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Tuesday, August 21, 2012

Northern Hemisphere Land Snow Cover Anomaly -- June 2012 beats 45-year low record a month early!

The untold drama of Northern snow cover

by M. A. Rodger, guest blogger, Neven's Arctic Sea Ice blog, August 21, 2012
Do we have time for another record while Arctic sea ice records are falling around us like ripe plums? I guess we'll have to make time. M. A. Rodger, who runs the Marclimategraphs page, sent me this guest blog concerning record snow anomalies:

The untold drama of Northern snow cover

When considering the impact of climate change on polar regions, the star of the show has always been Arctic sea ice. Playing supporting roles are the Greenland ice cap and Antarctica. Yet one actor in the drama remains badly overlooked: the snows that cover our Northern continents.
In June 2012, for instance, it was reported that Northern Hemisphere Land Snow Cover had broken a record. The June snow anomaly was the lowest figure for June in the whole 45-year record, besting the previous record set in 2010 by 1 million square kilometres. This statement, reported as the last item in the US NSIDC's first July Arctic Sea Ice News & Analysis bulletin understandably never gained great widespread coverage.
Yet this summer's Northern snow cover presents a far more dramatic story that surely deserve greater prominence. For a start, June 2012 snow cover was not just the record of June. Excluding Greenland with its ice cap, the June 2012 anomaly was the record for all months in the entire 45-year record. The anomaly stood at 5.74 million square kilometres, pipping the December 1980 record by 0.13 million square kilometres, although this again is hardly front page news.
It is only with analysis of the changing anomaly through the year that the true drama of the declining snow cover can be seen. At the height of this summer's melt, 2012 was 8.5 million sq kilometres ahead of the 1972-1979 average. This is a full month advance in the melt over a 27-year period. (That is twice the advance seen over recent decades in the UK's 250-year-long phenological record which is itself dramatic enough). Another way of visualising this early melt is that the average snow limit at the height of the melt season is now a whole 500 miles further North than it was 27 years ago.
And what is most dramatic is that this process is visibly accelerating. The average retreat North over the last 27 years, since the mid-1970s, is 18 miles per year. Since the mid-2000s, it is 38 miles. In this last dramatic year, at the height of the melt season, the snow has been melting away 71 miles further North than in any other previous year.
The decline for Northern Hemisphere Land Snow Cover is just as dramatic and just as consequential as the Arctic sea ice decline. We ignore it at our peril.

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