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February 1, 2011 

Backgrounder: It’s Cold and My Car is Buried in Snow. How Can Global Warming be Happening?

On a global scale, the most recent decade (2000-2009) has been declared the warmest decade on record since the 1880's, when temperatures were first recorded. But the recent snow storms have led to considerable confusion about how record snow relates to our changing climate.

Warming Climate and Ocean Evaporation

Snowfall is a combination of the moisture in the atmosphere and air temperature. As the Earth’s temperature warms, the oceans evaporate more water to the atmosphere which produces more precipitation—notably more extreme precipitation—including heavy snowfall when conditions are below freezing.

Contributing Factors

In the Northeastern United States, there is another major contributing factor to heavy snowfall—a phenomenon known as the North Atlantic Oscillation (NAO). During the positive NAO phase, pressure systems prevent frigid Arctic air from plunging southward. During the negative NAO phase, the pressure weakens and allows the jet stream to buckle and combine cold Arctic air with moisture laden southern air masses typically resulting in more snow.

The winter of 2010 recorded second lowest negative phase of the NAO since the 1970s and helps to explain the record snowfalls across the northeastern United States.

The current 2011 winter is also trending toward strong negative phase.


The Union of Concerned Scientists puts rigorous, independent science to work to solve our planet's most pressing problems. Joining with citizens across the country, we combine technical analysis and effective advocacy to create innovative, practical solutions for a healthy, safe, and sustainable future.

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