Overview of conditions

Average ice extent for November 2011 was 10.01 million square kilometers (3.86 million square miles), 1.30 million square kilometers (502,000 square miles) below the 1979 to 2000 average. This was 170,000 square kilometers (66,000 square miles) above the average for November 2006, the lowest extent recorded for that month in the satellite data record.

At the end of November, ice extent remained below the 1979 to 2000 average in the Chukchi, Barents and Kara seas, and Hudson Bay was still nearly ice free. Ice extent was near average in the East Greenland and the Bering seas. These ice conditions may be connected to a strong positive phase of the Arctic Oscillation, which began during the last week of November. A positive Arctic Oscillation tends to help move ice out of Fram Strait and into the North Atlantic.

Conditions in context

The Arctic sea ice cover grew at an average pace through November, despite a brief slowdown early in the month. However, the ice extent remained far below average. Overall, the Arctic gained 2.36 million square kilometers (911,000 square miles) of ice during the month, which was slightly more than the average ice gain for November of 2.13 million square kilometers (822,000 square miles). On November 30, Arctic sea ice extent was 10.85 million square kilometers (4.19 million square miles), 625,000 square kilometers (241,000 square miles) more than the ice extent on November 30, 2006, the lowest extent on November 30 in the satellite record.

November 2011 compared to past years

Ice extent for November 2011 was the third lowest in the satellite record for the month, behind 2006 and 2010. The linear rate of decline for November over the satellite record is now 53,200 square kilometers (20,500 square miles) per year, or 4.7% per decade relative to the 1979 to 2000 average.

Figure 4. This map of air temperature anomalies at the 925 hPa level (approximately 3000 feet) for November 2011 shows near-normal or lower-than-average temperatures over much of the Arctic basin, while air
temperatures over the Kara and Barents Seas and Greenland were warmer than normal.—Credit: NSIDC courtesy NOAA/ESRL PSD
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Atmospheric conditions and an Arctic storm

Low sea ice extent this summer may be contributing to warmer November temperatures and lower November ice extents in some areas. In recent years, low sea ice extent in the summer has been linked to unusually warm autumn air temperatures, resulting from the larger areas of open water that absorb more heat during the summer. This heat must escape back to the atmosphere in the fall, before the ocean can freeze over. This escaping heat contributes to warmer-than-average conditions, which have been most apparent in October but may also extend into November.

This November, air temperatures were near or slightly below average over most of the Arctic basin, but higher air temperatures were found over the Kara and Barents seas, the East Greenland Sea and the Canadian Archipelago: in general, the regions with above-average temperatures were the regions with below-average ice extent.

Lower than average temperatures in the Beaufort and Bering seas may be in part related to a strong low-pressure system that developed early in the month. In early November, a low-pressure system moved up from the Bering Sea into the Arctic, bringing strong winds and flooding to coastal villages in western Alaska. With a core pressure as low as 947 millibars, it was the strongest November storm to hit northwest Alaska since 1974. Much of the area affected by the storm was in areas that are typically ice-free, so the lack of sea ice probably did not play a direct role in the damage. For more information, see the Icelights article: An Arctic Hurricane?

Northern Hemisphere snow cover

The positive phase of the Arctic Oscillation also tends to be associated with unusually warm conditions over Scandinavia. According to Sweden’s meteorological office, the country’s average temperature for the month of November so far was 7 degrees Celsius (12.6 degrees Fahrenheit) above average. Typically by November, much of Scandinavia is already covered with snow, but maps from the Rutgers University Global Snow Lab show that snow cover levels were anomalously low over Scandinavia and northwestern Europe during November. Below-normal snow conditions were also evident over most of the continental United States, except for the northern Rockies.

However, overall Northern Hemisphere snow cover was more extensive than normal this November, with most of the extra snow cover found in Canada and Russia. Snow covered an average of 36.2 million square kilometers (14.0 million square miles) of Northern Hemisphere land. This is 2.79 million square kilometers (1.08 million square miles) above the 1971 to 2000 mean, and ranks as the fourth most extensive cover in the past 46 years of satellite-derived snow cover records.

Along with sea ice, change in snow cover can be an indicator of climate change. Higher air temperatures have resulted in a decline in snow cover in the spring, but in fall, the signal is more mixed. Some scientists also suspect there may be a link between early season high-latitude snow cover and winter weather patterns in the mid-latitudes. Judah Cohen and Justin Jones of Atmospheric and Environmental Research in Massachusetts have examined a potential link and suggest that this information could be used to improve winter forecasts. However, this research is still preliminary.

