WASHINGTON, March 11 (UPI) -- Two studies by U.S. researchers suggest carbon emissions have to end completely within this century to avert dangerous global warming.

The Washington Post (NYSE:WPO) said the studies contend the world would have to stop using fossil fuels by as early as mid-century.

Carnegie Institution senior scientist Ken Caldeira, co-author of a paper published in the journal Geophysical Research Letters, said radical change in the world's energy system is needed.

Oregon State University professor Andreas Schmittner said in the journal Global Biogeochemical Cycles that if global emissions do not drop to zero until 2300, the temperature rise at that point would be more than 15 degrees Fahrenheit. The newspaper said most scientists warn a temperature rise of 3.6 degrees Fahrenheit could have serious consequences.