Arctic Ocean sea ice coverage has shrunk to the lowest level since modern records began, smashing the previous record by 760,000 square kilometers (293,000 square miles).
On September 16, the day on which, according to the National Snow and Ice Data Center (NSIDC), the region's sea ice appeared to end its summer retreat and begin its winter rebound, the total extent was 3.41 million square kilometers (1.32 million square miles) – slightly more than half the average minimum extent between 1979 and 2000.
In 2007, when the previous record was set, a long-lasting high-pressure system that led to a combination of extensive summer sunlight and high winds conspired to create a 'perfect storm', resulting in a dramatic decrease on the previous year's extent.
This year, a powerful storm system that hit the Arctic Ocean in August likely accelerated the ice loss. But, "that exact same storm, had it occurred decades ago when the ice was thicker and more extensive, likely wouldn't have had as prominent an impact, because the ice wasn't as vulnerable then as it is now," said Claire Parkinson, a climate scientist at NASA Goddard Space Flight Center.
Whereas almost the entirety of Antarctic sea ice melts each summer, the Arctic ice cap has historically contained thick, multi-year ice that has survived the summer melt and thickened each winter. However, as temperatures have risen, that muti-year ice has thinned, and new ice has not had the opportunity to survive for a second year. With each year of melt, the ice cap overall is becoming more vulnerable to further melt.
"The strong late season decline is indicative of how thin the ice cover is," said NSIDC scientist Walt Meier. "Ice has to be quite thin to continue melting away as the sun goes down and fall approaches."
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"We are now in uncharted territory," added NSIDC Director Mark Serreze. "While we've long known that as the planet warms up, changes would be seen first and be most pronounced in the Arctic, few of us were prepared for how rapidly the changes would actually occur."
At least one scientist feels the complete disappearance of summer sea ice in the Arctic is now imminent.
"The final collapse ... is now happening and will probably be complete by 2015/16," Prof Peter Wadhams of Cambridge University told The Guardian.
Most other experts are far more circumspect in their predictions; for example, Cecilia Bitz of the University of Washington recently commented to Andy Revkin of the New York Times that she thinks a "50/50 chance" that summer sea ice disappears entirely or almost entirely within a few decades "is about right."
(It should be pointed out that this does not mean that the Arctic Ocean will have no sea ice at all; under even the most pessimistic models, ice will grow during the winter months, but will be almost entirely seasonal rather than multi-year, and thus all the more likely to melt completely at some point each summer.)
However, the genuine concern of many researchers over the fact that their worst predictions are coming to pass with some rapidity, is palpable.
"It's hard even for people like me to believe, to see that climate change is actually doing what our worst fears dictated," Jennifer Francis of Rutgers University told the New York Times last month. "It's starting to give me chills, to tell you the truth."
Image: Satellite data reveal how the new record low Arctic sea ice extent, from Sept. 16, 2012, compares to the average minimum extent over the past 30 years (in yellow). Sea ice extent maps are derived from data captured by the Scanning Multichannel Microwave Radiometer aboard NASA's Nimbus-7 satellite and the Special Sensor Microwave Imager on multiple satellites from the Defense Meteorological Satellite Program. Credit: NASA/Goddard Scientific Visualization Studio Video:This animation shows the 2012 time-series of ice extent using sea ice concentration data from the DMSP SSMI/S satellite sensor. The black area represents the daily average (median) sea ice extent over the 1979-2000 time period. Layered over top of that are the daily satellite measurements from January 1 - September 14, 2012. A rapid melt begins in July, whereby the 2012 ice extents fall far below the historical average. Credit: NOAA Visualizatons