A baby polar bear follows its mother across Arctic ice.
Credit: Sophie TRAN, Laboratoire des Sciences du Climat et de l'Environnement (LSCE), distributed by EGU under a Creative Commons license.
DENVER - The amount of Arctic sea ice hangs on through the summer is partly dependent on the storminess of the weather, according to a new study.
The research finds that in years when the weather in the Arctic is calm, more ice is lost by the end of the Arctic summer. Arctic sea ice has been in overall decline for decades now, reaching a record low in September 2007 and almost hitting that record again in 2011.
But while the trend is toward more melting of sea ice, the year-to-year measurements wobble up and down. The new research, presented Oct. 27 at the World Climate Research Program meeting here, found that storms account for much of that yearly variation.
In fact, it may have been a stormy summer that saved 2011 from beating the 2007 sea ice-loss record, said study researcher James Screen of the University of Melbourne. The ice seemed on track to melt faster than in 2007, but then storms ravaged the Arctic for several weeks in July, Screen told meeting attendees.
"Perhaps this little period of storminess actually prevented us from getting a new record this year," Screen said.
Screen and his colleagues have found that early-summer storms are a good thing for late-summer ice. The researchers matched storm tracks of Arctic cyclones from 1979 to 2010 to the extent of ice in September of those years. September ice is the ice that has survived the melt season and will provide the base for ice growth over the winter. Summer ice is also important for Arctic wildlife, such as walruses and polar bears. [Gallery: Polar Bears Swimming in the Arctic]
The researchers found an association between years in which ice was lost (as compared with the prior year) and years in which few early-season storms blew through the Arctic in May, June and July. In ice-loss years, they found an average of 38 early-summer storms, while ice-gain years had an average of 48.
Most notably, years in which ice was lost were marked by an almost complete absence of storms tracking up from the North Atlantic, Greenland, and the Norwegian and Barents seas, Screen said.
Sensitivity to storms
Storms tracking from below the pole tend to bring heat up toward the frigid Arctic, so you might expect storminess to break up and melt ice. But Screen and his colleagues found that patterns of atmospheric pressure and wind conspire to shunt ice into high-melt areas when the weather is calm. In these high ice-loss years, they found "anticyclonic" circulation patterns — a clockwise ice drift that transports sea ice toward the Chukchi Sea between Siberia and Alaska, and toward the Fram Strait between Greenland and the island of Spitsbergen. In these relatively southerly waters, ice melts easily.
In contrast, stormy Arctic summers are marked by a cyclonic circulation pattern that doesn't push as much ice out to sea.
The researchers failed to find any long-term trends in Arctic storminess, suggesting that summer weather hasn't been a major driver of the overall decades-long ice loss in the Arctic. (That's the result of global warming.) But as the ice pack thins, it becomes more sensitive to outside forces, they warn in the Journal of Geophysical Research, where they reported their results Aug. 4. That means that storms will only become more influential as time goes on.
"What's really important is the weather going on in the summer months," Screen said. "That's controlling what we see at the end of the melt season."