Burning fossil fuels has led to a warmer, moister atmosphere and a shifting background for extreme weather and climate events, according to a study that analyzes noteworthy weather events from the last two years.

The last 10 days have brought what may be the gentlest round of extreme weather ever to grace the United States. Beneath the pleasant veneer lies one of the most bizarre weather episodes in recent U.S. history.

Why would a cooling of the Pacific Ocean help stoke tornadoes in the United States? Researchers are beginning to dig deeper into the connections between severe U.S. thunderstorms and the sea.

Days lengthen as spring arrives, but several other signs of the season are showing up earlier and earlier. Some animals and insects aren’t adapting fast enough to this "asynchrony," and there's an increasing disconnect with legal dates that govern hunting and other resource management.

The winter of 2011–12 was the second in a row to feature La Niña, the quasi-cyclic cooling of the eastern tropical Pacific—but the two seasons departed from the La Niña script in strikingly different ways.