Archive for Friday, February 2, 2007

Report: Global warming ‘very likely’ caused by humans

February 2, 2007

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— The world's leading climate scientists said global warming has begun, is "very likely" caused by man and will be unstoppable for centuries, according to a report obtained today by The Associated Press.

The scientists - using their strongest language yet on the issue - said now that the world has begun to warm, hotter temperatures and rises in sea level "would continue for centuries" no matter how much humans control their pollution. The report also linked the warming to the recent increase in stronger hurricanes.

"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 report by the Intergovernmental Panel on Climate Change - a group of hundreds of scientists and representatives of 113 governments.

The phrase "very likely" translates to a more than 90 percent certainty that global warming is caused by man's burning of fossil fuels. That was the strongest conclusion to date, making it nearly impossible to say natural forces are to blame.

What that means in simple language is "we have this nailed," said top U.S. climate scientist Jerry Mahlman, who originated the percentage system.

The 20-page report, which was due to be officially released later in the day, represents the most authoritative science on global warming.

The new language 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 say it is "virtually certain" man causes global warming, which translates to 99 percent certainty.

The panel predicted temperature rises of 2-11.5 degrees Fahrenheit by the year 2100. That was a wider range than in the 2001 report.

However, the panel also said its best estimate was for temperature rises of 3.2-7.1 degrees Fahrenheit. In 2001, all the panel gave was a range of 2.5-10.4 degrees Fahrenheit.

On sea levels, the report projects rises of 7-23 inches by the end of the century. An additional 3.9-7.8 inches are possible if recent, surprising melting of polar ice sheets continues.

But there is some cold comfort. Some, but not all, of the projected temperature and sea level rises are slightly lower than projected in the report in 2001. That is mostly due to use of more likely scenarios and still would result in dramatic effects across the globe, scientists said.

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

Nevertheless, scientists agreed 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 and consensus.

"It's very conservative. Scientists by their nature are skeptics," he said.

The scientists wrote the report based on years of peer-reviewed research and 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 the role of man in global warming.

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