E-brief 105

Mopping up After a Leak: Setting the Record Straight on the "New" Findings of the Intergovernmental Panel on Climate Change (IPCC)
Every five years, the Intergovernmental Panel on Climate Change publishes a massive report on global climate change. These "Assessment Reports" become the central touchstone of the debate over climate change, laying out a consensus version of what is known, what is still uncertain, and how various actions might or might not cause changes in future climate conditions.

The last such publication was the IPCC's "Second Assessment Report (SAR),"published in 1995. The 1995 SAR argued that the Earth's climate was changing in ways that seemed unlikely to be of non-human origin, and that the weight of evidence suggested a "discernable" human impact upon the climate. Predicted future temperatures in the SAR ranged from 1 °C to 3.5 °C (1.8 °F to 6.5 °F) degrees centigrade by 2100, and sea level increases of 15 to 95 cm in the same timeframe.

The 1995 report is about to be supplanted by the IPCC "Third Assessment Report, or TAR, to be published early in 2001. The first volume of the TAR, the product of IPCC's Working Group 1 (WG1) reviews the massive body of climate change literature, and attempts to present a consensus view of the current understanding of climate change. This report was reviewed by a panel of experts in late 1999, was subsequently reviewed by governmental entities, was revised according to feedback, and is now undergoing "final government review." After a last round of revisions based on the final government review (which, theoretically will not alter any of the scientific conclusions of the report as it emerged from expert review), the TAR will be published in early 2001.

When the IPCC publishes a new major report, it also publishes a derivative document called the "Summary for Policymakers" (or Summary). These summaries attempt to condense the contents of the IPCC's full Assessment Report, and express findings in a language suitable for moderately educated readers.

Less than two weeks before the U.S. Presidential elections, copies of the draft Summary for Policymakers based on the Third Assessment Report were leaked to the Associated Press and other media commentators. The draft Summary became an instant issue in the election.

Working from more extreme �worst-case' estimates than previous IPCC reports, the Summary suggests a higher range of potential warming by 2100, and higher sea-level rise as well. Global average temperature in the new Summary is modeled to increase from 1.5 to 6.0 degrees Centigrade by 2100 (2.7 to 10.4 degrees Fahrenheit). Predicted sea-level increases under the new scenarios range from 14 to 80 cm by 2100.

But media coverage of the Summary lacks contextual information needed to allow people to decide whether the report was credible. The genesis of the Summary was not explained, and the "findings were not put in context with regard to either the previous assessment report, or the main body of the more scientifically rigorous and more carefully qualified Third Assessment Report.

Climate change is a concern worthy of serious attention, and the best quality scientific research that humanity can muster. It is an issue of great complexity, in which fine details of interpretation, and underlying assumptions are indispensable if sound policy is to be derived from sound use of scientific information.

The purpose of this document is to add some context and balance to the discussion, and to correct some of the mistaken impressions that recent news coverage of the leaked IPCC draft Summary for Policymakers may have created.

1. Predictions of future changes rest upon speculative scenarios that were not reviewed by technical reviewers of the main report.

The claims regarding the potential increase in global average temperatures and sea levels in the year 2100 are based upon "scenarios" about the future that enfold a panoply of assumptions about global development patterns, population growth, energy sources, economic development, technological change, and so on:

  • It is the addition of more pessimistic scenarios to those used in previous IPCC reports that produces greater estimated future temperatures, more than changes in understanding of past or present climate processes, or theoretical understanding of the relationship between human activity and climate;

  • Future temperature and sea-level predictions are not modeled with state-of-the-art computer models, but use "simple" computer models that are "calibrated" to the more accurate models. No mention is made of the fact that such simple models imitate their high-powered cousins poorly; have many well-known weaknesses that make them of limited use; and are of limited reliability even for modeling current climate trends;

  • Only the Summary of the report delineating scenario assumptions is currently available for download which limits analysis, but the new "worst case" scenario assumes that:
    • There are no mid-course programs implemented between now and 2100;
    • Population peaks at 8.7 billion in 2050, and declines to 7 billion by 2100;
    • Global deforestation is not abated;
    • The developing world will reach similar levels of development as developed countries;
    • World GDP will increase 10 times by 2100;
    • Most energy production will be from carbon-based fuels;
    • Carbon dioxide emissions will nearly quadruple by 2100;
    • Methane emissions will more than double by 2100;
    • Carbon monoxide emissions will nearly triple by 2100;
    • Volatile organic carbon emissions will nearly triple by 2100; and
    • Fluorocarbon levels will rise dramatically by 2100, in some cases by two orders of magnitude.

  • The assumptions used in these "scenarios" were only published in the Spring of 2000, more than six months after the actual "expert review" cycle was completed; and

  • Economic and population parameters are not published as part of the peer-reviewed Third Assessment Report, and must be retrieved from another report. This makes simultaneous comparison difficult for experts with access to the full reports, and nearly impossible for others who have only the Summary.

