It said Blair had held lengthy discussions with US President George W. Bush over a fresh initiative that would bypass Washington’s opposition to the Kyoto Protocol, which seeks to curb climate change.
The United States has not signed up to the Kyoto pact, which will go into effect in February after Russia ratified it last month.
Blair has made the environment and Africa his two top issues for next year when Britain assumes the presidency of the G8 group of rich nations.
"It is being given the highest priority," a Downing Street source was quoted as saying. "There is an awful lot of work going on in the background on this."
Blair’s spokesman later told reporters that discussions with Washington on climate change were no secret, and that the search was on for a consensus.
"We have always been involved in dialogue not only with the Americans but also with our European partners, with developed countries like Japan and also developing countries like China," he said.
"While we believe Kyoto is very important … we also have to recognise that Kyoto by itself is not enough to tackle this issue. What we have to do is push forward on the technological front … at the same time as not harming economic growth in the world," he added.
Environment pressure group Greenpeace said it welcomed any move to get America even to accept the reality of climate change.
"Too often we see Tony Blair standing side-by-side with Bush and not even mentioning what he has called the biggest threat we face," director Stephen Tindale said in a statement.
"On global warming Bush isn’t with us, he’s against us. It’s time the Prime Minister spent some of the political capital he’s amassed in Washington and demanded not just agreement on the science but huge cuts in US emissions," he added.