A look at Antarctica

Arctic Sea Ice News & Analysis generally focuses on sea ice conditions in the Arctic, since these conditions are closely tied to climate and weather in the Northern Hemisphere. A seasonal cover of sea ice also surrounds the continent of Antarctica. Since reaching its seasonal maximum in September, Antarctic sea ice has been near average in recent months. In November, Antarctic extent was 16.15 million square kilometers (6.24 million square miles), 87,000 square kilometers (33,600 square miles) less than the 1979 to 2000 average. In recent years, the sea ice cover that surrounds the Antarctic continent has been higher than average, even reaching near-record highs.

Antarctic sea ice varies much more from year to year than Arctic sea ice, but overall, ice extent around Antarctica has been growing slightly over the past 30 years. The ice cover around Antarctica also varies widely by region, with some regions, for example the Amundsen and Bellingshausen seas, showing strong declines over the past three decades, while other regions such as the Ross Sea have seen significant increases. For more information on Antarctic sea ice, see All About Sea Ice: Antarctic vs. Arctic. Antarctic sea ice data are available from the Sea Ice Index.

Figure 1. Arctic sea ice extent for October 2011 was 7.10 million square kilometers (2.74 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. —Credit: National Snow and Ice Data Center
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Overview of conditions

Average ice extent for October 2011 was 7.10 million square kilometers (2.74 million square miles), 2.19 million square kilometers (846,000 square miles) below the 1979 to 2000 average. This was 330,000 square kilometers (127,000 square miles) above the average for October 2007, the lowest extent in the satellite record for that month. By the end of October, ice extent remained below the 1979 to 2000 average in the Beaufort and Chukchi seas and in the Barents and Kara seas. Extent was near average in the East Greenland Sea. New ice growth has closed both the Northwest Passage and the Northern Sea Route.

Figure 2. The graph above shows daily Arctic sea ice extent as of November 6, 2011, along with the lowest ice extents in the preceding decades, 1984 and 1999. 2011 is shown in light blue. 2007, the year with the record low minimum, is dashed green. Purple indicates 1999 and light green shows 1984. 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 increased rapidly through October. Ice extent during October 2011 increased at an average rate of 114,900 square kilometers (44,360 square miles) per day, about 40% faster than the average growth rate for October 1979 to 2000. On October 30, Arctic sea ice extent was 8.41 million square kilometers (3.25 million square miles), 226,000 square kilometers (87,300 square miles) more than the ice extent on October 30, 2007, the lowest extent on that date in the satellite record.

During the month of October, the freeze-up that begins in September kicks into high gear. The rate of freeze-up depends on several factors including the atmospheric conditions and the amount of heat in the ocean that was accumulated during the summer. However, each decade, the October extent has started from a lower and lower point, with the record low extent during the 1980s (1984) substantially higher than the record low extent during the 1990s (1999), which in turn is substantially higher than the record low extent during the 2000s (2007).

Figure 3. Monthly October ice extent for 1979 to 2011 shows a decline of 6.6% per decade. —Credit: National Snow and Ice Data Center
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October 2011 compared to past years

Ice extent for October 2011 was the second lowest in the satellite record for the month, behind 2007. The linear rate of decline for October over the satellite record is now -61,700 square kilometers (-23,800 square miles) per year, or -6.6% per decade relative to the 1979 to 2000 average.

Figure 4. This map of air temperature anomalies at the 925 hPa level (approximately 3000 feet) for October 2011 shows unusually high temperatures over most of the Arctic Ocean (yellow shading) and unusually low temperatures over the eastern Canadian Arctic Archipelago and Greenland (blue shading). —Credit: National Snow and Ice Data Center
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Atmospheric conditions

In recent years, low sea ice extent in the summer has been linked to unusually warm temperatures at the surface of the Arctic Ocean in the fall. This pattern appeared yet again this fall.

Air temperatures over most of the Arctic Ocean for October 2011 ranged from 1 to 4 degrees Celsius (1.8 to 7.2 degrees Fahrenheit) above average, measured at the 925 millibar level, about 1,000 meters or 3,000 feet above the surface. However, over the eastern Canadian Arctic and Greenland, temperatures were as much as 3 degrees Celsius (5.4 degrees Fahrenheit) below average.

These temperature anomalies in part reflect a pattern of above-average sea level pressure centered over the northern Beaufort Sea, and lower than average sea level pressure extending across northern Eurasia. This pattern is linked to persistence of the positive phase of the Arctic Oscillation through most of the month. These pressure and temperature anomalies tend to bring in heat from the south, warming the Eurasian coast, but they also lead to cold northerly winds over the eastern Canadian Arctic Archipelago. However, along the Siberian coast and in the Beaufort and Chukchi seas, warmer temperatures came primarily from the remaining areas of open water in the region, as heat escaped from the water. These effects are more strongly apparent in the surface air temperatures: average October temperatures in the region were 5 to 8 degrees Celsius (9.0 to 14.4 degrees Fahrenheit) above average.

