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Arctic ice data shows double decline

Image of Arctic sea ice extent in August 2012.
Arctic sea ice extent for August 2012 was 1.8 million square miles (4.7 million square kilometers). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Image courtesy NSIDC.

The latest data from researchers at the US National Snow and Ice Data Center (NSIDC), and NASA show that Arctic sea ice extent is at its lowest point in the satellite era, which began in the 1970s. The area of ice lost per day is about the size of the Czech Republic or the US state of South Carolina.

"I'm on record saying that the Arctic Ocean could be essentially ice free at summer's end by the year 2030. I see no reason to change my opinion," said Mark Serreze, director of the NSIDC. "There will be winter ice for centuries to come, for even in a greenhouse-warmed world, it will get cold in the Arctic in winter, but the ice that forms will be thin, and will melt away in summer."

Sea ice extent is the area of ocean where there is at least some sea ice. As of 26 August 2012, arctic sea ice fell to 1.58 million square miles (4.10 million square kilometers). This area was 27,000 square miles (70,000 square kilometres) below the daily extent of 1.61 million square miles (4.17 million square kilometres) on 18 September 2007.

This new finding is taken from microwave data of Arctic brightness temperatures that are beamed from NASA's orbiting Terra and Defense Meteorological Satellite Program (DMSP) satellites. About 400 megabytes of data are received every day. "I think what is impressive is how quickly we get the information out," said Serreze. "In near real-time, we gather the satellite data, process it in-house, and then provide maps of sea ice extent the next day."

Algorithms are used to convert these brightness temperatures into ice concentrations. According to Serreze the newer generation computer models are somewhat conservative because the observed trend is bigger than the models are telling him. "Why this is so remains unclear," said Serreze.

The infrastructure that manages this analysis is made of two computing environments. One is the NSIDC/CU system, with over 80 servers and an advanced cooling and solar power system. It's linked to the CU MRI Janus high-performance computer in the University of Colorado, US, which has over 10,000 cores and one petabyte of disk storage. The other environment is the NASA EOSDIS, which provides archive services with over 500 terabytes of disk space.

A declining trend, but how bad is it?

Image of extent of Arctic sea ice on 26 August 2012.
The sea ice concentration from 26 August 2012 compared to the average sea ice minimum from 1979 through 2010 shown in orange. Image courtesy US Defense Meteorological Satellite Program's Special Sensor Microwave/Imager.

Since August 2012, the ice loss rate has averaged about 29,000 square miles (75,000 square kilometres) a day, which is about double the rate of decline normally seen at this time of year.

"The rapid loss of sea ice is unexpected," said James Overland, a research oceanographer at the US National Oceanic and Atmospheric Administration, who wasn't involved with this research. "Increased open water area in the Arctic summers allows more solar heat to be trapped by the Earth. This heat does not stay in the ocean but gets transferred to the atmosphere, where it can accelerate on-going changes in the Arctic, and have the potential to increase the frequency of extreme weather events further south."

But, further research is needed. The most recent paper published by NSIDC researchers in Geophysical Review Letterswas before the new data release. The NSIDC will publish a full analysis of the melt season in early October 2012.

- Adrian Giordani

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