IPCC Climate Change 2007 Report: Criticism

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IPCC Climate Change 2007 Report: Criticism


The Intergovernmental Panel on Climate Change (IPCC) is a group of scientists, economists, and government officials formed by the United Nations. Its purpose is to write summaries of the state of scientific knowledge and uncertainty about matters related to climate change. Since 1990, it has produced four overviews—or Assessment Reports—reviewing the state of climate knowledge. The fourth report was released in stages in 2007. Like the three earlier sets, the fourth report was the product of a many-sided process of scientific review and consensus-building overseen by the governments of scores of countries.

The 2007 report has received some criticism. Some critics alleged that the report exaggerated the extent and danger of climate change. However, it was also criticized by others for understating climate change. Some critics in both camps were qualified scientists, but the majority of the scientific criticism of the 2007 Assessment Report has argued that the document understates the dangers of climate change.

Historical Background and Scientific Foundations

Each IPCC report is prepared through a complex process in which drafts are created by scientists, economists, and other experts, then reviewed by other experts and by government officials. Several drafts are written, opened for comment, and revised before the final version is produced. Therefore, much criticism of an IPCC report occurs while the report is being written. The Physical Science Basis section of the 2007 Assessment Report was written by 152 lead authors from more than 30 countries and reviewed by some 620 science experts over a three-year period. The final document was approved by all countries participating in the IPCC, including governments that resist measures to reduce greenhouse-gas emissions.

The 2007 Assessment Report was released in three parts, each produced by a separate working group of scientists, other experts, and government officials. The first part to be released was the Physical Science Basis report. This reviewed the state of scientific knowledge and uncertainty about climate change of the past, present, and future. The second was the report on Impacts, Adaptation, and Vulnerability, which reviewed scientific knowledge about what effects climate change is likely to have on human and natural systems and how people and nature might respond. The third part was the Mitigation of Climate Change report, which discussed how humans can produce less of the greenhouse gases that are the main cause of present-day climate change.

Critics who argue that climate change is not real or not affected by human activity have vocally attacked the concept of anthropogenic (human-caused) warming since the 1980s. (Many of the critics are not qualified scientists and their opinions have had little influence in the scientific community.) Soon after the release of the first installment of the 2007 IPCC report, such critics attacked the document as a panic-inducing hoax. Insistent refusal to accept a scientific or historical claim in the face of overwhelming physical evidence and near-universal expert agreement is sometimes referred to as denialism. Deniers are, in general, different from skeptics, who make reasoned, fact-based arguments to support their doubts. Some scientific skeptics have challenged parts of the mainstream scientific community's views about climate change. Although outnumbered by scientists who affirm the mainstream view that climate change is real, mostly human-caused, and dangerous, these scientific skeptics are a valuable part of the scientific process. Also, many scientists criticized the Assessment Report as being watered down at the behest of governments resistant to acknowledging the dangers of climate change. Criticisms from all three categories are reviewed below.

Criticism by Climate-Change Deniers

The most criticized section of the 2007 IPCC Assessment Report has been the Physical Science Basis section. Shortly after the release of the report's “Summary for Policymakers” in early 2007, numerous Web sites ran commentaries that attacked the document as nonscientific propaganda. For example, Cybercast News Service ran the headline “UN Climate Summary Designed to Dupe, Critics Say” (February 2, 2007). Some climate-change denial groups are funded by corporations seeking to influence public opinion against the reality or urgency of climate change. For example, in 2006, the British Royal Society (the United Kingdom's national scientific academy) stated that the oil company ExxonMobil had distributed several million dollars to 36 groups in the United States alone—groups that, the society said in a letter to the company, “have been misinforming the public about the science of climate change.” In early 2007, the American Enterprise Institute, a think tank that received over $1.8 million from ExxonMobil from 1998 to 2006, offered $10,000 apiece to any scientist or economist who could produce an essay calling the IPCC's Physical Science Basis report into question. As of late 2007, it did not appear that any papers by authors receiving this bounty had yet been published in peer-reviewed scientific journals.


ANTHROPOGENIC: Made by people or resulting from human activities. Usually used in the context of emissions that are produced as a result of human activities.

