Arctic Sea Ice Near Record Low as Melt Season Ends
With Arctic sea ice falling near or just below its lowest level on record, there's more evidence than ever before that the dwindling ice cover in the Arctic is connected to manmade global warming, and that it brings potentially serious consequences for global weather patterns and wildlife.
Sea ice decline is a concern to more than just polar bears, since a white, frozen Arctic Ocean reflects huge amounts of sunlight back into space, acting as a giant natural reflector of incoming sunlight. When Arctic sea ice melts extensively, as it has this year, it opens up expansive areas of open ocean that is darker in color, and which absorb huge amounts of heat from the Sun. This in turn activates a feedback effect that can melt yet more sea ice, and may be altering global weather patterns in surprising ways.
Depending on what data you rely on, Arctic sea ice extent has either plummeted to its lowest level on record or the second-lowest level seen since the beginning of satellite monitoring in 1979. Regardless of whether a new record is set during the 2011 melt season, the long-term decline in Arctic sea ice cover is clearly continuing. A recent study by researchers at the National Center for Atmospheric Research found that manmade global warming is responsible for about half of the decline in Arctic sea ice from 1979 to 2005, with natural climate variability accounting for the rest.
Including this melt season, the five lowest sea ice extents in the satellite record have occurred in the past five years, according to Mark Serreze, the director of the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado.
A research group at the University of Bremen in Germany reported late last week that the sea ice cover had in fact set a new record low, breaking the benchmark set in 2007, when the Northwest Passage was open for the first time in human history. As the Bremen group stated in a press release, "It seems to be clear that this is a further consequence of the man-made global warming..." According to the NSIDC, Arctic sea ice extent is not likely to eclipse the record low, which occurred in 2007, but it has come remarkably close.
Sept. 15, 2011 Update: The NSIDC announced today the Arctic sea ice minimum for the 2011 melt season has occurred, and was the second-lowest extent observed since at least 1979. Sea ice declined to within 61,800 square miles of the 2007 record low level.
According to Serreze, the steep sea ice decline seen this year is an indication that warming air and sea temperatures have primed the system in favor of more extreme melt seasons. Unlike in 2007, this summer did not see the sustained return of weather conditions that would have favored major ice loss. In 2007, it was unusually sunny and mild throughout much of the Arctic, and a unique atmospheric circulation pattern was in place that caused winds to funnel older, thicker sea ice out of the Arctic Ocean and into the North Atlantic. The winds, in effect, flushed the Far North of older and thicker sea ice cover, which was more resistant to melting, leaving thinner and therefore more vulnerable sea ice in its place.
Serreze called the weather setup in 2007 "nearly perfect" for melting sea ice. By comparison, he says, this season was "nothing to write home about."
So if weather conditions weren't aligned in favor of a major melt season, why did sea ice decline so much this year?
Serreze says the key lies in the long-term thinning of the sea ice cover that is "just starting to catch up with us." Studies show that the sea ice in the Arctic has become progressively thinner during the past three decades, and thinner sea ice is more vulnerable to melting from warming sea and air temperatures. With a relatively thin sea ice cover going into this year's melt season, it didn't require unique weather patterns to result in a big melt.
Total Arctic sea ice volume from the PIOMAS model, showing the volume of the mean annual cycle, the current year, and the 2007 record year. (Shaded areas indicate one and two standard deviations from the mean.) Credit: U. Washington.
One indication of the thinner sea ice cover is the fact that this year also set a new record for low sea ice volume, which is a combined measurement of sea ice extent and thickness. A group at the University of Washington's Applied Physics Lab uses a computer model known as PIOMAS to estimate sea ice volume, and their information shows that a new record was set this past August, beating the old record established only last year. The University of Washington (UW) estimates August sea ice volume was 62 percent below the 1979-2010 average.
Clearer Consequences of Sea Ice Loss
The decline in Arctic sea ice has important implications for human activities and wildlife not only in the vast Arctic region, but also in lower latitudes, since sea ice helps regulate the global climate and influence weather patterns. The past two winters have featured unusual weather patterns that brought very heavy snow to the Mid-Atlantic and Northeastern states, along with milder than normal conditions in Greenland and other parts of the Arctic, and scientists have been investigating a possible sea ice connection.
The sea ice and snow on the planet, collectively known as the cryosphere, are responsible for reflecting back to space some of the sunlight beaming down on the planet. When sea ice cover is lost, some of this reflectivity is lost as well, and the newly open ocean absorbs more heat from the sun. A study published earlier this year, based on observations of changing levels of snow and sea ice and trends in the reflectance of snow-covered regions over the past 30 years, suggests the overall loss of reflectivity from the Arctic region is more than double than what models have predicted.
Other research has linked declining Arctic sea ice cover to changes in wintertime atmospheric circulation patterns across the Northern Hemisphere. With the reduced sea ice coverage in the later summer and fall during recent years, both air and water temperatures in much of the Arctic have been unusually warm. Some scientists think this may be redirecting the flow of Arctic air down towards North America and Europe. This “Arctic paradox,” where warming in the Arctic may be accompanied by cooler than average winters on the continents, may become more common if the Arctic continues to absorb more heat.
The threat that sea ice loss poses for wildlife, such as the iconic polar bear, is well known, since certain species depend on sea ice for sustenance and shelter. During the past two years, large numbers of walruses have been observed on Alaska's rocky Arctic shoreline in late summer, having hauled themselves out of the water once sea ice cover retreated too far offshore for them to safely reach it. The U.S. Geological Survey released video footage this week of thousands of walruses that congregated in August near Point Lay, Alaska, in a repeat of a mass haulout event that occurred in the same area last year.
As the USGS explains, female Pacific walruses and their calves usually spend summers diving for feed in the waters of the Chukchi Sea, where they use sea ice cover for rest between their hunts for food. However, the loss of sea ice cover can cause them to come ashore in large numbers, which poses a danger to young walruses that can be crushed to death underneath other members of the herd.
Data Sources Account for Different Rankings
Serreze said the NSIDC's data shows the current difference between the 2011 sea ice minimum and the record year of 2007 is it too large to make up in any remaining melt days. "We are sitting at number two and I am pretty confident we're going to stay at number two," he said. Whether this season hits the record mark or not is irrelevant, he says, since studies show that sea ice decline is accelerating due in part to manmade climate change.
The Bremen group based its analysis on data from a sensor on the NASA Aqua satellite, while the NSIDC researchers rely on a satellite run by the Defense Department. According to the NSIDC, the Bremen group's data incorporates more small ice and open water features, and since the sea ice is more dispersed this year than it was in 2007, that may be contributing to their finding of a new record low. The differences between data sets are minor, however.
"While the University of Bremen and other data may show slightly different numbers, all of the data agree that Arctic sea ice is continuing its long-term decline," an NSIDC statement said.