Washington (AP) — Scientists are warning Congress that the long-theorized, life-threatening overheating of the Earth from man-made air pollution is not a frightening reality.

“The fact that the greenhouse effect is real is proven,” said James Hansen, director of the National Aeronautics and Space Administration’s Goddard Institute for Space Studies.

Hansen said the average U.S. temperature has risen from 1 to 2 degrees since 1958 and is predicted to increase an additional 3 or 4 degrees sometime between 2010 and 2020.

He said that with an expected doubling of atmospheric carbon dioxide by 2040, the number of days each year with temperatures over 90 degrees would rise from 35 to 85 in Washington, D.C., and Omaha, Neb.