New data from the National Snow and Ice Data Center (NSDIC) reveal that Arctic ice is continuing to melt at an alarming rate. Summer ice in the Arctic may all but disappear over the next few decades, much earlier than scientists had previously predicted.
At end September 2012, the extent of sea ice in the Arctic reached a record low according to NASA measurements. This surpassed the previous low recorded at end August this year as reported in the Digital Journal article, Arctic sea ice melting, now at record low. In their August report, Colorado based NSDIC had referred to the possibility of the minimum extent falling even lower and so it has proved with the September 2012 data now released.
Summer 2012 in the Arctic has been warmer than usual and NASA’s analysis, reported in the earlier article, was confirmed by the NSDIC as well as meteorological agencies in Japan, Norway and Denmark. The extent of Arctic sea ice, measured at the end of August, at 1.58 million square miles, was 30000 square miles less than the previous low set in 2007 and the lowest since NASA records began in 1979.
Scientific Visualization Studio, NASA Goddard Space Flight Center
The extent of Arctic sea ice on Aug. 26, 2012, the day the sea ice dipped to its previous smallest extent before the release of the data for September 2012.The line on the image shows the average minimum extent from the period covering 1979-2010, as measured by satellites. Every summer the Arctic ice cap melts down to what scientists call its “minimum” before colder weather builds the ice cover back up.
"In the context of what has happened in recent years, this indicates that the ice cover in the Arctic is changing fundamentally," said Walt Meier, a scientist at the NSDIC commenting on the August data. While in 2007, the summer weather was very favorable to the melting ice, in 2012, it is the delicacy of the ice cover that has contributed to the record retreat of Arctic sea ice.
"The previous record, set in 2007, occurred because of near perfect summer weather for melting ice. Apart from one big storm in early August, weather patterns this year were unremarkable. The ice is so thin and weak now, it doesn't matter how the winds blow." said Mark Serreze, director of the NSDIC in a report on the NSDIC website.
Arctic melt continues but Antarctic sea ice expands
"The Arctic used to be dominated by multiyear ice, or ice that stayed around for several years. Now it's becoming more of a seasonal ice cover and large areas are now prone to melting out in summer." So said Meier when the August Arctic sea ice figures were released and so it has proved with the ice survey details for September 2012 now released by NSDIC.
One of the curious features of the latest set of data is that Antarctic sea ice has seen a record expansion. According to NSIDC the reasons for this are ‘complex and surprising’ but are inextricably linked to global climate change.
At end September, the extent of Antarctic ice was 7.509 million square miles (19.45 million square kilometres), the highest since measurements began, reports 20minutes. For 30 years, scientists have observed a gradual expansion of southern polar ice. At first glance this might suggest Antarctic cooling but the southern expansion does not, on its own, invalidate the theory of global warming. NSIDC reports that temperatures over Antarctica were unremarkably near average this austral (southern) winter, contemporaneous with summer in the northern hemisphere. Scientists largely attribute the expansion of Antarctic sea ice to stronger circumpolar winds, which blow the sea ice outward from Antarctica thereby increasing its extent.
NSIDC scientist Ted Scambos said, "Antarctica's changes—in winter, in the sea ice—are due more to wind than to warmth, because the warming does not take much of the sea ice area above the freezing point during winter. Instead, the winds that blow around the continent, the "westerlies," have gotten stronger in response to a stubbornly cold continent, and the warming ocean and land to the north."
Researchers believe that climate change has created a "wind wall" that keeps the cold around the South Pole while the rest of the globe is warming. Ozone, too, has an effect. The hole over Antarctica promotes westerly winds, thus lowering temperatures.
Arctic sea ice shatters previous low records
Credit: National Snow and Ice Data Center
Arctic sea ice extent for September 2012 was 3.61 million square kilometers (1.39 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole
In September 2012, Arctic sea ice declined to its lowest extent since records began, reports NSIDC. The lowest extent was reached on September 16, dropping to 1.32 million square miles (3.41 million square kilometres). The average for the whole month was also the lowest on record at 1.39 million square miles (3.61 million square kilometres). In context, this places 2012 as the lowest for Arctic ice extent both for the daily minimum extent and the monthly average. Ice extent was 1.27 million square miles (3.29 million square kilometres) below the 1979 to 2000 average.
This year’s ice melt occurred without the unusual weather conditions that contributed to the extreme melt of 2007. "Atmospheric and oceanic conditions were not as conducive to ice loss this year, but the melt still reached a new record low," said NSIDC scientist Walt Meier. "This probably reflects loss of multi-year ice in the Arctic, as well as other factors that are making the ice more vulnerable." Multi-year ice is ice that has survived more than one melt season and is thicker than first-year ice.
NSIDC Director Mark Serreze said, "It looks like the spring ice cover is so thin now that large areas melt out in summer, even without persistent extreme weather patterns."
What happens next?
Each winter the Arctic ice cap grows as the sun sets for several months causing winter darkness. During the Arctic summer, in sunlight, the icecap melts, usually reaching its lowest extent each September.
The 2012 summer low ice extent followed the downward trend seen over the last 33 years. Scientists largely attribute this to warming temperatures caused by climate change. Since 1979, September Arctic sea ice extent has declined at the rate of 13% each decade. Summer sea ice extent is important because, among other things, it reflects sunlight, keeping the Arctic region cool and moderating global climate.
Besides the decline in sea ice extent, the ice cover has grown thinner and less resistant to summer melt. Recent data on the age of sea ice, which scientists use to estimate the thickness of the ice cover, shows that the youngest, thinnest ice, which has survived only one or two melt seasons, now makes up by far the largest part of the ice cover. This means that as each year passes, the ice cover melts faster than previous years.
Climate models previously suggested that the Arctic could lose almost all of its summer ice cover by 2100, but in recent years, ice extent has declined faster than the models predicted. Serreze said, "The big summer ice loss in 2011 set us up for another big melt year in 2012. We may be looking at an Arctic Ocean essentially free of summer ice only a few decades from now."
NSIDC scientist Julienne Stroeve recently spent three weeks in the Arctic Ocean on an icebreaker ship, and was surprised by how thin the ice was and how much open water existed between the individual ice floes. "According to the satellite data, I expected to be in nearly 90% ice cover, but instead the ice concentrations were typically below 50%," she said.