Figure 5. The top panel of this figure shows the number of open water days for the approximate 75 kilometer (46.6 mi) coastal zone along the Beaufort Sea (data for each year and linear trend). The bottom panel shows the average annual coastal erosion rate for three periods, 1979-1999, 2000-2007 and 2008-2009. —Credit: NSIDC courtesy Irina Overeem, CU Boulder
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Sea ice loss and coastal erosion

Declining sea ice in the Arctic has led to increasing erosion rates along the coast of the Beaufort Sea over the past fifty years, according to a new study led by Irina Overeem of the University of Colorado Institute for Arctic and Alpine Research (INSTAAR). Their study used a wave model driven by sea ice position and wind data.

As the period of open water on the coast of the Beaufort Sea has increased, so has the mean annual erosion rate, the study showed. From 1979 to 1999, the average erosion rate was 8.5 meters (27.9 feet) per year. The average rate over the period 2000 to 2007 was 13.6 meters (44.6 feet) per year, while the rate for the last two years of the record, 2008 to 2009, was 14.4 meters (47.2 feet) per year.

With a longer open water season, ocean water warms more and waves eat away at the coastline. The sediments comprising the coastal bluffs are locked together by permafrost—hard frozen ground with a concrete-like consistency. As the waves lap at the permafrost, they also help to thaw it, making the ground much more vulnerable to erosion.

Figure 1. Arctic sea ice extent for September 2011 was 4.61 million square kilometers (1.78 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.—Credit: National Snow and Ice Data Center
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Overview of conditions

Average ice extent for September 2011 was 4.61 million square kilometers (1.78 million square miles), 2.43 million square kilometers (938,000 square miles) below the 1979 to 2000 average. This was 310,000 square kilometers (120,000 square miles) above the average for September 2007, the lowest monthly extent in the satellite record. Ice extent was below the 1979 to 2000 average everywhere except in the East Greenland Sea, where conditions were near average.

As in recent years, northern shipping routes opened up this summer. The Northern Sea Route opened by mid August and still appeared to be open as of the end of September. The southern “Amundsen Route” of the Northwest Passage, through the straits of the Canadian Arctic Archipelago, opened for the fifth year in a row. Overall, sea ice in the wider and deeper northern route through Parry Channel reached a record low, according to Stephen Howell of Environment Canada, based on Canadian Ice Service analysis. Parry Channel had a narrow strip of ice that blocked a short section of the channel, but it did appear to open briefly in early September.

For additional numbers for previous years, see Table 1.

Figure 2. The graph above shows daily Arctic sea ice extent as of October 1, 2011, along with daily ice extents for the previous three lowest years for the minimum ice extent. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, purple shows 2008, 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

While the melt season in 2011 got off to a slow start, the ice loss pace quickened during June. Ice retreated quite rapidly in the Kara and Barents seas, with rates more than double the average rate. Rapid ice loss continued during the first half of July but then slowed considerably as a series of low pressure systems moved over the central Arctic Ocean. By the end of July, ice extent was slightly above that seen in 2007.

Ice extent stayed above 2007 for the remainder of the melt season, reaching its minimum of 4.33 million square kilometers (1.67 million square miles) on September 9, 2011. Since the minimum, a rapid freeze-up has begun. On October 1, the five-day average extent rose above 5 million square kilometers (1.93 million square miles).

Figure 3. Monthly September ice extent for 1979 to 2011 shows a decline of 12.0% per decade.—Credit: National Snow and Ice Data Center
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September 2011 compared to past years

Ice extent for September 2011 was the second lowest in the satellite record for the month. The last five years (2007 to 2011) have had the five lowest September extents in the satellite record. The linear rate of decline is now -84,700 square kilometers (-32,700 square miles) per year, or -12% per decade relative to the 1979 to 2000 average. In contrast to 2007, when a “perfect storm” of atmospheric and ocean conditions contributed to summer ice loss, this year’s conditions were less extreme. From the beginning of the melt season in March, to the minimum extent on September 9, the Arctic Ocean lost 10.3 million square kilometers (4.0 million square miles) of sea ice. It was the fifth year in a row with more than 10 million square kilometers of ice extent change from maximum to minimum. In comparison, the average seasonal ice loss during the 1980s was 9.0 million square kilometers (3.5 million square miles)

Figure 4. Ice motion charts for August 2011 show different movement patterns for this summer compared to 2007. The arrows show the direction of ice motion, with larger arrows indicating stronger motion. In 2007, northward ice motion helped push the ice together and flush it out of the Arctic.—Credit: National Snow and Ice Data Center
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Atmospheric conditions

In 2007, a persistent dipole anomaly weather pattern, with unusually high pressure over the Beaufort Sea and unusually low pressure over the Kara Sea, helped contribute to the record ice loss. This pattern resulted in strong southerly winds from the Bering Strait region across the North Pole, which brought warmer winds and ocean waters northward to melt the ice edge and push the ice northward. In addition, especially strong high pressure over the Beaufort and Chukchi Seas in June 2007 resulted in less than average cloudiness, allowing more sunlight to reach the ice.

