Confidence Melting Away: Can Climate Forecasts Still Be Trusted?

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For years, malaria expert Paul Reiter of the Paris-based Pasteur Institute has criticized the warning, as expressed in the third IPCC report, that climate change will lead to the spread of malaria, saying that there is no evidence to support such a claim. Reiter accuses many climatologists of perceiving themselves too strongly as activists who are more interested in spreading an alarmist message.

Scientists already feel that the second part of the IPCC report, which addresses the consequences of global warming, is not as sound as the first part, which deals with the underlying physical factors contributing to climate change. This could, in fact, explain how the erroneous Himalayan prognosis slipped into the report in the first place. The report's lead author, Murari Lal, defends himself by saying that "the melting of the glaciers is such a huge threat to so many people" and, for that reason, had to be included in the report. According to malaria researcher Reiter, it is precisely this passion that is so dangerous to science.

The e-mails hackers stole from the Climatic Research Unit at the University of East Anglia last November and placed on the Internet have also provided critics with new ammunition. An e-mail exchange between climate modelers that took place in the fall of 1999 suggests that the scientists were biased.

Abnormal Temperature Graph

The exchange involved the validity of a controversial temperature curve. The so-called hockey stick graph was intended to prove that the average global temperature in the last 1,000 years was never as high as it is today. To arrive at the date, several groups of researchers reconstructed past temperatures, to a large extent based on tree-ring data.

But one of the graphs differed markedly from the rest, leading to a controversy in the run-up to a conference of paleo-climatologists in Tanzania in September 1999. The abnormal temperature graph was "a problem and a potential distraction/detraction from the reasonably consensus viewpoint we'd like to show," paleo-climatologist Michael Mann wrote in an e-mail, adding that he didn't want to be the one to offer "the skeptics … a field day." The lead author of the IPCC chapter, Chris Folland, wrote in another e-mail that the divergent data set "dilutes the message rather significantly."

Keith Briffa, whose team reconstructed the contradictory temperature graph, was furious, and wrote: "I know there is pressure to present a nice tidy story as regards 'apparent unprecedented warming in a thousand years or more in the proxy data.'"

For the IPCC report that was written at the time, the scientists eventually resorted to an underhanded solution to downplay the data behind Briffa's graph, which showed temperatures falling since the 1960s: the graph was simply cut off at 1960 in the IPCC report. "This sort of approach is considered problematic in science," says climate scientist Storch.

Controversial Passages

Briffa's unusually declining temperature graph points to a serious conundrum that no one has been able to explain yet: Since the 1960s, the tree-ring data no longer reflect actual temperature changes. But why, then, should tree-ring data be valid for periods before that?

At least the fourth IPCC report, published in 2007, discusses the problems with the tree-ring data at length. But even the current, valid report contains controversial passages.

Chapter 1.3.8, for example, contains a discussion of the possible relationship between climate change and the increased incidence of natural disasters, which, after Hurricane Katrina in the United States, have now become a politically charged issue.

At the IPCC report, the damage associated with such events "are very likely to increase due to increased frequencies and intensities of some extreme weather events" (italics in original). The report cites as evidence a study that supposedly demonstrates precisely this trend.

The only problem is that the study in question had not been subjected to outside peer review before the IPCC report went to press. This has since been done, and the conclusions are surprising: "We find insufficient evidence to claim a statistical relationship between global temperature increase and normalized catastrophe losses," read the report published in the compendium "Climate Extremes and Society."

Roger Pielke, a leading expert in this field, wrote in his blog: "The claims were not just wrong. The claims were based on knowledge that just doesn't exist."

Calculating Risk

Representatives of the insurance industry hold a completely different view, which presents an additional problem for the IPCC. Reinsurers, such as Munich Re, calculate their premiums on the basis of risk, so that an increase in the frequency and severity of natural disasters can translate into additional profits when new policies are concluded.

"We see, in our databases, significant evidence for a correlation between climate change and the increase in natural disasters," says Ernst Rauch, director of German insurer Munich Re's "Corporate Climate Centre." Unlike scientists, he adds, the insurance industry cannot wait until all doubts have been set aside. "We are a business operation that has to act today," says Rauch. He also points out that his company is "extremely satisfied" with the conclusions of the IPCC report. This is hardly surprising: A 2005 publication by Munich Re served as one of the sources for the IPCC's cautionary predictions.

Climatologists are now calling for reforms. Pielke, for example, is concerned about the way authors and peer reviewers work, how they are appointed by the IPCC and how literature is used that, as in the case of the Himalayan glacier, does not come from peer-reviewed professional journals.

One of the problems is that working for the IPCC is a time-consuming honorary appointment for scientists. "This means that it is not always the best people in their field who are willing to contribute their time and effort," says epidemiologist Reiter.

On the other hand, the community is sometimes reluctant to include troublesome critics in its efforts. For instance, when the IPCC recently set up a special working group to address natural disasters, the US government nominated ecologist Pielke. The IPCC declined to appoint him.

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• Part 1: Can Climate Forecasts Still Be Trusted?
• Part 2: New Ammunition from an E-Mail Scandal