Grim Climate Predictions Not Exaggerated, Analysis Says

John Roach
for National Geographic News
February 1, 2007
Tomorrow the United Nations-backed Intergovernmental Panel on Climate
Change (IPCC) will release a major report with grim predictions about
global warming for the coming decades, according to journalists who have
seen draft versions of the paper.

If the IPCC's recent track record is any indication, the predictions will be no exaggeration, an analysis posted today on the Web site of the journal Science suggests.

The Science study compared actual climate measurements with the computer models from a 2001 IPCC report.

In recent years actual concentrations of carbon dioxide—a greenhouse gas linked to global warming—have followed almost exactly the projections of the 2001 IPCC report.

If anything, the IPCC may have underestimated some climate threats in 2001. For example, actual temperatures were at the high end of the predicted range. And sea levels have actually risen faster than predicted.

"The real climate system is changing as fast or in some components even faster than expected by [the] IPCC," Stefan Rahmstorf, an ocean physicist at Potsdam University in Germany, said by email.

Rahmstorf is the Science study's lead author. He is also among the scientists gathered in Paris to finalize the IPCC's 2007 assessment report.

Friday's study will be the fourth report compiled by the IPCC since the United Nations and World Meteorological Organization established the panel in 1988. Hundreds of scientists contribute to each report.

Richard Alley is a glaciologist at Pennsylvania State University who was not involved in the Science study but is an IPCC report author.

The study vindicating the 2001 report is "great and important," Alley said in an email from Paris.

"There has long been a muttering, out in the blogosphere and other places, that the scientists have been exaggerating and trying to scare people so as to generate more research money," he said.

"If you wish to accuse scientists of systematic error, Rahmstorf et al show that we have been a bit conservative, and clearly not alarmist," Alley added.

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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