The Arctic saw a similar weather pattern this summer, but not as strong and persistent as in 2007. The location of the high and low pressure centers was also shifted, so that the winds blew east to west instead of toward the north as in 2007. This shift is reflected in the movement of the sea ice, particularly during August.

Patterns of air temperatures (measured at the 925 millibar level or about 1,000 meters or 3,000 feet above the surface) were also quite different this year compared to 2007. In summer 2007, temperatures in the Beaufort and Chukchi Seas were 5 degrees Celsius (9 degrees Fahrenheit) above average. This year, temperatures in that region were near average, but north of Greenland and in the Canadian Archipelago, conditions were even warmer than in 2007. These high temperatures likely played a role in the opening of the Northwest Passage.

Figure 5. Sea surface temperatures this year were generally lower than in 2007, although some areas of the ocean surface still had higher than average temperatures.—Credit: NSIDC courtesy M. Steele and W. Ermold, Univ. Washington PSC, and NOAA
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Sea surface temperatures

Ocean sea surface temperatures (SSTs), based on National Oceanographic and Atmospheric Administration (NOAA) data provided by Michael Steele and Wendy Ermold of the University of Washington Polar Science Center, indicate above normal temperatures on the surface of the Arctic Ocean. However, the temperatures anomalies were not as extreme as in 2007 and were comparable to those recorded for 2009 and 2010. These lower temperatures may be the result of less solar heating of the exposed ocean surface or less transport of warm waters from the south. In 2007, ice retreated early from the shores of Alaska and Siberia, allowing the ocean mixed layer to heat up and enhance melting of the ice from below. In contrast, ice was slower to retreat in this region in summer 2011, and less bottom melt was observed.

Figure 6. Data on ice age show that coverage of the oldest, thickest ice types (ice four years or older) has declined over the past 28 years.—Credit: National Snow and Ice Data Center courtesy J. Maslanik, C. Fowler, and M. Tschudi, U. Colorado Boulder
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Ice remains younger, thinner

Why did ice extent fall to a near record low without the sort of extreme weather conditions seen in 2007? One explanation is that the ice cover is thinner than it used to be; the melt season starts with more first-year ice (ice that formed the previous autumn and winter) and less of the generally thicker multi-year ice (ice that has survived at least one summer season). First- and second-year ice made up 80% of the ice cover in the Arctic Basin in March 2011, compared to 55% on average from 1980 to 2000. Over the past few summers, more first-year ice has survived than in 2007, replenishing the younger multi-year ice categories (2- to 3-year-old ice). This multi-year ice appears to have played a key role in preserving the tongue of ice extending from near the North Pole toward the East Siberian Sea. However, the oldest, thickest ice (five or more years old) has continued to decline, particularly in the Beaufort and Chukchi Seas. Continued loss of the oldest, thickest ice has prevented any significant recovery of the summer minimum extent. In essence, what was once a refuge for older ice has become a graveyard.

Figure 1. Arctic sea ice extent on September 9, 2011 was 4.33 million square kilometers (1.67 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.—Credit: National Snow and Ice Data Center
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Overview of conditions

On September 9, 2011 sea ice extent dropped to 4.33 million square kilometers (1.67 million square miles). This appears to have been the lowest extent of the year, and may mark the point when sea ice begins its cold-season cycle of growth. However, a shift in wind patterns or late season melt could still push the ice extent lower.

This year’s minimum was 160,000 square kilometers (61,800 square miles) above the 2007 record minimum extent, and 2.38 million square kilometers (919,000 square miles) below the 1979 to 2000 average minimum. Note that our estimated uncertainty for extent is plus or minus 50,000 square kilometers (about 20,000 square miles). The minimum ice extent this year is very close to 2007, and indeed some other research groups place 2011 as the lowest on record. At this point, using our processing and sensor series, the 2011 minimum is a close second.

Figure 2. The graph above shows daily Arctic sea ice extent as of September 13, 2011, along with daily ice extents for the previous three lowest years for the minimum ice extent. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, purple shows 2008, 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

The last five years (2007 to 2011) have been the five lowest extents in the continuous satellite record, which extends back to 1979. While the record low year of 2007 was marked by a combination of weather conditions that favored ice loss (including clearer skies, favorable wind patterns, and warm temperatures), this year has shown more typical weather patterns but continued warmth over the Arctic. This supports the idea that the Arctic sea ice cover is continuing to thin. Models and remote sensing data also indicate this is the case. A large area of low concentration ice in the East Siberian Sea, visible in NASA Moderate Resolution Imaging Spectroradiometer (MODIS) imagery, suggests that the ice cover this year is particularly thin and dispersed this year.

