U.S. scientists have been pressured to make their writings on global warming fit with the Bush administration's skepticism on the topic, a U.S. Congressional committee has been told.

A survey by the Union of Concerned Scientists found 150 climate scientists had personally experienced political interference in their work over the past five years. The survey had 279 respondents.

At least 435 incidents were recorded, representatives of the watchdog group told the House Oversight and Government Reform Committee.

"Nearly half of all respondents perceived or personally experienced pressure to eliminate the words 'climate change,' 'global warming' or other similar terms from a variety of communications," said Francesca Grifo.