BANGKOK, Thailand - Delegates from 120 countries approved the first roadmap for stemming greenhouse gas emissions today, laying out what they said was an affordable arsenal of anti-warming measures that must be rushed into place to avert a disastrous spike in global temperatures.

But a U.S. official raised concern about the economic costs.

The report, a summary of a study by a U.N. network of 2,000 scientists, said the world has to make significant cuts in gas emissions through increasing the energy efficiency of buildings and vehicles, shifting from fossil fuels to renewable fuels, and reforming both the forestry and farming sectors.

The document made clear that nations have the technology and money to decisively act in time to avoid a sharp rise in temperatures that scientists say would wipe out species, raise ocean levels, wreak economic havoc and trigger droughts in some places and flooding in others.

Under the most stringent scenario, the report said the world must stabilize the amount of greenhouse gases in the atmosphere by 2015 - eight years from now - at 445 parts per million to keep global temperatures from rising more than 3.6 degrees over preindustrial levels.

Delegates said the approval of the report should conclusively debunk arguments by skeptics that combatting global warming was too costly, that it would stifle development in poorer countries, or that the temperature rise had gone too far to change.

"If we continue doing what we are doing now, we are in deep trouble," said Ogunlade Davidson, the co-chair of group responsible for finalizing the report this week.

Delegates hailed the policy statement as a key advance toward battling global warming and setting the stage for an even stronger international agreement to replace the 1997 Kyoto Protocol on greenhouse emissions when it expires in 2012.

"It's stunning in its brilliance and relevance," Rajendra Pachauri, chair of the group responsible for the report, the Intergovernmental Panel on Climate Change, said of the study. "It's a remarkable step forward."

"Clearly, the signs that the IPCC assess will have a direct and profound influence on the discussion that take place and the direction toward [a post-Kyoto] agreement," he said.

The United States was pleased that the report "highlights the importance of a portfolio of clean energy technologies consistent with our approach," said the head of the U.S. delegation, Harlan Watson.

But James Connaughton, chairman of the White House Council on Environmental Quality, raised concerns about reaching the lowest emission targets proposed in the report, saying "it would cause a global recession."

"Our goal is reducing emissions and growing the economy," he said.

Coming out of the meeting, delegates said science appeared to have trumped politics - especially opposition from booming China, which wanted language inserted allowing for a greater buildup of greenhouse gases in the environment before action would be taken.

Beijing, the second-largest emitter after the United States, and its supporters had argued that moves to make deep cuts in carbon dioxide emissions risked stifling its spectacular economic growth, delegates said. But the final report included mention of a stringent emission target from an earlier draft.

Zhou Dadi, a Chinese author in the report and a researcher at the country's top planning agency, denied China had "opposed" the key findings and was only working to improve the text.

"The Chinese government was constructive and was contributing to making the report reflect the science," Zhou said. "We are not threatened by the report."

In Europe, several countries and the European Union welcomed the report.

"The report shows - and this is encouraging - that ambitious climate protection is economically manageable," German government spokesman Ulrich Wilhelm said.

At a briefing in Berlin, the U.N.'s top climate change official, Yvo de Boer, said the report "clearly rebuts fears that economic development and wealth conflict with active protection of the climate."

Delegates had wrestled over how to share the burden of cutting emissions, how much such measures would cost, and how much weight to give certain policy measures, such as advanced nuclear power, an option supported by the United States.

For many delegates, the strongest message was that reaching the lowest targets could be done at less than 3 percent of the global gross domestic product by 2030 - or 0.12 annually.

That compares favorably to global economic growth that every year has averaged almost 3 percent since 2000. The damage from unabated climate change, meanwhile, might eventually cost the global economy between 5 percent and 20 percent of GDP every year, according to a British government report last year.

"I would say it [the GDP estimates] looks like a reasonable risk to take, compared to the impact of projected climate change," said Jayant Sathaye, a scientist at the Lawrence Berkeley National Laboratory in California.

The report follows two studies by the IPCC earlier this year warning that unabated greenhouse gas emissions could drive global temperatures up as much as 11 degrees by 2100, triggering a surge in ocean levels, destruction of vast numbers of species, economic devastation in tropical zones and mass human migrations.

Even the most stringent efforts outlined in the report, however, would not prevent suffering. An increase in temperatures to 3.6 degrees could still subject up to 2 billion people to water shortages by 2050 and threaten extinction for 20 percent to 30 percent of the world's species, the IPCC said.

Environmental groups 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."