But his high-profile commitment contrasts sharply with the Bush administration which has refused to sign up to the benchmark Kyoto treaty to combat global warming.

"I have always thought that it was a very high risk strategy for Tony Blair to put climate change so high on the G8's agenda," Victor Bulmer-Thomas, director of the Royal Institute of International Affairs think-tank, told Reuters.

"The question is -- can he persuade the United States to move closer to the European view on the environment, and the answer is 'no,'" he added.

Environmentalists insist that now is payback time. "It is time Blair used his diplomatic capital and persuaded the United States to agree to international commitments to cut greenhouse gas emissions," said Greenpeace head Stephen Tindale.

"But the signs are not good. At the moment it looks like Blair is all mouth and no trousers on climate change and that he is a serial flunker of challenges. He has yet to stand up to Bush on anything," he told Reuters.

And if Blair can't do it, no one can, Friends of the Earth head Tony Juniper said.

"If there is anyone in the world who can challenge the Bush administration's position on the environment it is him," he told Reuters. "But climate seems to be treated almost as a taboo subject in meetings between them."

The government has already scheduled a three-day climate change conference in Exeter, south western England in February, a meeting of G8 energy and environment ministers in London in March and another of environment and development ministers in central England a few days later.

The G8 summit in Scotland in July will also focus firmly on climate change.

The Kyoto treaty, derided by many as too little, too late, is aimed at cutting carbon dioxide emissions by 5.2 percent below 1990 levels by 2012.

Years in negotiation and then abeyance waiting for enough nations to sign up, Kyoto finally comes into force in February after Russia ratified it.

But the world's greatest polluter does not even accept that man-made climate change is happening and Blair's officials have been negotiating to try to produce some agreement on the science of climate change.

"If they could persuade the Bush administration to accept that man-made climate change is happening it would be a small but welcome step," Tindale said. "But even that is a long shot."

"Anything is better than nothing. If they could persuade them to sign up to the science it would make some of their existing policies look bizarre if not insane," said Juniper.

However, Bulmer-Thomas said trying and failing might not necessarily be damaging to Blair -- facing an election expected in May.