Figure 1. The graph above shows ice extent this year, along with daily ice extents for the previous three lowest extent years. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, purple shows 2008, 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. About the data. —Credit: National Snow and Ice Data Center
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Overview of conditions

On September 10, Arctic sea ice extent was 4.34 million square kilometers (1.68 million square miles). This was 110,000 square kilometers (42,500 square miles) above the 2007 value on the same date. The record minimum Arctic sea ice extent, recorded in 2007, was 4.17* million square kilometers (1.61 million square miles).

The rate of decline has flattened considerably the last few days: Arctic sea ice is likely near its minimum value for the year. However, weather patterns could still push the ice extent lower. NSIDC scientists will make an announcement when ice extent has stopped declining and has expanded for several days in a row, indicating that the Arctic sea ice has reached its lowest extent for the year and has begun freezing over. During the first week of October, after data are processed and analyzed for the month of September, NSIDC scientists will issue a more detailed analysis of this year’s melt season and the state of the sea ice.

NSIDC’s sea ice data come from the Special Sensor Microwave Imager/Sounder (SSMIS) sensor on the Defense Meteorological Satellite Program (DMSP) F17 satellite. This data record, using the NASA Team algorithm developed by scientists at NASA Goddard Space Flight Center, is the longest time series of sea ice extent data, extending back to 1979.

Other sea ice data are available from other data providers, using different satellite sensors and sea ice algorithms. For example, data from the University of Bremen indicate that sea ice extent from their algorithm fell below the 2007 minimum. They employ an algorithm that uses high resolution information from the JAXA AMSR-E sensor on the NASA Aqua satellite. This resolution allows small ice and open water features to be detected that are not observed by other products. This year the ice cover is more dispersed than 2007 with many of these small open water areas within the ice pack. 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.

For more information about the Arctic sea ice minimum, see the NSIDC Icelights article, Heading Towards the Summer Minimum Ice Extent.

*Near-real-time data initially recorded the 2007 record low as 4.13 million square kilometers 1.59 million square miles). The final data, reprocessed by NASA Goddard Space Flight Center using slightly different processing and quality control procedures, record the number as 4.17 million square kilometers (1.61 million square miles). NSIDC reports daily extent as a 5-day average. For more about the data, see the FAQ, Do your data undergo quality control?

Figure 1. Arctic sea ice extent for August 2011 was 5.52 million square kilometers (2.13 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 August 2011 was 5.52 million square kilometers (2.13 million square miles). This is 160,000 square kilometers (61,800 square miles) above the previous record low for the month, set in August 2007, and 2.15 million square kilometers (830,000 square miles), or 28% below the average for 1979 to 2000. Sea ice coverage remained below normal everywhere except the East Greenland Sea. In addition, several large areas of open water (polynyas) have opened within the ice pack.

On August 31, 2011 Arctic sea ice extent was 4.63 million square kilometers (1.79 million square miles). This is 100,000 square kilometers (38,600 square miles) higher than the previous record low for the same day of the year, set in 2007. As of September 5, ice extent had fallen below the minimum ice extents in September 2010 and 2008 (previously the third- and second-lowest minima in the satellite record). If ice stopped declining in extent today it would be the second-lowest minimum extent in the satellite record.

Higher-resolution Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) data processed by the University of Bremen showed ice extent on September 5 as falling below the same date in 2007.

Figure 2. The graph above shows daily Arctic sea ice extent as of September 5, 2011, along with daily ice extents for previous low-ice-extent years. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, purple shows 2008, 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

In August, sunlight wanes in the Arctic and the sea ice decline starts to slow down. Although the decline slowed somewhat during August, ice extent retreated at a faster pace than average, at a pace of 67,700 square kilometers (26,100 square miles) per day. In comparison, the average rate of decline for August 1979 to 2000 was 53,700 square kilometers (20,700 square miles) per day.

Air temperatures were 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) higher than average (relative to the 1981 to 2010 climatology) over the Arctic Ocean (measured approximately 1000 meters above the surface). The strongest anomalies were over the Northwest Passage region. High pressure persisted over much of the central Arctic Ocean, associated with a wind pattern that helped to push ice from the Beaufort Sea westward into the Chukchi Sea. This may have slowed some ice loss in the Chukchi Sea region. However, the wind pattern also transported ice into open waters warmed during the summer, fostering melt.

Figure 3. Monthly August ice extent for 1979 to 2011 shows a decline of 9.3% per decade. —Credit: NSIDC
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August 2011 compared to previous years

Average Arctic sea ice extent for August 2011 was the second-lowest for August in the satellite data record. Including 2011 the linear trend for August now stands at –9.3% per decade.

Figure 5. This photograph from the NASA ICESCAPE mission in July shows melt ponds on the surface of the Arctic sea ice cover. Surface melt has now stopped as air temperatures have cooled. But relatively warm water will continue to melt the ice from below for another couple of weeks.—Credit: NASA/Kathryn Hansen
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Will Arctic sea ice extent reach a new record in 2011?

