PARIS – Scientists from 113 countries issued a landmark report Friday saying they have little doubt global warming is caused by man, and predicting that hotter temperatures and rises in sea level will "continue for centuries" no matter how much humans control their pollution.
A top U.S. government scientist, Susan Solomon, said "there can be no question that the increase in greenhouse gases are dominated by human activities."
Environmental campaigners urged the United States and other industrial nations to significantly cut their emissions of greenhouse gases in response to the long-awaited report by Intergovernmental Panel on Climate Change.
"It is critical that we look at this report ... as a moment where the focus of attention will shift from whether climate change is linked to human activity, whether the science is sufficient, to what on earth are we going to do about it," said Achim Steiner, the executive director of the U.N. Environment Program.
"The public should not sit back and say 'There's nothing we can do'," Steiner said. "Anyone who would continue to risk inaction on the basis of the evidence presented here will one day in the history books be considered irresponsible."
The 21-page report represents the most authoritative science on global warming as the panel comprises hundreds of scientists and representatives.
It only addresses how and why the planet is warming, not what to do about it.
Another report by the panel later this year will address the most effective measures for slowing global warming.
One of the authors, Kevin Trenberth, said scientists are worried that world leaders will take the message in the wrong way and throw up their hands.
Instead, world leaders should reduce emissions and adapt to a warmer world with wilder weather, he said.
"This is just not something you can stop. We're just going to have to live with it," said Trenberth, the director of climate analysis for the National Center for Atmospheric Research in Boulder, Colo. "We're creating a different planet. If you were to come up back in 100 years time, we'll have a different climate."
The scientists said global warming was "very likely" caused by human activity, a phrase that translates to a more than 90 percent certainty that it 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.
It also said no matter how much civilization slows or reduces its greenhouse gas emissions, global warming and sea level rise will continue on for centuries.
"Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level," the scientists said.
The report blamed man-made emissions of greenhouse gases for fewer cold days, hotter nights, killer heat waves, floods and heavy rains, devastating droughts, and an increase in hurricane and tropical storm strength — particularly in the Atlantic Ocean.
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.
Hays stopped short of saying whether or how the report could bring about change in President Bush's policy about greenhouse gas emissions.
The panel predicted global average temperature rises of 2 to 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 to 7.1 degrees Fahrenheit. In 2001, all the panel gave was a range of 2.5 to 10.4 degrees Fahrenheit.
On sea levels, the report projects rises of 7 to 23 inches by the end of the century. An additional 3.9 to 7.8 inches are possible if recent, surprising melting of polar ice sheets continues.
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 point here is to highlight what will happen if we don't do something and what will happen if we do something," said another author, Jonathan Overpeck at the University of Arizona. "I can tell if you will decide not to do something the impacts will be much larger than if we do something."
As the report was being released, environmental activists repelled off a Paris bridge and draped a banner over a statue used often as a popular gauge of whether the Seine River is running high.
"Alarm bells are ringing. The world must wake up to the threat posed by climate change," said Catherine Pearce of Friends of the Earth.
Stephanie Tunmore of Greenpeace said "if the last IPCC report was a wake up call, this one is a screaming siren."
"The good news is our understanding of the climate system and our impact on it has improved immensely. The bad news is that the more we know, the more precarious the future looks," Tunmore said in a statement. "There's a clear message to governments here, and the window for action is narrowing fast."