This Year’s Winter: Consistent with Global Warming?

By John Krenn

Even the most rabid Minnesota environmentalists have had that question come to mind this April as we have looked out each morning to a fresh coat of snow accompanied by cooler than normal temperatures.  The question has at least a couple of answers, ranging from what we clearly know to be correct to the more theoretical.  First, we know that a weather pattern, even one lasting a whole season or year, is not “climate.”  Climate is the sum of the weather events in an area over a long period of time.  Just as last year’s incredibly warm and short Minnesota winter could not be used, by itself, to announce the advent of global warming,  this year’s longer colder winter does not put  global warming in doubt.  Unfortunately, global warming is still on track, as the earth’s average surface temperature has now been higher than the 20th Century average for 335 months in a row — yes, since before many of you were born! (National Oceanic and Atmospheric Administration, Feb. 21, 2013.)

Photo credit: Tom Thompson

Photo credit: Tom Thompson

Ironically, our long cold winter may have been caused by climate change.  One climatologist, Charles Greene of Cornell University, explains that the melting Arctic sea ice is changing weather patterns by pushing arctic cold down into lower latitudes when certain conditions are present.

There is no question the arctic ice is melting.  The area covered by permanent ice in the arctic is now one-half of what it was as recently as 1989.  Many scientists have noted that as melting causes more open water during the Arctic summer, the water absorbs heat from the sun, which causes even more melting.

With less arctic ice, Professor Greene states, the low atmospheric pressure area over the Arctic is weakened, which decreases the strength  of the polar vortex holding cold air in the Arctic.  The cold air can then more readily move south to lower latitudes.  This process also has weakened the jet stream, causing the jet stream to follow a more S-shaped curve into lower latitudes, rather than the relatively straight path from west to east that it typically has followed in the winter in the upper northern latitudes.  Making matters worse, the weakened S-shaped jet stream gets stalled in place, causing the cold weather to remain in place for longer periods of time.  As Jennifer Francis, research professor with the Rutgers Institute of Coastal and Marine Science, explains, the loss of Arctic ice “is affecting the jet stream and leading to the extreme weather we are seeing in mid-latitudes… It allows the cold air from the Arctic to plunge much further south. The pattern can be slow to change because the [southern] wave of the jet stream is getting bigger. It’s now at a near record position, so whatever weather you have now is going to stick around.” (Minnesota Public Radio, March 28, 2013.)

From year to year, a variety of climate phenomena will impact these patterns, such as the El Nino effect, but the concern is that the globe no longer has the constant of a huge permanent Arctic ice pack.  As a result, more unusual weather patterns, like our long, cold winter, are likely.

John Krenn is a volunteer with the Sierra Club North Star Chapter Clean Air and Renewable Energy Committee.

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