DENIALISM: Insistent refusal to accept a scientific or historical fact in the face of overwhelming physical evidence and near-universal expert agreement.

GREENHOUSE GASES: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth's surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth's atmosphere, causing global warming and global climate change.

SKEPTICISM: Doubt about the truth of a claim. Skepticism, as opposed to denialism, may have a reasonable basis: in fact, skepticism is essential to the scientific process of discovering new knowledge, in which claims are carefully tested before being accepted as correct.

Scientific Criticism that IPCC Is Pessimistic

A prominent scientific critic of the IPCC's 2007 Assessment Report is Christopher Landsea. Landsea, a meteor-ologist who has worked with the U.S. National Oceanic and Atmospheric Administration (NOAA) and the National Hurricane Center (NHC), announced in early 2005 that he was withdrawing as a participant in the IPCC on the grounds that, as he stated in an open letter, he had “come to view the part of the IPCC to which my expertise is relevant as having become politicized.” Specifically, Landsea stated that fellow lead author Kevin Trenberth used his IPCC position to “promulgate to the media and general public his own opinion that the busy 2004 hurricane season was caused by global warming, which is in direct opposition to research written in the field and is counter to conclusions in the [IPCC's 2001 Assessment Report].” Landsea contends that global warming has had no demonstrable affect on hurricane activity so far and that “studies that any impact in the future from global warming upon hurricane (s) will likely be quite small.”

Landsea has not questioned other aspects of the 2,700-page IPCC report and has not argued that global warming is not real, or that it is not mostly human-caused, or that changes in human behavior cannot affect its future course. In this regard, Landsea's criticism of the IPCC is typical of the majority of scientific climate skeptics: these skeptics question specific points, but rarely argue that human-caused climate change is an illusion.

Landsea's protest may have had an effect: the final version of the 2007 IPCC report did not assert that anthropogenic global warming was definitely responsible for increased hurricane severity. It also noted that “[t]here is no clear trend in the annual numbers” of hurricanes. Some scientists have published data later in 2007, however, showing that hurricane intensity and frequency may have increased over the last century as a result of anthropogenic ocean warming.

Scientific Criticism that the IPCC Is Optimistic

Most criticisms by scientists have complained of over-optimism or the censorship of controversial language. For example, the IPCC's relatively low estimates for future sea-level rise resulting from global warming—at most 23 in (59 cm) in the twenty-first century—have been widely criticized as omitting post-2005 data on the accelerated melting of the Greenland ice sheet. (All scientific papers published after December 2005 were excluded during preparation of the 2007 report.) Uncertainties about future sea-level rise remain large because the current and future behavior of the large ice sheets of Antarctica and Greenland—which contain enough water to raise sea levels by hundreds of feet, though they are very unlikely to melt completely—is still poorly understood.

Recent evidence shows that sea-level rise could easily be greater, some critics claim, than the range indicated by the IPCC. A May 2007 paper in the journal Science by Stefan Rahmstorf and colleagues found that the IPCC's predictions of climate change since 1990 had tended to underestimate future change (now past change): both sea level and average global temperature have risen faster than predicted.

The scenarios or possible-future storylines used by the IPCC to forecast possible impacts of global warming have been questioned by many economists, according to the journal Nature (2006). These critics argue that the scenarios rely on outdated economic theories and do not accurately describe how the economies of poor countries will probably change in the future. This, in turn, they say, flaws the report's predictions of the impacts of climate change on those countries.

News outlets have reported that in some cases, governments have had language, of which they disapproved, removed from the final draft of the report. Saudi Arabia and China had a sentence removed that stated that the human impact on Earth's heat balance is fivefold greater than the impact of variations in the sun's heat output. (According to one of the IPCC's lead authors, the difference is actually about tenfold.) The United States and China had a sentence removed that said it would not be possible to simply adapt to all the consequences of climate change, but that action would have to be taken to reduce climate change itself. The sentence read, “Mitigation measures will therefore also be required.”

