Record Snows Due to... Global Warming?!

There are two mechanisms making our winters more variable, with heavier snows. The first reason we have gotten record snowfalls because warmer oceans are evaporating more water, at the same time that warm air holds more water. In fact, the amount of water held increases exponentially as the air warms. When this wet air moves over land during winter, the result is unusually heavy snowfall. The Washington, DC area, for example, would expect a 16+ inch snowfall once every 25 years. In the Winter of 2009-10 it got two in one season, not to mention the ones in 1996 and 2003!

The second mechanism, which is ultimately more ominous, is that we seem to be altering the behavior of the jet stream. The engine that drives the northern jet stream is the difference in temperature between air over the tropics and air over the Arctic. As predicted by climate models, the Arctic is warming faster than the rest of the planet. This loss of temperature difference between the tropics and the Arctic is causing the jet stream to slow down. As it slows down, masses of air tend to break off, causing "blocking patterns" where cold air sits in one place for an extended period. At the same time another mass of warm air may be held in place. In 2012, for example, the abnormal behavior of the jet stream caused a cold winter in Europe followed by a cool and extraordinarily rainy spring and summer.

For more information about global warming and heavy snowfalls, see this blog post by meteorologist Jeff Masters: Heavy snowfall in a warming world. For more about our impact on the jet stream, including a much fuller but very intelligible explanation, see the NewScientist.com article: How global warming is driving our weather wild (free registration required).

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