American officials questioned the economic cost, and the Chinese questioned whether fast results could be achieved. But a leading expert said there was little choice.
"If we continue doing what we are doing now, we are in deep trouble," said Ogunlade Davidson, co-chairman of the U.N.-sponsored group that produced the report, approved by consensus by more than 120 nations Friday at the end of a weeklong meeting.
A 35-page summary of a 1,000-plus-page study, the report said the world must significantly cut emissions of carbon dioxide and other greenhouse gases by sharply improving energy efficiency in buildings, vehicles and even kitchen appliances; shifting from fossil fuels to nuclear, wind, solar and other renewable energy sources; saving forests as "carbon sinks"; capping agricultural emissions, and taking many other steps.
The document says the world has the technology and wealth now to act decisively in time to avoid a sharp rise in temperatures that scientists say would wipe out species, raise ocean levels, trigger droughts in some places and flooding in others, and wreak economic havoc.
The assessment by the Intergovernmental Panel on Climate Change builds on reports by two other IPCC working groups issued earlier this year, which said unabated emissions from power plants, auto exhausts and other sources could drive global temperatures up as much as 11 degrees Fahrenheit by 2100, and reported that warming was already affecting animal and plant life.
The Working Group III study looks in detail at the most promising technologies for reining in the heat-trapping gases and at policies, such as taxes or quotas on carbon emissions, that might encourage development of those technologies. It also looks how much that might cost economies.
It estimates the world must stabilize the amount of greenhouse gases in the atmosphere by 2015 at 445 parts per million to keep global temperatures from rising 3.6 degrees Fahrenheit above preindustrial levels. Scientists fear temperatures higher than that might cause severe damage. Current atmospheric concentrations are believed to have passed 400 parts per million.
Delegates hailed this latest assessment, the first by IPCC since 2001, as setting the stage for a strong international agreement to replace the 1997 Kyoto Protocol, with its relatively weak mandated emissions cuts, when it expires in 2012.
"Clearly, the signs that the IPCC assessed will have a direct and profound influence on the discussions that take place and the direction toward (a post-Kyoto) agreement," said the IPCC chairman, climatologist Rajendra Pachauri.
The assessment offers a range of emissions scenarios showing temperatures rising as much as 9.7 degrees Fahrenheit. Under the most stringent scenario, capping concentrations at 445 ppm, the experts projected an economic loss of under 3 percent of global gross domestic product by 2030, that is, spread over 23 years.
The report acknowledges this is an improbable scenario, requiring all nations to deploy the best available technologies. And the U.S and Chinese delegations here complained that attempting to meet the stringent target would be too economically damaging.
"That would, of course, cause a global recession. So that is something we'd probably want to avoid," said James Connaughton, chairman of the White House Council on Environmental Quality. "Our goal is reducing emissions and growing the economy."
Chinese researcher Zhou Dadi, one of the summary's 33 authors, said such low targets were "unachievable" and would put an unfair burden on countries like his that are climbing out of poverty.
"If we want to change current trends so dramatically, it will not be easy," he said. "We should focus on what we can do right now. It's not good to just talk about targets."
Beijing unsuccessfully tried to strike the 445 ppm figure from the final report.
The Bush administration has rejected the Kyoto Protocol, which 35 other industrialized countries have ratified, requiring them to cut emissions by 5 percent below 1990 levels by 2012. China, India and other poorer countries are exempted from those requirements, but negotiators want cutback commitments from China and others - including Washington - in the global talks that resume this December in Bali, Indonesia.
Co-chair Davidson insisted the report offers poorer countries a roadmap to balancing economic development with cleaning up their environment. It also encourages richer countries to help developing nations with financial and technical assistance to shift away from dirty fossil fuels, he said. The summary did not attempt to estimate economic damage that might occur if the world does nothing about warming, but a British government report last year said unabated climate change might eventually cost between 5 and 20 percent of global GDP every year. Environmentalists said the report demonstrates the world can afford to battle global warming and must do so immediately. "This is a roadmap that the IPCC is delivering," said Hans Verolme of WWF International. "It's time for the politicians to do more than just pay lip service to the issue of global warming, and to stop climate change before it's too late." (AP) On the Net: IPCC Working Group III Report: http://www.ipcc.ch/SPM040507.pdf AP-CS-05-04-07 1522EDT