The US vice-president, Dick Cheney, intervened to gag a senior official from testifying last year to the public health problems caused by climate change, according to a Bush administration whistleblower.
In a letter released today, the former climate adviser at the US environmental protection agency (EPA) said Cheney's office pushed to delete "any discussion of the human health consequences of climate change" from testimony by America's senior disease control official.
The testimony on climate change, given last October by the head of the head of the US centres for disease control (CDC), was ultimately cut from 14 to six pages.
When CDC officials anonymously told the media that the White House had "eviscerated" the document, removing any mention of specific diseases caused by pollution, a spokeswoman for George Bush said the deletions were made to reflect scientific uncertainty on the issue.
But Jason Burnett, 31, who resigned last month after the EPA blocked California from setting strong emissions limits, said the deletions were made to "keep options open" after the supreme court required the agency to determine whether climate change endangers public health.
"We know that the administration's efforts have been about covering up the real dangers of global warming and hiding the facts from the public," the Democratic senator who received Burnett's letter, environment committee chairwoman Barbara Boxer, said.
"This cover-up is being directed from the White House and the office of the vice-president."
The EPA still has not complied with the Supreme Court and released an opinion on the health effects of warming caused by carbon emissions. Three major US cities and 17 states have sued the agency to protest the lengthy delay.
When the EPA completed an initial finding in December that climate change poses public health risks, the White House refused to open the message to avoid acknowledging its existence. Burnett was asked to pretend the document was a mistake, he wrote to Boxer.
"When we explained that the document had been sent, I was asked to send a follow-up note saying that the email had been sent in error," Burnett wrote. "I explained that I could not do this because it was not true."
Burnett also wrote to Boxer that the vice president tried to prevent EPA chief Stephen Johnson from merely using the phrase "greenhouse gas emissions harm the environment" in January testimony that explained why he blocked the California pollution plan.
"We received a suggestion to avoid the phrase … an official [representing Cheney] called to tell me his office wanted the language changed," Burnett wrote.
Burnett ultimately declined to alter the testimony, which was delivered as the EPA had written it.
Allegations of political interference with scientific judgment have plagued the Bush administration since its first days in 2001, when Cheney convened a "task force" of oil and gas executives to help shape official energy policy.
Tensions have flared so much between the administration and independent government scientists that a recent survey of more than 1,500 EPA staffers found 60% reporting that their work was politically influenced.
Burnett has not hidden his political beliefs, donating more than $100,000 to Democratic candidates, including the maximum legal amount to Barack Obama's presidential campaign. The Bush administration made the rare choice to overlook his party affiliation in naming him EPA associate deputy administrator.