2. The Summary for Policymakers presents findings devoid of vital contextual information.

When discussing the findings of how the Earth's climate has changed in recent years, the Summary for Policymakers presents hard evidence regarding temperature readings, rain measurements, snow measurements, and so on. But the Summary presents this information without vitally important contextual and qualifying information found in the body of the IPCC report:

  • Increases in temperature are presented without pointing out that:
    • The majority of physically observed warming since 1860 happened from 1910-1945, and the majority of that early warming is attributed to non-human climate forces in the body of the report;

    • The warming observed since 1860 was not continuous, but happened in two bursts;

    • Twice as much of the observed warming since 1860 appears as warming of nighttime low temperatures in the coldest parts of the Earth, rather than increases of daytime highs in the warmer parts of the Earth;

    • The difference between ground-level temperature readings and high-altitude readings from balloons and satellites reveals a critical weakness of the climate models used to predict future impacts discussed later in the Summary; and

    • Estimated increases in temperature for the last 1000 years, are based on disputed climate reconstructions rather than observed data. No mention is made that evidence documents sharper temperature shifts in the climate record from before humans existed, suggesting that recent changes could be of non-human origin.

  • Decreases in global ice extent (glaciers, icebergs, etc) and snowfall trends are presented without explaining that:
    • Measurements of historical snow depth and extent are extremely limited;

    • Glaciers in some regions are growing, not shrinking;

    • Reductions in snow and ice are not happening in the seasons where increased warmth has actually been observed;

    • Estimates of Arctic sea ice thickness show a wide range, from 1 to 4 centimeters of shrinkage per year because the sampling of evidence is too small to be conclusive; and

    • Antarctic sea ice has been stable or shows what seems to be a slight increase in extent since the 1970s.

  • Evidence of sea level rise of 0.1 to 0.2 meters during the 20th Century is presented without reference to the fact that:
    • Sea level has been rising for nearly 20,000 years, by about 120 meters since the last glacial maximum;

    • The rate of sea level rise is not steady, but fluctuates;

    • Sea level rise did not speed up during the 20th Century, though theoretically, global average temperatures were increasing; and

    • While sea level rose between one-tenth and two-tenths of a meter during the 20th Century, the body of the report attributes only two-hundredths to six-hundredths of a meter to human activity from 1910 to 1990.

  • The claim that human activities "continue to alter the atmosphere in ways that affect the climate system" is made without mentioning that:
    • This conclusion, unlike those regarding actual climate changes, are purely based on still-developing theories and highly uncertain computer modeling, not on any measurable cause-and-effect relationship between any particular activity and global climate;

    • Greenhouse gases including both carbon dioxide and methane rose and fell along with global average temperatures before human beings were around to influence their concentrations;

    • At least two of these human activities expected to contribute to greater warming in the future are pollution reduction initiatives to reduce sulfur aerosols, and to eliminate the use of ozone-destroying chlorofluorocarbons;

    • While computer models agree that human activities have some role in observed 20th Century warming, individual models give very different estimates for the extent of the human role;

    • Uncertainties are still large in key modeling areas that underpin the entire claim of human causality in observed changes. These uncertainties involve the role of water vapor, cloud formation, and aerosol impacts in climate regulation.

3. The leaked "Summary for Policymakers" is not peer-reviewed, the author is anonymous, the document is created independently of the actual Assessment Report, and the Summary is so short that issues are overly simplified.

  • Unlike the main body of the IPCC Third Assessment Report which represents an herculean effort to assess the current state of knowledge about climate change, and which speaks with great credibility because of extensive peer-review, the leaked Summary for Policymakers is not reviewed by the main body of IPCC experts and thus lacks the credibility of the technical reports they claim to summarize.

  • The author of the summary is not identified, and there is no explanation of the process that generated the Summary, nor specifies whether it was or was not reviewed by the main authors, contributing authors, or expert reviewers that vetted the body of the Third Assessment report.

  • The Summary for Policymakers is 12 pages long, and theoretically summarizes the Working Group I report (which) is over 1000 pages long as well as parts of the not-yet-finalized Working Group II report, which will probably be over 1000 pages.


News coverage of the recently leaked "Summary for Policymakers" from the pending Third Assessment Report of the Intergovernmental Panel on Climate Change lacks information vital to putting the leaked document in meaningful perspective.

Specifically, the leaked report:

  • Does not explain that increases in predicted future temperatures from the last IPCC report are due to added worst-case scenarios generated outside the careful, peer-reviewed publication process of the Third Assessment Report rather than changes in gathered evidence or empirically documented trends in climate, energy use, or greenhouse gas production;

  • Does not spell out how extreme the worst-case scenarios are;

  • Does not explain that predictions of future climate were generated not with state-of-the-art models, but with simple climate models that cannot reliably reproduce known temperature changes of recent years.

  • Does not provide the contextualizing information needed to accurately communicate what scientists have learned about past climate changes, current climate function, or future climate expectations;

  • Does not mention that observed climate changes are only partially due to human activity; and

  • Was not peer-reviewed by the same experts who reviewed the technical reports from which it is ostensibly extracted.

The forthcoming Third Assessment Report of the Intergovernmental Panel on Climate Change will serve as the central touchstone of climate change debate for the next five years. Climate change is a serious and important subject, and concerns about rapid changes in climate � whatever the cause might be — should not be treated lightly. Accuracy in the understanding of the underlying science is equally critical, and should not be misrepresented or politicized by partisans of any particular control approach.

Activities which weaken the credibility of the TAR impede not only the search for knowledge, but insure greater divisiveness in the debate over whether the report represents a scientific consensus, or is a document biased by political forces outside of the scientific process of discovery.

The leak of the Summary report of the IPCC Third Assessment Report may be seen, by some, as a way of creating a short-term ripple in the political landscape of the United States Presidential campaign. But in the long term, this leak can only harm the search for a consensus statement of knowledge, and the search for appropriate responses to the risks posed by climate change.

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Dr. Kenneth Green is Director of the Environmental Program at Reason Foundation.