Figure 1. Arctic sea ice extent on July 17, 2011 was 7.56 million square kilometers (2.92 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data Center
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Overview of conditions

As of July 17, 2011, Arctic sea ice extent was 7.56 million square kilometers (2.92 million square miles), 2.24 million square kilometers (865,000 square miles) below the 1979 to 2000 average. Sea ice is particularly low in the Barents, Kara, and Laptev Seas (the far northern Atlantic region), Hudson Bay and Baffin Bay.

Figure 2. The graph above shows daily Arctic sea ice extent as of July 17, 2011, along with daily ice extents for previous low-ice-extent years. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, and dark gray shows the 1979 to 2000 average. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data Center
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Conditions in context

Arctic sea ice extent declined rapidly through the first two weeks of July, at a rate averaging nearly 120,000 square kilometers (46,000 square miles) per day. Ice extent is now tracking below the year 2007, which saw the record minimum September extent.

During the first half of July, a high-pressure cell persisted over the northern Beaufort Sea, as it did in June, and is linked to the above-average air temperatures over much of the Arctic Ocean. To date in July, air temperatures over the North Pole (at the 925 millibar level, or roughly 1,000 meters or 3,000 feet above the surface) were 6 to 8 degrees Celsius (11 to 14 degrees Fahrenheit) higher than normal, while temperatures along the coasts of the Laptev and East Siberian seas were 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) higher than average. By contrast, temperatures through the first half of July over the Kara Sea have been 2 to 5 degrees Celsius (4 to 9 degrees Fahrenheit) lower than average.

Figure 3. Satellite images from the NASA AMSR-E sensor (large image) and MODIS (inset), show areas of low ice concentration north of Alaska. Both images were obtained on July 15, 2011. In the AMSR-E image, purple indicates areas of high sea ice concentration, while yellow and red indicates lower ice concentration. Blue shows open water and green shows land.—Credit: National Snow and Ice Data Center courtesy IUP Bremen AMSR-E (main image), NASA MODIS Rapid Response Arctic Mosaic (inset)
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A closer look at sea ice concentration

The sea ice extent data that NSIDC uses come from the Special Sensor Microwave Imager/Sounder (SSMIS) on U.S. Department of Defense satellites. Data from other satellites, while not as useful for studying long-term trends, can show more detail about ice cover in particular regions. Currently data from two NASA satellite sensors, the Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer for EOS (AMSR-E), show areas of low ice concentration north of Alaska. Ice in these areas is likely to melt out in coming weeks.

Both the Northwest Passage (through the channels of the Canadian Arctic Islands) and the Northern Sea Route (along the Siberian coast) are still choked with ice.

Figure 4. This map shows the difference between average date of melt onset, when ice melt starts, and the date of melt onset this year. Red indicates earlier than normal melt, blue shows later than normal melt. The darkest red is an anomaly of 50 days early or more. White areas show no anomaly, that is they melted no earlier or later than normal. The gray area over the North Pole indicates where no data are available.—Credit: NSIDC, data from Jeffrey Miller and Thorsten Markus, NASA GSFC.
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Early start to Arctic melt

When sea ice starts to melt in spring, small ponds known as melt ponds form on its surface. The small pools create a darker surface (a lower albedo) that fosters further melt. How early sea ice melt starts is one indicator of how much the ice will melt in a given year. New research by Don Perovich and colleagues shows that an early start to sea ice melt increases the total amount of sunlight absorbed through the melt season.

Data processed by researchers Thorsten Markus and Jeffrey Miller at the NASA Goddard Space Flight Center reveal that melt began earlier than normal in both the Chukchi Sea, just north of the Bering Strait, and the Barents, Kara, and Laptev seas. Surface melting on the sea ice began from two weeks to two months earlier than the 1979 to 2000 average in these areas. However, in Baffin Bay and Hudson Bay, a cool spring led to a later start for surface melt, especially in Hudson Bay. Subsequent warm conditions have nevertheless led to rapid ice melt.

Figure 5. This snow cover anomaly map for May and June, 2011 shows the percent difference between snow cover extent this summer, compared with average snow cover for May and June 1971 to 2000. Areas in orange and red indicate lower-than-usual snow cover, while regions in blue had more snow than normal. —Credit: NSIDC courtesy D. Robinson, Global Snow Cover Lab, Rutgers University
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Low summer snow cover in the Northern Hemisphere

As noted in our May 4 post, snow cover in central Russia retreated early in response to warm conditions this spring. Updated analyses provided by the Global Snow Cover Lab at Rutgers University reveal that snow cover remained very low for May and June. Even though some mountain regions in the U.S. and Canada saw greater-than-normal snow cover, snow cover for the Northern Hemisphere as a whole for May and June was the second lowest since the start of snow cover records in 1966.

