The number of Americans who believe in global warming has plummeted, falling 20% in two years, a survey has said. Only 57% of Americans believe there is solid scientific evidence that the Earth's atmosphere is warming, said the poll of 1,500 people by the Pew Research Centre for the People & the Press. The number of people who believe that human activity is causing global warming also fell to just 36%, down from 47% last year. The decline was sharpest among independent voters and Republicans. Republicans in Congress have almost uniformly lined up against climate change legislation. There were also regional differences, with people in the mid-west and Rocky mountain states less inclined to see climate change as a serious problem.