According to the English organizational analyst and official reviewer of the IPCC Physical Science Basis report, David Wasdell, the involvement of government officials in approving IPCC documents “carries within its structure a conflict of interests which lays it open to the charge of collusion in the management of scientific analysis of climate change.” This, Wasdell argues, led to the deletion of many statements in the draft of the Physical Science Basis report that would have made climate change appear more rapid, dangerous, or urgent to remedy. References to positive feedbacks and acceleration of climate change were, he says, systematically deleted. For example, a draft paragraph emphasizing that positive feedback from increased water vapor might produce a “40-50% amplification of global mean warming” appeared in the draft but not in the final version.

Other Criticisms

Some government officials have disagreed with the conclusion of the third part of the 2007 report (Mitigation of Climate Change) that expenditure of 3% of the world's economic product on mitigating (reducing) climate change would be acceptable, reducing world economic growth by less than 0.2%. James Connaughton, chairman of the White House Council on Environmental Quality, stated that a reduction in GDP (gross domestic product) of 3% could lead to a global recession.

Impacts and Issues

In outline, the IPCC's view of global warming as expressed in the 2007 Assessment Report is agreed upon by the great majority of the world's climate and weather scientists. The National Academy of Sciences, the American Meteorological Society, the American Geophysical Union, the American Association for the Advancement of Science, and numerous other scientific groups around the world have affirmed its basic points: climate change is real, mostly human-caused, and can be mitigated by our decisions. The IPCC states a minimum, centrist, or consensus view, not a fringe, radical, or extreme view.

If all or most scientific criticisms of the IPCC are correct, then the report does not significantly or systematically exaggerate the scale or hazards of climate change, although its 2,700-plus pages probably contain some relatively minor errors. By omitting statements that provoke disagreement not only from scientists but from government officials, many appointed by governments that are reluctant to act on climate change, the IPCC has been more likely to err on the side of understatement than on that of panic or exaggeration. Its statements are the minimum common ground on which a wide range of participants with sometimes conflicting interests have been able to agree. Despite this conservatism, its statements that human-caused climate change is “unequivocal,” that some impacts of climate change may be severe, and that action in the near future can mitigate those impacts have altered the global discourse on climate change.

Discussion of a possible fifth Assessment Report has already begun, probably to be released in or about 2013. The 2007 report is therefore certain to dominate global discussion of climate change for years to come, whatever its limitations.

See Also Climate Change Skeptics; IPCC Climate Change 2007 Report; IPCC Climate Change 2007 Report: Impacts, Adaptation and Vulnerability; IPCC Climate Change 2007 Report: Mitigation of Climate Change; IPCC Climate Change 2007 Report: Physical Science Basis.



Metz, B., et al, eds. Climate Change 2007: Mitigation of Climate Change: Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Parry, M. L., et al, eds. Climate Change 2007: Impacts, Adaptation and Vulnerability: Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Solomon, S., et al, eds. Climate Change 2007: The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.


Biello, David. “Conservative Climate: Consensus Document May Understate the Climate Change Problem.” Scientific American (March 18, 2007).

Dean, Cornelia. “Even Before Its Release, World Climate Report Is Criticized as Too Optimistic.” The New York Times (February 2, 2007).

Eilperin, Juliet. “U.S., China Got Climate Warnings Toned Down.” The Washington Post (April 7, 2007).

Oreskes, Naomi. “The Scientific Consensus on Climate Change.” Science 306 (2004): 1686.

Pearce, Fred. “Climate Report Was ‘Watered Down.’” New Scientist (March 10, 2007): 10.

Rahmstorf, Stefan, et al. “Recent Climate Observations Compared to Projections.” Science 316 (2007): 709.

Sample, Ian. “Scientists Offered Cash to Dispute Climate Study.” The Guardian (February 2, 2007).

Web Sites

Landsea, Christopher. “An Open Letter to the Community from Chris Landsea.” The Lavoisier Group,January17, 2005. <http://www.lavoisier.com.au/papers/articles/landsea.html> (accessed October 9, 2007).

Mooney, Kevin. “UN Climate Summary Designed to Dupe, Critics Say.” CNSNews.com, February 2, 2007. <http://www.cnsnews.com/ViewCulture.asp?Page=/Culture/archive/200702/CUL20070202a.html> (accessed October 9, 2007).

Larry Gilman

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