Secretary General Ban Ki-moon, describing climate change as "the defining challenge of our age," released the final report of a UN panel on climate change here yesterday and called on the United States and China to play "a more constructive role."

..."If there's no action before 2012, that's too late," said Rajendra Pachauri, a scientist and economist who heads the IPCC. "What we do in the next two to three years will determine our future."

He said that since the IPCC began its work five years ago, scientists have recorded "much stronger trends in climate change," like a recent melting of polar ice that had not been predicted. "That means you better start with intervention much earlier."