MADRID, Spain - Emerging economies such as China are justified in holding back on fighting greenhouse gas emissions until richer polluters like the United States do more to solve the problem, former Vice President Al Gore said Wednesday.

The world's top climate scientists warned in a report last week that global warming was very likely caused by humanity and would last for centuries.

Chinese officials said they would act after industrial countries such as the United States and others make changes themselves, Gore said, addressing a conference in Madrid on global warming.

"They're right in saying that. But we have to act quickly," said Gore, who was nominated last week for a Nobel Peace Prize for his work in drawing attention to global warming.

"China's reaction to the scientific report last week was disappointing, but it was instructive," Gore said.

The United States is the world's leading emitter of greenhouse gas and has refused to ratify the 1997 Kyoto Protocol on curbing such emissions. President Bush contended that it would slow the U.S. economy intolerably and that it should have required reductions by poorer but fast-growing nations, such as China and India.

Gore narrated an hourlong slide presentation with graphic evidence of global warming: Antarctic ice shelves cracking and collapsing into the sea, before-and-after shots of glaciers reduced to lakes and small patches of ice, and forecasts of heavily populated land masses such as Florida shrinking drastically if glacial meltdown reaches a worst-case scenario and floods the seas.

"Never before has all of civilization been threatened," Gore said. "We have everything we need to save it, with the possible exception of political will. But political will is a renewable resource."