Hate the cold? Well hey, here's a cynically silver-lined perk to global warming: Hot days come earlier than they once did.

Earth's average temperature increased by 1.33 degrees Fahrenheit (0.7 degree Celsius) from 1905 to 2005, according to the Intergovernmental Panel on Climate Change (IPCC). Over the past 50 years, each season has begun nearly two days earlier than in the century before, Harvard University and University of California, Berkeley, scientists report today in Nature. Scientists have previously noted earlier springs, but the new findings (based on an analysis of land and ocean surface temps between 1850 and 2007) suggest that every season is getting an early start.

The reason for the shift isn’t entirely clear, but the study authors suspect that the Northern Annular Mode, a pattern of air movements across the Northern Hemisphere,  may play a role. That pattern has brought stronger winter winds— and, therefore, warmer ocean air—to land, driving up winter temps and, perhaps, the researchers say, triggering earlier springs. And premature spring thaws mean drier soil earlier in the year; the drier the soil, the greater its ability to absorb and trap heat.

The combination could cause a vicious cycle of premature springs and summer droughts, says study co-author Inez Fung, co-director of the university's Berkeley Institute of the Environment. "Because the soil is dry, it will get hotter. If it gets hotter, the evaporation [of winter snow and rain] will go faster," Fung tells ScientificAmerican.com. "More droughts, more intense droughts, longer droughts—that’s what I very much worry about."

Image © iStockphoto/Clint Spencer