Grim Climate Predictions Not Exaggerated, Analysis Says

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Grim Within Reason

According to Potsdam University's Rahmstorf, the main message of the brief Science analysis posted today is to counter claims that the IPCC paints "unduly grim future scenarios.

"Unfortunately, this is not true," he added.

Media reports based on early drafts of the IPCC assessment due Friday indicate that it predicts a transformed planet due to climate change.

Among the reported projections: more frequent damaging storms, disappearing mountain glaciers, acidic oceans, and destroyed coral reefs (photo gallery: melting glaciers).

The report is also expected to say these changes are mostly due, with a 90 percent certainty, to human-caused emission of greenhouse gases.

"I hope this report will shock people, governments into taking more serious action," Rejendra Pachauri, the IPCC chairman, told the Reuters news agency last week.

Too Conservative?

Rahmstorf also noted what may be the upcoming report's Achilles heel.

The models summarized in the IPCC report fail to incorporate the recent instability of ice sheets in Greenland and Antarctica, which affects sea level. (See "Greenland Ice Sheet Is Melting Faster, Study Says" [August 10, 2006].)

"While the ice sheet contribution [to rising sea levels] has been small, observations are indicating that [the role of ice sheets in determining sea levels] is rapidly increasing," Rahmstorf and colleagues write in the Science article.

Penn State's Alley said the IPCC literature review process prevented the inclusion of these recent observations in the upcoming assessment report because the deadline has passed.

"This does make the assessment slightly out of date when it comes out," Alley said. But having a relatively early submission deadline "improves quality control and enhances the believability" by allowing hundreds of scientists time to pore over the data, he added.

Konrad Steffen, a professor of geography at the University of Colorado, studies how melting ice sheets and glaciers contribute to sea level rise.

He said in an email that the exclusion of the latest ice observations will make the IPCC's sea level predictions "too conservative."

But Rahmstorf said he expects the IPCC report to acknowledge the "well-recognized uncertainty about future ice sheet behavior."

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