Shortly after the third of three major snowstorms brought record-setting snowfall to the U.S. mid-Atlantic region, NOAA’s Climate Scene Investigators (CSI) assembled to analyze why the snowstorms happened. The CSI is a team of “attribution” experts in NOAA whose job is to determine the causes for climate conditions. By distinguishing natural variability from human-induced climate change, they aim to improve decision-making and inform adaptation strategies.

Annual snowfall at Reagan National Airport site for 1888-89 through 2009-2010. The red bar shows the 55.9 inches accumulated through February 11, 2010 that broke the former record from 1898-99. Note that only 3 years of the last 20 have more than the long-term average of 15.2 inches of snow. Data courtesy of NOAA National Weather Service.

The CSI team was formed in 2007, following chaotic media coverage of the record U.S. warmth in 2006 (see CSI: NOAA Climate Scene Investigators). Here they have been called to the scene again, but now to explain cold, snowy conditions, and to reconcile those with a warming planet. After a series of record-setting snowstorms hit the mid-Atlantic region this winter, some people asked NOAA if humans could somehow be to blame. Specifically, they wanted to know if human-induced global warming could have caused the snowstorms due to the fact that a warmer atmosphere holds more water vapor.

The CSI Team’s analysis indicates that’s not likely. They found no evidence — no human “fingerprints” — to implicate our involvement in the snowstorms. If global warming was the culprit, the team would have expected to find a gradual increase in heavy snowstorms in the mid-Atlantic region as temperatures rose during the past century. But historical analysis revealed no such increase in snowfall. Nor did the CSI team find any indication of an upward trend in winter precipitation along the eastern seaboard.

In early February, two weather systems brought record snowfalls to Washington, D.C., and other parts of the U.S. mid-Atlantic region. This image shows the depth of snow that had accumulated at locations across the contiguous United States as of February 11, 2010. (Image by NOAA Environmental Visualization Laboratory using data courtesy of NOAA’s National Operational Hydrologic Remote Sensing Center.)

The CSI team turned its attention to natural factors that control the ordinary ups and downs of weather. Many extreme weather events are due to cyclical, large-scale anomalies in air pressure and sea surface temperature across large tracts of ocean. Such fluctuations spawn weather systems that can cause droughts, floods, and massive snowstorms. While El Niño is the most famous, scientists have identified other climate anomalies throughout Earth’s climate system as well. Their names may seem unimpressive — the Arctic Oscillation, North Atlantic Oscillation, Pacific Decadal Oscillation, to name a few — but they can pack quite a punch!