PARIS — 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 Friday 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.
Sharon Hays, associate director of the Office of Science and Technology Policy at the White House, welcomed the strong language of the report.
"It's a significant report. It will be valuable to policy makers," she told The Associated Press in an interview in Paris, where hundreds of scientists and government officials were meeting to discuss global warming.
Hays stopped short of saying whether or how the report could bring about change in President Bush's policy about greenhouse gas emissions.
The 20-page summary of the panel's findings, 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 a previous report in 2001. That is mostly due to use of more likely scenarios and would still 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."
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.
The panel quickly agreed Thursday on two of the most contentious issues: attributing global warming to man-made burning of fossil fuels and connecting it to a recent increase in stronger hurricanes.
Negotiations over a third and more difficult issue — how much the sea level is predicted to rise by 2100 — went into the night Thursday with a deadline approaching for the report.
While critics call the panel overly alarmist, it is by nature relatively cautious because it relies on hundreds of scientists, including skeptics.
"I hope that policymakers will be quite convinced by this message," said Riibeta Abeta, a delegate whose island nation Kiribati is threatened by rising seas. "The purpose is to get them moving."
The Chinese delegation was resistant to strong wording on global warming, said Barbados delegate Leonard Fields and others. China has increasingly turned to fossil fuels for its huge and growing energy needs.
The U.S. government delegation was not one of the more vocal groups in the debate over whether warming is man-made, said officials from other countries. And several attendees credited the head of the panel session, Susan Solomon, a top U.S. government climate scientist, with pushing through the agreement so quickly.
The Bush administration acknowledges that global warming is man-made and a problem that must be dealt with, Bush science adviser John Marburger has said. However, Bush continues to reject mandatory limits on so-called "greenhouse" gases.
But this is more than just a U.S. issue.
"What you're trying to do is get the whole planet under the proverbial tent in how to deal with this, not just the rich countries," Mahlman said Thursday. "I think we're in a different kind of game now."
The panel, created by the United Nations in 1988, releases its assessments every five or six years — although scientists have been observing aspects of climate change since as far back as the 1960s. The reports are released in phases — this is the first of four this year.
The next report is due in April and will discuss the effects of global warming. But that issue was touched upon in the current document.
The report says that global warming has made stronger hurricanes, including those on the Atlantic Ocean, such as Hurricane Katrina.
The report said that an increase in hurricane and tropical cyclone strength since 1970 "more likely than not" can be attributed to man-made global warming. The scientists said global warming's connection varies with storms in different parts of the world, but that the storms that strike the Americas are global warming-influenced.
That's a contrast from the 2001 which said there was not enough evidence to make such a conclusion. And it conflicts with a November 2006 statement by the World Meteorological Organization, which helped found the IPCC. The meteorological group said it could not link past stronger storms to global warming.
Fields — of Barbados, a country in the path of many hurricanes — said the new wording was "very important." He noted that insurance companies — which look to science to calculate storm risk — "watch the language, too."
Associated Press Writer Angela Charlton contributed to this report.
By AP/SETH BORENSTEIN from TIME