According to David Robinson, head of the Rutgers Snow Cover Lab, a new pattern is emerging in which the Northern Hemisphere is cloaked in above-average snow during late autumn, winter, and early spring, followed by rapid melt and retreat in May and June. While snow cover varies from year to year, the far north has seen a clear trend towards less spring snow cover over the last thirty years.

Figure 1. Arctic sea ice extent for June 2011 was 11.01 million square kilometers (4.25 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data Center
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Overview of conditions

Average ice extent for June 2011 was 11.01 million square kilometers (4.25 million square miles). This is 140,000 square kilometers (54,000 square miles) above the previous record low for the month, set in June 2010, and 2.15 million square kilometers (830,000 square miles) below the average for 1979 to 2000.

June ice extent was lower than normal in much of the Arctic, but the Kara Sea region had particularly low ice extent. Ice has also started to break up off the coast of Alaska in the Beaufort Sea. These open water areas absorb the sun’s energy, which will help to further ice melt through the summer.

Figure 2. The graph above shows daily Arctic sea ice extent as of July 4, 2011, along with daily ice extents for previous low-ice-extent years in the month of May. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, and dark gray shows the 1979 to 2000 average. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data Center
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Conditions in context

Ice extent during June 2011 declined at an average rate of 80,800 square kilometers (31,200 square miles) per day, about 50% faster than the average decline rate for June 1979 to 2000. Ice extent declined more slowly than in June 2010, the year with the lowest average ice extent for the month. However, ice declined faster than in June 2007, the year when September sea ice extent reached the lowest in the satellite record. Ice loss in the Kara Sea was especially fast, more than double the average rate and close to double the rate of the past four years (2007 to 2010). Sea ice has largely disappeared in the southern Kara Sea, which normally still has considerable ice cover at this time of year.

At the end of June, Arctic sea ice extent was 9.54 million square kilometers (3.68 million square miles), 375,000 square kilometers (145,000 square miles) less than the ice extent on June 30, 2007 and 264,000 square kilometers (102,000 square miles) above the record low for June 30, set in 2010.

Figure 3. Monthly June ice extent for 1979 to 2011 shows a decline of 3.6% per decade. —Credit: National Snow and Ice Data Center
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June 2011 compared to past years

Arctic sea ice extent in June 2011 was the second lowest in the satellite record, consistent with the overall downward trend of the past thirty years. The lowest year for June was 2010. June average ice extent exceeded 12 million square kilometers (4.6 million square miles) 16 out of 21 years between 1979 and 1999, but has been below that value every year since.

Figure 4. This map of air temperature anomalies for June 2011 shows warmer than average temperatures over much of the Arctic Ocean, except in the Greenland and Beaufort seas, where temperatures were near and slightly below normal.

—Credit: NSIDC courtesy NOAA ESRL PSD
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Warmer than average temperatures continue

Air temperatures for June were 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) warmer than average over most of the Arctic Ocean, except in the Beaufort and Greenland seas, where temperatures were near normal or slightly below normal. High pressure dominated most of the central Arctic, with the highest pressures over the Beaufort Sea. The monthly averaged pressure field shows a circulation pattern somewhat similar to a pattern known as the dipole anomaly, with unusually high pressure over the Beaufort Sea and unusually low pressure over central Siberia. Similar patterns have become common in recent summers.

Figure 5. This MODIS image from June 28 shows ice in the Beaufort Sea region off the coast of Barrow, breaking up into smaller floes and open water. But while open water is apparent, a layer of ice still clings to the coastline.—Credit: NSIDC courtesy MODIS Rapid Response System Arctic Mosaic
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A detailed view from MODIS data

Data from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) provide a detailed view of seasonal ice breakup. Along the Alaska coast, large ice floes are breaking away near the coast southwest of Barrow. However, in this image from June 28, a narrow strip of landfast ice remained anchored to the coast, bounded on the seaward side by grounded ridged ice. That last bit of ice broke up around July 3, according to the Geophysical Institute at the University of Alaska, Fairbanks

Sea ice breakup in Barrow is defined as the time when the landfast ice along the coast starts to move. The timing of this breakup is closely tied to the cumulative amount of solar energy input to the Barrow region—the amount of sunshine the area receives—after June 5. The Geophysical Institute uses this relationship to forecast the breakup: this year they predicted the breakup to occur on July 11.