Sen. Barbara Boxer (D-Calif.), who is shepherding climate legislation through the Senate as chairman of the Environment and Public Works Committee, said the new findings "make it clear we must ACT NOW to address global warming."

"It won't be easy, given the makeup of the Senate, but the science is compelling," she said. "It is hard for me to see how my colleagues can duck this issue and live with themselves."

The Earth has already warmed by 0.76 degrees Celsius (nearly 1.4 degrees Fahrenheit) above pre-industrial levels. Most scientists warn that a temperature rise of 2 degrees Celsius (3.6 degrees Fahrenheit) could have serious consequences.