"WASHINGTON — Heat-trapping pollution from U.S. power plants hit a 27-year low in April, the Department of Energy announced Wednesday.

A big factor was the long-term shift from coal to cleaner and cheaper natural gas, said Energy Department economist Allen McFarland. Outside experts also credit more renewable fuel use and energy efficiency.

Carbon dioxide — from the burning of coal, oil and gas — is the chief greenhouse gas responsible for man-made global warming.

'While good news for the environment, we certainly would not want to assume that this trend will continue and that we can simply relax,' said John Reilly, co-director of MIT's Joint Program on the Science and Policy of Global Change."

Seth Borenstein reports for the Associated Press August 5, 2015. [2]