Now it’s official: as of September 16, according to the National Snow and Ice Data Center, the sea ice covering the Arctic Ocean reached a record low minimum extent.
What makes this year unique is that the 2012 minimum is lower than any since modern satellite observations first began in the late 1970s – and by a wide margin. The 2012 minimum of 1.32 million square miles (3.41 million square kilometers) shatters the previous mark of 1.61 million square miles (4.17 million square kilometers), which was set in 2007, by 18 percent.
This image compares the sea ice extent minimum on Sept. 16 (in white) to the average minimum during the past 30 years (yellow line). Credit: NASA.
The difference between the new and old record is about equal to the entire state of Texas, the NSIDC reported. The amount of Arctic sea ice that vanished since March is equivalent to the combined areas of Canada and Texas.
The continued steep decline of Arctic sea ice is bad news for polar bears, seals and the Inuit and other indigenous Arctic peoples who call the region home, but it also has repercussions for the rest of the world. When bright, white, reflective ice melts to reveal darker ocean water, sunlight that would normally bounce back into space is absorbed instead.
That accelerates local warming, and leaks extra heat to the rest of the globe. It also melts long-frozen permafrost, which can release extra heat-trapping carbon dioxide to accelerate global warming even more. It may bring up heat-trapping methane from the seafloor as well, adding yet another boost to an already-warming planet.
Another possible effect is the disruption of weather patterns outside the Arctic. Climate Central has been reporting on preliminary research suggesting that warmer air in the Arctic may be disrupting the jet stream, leading (although not consistently) to some unusually cold winters in recent years in both North America and Europe.
None of this would matter much if this year’s meltback were a one-shot anomaly, but that’s not likely. When open Arctic water re-freezes in winter, it tends to form a relatively thick layer of what’s called first-year ice – and first-year ice is much more prone to melting the following summer than the thicker, multi-year ice that once covered much of the Arctic Ocean. Even the multi-year ice, according to some reports, is slushier and less solid than normal, so it could melt more easily than normal as well.
What sets this melt season apart from 2007 is that unlike during the previous record year, the weather conditions throughout the melt season were not particularly favorable for melting. Sea ice experts said the ice cover may have become so thin and brittle that it doesn’t need unusually sunny and warm weather in order to melt to a record low anymore, even a typical Arctic summer can do the job. Sea ice volume measurements, which take ice thickness into account, also hit a record low this year.
“I think the minimum this year is more remarkable than in 2007,” said NSIDC scientist Julienne Stroeve in an email, “since the 2007 minimum was in large part driven by [unusual weather patterns], and this summer we shattered the 2007 minimum under more normal summer circulation patterns.”
One exception was an unusual and powerful storm system that struck the Arctic Ocean during August, which may have helped accelerate the ice melt. "The storm definitely seems to have played a role in this year's unusually large retreat of the ice," said Claire Parkinson, of NASA’s Goddard Space Flight Center in Maryland, in a press release. "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."
Regardless of the storm’s effect, “the ice is thin,” said NSIDC's Stroeve, “so it certainly could be that extents below 4 million [square kilometers] will become more frequent.” She spent part of this melt season observing the sea ice by ship, and found the ice cover to be unusually thin and patchy.
In fact, said her NSIDC colleague Walt Meier in a press release, “The strong late season decline [in area] is indicative of how thin the ice cover is. Ice has to be quite thin to continue melting away as the sun goes down and fall approaches.” It also had a pretty good head start: as early as June, scientists were noting that ice was melting at a record rate. During August, the Arctic lost an average of 35,400 square miles of ice per day, which was the fastest rate ever observed for the month. That is the equivalent of losing an area of ice equal to the state of Maine every day for 31 days.
Most worrisome of all is the fact that while scientists have long predicted a gradual disappearance of summer sea ice over this century it seems to be happening faster than anyone expected. “We are now in uncharted territory,” said NSIDC Director Mark Serreze in the NSIDC press release. “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.”
This year’s minimum, the NSIDC said, is nearly 50 percent lower than the average minimum for the years 1979-2000 — an almost shocking development, since as Stroeve pointed out, the melting is proceeding faster than any model projected it would.