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National Academy of Sciences Raises More Climate Questions

Report acknowledges limitations of scientific understanding

Kenneth Green
June 7, 2001

On June 6, 2001, an 11-member panel of the National Academy of Sciences (NAS) released "Climate Change Science: An Analysis of Some Key Questions," a report they prepared for President George W. Bush. The report confirms important points that many analysts critical of mainstream portrayals of climate change science and policy have argued for years.

In this report, NAS points out that:

The NAS report begins with an adamant statement that "temperatures are, in fact, rising." This is not news, however; virtually no one has argued that this is not the case. While the NAS goes on to affirm some of the technical claims from both the third Assessment Report of the U.N�s IPCC and the National Assessment Report of the United States Global Change Research Project, the NAS report has many sharply cautionary warnings scattered throughout.

This document culls key statements from the NAS report into discrete categories:

  1. Key statements on understanding of the climate system and our forecasting abilities;

  2. Key statements on human causation of observed 20th century climate changes;

  3. Key statements on research needs (the only actual recommendations given by the NAS); and

  4. Key statements on the IPCC process, scientific representation, and political influence on the "Summary for Policymakers" in the U.N.'s third Assessment Report.


1. Key Statements on Understanding of the Climate System and our Forecasting Abilities

While the NAS "generally agrees with the assessment of human-caused climate change" presented by the United Nations' IPCC, the authors of the NAS report seek to "articulate more clearly the level of confidence that can be ascribed to those assessments, and the caveats that need to be attached to them."

The following quote from the NAS report summarizes that effort quite well:

The NAS report points out the many weaknesses in current understanding of climate processes:

And while the NAS report clearly affirms the usefulness and importance of climate models, it observes that:

Finally, in another powerfully cautionary statement, the NAS confirms that some of the proposed factors involved in climate change are so uncertain that it is unknown whether the factors will cause warming or cooling:


2. Key Statements on Human Causation of Observed 20th Century Climate Changes

When it comes to the all-important question of causality, the NAS report contains cautionary statements far stronger than those seen from other august scientific panels:


3. Key Statements on Research Needs

While the NAS report does not make outright recommendations, it does point out research needs and encourages additional research. This itself points to weaknesses in the underlying scientific understanding of climate change.


4. Key Statements on the IPCC Process, Scientific Representation, and Political Influence on the "Summary for Policymakers" in the U.N.'s Third Assessment Report

Perhaps the most fascinating element of the NAS report is its inquiry into the limitations of the IPCC process, and its questioning whether the IPCC "Summary for Policymakers" the most widely quoted element of all the IPCC publications faithfully represents the underlying technical reports.

While the NAS finds the underlying technical reports of the IPCC on the science of climate change (a.k.a. the "Working Group 1" section of the Third Assessment Report) to be rigorous and representative of mainstream scientific thought, it raised many concerns about the influence of political forces on the IPCC's overall reporting process and on key documents such as its "Summary for Policymakers" in the Third Assessment Report.

The NAS also confirms a practice that many critics of past IPCC reports have questioned: that of retroactively altering the technical studies to support the statements given in the "Summary for Policymakers." While "most" of these changes were acceptable to the IPCC chapter authors, the NAS suggests that "some scientists may find fault with some of the technical details, especially if they appear to underestimate uncertainty" (page 23).

Additional points raised by the NAS report include the following:

The newly released "Climate Change Science: An Analysis of Some Key Questions" report of the National Academy of Sciences is a noteworthy contribution to the ongoing debate over climate policy. While understanding that the Earth�s average temperature has increased recently, and affirming the mainstream scientific view that some of this warming is attributable to human action, the NAS report also acknowledges the current limitations of scientific understanding, and the dangers of mischaracterizing those limitations by exaggerated reporting that downplays uncertainty.

Dr. Kenneth Green is senior fellow at Reason Foundation and Chief Scientist at Frasier Institute.


Relevant Reason Publications

Plain English Guide 3: Exploring the Science of Climate Change

E-brief 105: Mopping Up After a Leak: Setting the Record Straight on the "New" Findings of the Intergovernmental Panel on Climate Change (IPCC)

Evaluating the Kyoto Approach to Climate Change (.pdf)

A Baker's Dozen: 13 Questions People Ask about Climate Change



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