The melt season for Arctic sea ice will soon draw to a close. Surface melt has already largely ended and the ocean waters are cooling. Air temperatures at the North Pole have fallen below freezing. However, with the ice cover now thinner than in years past, there is a greater potential for late-season ice loss, caused by warm water melting ice from below or winds that push the ice together.

Whether Arctic sea ice breaks a new record hinges on three factors: First, how much heat is left in the ocean to eat away at the ice edge and bottom? Second, will wind patterns blow the ice together and reduce ice extent or will they disperse the ice and expand ice extent? Finally, just how thin is the remaining ice cover? Thin ice quickly melts away when it is surrounded by warm water.

Figure 1. Arctic sea ice extent on August 14, 2011 was 5.56 million square kilometers (2.15 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 August 14, 2011, Arctic sea ice extent was 5.56 million square kilometers (2.15 million square miles), 2.11 million square kilometers (815,000 square miles) below the 1979 to 2000 average for that day, and 220,000 square kilometers (84,900 square miles) above the extent on that day in 2007.

Sea ice is low across almost all of the Arctic, with the exception of some areas of the East Greenland Sea. It is exceptionally low in the Laptev and Kara Sea areas.

The southern route of the Northwest Passage now appears to be free of sea ice according to imagery from the University of Bremen and the NSIDC Multisensor Analyzed Sea Ice Extent (MASIE) analyses. However, U.S. National Ice Center analyses indicate that there may be up to 20% ice concentration remaining in some parts of the route.

Figure 2. The graph above shows daily Arctic sea ice extent as of August 14, 2011, along with daily ice extents for previous low-ice-extent years. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, purple shows 2008, 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 loss slowed down in late July through early August; then over the past week, the rate of ice loss sped up. At present there is more ice than at the same time in 2007, which saw the record minimum September extent.

Data from the Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E) sensor, processed by the University of Bremen, show ice tracking near 2007 levels. The AMSR-E instrument can detect small but widespread areas of open water within the ice pack in the Beaufort and East Siberian seas, because of its resolution (6.25 kilometers or 3.88 miles). Normally, NSIDC uses data from the Defense Meteorological Satellite Program (DMSP) F17 Special Sensor Microwave Imager/Sounder (SSMIS). F17 provides a longer time series of data, but at a 25-kilometer (15.5-mile) resolution.

Figure 3. The map of sea level pressure for the first half of August shows high pressure over Greenland and the central Arctic, surrounded by low-pressure areas. This weather pattern has contributed to a speed-up in ice loss so far in August.—Credit: NSIDC courtesy NOAA/ESRL Physical Sciences Division
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A change in the weather

During early summer, a high-pressure cell persisted over the northern Beaufort Sea, promoting ice loss. This weather pattern broke down toward the end of July, slowing ice loss but spreading out the ice pack, making it thinner on average. The weather has now changed again, bringing another high-pressure pattern. Winds associated with this pressure pattern generally bring warm temperatures, and tend to push the ice together and reduce overall extent. In the Kara Sea, the combination of a high-pressure cell with low pressure to the west has resulted in strong northward ice movement, pushing the ice pack away from the coast and reducing ice extent. The same weather pattern is also increasing the movement of ice out of Fram Strait, between Greenland and Spitsbergen.

Figure 4. This map shows surface melt (in red) and bottom melt (in yellow) of the sea ice cover at ice mass balance buoy (IMB) sites on July 20, 2011. Surface melt at IMB sites located in the vicinity of the ice edge are consistent with past years. IMB sites located closer to the North Pole are melting more on the surface than on the underside. Data provided by D. Perovich and J. Richter-Menge.—Credit: NSIDC courtesy US Army Cold Regions Research and Engineering Laboratory
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Summer melt and sea ice thickness

Data indicate that the Arctic ice cover continues to thin. Sea ice thickness is also an indicator of the health of the ice cover; thick ice is resistant to melt. Specialized buoys managed by the U.S. Army Cold Regions Research and Engineering Laboratory help supplement limited satellite measurements of sea ice thickness. The buoys provide accurate data at specific locations, and can tell us whether thickness changes are due to surface melt, melt at the bottom of the ice floe, or ice growth. These buoys are deployed on thick multiyear ice, which provide long-lasting, stable platforms.

Data from six of these buoys through July 20 show that this year, the ice surface is melting faster than the underside of the ice. As the sun starts to sink on the horizon, surface melt will slow. However, ocean waters warmed during the summer will continue to melt the ice from below, reducing ice thickness and extent into September.

