change in the United States” (see for the full report).

In January 2009, I was asked to review the draft version of the report. Unfortunately, however, the report did not discuss the major substantive issues that I raised. While I was pleased to see land use change elevated to a first order forcing, the report, despite recognizing major remaining uncertainties with respect to our ability to skillfully predict the future climate, the report still perpetuates the erroneously narrow view of the IPCC and CCSP reports.

My January review is reproduced below:

This CBO draft report is based primarily on the 2007 Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), and the national assessment recently released by the National Science and Technology Council (NSTC).  The CBO report accepts the conclusions of these reports that

“Human activities around the world-primarily fossil fuel use, forestry, and agriculture-are producing growing emissions of greenhouse gases-most importantly carbon dioxide (CO2)-as well as emissions of other gases and particulates. If allowed to continue unabated, the accumulation of those substances in the atmosphere and oceans is expected to have extensive, potentially serious and costly, but highly uncertain impacts on regional climate and ocean conditions throughout the world.”

and that the report

“…..summarizes the current state of scientific understanding of the potential effects of projected changes in climate and related developments. The [CBO report] describes the wide range of potential impacts, including changes in seasonal weather patterns; the amount and type of precipitation; storms and sea level; regular climate fluctuations; ocean acidity; ecosystems and biodiversity; agriculture, forestry, and fishing; water supply and other infrastructure; and human health. The discussion focuses mainly on projections of impacts in the United States but also refers to impacts elsewhere that could indirectly affect the United States.”

The report recognizes, however, that there remain significant uncertainties; i.e. it is written that

“The paper [the CBO report] emphasizes the extensive uncertainty about future climate-related developments and its implications for climate policy. Uncertainty arises from several sources, including limitations in current data, imperfect understanding of physical processes, and the inherent unpredictability of some aspects of the interacting components (land, air, water and ice, and life) that make up the Earth’s climate system.”

Reviewer Comment

The IPCC and NSTC reports (which is built on the IPCC report, and thus is not an independent assessment) do not adequately address the broader, more societally relevant conclusion with respect to the human involvement within the climate system, and the resultant  larger range of uncertainty that is reported in other assessments; e.g.

National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp.


Kabat, P., Claussen, M., Dirmeyer, P.A., J.H.C. Gash, L. Bravo de Guenni, M. Meybeck, R.A. Pielke Sr., C.J. Vorosmarty, R.W.A. Hutjes, and S. Lutkemeier, Editors, 2004: Vegetation, water, humans and the climate: A new perspective on an interactive system. Springer, Berlin, Global Change – The IGBP Series, 566 pp.

The 2005 NRC report had the following findings,

“…..the traditional global mean TOA radiative forcing concept has some important limitations, which have come increasingly to light over the past decade. The concept is inadequate for some forcing agents, such as absorbing aerosols and land-use changes, that may have regional climate impacts much greater than would be predicted from TOA radiative forcing. Also, it diagnoses only one measure of climate change-global mean surface temperature response-while offering little information on regional climate change or precipitation.”


“Several types of forcings-most notably aerosols, land-use and land-cover change, and modifications to biogeochemistry-impact the climate system in nonradiative ways, in particular by modifying the hydrological cycle and vegetation dynamics. Aerosols exert a forcing on the hydrological cycle by modifying cloud condensation nuclei, ice nuclei, precipitation efficiency, and the ratio between solar direct and diffuse radiation received. Other nonradiative forcings modify the biological components of the climate system by changing the fluxes of trace gases and heat between vegetation, soils, and the atmosphere and by modifying the amount and types of vegetation. No metrics for quantifying such nonradiative forcings have been accepted. Nonradiative forcings have eventual radiative impacts, so one option would be to quantify these radiative impacts. However, this approach may not convey appropriately the impacts of nonradiative forcings on societally relevant climate variables such as precipitation or ecosystem function. Any new metrics must also be able to characterize the regional structure in nonradiative forcing and climate response.”

What this means is that the concept of emissions of CO2dominating climate change (and the concept of “global warming”), by itself, does not accurately communicate the regional responses to the diverse range of human climate forcings. Regional variations in warming and cooling for example, such as from tropospheric aerosols and landscape changes, as concluded in the National Research Council report, have important regional and global impacts on weather.

The human climate forcings that have been ignored, or are insufficiently presented in the IPCC and NSTC reports, include

  • The influence of human-caused aerosols on regional (and global) radiative heating
  • The effect of aerosols on clouds and precipitation
  • The influence of aerosol deposition (e.g. soot; nitrogen) on climate
  • The effect of land cover/ land use on climate
  • The biogeochemical effect of added atmospheric CO2

What this means is that of the three hypotheses

  • The human influence is minimal and natural variations dominate climate variations on all time scales;
  • While natural variations are important, the human influence is significant and involves a diverse range of first-order climate forcings, including, but not limited to the human input of CO2;
  • The human influence is dominated by the emissions into the atmosphere of greenhouse gases, particularly carbon dioxide

the first and third hypotheses have been rejected.

The CBO draft report, however, accepts the third hypothesis as being correct, and that this framework can be used to predict regional impacts in the United States decades into the future.

A necessary (but still not sufficient condition) for accurate projections decades into the future of even changes in probabilities of weather events cannot be achieved without including these climate forcings. Thus, the CBO draft presentation of the expected impacts of climate change in the United States is based on a scientifically incomplete study in which there are serious omissions of scientific research.

