Does global warming mean more or less snow?

by
Kevin Trenberth in The Conversation

...the heaviest snowfalls occur with surface temperatures from about 28°F to 32°F – just below the freezing point. Of course, once it gets much above freezing point, the snow turns to rain. So there is a “Goldilocks” set of conditions that are just right to result in a super snow storm. And these conditions are becoming more likely in mid-winter because of human-induced climate change.

...

Recent winter storms and climate change

Extra-tropical storms in winter form and develop on differences in temperature, which are greatest between continents and adjacent oceans.

In winter, the cold dry air over North America forms a sharp contrast with the relatively warm moist air over the Gulf Stream and the North Atlantic. A cold front leads the southern outbreak of cold air while a warm front leads the warm moist air heading northwards as it rises upwards and produces precipitation within the storm.

...

In February 5-6, 2010 a snow “bomb” occurred and led to what was referred to at the time as “Snowmaggedon,” which was used by several conservative Senators to mock global warming and Al Gore. Yet it was winter and there was plenty of cold continental air. There was a storm in the right place. And there were unusually high surface sea temperatures in the subtropical Atlantic Ocean – up to 3°F (1.5°C) above normal – which led to extraordinary amounts of moisture being fed into the storm. And it resulted in exceptional snow amounts in the Washington DC area.

Earlier this week, between January 26-28, 2015, the area targeted by the latest winter storm, called Juno by some, was a bit further north. The developing storm was in just the right position to tap into the high moisture over the ocean and develop as it experienced the sharp contrast between the continent and the relatively warm ocean.

Over three feet of snow fell in some areas, blizzard conditions were experienced in New England, and heavy seas and erosion occurred in coastal regions in association with the higher sea levels associated with global warming.

Going forward, in mid winter, climate change means that snowfalls will increase because the atmosphere can hold 4% more moisture for every 1°F increase in temperature. So as long as it does not warm above freezing, the result is a greater dump of snow.

In contrast, at the beginning and end of winter, it warms enough that it is more likely to rain, so the total winter snowfall does not increase. Observations of snow cover for the northern hemisphere indeed show slight increases in mid-winter (December-February) but huge losses in the spring...