Figure 5. This graph shows total Arctic sea ice volume averaged by month. The 1979 to 2010 average is marked by black circles, 2007 is represented by black crosses, and the current year is shown with blue triangles. The dark gray and light gray areas represent the 1 and 2 standard deviation range of the data. The data were estimated by the University of Washington Polar Science Center PIOMAS model. —Credit: NSIDC courtesy Unviersity of Washington APL/PSC
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Ice volume

Combining ice thickness with sea ice area gives the total sea ice volume. At present, researchers cannot measure volume directly, so they estimate the volume with computer models. The University of Washington’s Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) model combines data on sea ice concentration with models of ocean and atmospheric conditions to estimate total ice volume. Sea ice volume normally changes with the seasons, but monthly estimates through July 2011 show that the volume for each month has tracked well below the 1979 to 2010 average, and below the volume for 2007, which saw the record low ice extent. PIOMAS projects that this year’s minimum volume in September will very likely finish below 2007 and could even reach a record low volume.

References

Perovich, D.K., J.A. Richter-Menge, B. Elder, K. Claffey, and C. Polashenski. 2009. Observing and understanding climate change: Monitoring the mass balance, motion, and thickness of Arctic sea ice. http://IMB.crrel.usace.army.mil.

Schweiger, A., R. Lindsay, J. Zhang, M. Steele, H. Stern. 2011. Uncertainty in modeled Arctic sea ice volume, Journal of Geophysical Research. doi:10.1029/2011JC007084. In press.

Zhang, J.L. and D.A. Rothrock. 2003. Modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates, Monthly Weather Review, 131, 845-861.

For previous analyses, please see the drop-down menu under Archives in the right navigation at the top of this page.

Figure 1. Arctic sea ice extent for July 2011 was 7.92 million square kilometers (3.06 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 July 2011 was 7.92 million square kilometers (3.06 million square miles). This is 210,000 square kilometers (81,000 square miles) below the previous record low for the month, set in July 2007, and 2.18 million square kilometers (842,000 square miles) below the average for 1979 to 2000.

On July 31, 2011 Arctic sea ice extent was 6.79 million square kilometers (2.62 million square miles). This was slightly higher than the previous record low for the same day of the year, set in 2007. Sea ice coverage remained below normal everywhere except the East Greenland Sea.

Figure 2. The graph above shows daily Arctic sea ice extent as of August 2, 2011, along with daily ice extents for previous low-ice-extent years. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, purple shows 2008, 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

During the first half of July, Arctic sea ice extent declined at a relatively fast pace (see July 18 post). But ice loss slowed substantially over the latter half of the month as the weather changed.

Through July, sea ice declined at an average pace of 90,200 square kilometers (34,800 square miles) per day, which is slightly faster than the average for 1979 to 2000 of 84,400 square kilometers (32,600 square miles) per day. Ice loss slowed towards the end of July as a high-pressure cell centered over the northern Beaufort Sea broke down and a series of low-pressure systems moved over the central Arctic Ocean. This change brought cooler conditions and likely pushed the ice apart into a thinner but more extensive ice cover.

Figure 3. Monthly July ice extent for 1979 to 2011 shows a decline of 6.8% per decade. —Credit: National Snow and Ice Data Center
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July 2011 compared to previous years

Average Arctic sea ice extent for July 2011 was the lowest for July in the satellite data record. The previous lowest year for July was 2007, which went on to break the record for the lowest ice extent at the end of the melt season. Including 2011 the linear trend for July now stands at -6.8% per decade.

Figure 4. These maps show sea ice concentration (left) and ice age (right) over the Arctic Ocean. In the Beaufort Sea off the coast of Alaska, ice has melted back to the edge of a tongue of older, thicker ice. In the ice age image, red shows ice 5 years old and older, green shows 4-year-old ice, light blue shows 3-year-old ice, dark blue is second-year ice, and purple shows first-year ice.

—Credit: NSIDC, data courtesy M. Tschudi
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New ice age measurements show decline in oldest, thickest ice

Researchers look at ice age as a way to estimate ice thickness. Ice thickness matters to the overall stability of the ice cover, because older ice grows thicker over multiple seasons, while newly formed ice tends to be thin and vulnerable to melt. While the amount of older sea ice has increased somewhat since September 2007, an updated analysis of satellite-derived sea ice age recently published by James Maslanik and co-authors show the oldest ice (ice older than five years) has continued to decline.

Until recently, the central Arctic Ocean and Canadian Archipelago served as refuges for some of the oldest, thickest ice. However, the new data show that ice age is now declining in these areas. A map of ice age for the third week of July, combined with sea ice concentration for July 31, 2011 (Figure 4) shows that in the eastern Beaufort Sea, the ice has essentially melted back to the edge of the multi-year ice cover (ice older than one year). Multi-year ice is more resistant to melting completely in summer, so it is not yet clear how much more ice will melt. Another tongue of old ice extends from near the pole towards the New Siberian Islands.

