THE Bush Administration has run a systematic campaign to play down the dangers of climate change, demanding hundreds of politically motivated changes to scientific reports and muzzling a pre-eminent expert on global warming, the US Congress has been told.

The testimony on Monday to the House Committee on Oversight and Government Reform painted the Administration as determined to maintain its line on climate change even when it clashed with the findings of scientific experts.

James Hansen, who heads the Goddard Institute for Space Science in New York, said in testimony: "The effect of the filtering of climate change science during the current Administration has been to make the reality of climate change less certain than the facts indicate, and to reduce concern about the relation of climate change to human-made greenhouse gas emissions."