Starship Asterisk*

[i]This visualization shows the extent of Arctic sea ice on Aug. 26, 2012, the day the sea ice dipped to its smallest extent ever recorded in more than three decades of satellite measurements, according to scientists from NASA and the National Snow and Ice Data Center. The data is from the U.S. Defense Meteorological Satellite Program’s Special Sensor Microwave/Imager. 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. The size of this minimum remains in a long-term decline. The extent on Aug. 26. 2012 broke the previous record set on Sept. 18, 2007. But the 2012 melt season could still continue for several weeks. (Image credit: Scientific Visualization Studio, NASA Goddard Space Flight Center)[/i]

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The extent of the sea ice covering the Arctic Ocean has shrunk. According to scientists from NASA and the NASA-supported National Snow and Ice Data Center (NSIDC) in Boulder, Colo., the amount is the smallest size ever observed in the three decades since consistent satellite observations of the polar cap began.

The extent of Arctic sea ice on Aug. 26, as measured by the Special Sensor Microwave/Imager on the U.S. Defense Meteorological Satellite Program spacecraft and analyzed by NASA and NSIDC scientists, was 1.58 million square miles (4.1 million square kilometers), or 27,000 square miles (70,000 square kilometers) below the Sept. 18, 2007, daily extent of 1.61 million square miles (4.17 million square kilometers).

The sea ice cap naturally grows during the cold Arctic winters and shrinks when temperatures climb in the spring and summer. But over the last three decades, satellites have observed a 13 percent decline per decade in the minimum summertime extent of the sea ice. The thickness of the sea ice cover also continues to decline.

"The persistent loss of perennial ice cover -- ice that survives the melt season -- led to this year's record summertime retreat," said Joey Comiso, senior research scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "Unlike 2007, temperatures were not unusually warm in the Arctic this summer."

The new record was reached before the end of the melt season in the Arctic, which usually takes place in mid- to late-September. Scientists expect to see an even larger loss of sea ice in the coming weeks.

"In 2007, it was actually much warmer," Comiso said. "We are losing the thick component of the ice cover. And if you lose the thick component of the ice cover, the ice in the summer becomes very vulnerable."

"By itself it's just a number, and occasionally records are going to get set," NSIDC research scientist Walt Meier said about the new record. "But in the context of what's happened in the last several years and throughout the satellite record, it's an indication that the Arctic sea ice cover is fundamentally changing."

For images, video and background on sea ice, go to:
http://svs.gsfc.nasa.gov/Gallery/Arctic ... urces.html

For National Snow and Ice Data Center information on Arctic Sea Ice, go to:
http://nsidc.org/arcticseaicenews/

http://www.flickr.com/photos/gsfc/sets/ ... 7568/show/

[attachment=0]npseaice_ssi_2012239_captioned.png[/attachment][/i][/b]

On August 26, 2012, the extent of Arctic water covered by sea ice fell below 4.17 million square kilometers (1.61 million square miles), the record minimum set in 2007. Arctic sea ice stood at 4.10 million square kilometers (1.58 million square miles), the National Snow and Ice Data Center (NSIDC) and NASA reported on August 27.

This image was made from observations collected by the Special Sensor Microwave Imager/Sounder (SSMIS) on the satellites of the U.S. Defense Meteorological Satellite Program. Sea ice appears in shades of white and light blue, with white indicating the greatest concentrations of ice. Open ocean water is blue, and land is gray. The yellow outline shows the median minimum ice extent for 1979-2000—in other words, areas that were at least 15 percent ice-covered in at least half the years between 1979 and 2000—on August 26.

In April 2012, Arctic sea ice reached a near-average extent, but periods of intense ice loss in June and August 2012 helped push Arctic sea ice below the previous record from 2007. In 2007, high pressure over the Beaufort Sea and low pressure over northeastern Eurasia pulled in warm winds, which melted the ice and pushed it away from the Siberian and Alaskan coastlines. Although these pressure patterns also occurred in 2012, they were much less persistent. Nonetheless sea ice melt rates still reached up to 150,000 square kilometers (57,900 square miles) per day in 2012, more that twice the long-term rate.

By early July, Arctic sea ice melting was three weeks ahead of schedule, but then slowed somewhat. Ice loss rates picked up again in early August, “probably the highest in the record for that period,” according to NSIDC staff scientist Walt Meier. Because the old record has been passed in August 2012—and Arctic sea ice generally reaches its lowest annual extent in September—it is likely that the amount of ice cover may continue to shrink. NSIDC provides an overview of melt rates in its Arctic Sea Ice News and Analysis blog.

Arctic sea ice reached previous record lows in 2002, 2005, and 2007. (The 2007 record low was previously recorded as 4.13 million square kilometers, or 1.59 million square miles. Slightly different processing and quality-control procedures used by NASA Goddard Space Flight Center led to revised estimates of sea ice extent.) Over the past decade, sea ice extent in the Arctic has been well below the 1979–2000 average.

