The Snowfall to Warming Connection, Part 2
As explained in the previous post-Part 1-, a warming planet means more evaporation from the oceans. More moisture in the air turns into more rain (like the recent deluges) or more snow (the recent record snowfall, or blizzards) depending on whether the temperature is below freezing or not. That leaves the interesting question of why we are seeing so many colder days in North American and Europe in recent years.
The location of the cold air masses in the northern hemisphere is largely a result of the jet stream, that strong current of high level air that results from the spinning of the earth. Generally speaking the jet stream moves from West to East, and drifts southward. It is greatly affected by the large ice mass around the north pole, as well as a lot of other inputs.
As most everyone is aware the polar ice cap has been shrinking quite rapidly (documented in one of my posts here a few months ago). The ocean below is a lot warmer than the ice cap. Thus, the shrinking ice cap means that more heat goes into the atmosphere now, compared to the last hundred thousand years when the polar ice cap was in full extent. This causes changes in the meandering jet stream. There was a great explanation by Judah Cohen in the New York Times describing the forces moving the jet stream. http://www.nytimes.com/2010/12/26/opinion/26cohen.html Amazingly unusual amounts of snowfall in Siberia have altered the pattern of the jet stream.
The map below of temperature anomalies shows that while we may have felt unusual cold in the mid Atlantic and Southeast areas of the US, the polar regions and Scandanavia were much warmer than usual.
This general situation occurred several times during this winter (2010-11). It gives us a visual picture for the excessive amounts of snow.
More moisture in the air due to global warming.
Shifting jet stream due to record snow in certain areas like Siberia.
Excess moisture shows up as record snow due to the usual jet stream.
Of course we tend to judge weather by what we experience locally. What we are usually unaware of, is some other event, in the other direction, as shown here.
Indeed Greenland and the Arctic have had an unusually warm winter, causing more melting. In parts of Greenland the freezing rain and slush continued into January, when the temperatures would usually be well below zero.
That warming means that the polar ice cap will continue its extreme melt rates. As referenced in Part 1, that means more evaporation. This is another example of the ‘positive feedback loops’ cited by scientists.