Climate change report will point a finger at humans

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A landmark report from the world's top climate scientists this week is likely to say with heightened certainty that humans are behind the planet's rising temperatures, and that surface temperatures are not the only indicators of climate change.

Senior scientist Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colo., who was a review editor on the report, says other signs that bear witness to changes include shrinking Arctic sea ice, melting Greenland ice, warming oceans (especially the deep ocean) and sea-level rise.

This will help "defuse the issue of the supposed hiatus in global warming," which Trenberth says really isn't a hiatus at all. The leveling off of average surface temperatures since 1998 is what some are calling a "hiatus" or "pause" in global warming, but that's due in part to the fact that 1998 was such an unusually warm El Nino year. El Nino is a periodic natural warming of Pacific Ocean water that affects global weather patterns.

Also, much of the heat may be sinking into the deep oceans, according to a study released earlier this year.

One of the expected conclusions of the report to be released Friday in Stockholm from the Intergovernmental Panel on Climate Change — the international group that assesses the science related to climate change and its impacts — is that there's 95% certainty that man-made global warming is real. A 2007 IPCC report put the confidence level at about 90%.

The report, the fifth the group has produced since it was established in 1988 by the United Nations, is likely to be the most thorough study ever written on the science behind climate change. Reports are issued every few years and are a synthesis of the research published in the years since the last report.

The report is the work of more than 2,000 scientists, whose drafts were reviewed by scores of governments, industry and environmental groups. "I know of no other document that has undergone this scrutiny," Thomas Stocker, co-chairman of the working group that wrote the report, said this week from Stockholm. "It stands out as a reliable and indispensable source of knowledge about climate change."

The primary U.S. agency that deals with climate and weather also praises the expertise of the IPCC: "The periodic IPCC assessments are widely considered the world's most comprehensive and authoritative assessment of climate change," says Brady Phillips, a spokesman with the National Oceanic and Atmospheric Administration.

"They synthesize our scientific understanding about how Earth's climate system works, project changes over time and discuss potential impacts and mitigation measures," he adds.

The report being completed in Stockholm deals with the physical science aspects of the climate system and is the first of a four-part assessment that covers several aspects of global warming.

Will the report have any influence on U.S. policy as it relates to climate change? "Not really," Trenberth predicts. He adds that those who matter in the administration are well informed, but that those in Congress who don't believe in global warming won't budge.

Contributing: Associated Press