The winter extent of Arctic sea ice topped out for the 2010-11 season a few weeks ago, tying the previous lowest winter maximum in what could signal a grim beginning for the six-month melt season ahead.
Ice coverage of the Arctic Ocean and various northern seas reached 5.56 million square miles on March 7, according to the latest sea ice report posted online by the National Snow and Ice Data Center. A final analysis of the season will be posted next month.
Let's put that figure in perspective. This frozen habitat covered a vast area — slightly larger than Alaska, Canada and Greenland combined. It's three times larger than the minimum ice extent seen last September, which was the third lowest ever recorded during the age of satellite monitoring.
But despite a reach that spanned from the shores of Kamchatka to Newfoundland, the 2011 climax remained far below the 30-year-average of 6.12 million square miles and was within .01 percent of the previous smallest winter maximum recorded during the 2006-07 season
In a sense, a chunk of seasonal ice cap twice the size of Texas never reappeared in its winter home.
For the next couple of weeks, the overall ice cover oscillated in size, according to monitoring by satellites. Then it began slowly to shrink.
"As of March 22, ice extent has declined for five straight days," the NSIDC reported on March 23. "However there is still a chance that the ice extent could expand again. Sea ice extent in February and March tends to be quite variable, because ice near the edge is thin and often quite dispersed."
These latest developments are part of a decades-long trend of ever decreasing ice cover across the Arctic, especially during the summer melt season when shrinking ice floes eliminate important hunting and resting habitat for polar bears, walruses and seals.
The loss of summer ice also feeds and accelerates regional climate warming because the darker open water absorbs more heat from the sun than do the bright white floes.
Scientists say winter ice cover grows or shrinks depending mostly on seasonal weather patterns and isn't really a direct signal of climate change. This winter's near-record decline hinged largely on stunning ice free conditions seen through December near Hudson Bay, Baffin Island and Greenland, a situation scientists attributed to a weather pattern called the Arctic Oscillation. During much of the winter, ice extent closest Alaska was above normal.
But a weak winter season gives the summer meltdown a head start, so to speak, leaving the overall ice cap in a diminished state that can potentially lead to an even greater loss as summer heats up.
The 2010 ice minimum recorded on Sept. 19 was the third-smallest extent seen since 1979 — about 1.78 million square miles, the NSIDC reported last October.
With such a low winter extent, the threatened polar bears could face stressful conditions as summer melt proceeds, a leading bear expert told Mike Campbell of the Anchorage Daily News.
"Because polar bears depend on the surface of the sea ice to catch seals, those things are not favorable for polar bear survival," said Steven Armstrup, senior scientist for the nonprofit Polar Bears International. "So, if you are a polar bear, this could be a tough year — with increased starvation especially among the young and very old."
Contact Doug O'Harra at doug(at)alaskadispatch.com