Loss of northern hemisphere spring snow cover likely to amplifiy overall global warming signal

More midwinter snow, but faster spring meltout seems to be the new climate norm in the northern hemisphere.

‘As shifts in the timing of meltout occur, we lose an important and relatively stable snowpack reservoir …’

FRISCO —Dwindling spring snow cover in the northern hemisphere could accelerate the pace of global warming, as darker-colored ground emerges earlier in the year, absorbing more of the sun’s heat and intensifying atmospheric warming.

The spring decline is evident despite a trend toward more snow in mid-winter — but June snowcover in the northern hemisphere has been below average 10 years in a row. The downward trend is mainly due to warmer temperatures, not to any big changes in overall precipitation totals, according to the most recent IPCC climate assessment.

As recently as the early 2000s, June snow cover extent in the northern hemisphere was as high as 3.8 million square miles, about te size of the U.S. including Alaska. But since then, that bright, reflective snow has been shrinking about 19 percent per decade.

And the loss of snow cover is peaking right around the time the sun is highest in the sky, and researchers say snow cover in June has a much larger climate-cooling effect than the same amount of snow would have in January. A 2011 study concluded that the loss of snow cover is having a huge impact on Earth’s overall radiative balance — as significant as the loss of Arctic ice.

The melting snow also has other effects on the bigger climate picture. Relatively warm waters flowing into the Arctic Ocean region can speed the breakup of coastal sea ice, once again amplifying the climate-warming effect.

“As shifts in the timing of meltout occur, we lose an important and relatively stable snowpack reservoir,” says NCAR’s David Gochis. “This affects a variety of other hydrologic processes, such as the amount of water in streams and how much is left in local water tables at the end of the summer.”



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