The loss of so much sea ice means that when ice reforms over the winter, it is “first-year ice,” which is much thinner than sea ice that has persisted over multiple years. Joey Comiso, senior research scientist at NASA Goddard Space Flight Center, explained that the loss of this multiyear ice contributed to record low ice extent in 2012. Another possible factor at work in the summer of 2012, Comiso suggested, may have been a strong summer cyclone, which broke up ice in the Central Arctic and dispersed it into warmer waters.

NSIDC director Mark Serreze differed with Comiso somewhat on the role of the storm. “The ice was already so thin it was ready to go,” said Serreze. “2012 likely would have set a new record without the storm.”

Once sea ice loss gets underway, it can become a self-reinforcing process. Because there is less light-colored ice to reflect the Sun’s energy back into space, more energy is absorbed by darker ocean water.

A new record for sea ice was not the only unusual event in the Arctic in the summer of 2012. July 2012 saw widespread melt on the Greenland Ice Sheet and the calving of a new iceberg from Greenland’s Petermann Glacier. By early August, rapid sea ice retreat left the Northwest Passage nearly open, although ice moved back into parts of the passage later in the month.

The new record low for sea ice in 2012 fits into a larger pattern of a changing Arctic. Regarding the rapid loss of Arctic sea ice, Serreze remarks, “What is perhaps most surprising is that we are no longer surprised.”

The American Meteorological Society today released an updated Statement on Climate Change (pdf), replacing the 2007 version that was in effect. The informational statement is intended to provide a trustworthy, objective, and scientifically up-to-date explanation of scientific issues of concern to the public. The statement provides a brief overview of how and why global climate has changed in recent decades and will continue to change in the future. It is based on the peer-reviewed scientific literature and is consistent with the majority of current scientific understanding as expressed in assessments and reports from the Intergovernmental Panel on Climate Change, the U.S. National Academy of Sciences, and the U.S. Global Change Research Program.

“This statement is the result of hundreds of hours of work by many AMS members over the past year,” comments AMS Executive Director Keith Seitter. “It was a careful and thorough process with many stages of review, and one that included the opportunity for input from any AMS member before the draft was finalized.” The AMS releases statements on a variety of scientific issues in the atmospheric and related sciences as a service to the public, policy makers, and the scientific community.

[i]2012 Sep 26 - Credit: Jesse Allen; Data: DMPS SSMIS/NSIDC[/i]

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Two weeks after a new record was set in the Arctic Ocean for the least amount of sea ice coverage in the satellite record, the ice surrounding Antarctica reached its annual winter maximum—and set a record for a new high. Sea ice extended over 19.44 million square kilometers (7.51 million square miles) in 2012, according to the National Snow and Ice Data Center (NSIDC). The previous record of 19.39 million kilometers (7.49 million square miles) was set in 2006.

The map above shows sea ice extent around Antarctica on September 26, 2012, when ice covered more of the Southern Ocean than at any other time in the satellite record. The map is based on an NSIDC analysis of data from the Special Sensor Microwave/Imagers flown in the Defense Meteorological Satellite Program. Land is dark gray, and ice shelves—which are attached to land-based glaciers but floating on the ocean—are light gray. The yellow outline shows the median sea ice extent in September from 1979 to 2000. Sea ice extent is defined as the total area in which the ice concentration is at least 15 percent.

The graph of NSIDC data shows the maximum extent for each September since 1979 in millions of square kilometers. There is a lot of variability from year to year, though the overall trend shows growth of about 0.9 percent per decade.

According to a recent study by sea ice scientists Claire Parkinson and Donald Cavalieri of NASA’s Goddard Space Flight Center, Antarctic sea ice increased by roughly 17,100 square kilometers per year from 1979 to 2010. Much of the increase, they note, occurred in the Ross Sea, with smaller increases in Weddell Sea and Indian Ocean. At the same time, the Bellinghausen and Amundsen Seas have lost ice. “The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation,” they noted.

“The year 2012 continues a long-term contrast between the two hemispheres, with decreasing sea ice coverage in the Arctic and increasing sea ice coverage in the Antarctic,” Parkinson added. “Both hemispheres have considerable inter-annual variability, so that in either hemisphere, next year could have either more or less sea ice than this year. Still, the long-term trends are clear, but not equal: the magnitude of the ice losses in the Arctic considerably exceed the magnitude of the ice gains in the Antarctic.”

On their Arctic Sea Ice News and Analysis blog, scientists from the University of Colorado wrote: “Comparing winter and summer sea ice trends for the two poles is problematic since different processes are in effect. During summer, surface melt and ice-albedo feedbacks are in effect; winter processes include snowfall on the sea ice, and wind. Small changes in winter extent may be a more mixed signal than the loss of summer sea ice extent. An expansion of winter Antarctic ice could be due to cooling, winds, or snowfall, whereas Arctic summer sea ice decline is more closely linked to decadal climate warming.”