The disclosure will anger environment campaigners who claim that efforts to cut greenhouse gas emissions are being sabotaged because of President George W. Bush's links to the oil industry.

Emails and internal government documents obtained by The Observer show that officials have sought to edit or remove research warning that the problem is serious. They have enlisted the help of conservative lobby groups funded by the oil industry to attack US government scientists if they produce work seen as accepting too readily that pollution is an issue.

Central to the revelations of double dealing is the discovery of an email sent to Phil Cooney, chief of staff at the White House Council on Environmental Quality, by Myron Ebell, a director of the Competitive Enterprise Institute (CEI). The CEI is an ultra-conservative lobby group that has received more than $1 million in donations since 1998 from the oil giant Exxon, which sells Esso petrol in Britain.

The email, dated 3 June 2002, reveals how White House officials wanted the CEI's help to play down the impact of a report last summer by the government's Environmental Protection Agency (EPA), in which the US admitted for the first time that humans are contributing to global warming. 'Thanks for calling and asking for our help,' Ebell tells Cooney…...