Burning fossil fuels in power plants and automobiles is most likely responsible for global warming, according to a Bush administration report that confirms climate risks already accepted by most of the world's scientists. Carbon dioxide, the byproduct of burning coal and oil, has contributed most to warming in the last century, the U.S. Climate Change Science Program and the White House National Science and Technology Council reported today. The assessment from President George W. Bush's top science advisers is the strongest endorsement yet of a global scientific consensus on the causes of climate change, said Jay Gulledge, senior scientist at the Pew Center on Global Climate Change, a nonprofit research group.