One of the most alarming conclusions from the Intergovernmental Panel on Climate Change (IPCC), a widely respected organization established by the United Nations, is that glaciers in the Himalayas could be gone 25 years from now, eliminating a primary source of water for hundreds of millions of people. But a number of glaciologists have argued that this conclusion is wrong, and now the IPCC admits that the conclusion is largely unsubstantiated, based on news reports rather than published, peer-reviewed scientific studies.
In a statement released on Wednesday, the IPCC admitted that the Working Group II report, "Impacts, Adaptation and Vulnerability," published in the IPCC's Fourth Assessment Report (2007), contains a claim that "refers to poorly substantiated estimates. " The statement also said "the clear and well-established standards of evidence, required by the IPCC procedure, were not applied properly." The statement did not quote the error, but it did cite the section of the report that refers to Himalayan glaciers. Christopher Field, director of the Carnegie Institution's Department of Global Ecology, who is now in charge of Working Group II, confirms that the error was related to the claim that the glaciers could disappear by 2035.
The disappearance of the glaciers would require temperatures far higher than those predicted in even the most dire global warming scenarios, says Georg Kaser, professor at the Institut für Geographie der Universität, Innsbruck. The Himalayas would have to heat up by 18 degrees Celsius and stay there for the highest glaciers to melt--most climate change scenarios expect only a few degrees of warming over the next century.
The mistake has called into question the credibility of the IPCC, which has been considered an authoritative source for information about climate change because of its policy of carefully reviewing and analyzing hundreds and even thousands of published, peer-reviewed scientific studies. But the scientists who uncovered the error say that the mistake, and the reliance on news reports and unpublished studies, is rare. "I don't think it ought to affect the credibility of the edifice as a whole," says J. Graham Cogley, professor of geography at Trent University, who was key to identifying the original sources of the information in the IPCC report.The error has been traced to the fact that the IPCC permits the citation of non-peer-reviewed sources, called "grey literature," in cases where peer-reviewed data is not available. It requires that these sources be carefully scrutinized, but that didn't happen in this case. The process has "gone spectacularly wrong in this particular instance," Cogley says.
That claim went unchallenged during the normal, multistep review process used by the IPCC. The error wasn't widely noticed until last November, when a group of scientists began discussing a new study of the Himalayan glaciers. The discussion led Cogley to look up the original sources for the claims in the IPCC report. He found two sources, a news report in the London-based magazine New Scientist about an as-yet unpublished study, and an article that estimated the glaciers could shrink to one-fifth their current area by 2350, rather than 2035, putting the IPCC report off by about 300 years. His finding is described in a letter to the editor to be published January 29 in the journal Science. Field confirms that the New Scientist was one of the sources, but not the report giving the date of 2350.
David Victor, the director of the Laboratory on International Law and Regulation at the University of California, San Diego, says that the error should not lead to a major change in the IPCC's process. "A very small fraction of IPCC reports stems from grey literature," and an outright ban on such sources would be a bad idea, since it would prevent the organization from drawing on certain types of valuable information. For example, government reports, or even raw data on greenhouse gas levels or measurements of the extent of glaciers, are often not a part of peer-reviewed literature.
Cogley recommends two main changes. First, all sources cited should be readily available to reviewers, which would have made it easier to see that the source for the 2035 date was a news report. (The IPCC report does not cite the New Scientist, but rather another document, which in turn cited the New Scientist.) Second, he says, researchers working on different parts of the IPCC report should work together more closely. Kaser says that if during the normal review process even one glaciologist of the many who worked on the Working Group I report ("The Physical Science Basis") would have carefully read the Working Group II report, the error would have been caught.
(The claim that the Himalayan glaciers could disappear within 25 years was included in the recent Technology Review feature "The Geoengineering Gambit." A correction can be found here.)
By Kevin Bullis