Greenpeace activists wrap the Zouave statue, used as a popular gauge of whether the Seine River is running high, Friday in Paris. The banner and wrapping tape, inscribed with its-not-too-late.com, refers to a future Greenpeace-sponsored Web site aimed at raising awareness about climate change. The words of warning about global warming from the top panel of international scientists Friday warned that global warming is so severe it will continue

Paris ? Global warming is so severe that it will “continue for centuries,” leading to a far different planet in 100 years, warned a grim landmark report from the world’s leading climate scientists and government officials. Yet, many of the experts are hopeful that nations will now take action to avoid the worst scenarios.

They tried to warn of dire risks without scaring people so much they’d do nothing – inaction that would lead to the worst possible scenarios.

“It’s not too late,” said Australian scientist Nathaniel Bindoff, a co-author of the authoritative Intergovernmental Panel on Climate Change report issued Friday. The worst can be prevented by acting quickly to curb greenhouse gas emissions, he said.

The worst could mean more than 1 million dead and hundreds of billions of dollars in costs by 2100, said Kevin Trenberth of the National Center for Atmospheric Research in Colorado, one of many study co-authors. He said that adapting will mean living with more extreme weather such as severe droughts, more hurricanes and wildfires.

“It’s later than we think,” said panel co-chairwoman Susan Solomon, the U.S. National Oceanic and Atmospheric Administration scientist who helped push through the document’s strong language.

Solomon, who remains optimistic about the future, said it’s close to too late to alter the future for her children – but maybe it’s not too late for her grandchildren.

The report was the first of four to be released this year by the panel, which was created by the United Nations in 1988.

The report spurred bleak reactions from world leaders.

“We are on the historic threshold of the irreversible,” warned French President Jacques Chirac, who called for an economic and political “revolution” to save the planet.

“While climate changes run like a rabbit, world politics move like a snail: Either we accelerate or we risk a disaster,” said Italy’s environment minister, Alfonso Pecoraro Scanio.

And South Africa’s Environmental Affairs Minister, Marthinus van Schalkwyk, said failure to act would be “indefensible.”

In Washington, Bush administration officials praised the report but said they still oppose mandatory cuts in greenhouse gas emissions. The problem can be addressed by better technology that will cut emissions, promote energy conservation and hasten development of nonfossil fuels, said Energy Secretary Samuel Bodman.