President Barack Obama has been armed with new ammunition for the Copenhagen summit on climate change with an announcement yesterday giving the US administration enhanced authority to regulate carbon dioxide emissions.

A formal ruling issued by the Environmental Protection Agency that carbon dioxide and five other gases were a danger to human health will allow the administration to use the Clean Air Act to crack down on emissions from large industrial plants. But the decision to use regulation rather than legislation to cut carbon emissions is politically contentious, with big business and Republicans already protesting that the decision is heavy-handed.

Mr Obama, who will travel to Denmark on Friday next week, had hoped that Congress would pass a climate-change law that would legislate for reductions, but the bill has become mired in the Senate and is not expected to be debated until well into next year.