If global warming is occurring, why was winter 2007-2008 so cold and snowy?
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It wasn’t all that cold a winter globally. While it was the coolest since 2000, temperatures were still above normal for the last 30-year period and warmer than any winter on record before 1974.
The relative coolness was likely shaped by La Niña, which tends to lower global temperature by several tenths of a degree Fahrenheit, just as El Niño tends to raise it. The United Kingdom’s Met Office predicted in 2007 that 2008 might be cooler than other years this decade, based on La Niña and other existing ocean patterns. The same 10-year prediction suggests that global temperatures will head upwards again, beginning in 2009, with more global records likely in store afterward.
There were several areas of very heavy snowfall in China and North America through the winter of 2007-08, with all-time records set in Madison, Wisconsin, and in Québec City. These areas of heavy snow are also broadly consistent with La Niña, and they may have been accentuated by the global increase in atmospheric moisture associated with climate change.
These events remind us that cold snaps, or even unusually cold seasons, will continue to occur, even on a warming planet. Global warming does not mean it is always warm everywhere, or that temperature is the only change occurring. A changing climate also involves changes in precipitation and a shakeup in what we’ve come to think of as familiar weather and climate patterns.
More Information: National Climatic Data Center. “Climate of 2008: February in Historical Perspective.”