The CBO report also makes the following statement:

  • The accumulation of warming substances has tended to dominate, triggering an irregular but accelerating warming of the Earth’s surface and various consequent changes.

Reviewer comment

The observational data in the last decade conflict with the finding reported in the CBO draft report. For example, the global average lower tropospheric temperatures have not increased for at least 7 years, and indeed, show a recent decline. See (from

The tic marks on the x-axis are at yearly intervals starting in 1979 and continuing to the present. The vertical axis is the global average temperature anomaly in degrees Celsius in the lower troposphere from the RSS MSU satellite analysis.

There is no acceleration of warming. Studies of the surface temperature data are similarly finding a lack of accelerated warming, and, in fact, are even finding that for the last 8 years or so, that the IPCC model predictions of the global average surface temperature trend are not consistent with the observations. Moreover, there is new evidence of a significant warm bias in the land portion of the surface temperature data base that is used to construct the global average trend (e.g., see Pielke et al. 2007; Lin et al. 2007)

Another statement in the CBO draft is that

  • The models replicate seasonal and large-scale regional variations in temperature and, to a lesser extent, precipitation; large-scale ocean currents; large-scale ocean and climate oscillations; and storms and jet streams in the middle latitudes.

Reviewer Comment

The IPCC predictions have not demonstrated seasonal or large-scale regional prediction skill on any climate time periods.  The inability of even the NOAA’s seasonal prediction models to skillfully predict the severe winter cold in the United States and Europe this winter illustrates how challenging this task is.

Also, the CBO draft writes

  • The models plausibly replicate 20th century climate trends when they are run with historical emissions of greenhouse gases, other types of emissions, and variations in natural forces such as volcanic eruptions and fluctuations in solar energy. No model replicates those climate trends through variations in natural forces alone.

Reviewer Comment

None of the IPCC models skillfully predicted the major weather pattern variations (and their observed variations in frequency over time) for the 20th century. The 1930s and 1950s droughts in the United States, for example, have not been accurately simulated by the IPPC models. The one climate metric that they focus on (the global average surface temperature trend) has been reasonably simulated primarily because they can determine what level of aerosols in the atmosphere over the past decades is required to explain the observed variations of warming and cooling during this time period.

The last specific CBO commented on in this review is

  • Recent projections even suggest that annual temperatures may cool slightly over the next decade in Europe and North America while the global average temperature remains fairly steady. Such fluctuations are not necessarily inconsistent with an ongoing long-term warming trend brought about by human activities.

Reviewer Comment

This finding conflicts with the statement made earlier in the CBO that “The accumulation of warming substances has tended to dominate, triggering an irregular but accelerating warming of the Earth’s surface and various consequent change”!

This finding is an effort to cover a recently observed observation that global warming has stalled, at least for the present.

Conclusion by the Reviewer

The foundation of the CBO draft is that the hypothesis

  • The human influence is dominated by the emissions into the atmosphere of greenhouse gases, particularly carbon dioxide

 is correct.  The impacts that are predicted in the CBO report are predicated on this hypothesis being valid. However, it has been rejected in a variety of assessments and peer reviewed papers which were ignored on inadequately reported on in the IPCC and NSTC reports.  The hypothesis that has the support of a broad range of papers is that

  • While natural variations are important, the human influence is significant and involves a diverse range of first-order climate forcings, including, but not limited to the human input of CO2.

Thus, as reported in Pielke (2008),

 “Climate policy that is designed to mitigate the human impact on regional climate by focusing only on the emissions of CO2is seriously incomplete unless these other first-order human climate forcings are included, or complementary policies for these other human climate forcings are developed. Moreover, it is important to recognize that climate policy and energy policy, while having overlaps, are distinctly different topics with different mitigation and adaptation options.

A way forward with respect to a more effective climate policy is to focus on the assessment of adaptation and mitigation strategies that reduce vulnerability of important societal and environmental resources to both natural and human caused climate variability and change. For example, restricting development in flood plains or in hurricane storm surge coastal locations is an effective adaptation strategy regardless of how climate changes.” 

My complete testimony in Pielke (2008) is added as an appendix to this review, since I was asked to testify on the same topic as in the CPO draft. 

To provide a more objective and balanced assessment of the role of humans within the climate system, as well as provide an accurate evaluation of the ability to make skillful multidecadal regional climate predictions, the CBO should contract with the National Research Council to convene a Panel for this purpose. Unlike what was chosen for the CCSP process, however, the individuals chosen should not be IPCC contributors, but involve climate scientists with less of a vested interest in the independent assessment.


Lin, X., R.A. Pielke Sr., K.G. Hubbard, K.C. Crawford, M. A. Shafer, and T. Matsui, 2007: An examination of 1997-2007 surface layer temperature trends at two heights in Oklahoma. Geophys. Res. Letts., 34, L24705, doi:10.1029/2007GL031652.

Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2007: Unresolved issues with the assessment of multi-decadal global land surface temperature trends.J. Geophys. Res., 112, D24S08, doi:10.1029/2006JD008229.

Pielke Sr., Roger A., 2008: A Broader View of the Role of Humans in the Climate System is Required In the Assessment of Costs and Benefits of Effective Climate Policy. Written Testimony for the Subcommittee on Energy and Air Quality of the Committee on Energy and Commerce Hearing “Climate Ch Costs of Inaction” – Honorable Rick Boucher, Chairman. June 26, 2008, Washington, DC., 52 pp. View Oral Summary at ADD House Testimony





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