Between late March and late July first-year (younger) Arctic sea ice has declined by 30%, multi-year ice has declined by 14%, and the oldest ice, or ice older than 5 years, has declined by 16% . For background information on ice thickness, see the new post on NSIDC’s Icelights.

Figure 5. This time series shows total sea ice area (top) and multi-year ice area (bottom) for selected years within the Western Parry Channel route of the Northwest Passage. The black line with red dots shows 2011, and other colors show ice conditions in different years.—Credit: NSIDC courtesy Stephen Howell, Environment Canada, from Canadian Ice Service data
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Ice loss in Arctic shipping routes

Over the past few weeks, the sea ice edge has retreated from the shores of Siberia and Eurasia, potentially opening up much of the Northern Sea Route, the shipping lane that runs along the Eurasian Arctic coast from Murmansk on the Barents Sea, along Siberia, and through the Bering Strait. Higher resolution data such as the Multisensor Analyzed Sea Ice Extent (MASIE) indicate that some ice remains, particularly in the East Siberian Sea, but the reduced ice cover in the region has already made the route feasible this year. Taking advantage of the early retreat of sea ice in the Kara and Barents seas, the tanker Perserverance set sail on June 29, 2011 from Murmansk, Russia, aided by two icebreakers and completed the passage on July 14. The company plans to send six to seven more ships through the Northern Sea Route this summer.

On the other side of the Arctic, the Northwest Passage is still choked with ice. However, data provided by Stephen Howell of Environment Canada show that ice loss in the Northwest Passage is well ahead of average (Figure 5), nearly matching last year when, according to Canadian Ice Service (CIS) analyses, sea ice in the Parry Channel (the northern part of the Northwest Passage) reached the lowest levels in the CIS records dating back to 1968. Whether a navigable channel does indeed open this year will depend on weather conditions through the next few weeks, but so far, it looks possible.

Please note that NSIDC is not an operational ice forecasting center. For shipping purposes, please consult the Canadian Ice Service or the US National Ice Center.

Do you have questions about the upcoming Arctic sea ice minimum extent? Read Heading towards the summer minimum ice extent, on NSIDC’s new Icelights: Your burning questions about ice and climate.

References

Markus, T., J. C. Stroeve, and J. Miller. 2009 Recent changes in Arctic sea ice melt onset, freezeup, and melt season length, J. Geophys. Res., 114, C12024, doi:10.1029/2009JC005436.

Kunkel, K. E., M. Palecki, L. Ensor, K. G. Hubbard, D. Robinson, K. Redmond, D. Easterling. 2009. Trends in Twentieth-Century U.S. Snowfall Using a Quality-Controlled Dataset. J. Atmos. Oceanic Technol., *26*, 33–44. doi: 10.1175/2008JTECHA1138.1

Ghatak, D., A. Frei, G. Gong, J. Stroeve, and D. Robinson. 2010. On the emergence of an Arctic amplification signal in terrestrial Arctic snow extent, J. Geophys. Res., 115, D24105, doi:10.1029/2010JD014007.

Perovich, D.K., K.F. Jones, B. Light, H. Eicken, T. Markus, J. Stroeve, R. Lindsay. 2011. Solar partitioning in a changing Arctic sea-ice cover, Annals of Glaciology, 52(57), 192-196.

For previous analyses, please see the drop-down menu under Archives in the right navigation at the top of this page.

An article published recently in the journal Science showed that the flow of ocean heat into the Arctic Ocean from the Atlantic is now higher than any time in the past 2000 years. The warm, salty Atlantic water flows up from the mid-latitudes and then cools and sinks below the cold, fresh water from the Arctic. The higher salt content of the Atlantic water means that it is denser than fresher Arctic water, so it circulates through the Arctic Ocean at a depth of around 100 meters (328 feet). This Atlantic water is potentially important for sea ice because the temperature is 1 to 2 degrees Celsius (1.5 to 3 degrees Fahrenheit) above freezing. If that water rose to the surface, it could add to sea ice melt.

Spielhagen, R.F., K. Werner, S. Sorensen, K. Zamelczyk, E. Kandiano, G. Budeus, K. Husum, T.M. Marchitto, M. Hald, 2011. Enhanced modern heat transfer to the Arctic by warm Atlantic Water, Science, vol. 331, pp. 450-453, 28.

New ice thickness data

The first preliminary map of sea ice thickness data from the European Space Agency’s Cryosat-2 was released in June. This radar altimeter measures the height of features such as snow and sea ice on the Earth surface. This initial map is very preliminary and considerable work will be required before the thickness retrievals are validated and useful for scientific study. Researchers expect that Cryosat-2 will eventually provide additional information about changes in sea ice thickness and volume. http://www.esa.int/esaLP/SEMAAW0T1PG_LPcryosat_0.html

For previous analyses, please see the drop-down menu under Archives in the right navigation at the top of this page.