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Humans ‘Very Likely’ Cause of Global Warming, Report Warns February 2, 2007

Posted by Dan in Main, Must Read, News, Politics, Science, Technology.
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NY Times Reporter Andrew C. Revkin brings some great insight:

PARIS, France (AP) — The world’s leading climate scientists, in their most powerful language ever used on the issue, said global warming is “very likely” man-made, according to a new report obtained Friday by The Associated Press.

The report provides what may be cold comfort in slightly reduced projections on rising temperatures and sea levels by the year 2100. But it is tempered by a flat pronouncement that global warming is essentially a runaway train that cannot be stopped for centuries.

“The observed widespread warming of the atmosphere and ocean, together with ice-mass loss, support the conclusion that it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing, and very likely that is not due to known natural causes alone,” said the 20-page report.

Human-caused warming and rises in sea-level “would continue for centuries” because the process has already started, “even if greenhouse gas concentrations were to be stabilized,” said the 20-page report from the Intergovernmental Panel on Climate Change.

The report by a group of hundreds of scientists and representatives of 113 governments contains the most authoritative science on the issue. It was due for official release later Friday morning in Paris.

The phrase “very likely” translates to a more than 90 percent certainty that global warming is caused by man.

What that means in layman’s language is “we have this nailed,” said top U.S. climate scientist Jerry Mahlman, who originated the percentage system.

It marked an escalation from the panel’s last report in 2001, which said warming was “likely” caused by human activity. There had been speculation that the participants might try to up the ante to “virtually certain” man causes global warming, which translates to 99 percent chance.

On sea levels, the report projects rises of 7-23 inches by the end of the century. That could be augmented by an additional 4-8 inches if recent surprising polar ice sheet melt continues.

The 2001 report projected a sea level rise of up to 35 inches.

Many scientists had warned that this was being too cautious and said sea level rise could be closer to 3 to 5 feet because of ice sheet melt.

But despite losing on that battle, scientists said the report is strong.

“There’s no question that the powerful language is intimately linked to the more powerful science,” said one of the study’s many co-authors, Andrew Weaver of the University of Victoria, who spoke by phone from Canada. He said the report was based on science that is rock-solid, peer-reviewed, conservative and consensus.

“It’s very conservative. Scientists by their nature are skeptics.”

The scientists wrote the report, based on years of peer-reviewed research; government officials edited it with an eye toward the required unanimous approval by world governments.

In the end, there was little debate on the strength of the wording about human activity most likely to blame.

“That is a big move. I hope it is a powerful statement,” said Jan Pretel, head of the department of climate change at the Czech Hydrometeorological Institute.

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