Figure 1. Arctic sea ice extent for April 2011 was 14.15 million square kilometers (5.46 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

Mean ice extent for the month was 14.15 million square kilometers (5.46 million square miles). This is 850,000 square kilometers (328,000 square miles) below the average for the reference period of 1979 to 2000.

Ice extent was lower than average in much of the northern North Atlantic, including the Barents Sea and Greenland Sea, and in the Canadian Maritime regions and Sea of Okhotsk. Only scattered areas in the Bering Sea and Baffin Bay had more extensive sea ice than average for this time of year.

Figure 2. The graph above shows daily Arctic sea ice extent as of May 1, 2011, along with daily ice extents for previous low-ice-extent years in the month of April. Light blue indicates 2011, dashed green shows 2007, pink indicates 2006, 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 declined through the month more slowly than usual, at an average rate of 29,950 square kilometers per day (11,560 square miles per day). The average daily rate of decline for 1979 to 2000 was 40,430 square kilometers (15,610 square miles) per day.

Cool conditions helped retain ice in Baffin Bay, between Canada and Greenland. Most of the ice loss during April was in the Kara Sea, north of Siberia, and the northern Baltic Sea in Europe. Ice also retreated rapidly in the western Bering Sea and the Sea of Okhotsk.

Towards the end of April, ice loss accelerated in the eastern Arctic as temperatures warmed there, leading to the formation of open water areas, or polynyas, near Franz Joseph Land and along the coast in the Kara Sea. Open water also started to form in Hudson Bay and Hudson Strait.

Figure 3. Monthly April ice extent for 1979 to 2011 shows a decline of 2.6% per decade. —Credit: National Snow and Ice Data Center
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April 2011 compared to past years

April 2011 continued the overall downward trend of the past thirty years, ranking fifth lowest in the satellite record. The two lowest years for April were 2007 and 2006.

Warm temperatures for Asian Arctic; cool for northern North America

For most of April, nearly all of the eastern Arctic, north of Europe and Russia, remained warmer than average. The largest anomalies were over central Russia, northern Siberia and the Laptev and East Siberian Seas, where temperatures averaged over the month were approximately 6 degrees Celsius (11 degrees Fahrenheit) above average. In contrast, most of the western Arctic was cooler than normal, with temperatures 6 degrees Celsius (11 degrees Fahrenheit) cooler than average over Davis Strait and Baffin Bay.

The eastern Arctic remained warmer than average all winter. This suggests that that sea ice there did not thicken as much as in past winters, and may retreat rapidly as the summer melt season progresses. University of Washington’s Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) model of sea ice volume reflects this, showing continued very low ice mass in the Arctic compared to previous decades.

Meanwhile, the atmospheric circulation for April was characterized by a strong positive phase of the Arctic Oscillation (AO), with unusually low sea level pressure over much of the Arctic Ocean, and the lowest pressures between Greenland and Iceland. This pattern helped to draw warm air into the eastern Arctic. How this will affect observed sea ice conditions at the end of this summer remains to be seen.

Figure 5. This snow cover anomaly map for April 2011 shows the difference between snow cover this April, compared with average snow cover for April 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 Dave Robinson and Thomas Estilow, Rutgers University
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Snow cover update

Warm conditions in central Russia, linked to the positive phase of the Arctic Oscillation, promoted an early retreat of snow cover in a broad band stretching from the Urals to far eastern Siberia. However, in North America several late snowstorms led to higher-than-average monthly snow extents in the northern Plains states and western Canadian provinces. Greater-than-average snowcover was seen in the Tibetan plateau and east of the Urals.

Figure 1. Arctic sea ice extent for March 2011 was 14.56 million square kilometers (5.62 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

Arctic sea ice extent averaged over the month of March 2011 was 14.56 million square kilometers (5.62 million square miles). This is the second-lowest March extent on record, after 2006.

In March, ice extent remained below normal in both the Atlantic and Pacific sectors of the Arctic, particularly in the Labrador Sea and the Gulf of St. Lawrence.

Figure 2. The graph above shows daily Arctic sea ice extent as of April 4, 2011, along with daily ice extents for previous low-ice-extent years in the month of March. Light blue indicates 2011, dashed green shows 2007, light green shows 2006 (the record low for the month), 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 showed little change through the month of March, as is typical this time of year. The ice reached its winter maximum extent on March 7, and over the next few weeks, ice extent declined only slightly. New ice was still growing in some areas, but it was melting in others. Overall, the ice changes in these regions canceled each other out.

Late in the month, extent again increased, though not above the previously reported level of March 7. This late increase is due mainly to increases of extent in the Kara, Barents, and Greenland Seas. The Greenland Sea increase is likely due primarily to ice that was exported from the Arctic Ocean to the Greenland Sea by winds and ocean currents, though some ice growth is also apparent. The increase in the Kara and Barents Seas appears primarily due to ice growth resulting from unusually cold weather in the region.

Figure 3. Monthly March ice extent for 1979 to 2011 shows a decline of 2.7% per decade. —Credit: National Snow and Ice Data Center
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March 2011 compared to past years

March 2011 had the second-lowest ice extent for the month in the satellite record, after 2006. Including 2011, the March trend in sea ice extent is now at -2.7 percent per decade.

Warm temperatures continue

Air temperatures over almost all of the Arctic Ocean were above average, reaching 7 to 9 degrees Celsius (13 to 16 degrees Fahrenheit) above average over the Chukchi Sea. Below-average temperatures were found over Greenland, the Norwegian Sea and part of Canada.

Atmospheric circulation for March was dominated by a broad low-pressure area, centered over the northern Barents Sea. Winds associated with this pattern drew warm, southerly air into the Chukchi Sea region.

As in February, the Arctic Oscillation (AO) mainly stayed in its positive phase, which tends to bring lower-than-average pressure over much of the Arctic, and higher-than-normal pressure in middle latitudes. For more information on current AO conditions, visit the NOAA Climate Prediction Center Web page.

Figure 5. These images show ice age during the third week of March, for 2011 and averaged over the reference period of 1979 to 2000. The bottom figure shows ice age as a percentage of total ice in the Arctic.
—Credit: NSIDC courtesy J. Maslanik and C. Fowler, University of ColoradoHigh-resolution image

Ice age

Every year at the start of the melt season, scientists look at sea ice age, using data from satellites and buoys. Older ice that has survived several summer melt seasons tends to be thicker, while newer ice is thinner and more vulnerable to melt in summer. Over the past several decades, the spring ice cover has become increasingly dominated by younger and generally thinner ice, because of strong summer melting in recent years that has reduced the amount of ice surviving into winter.

This year the older, thicker ice has increased somewhat over last year, although it remains younger than the 1979 to 2000 average ice age. Data through the third week of March shows an increase in sea ice one to two years old, and older than two years old, compared to recent years. However, the amount of older ice remains much lower than in the mid-1980s, and there is still almost none of the oldest ice, older than four years old, that used to dominate much of the Arctic Ocean.

The distribution of old and young ice at the end of March 2011 also looks different than the standard comparison period of 1981 to 2000. Winds and ocean currents this winter resulted in an unusual tongue of old ice extending from north of the Canadian Arctic Archipelago into the Beaufort and Chukchi Seas, in a region that used to be dominated by old ice that usually survived the summer melt season. A similar tongue of old ice appeared in March 2010, which almost completely melted away during the summer of 2010. Whether the tongue of old ice seen this spring melts away this summer will depend largely on ocean temperature and the weather patterns that set up over the next six months.

Note: James Maslanik and colleagues recently recalculated their entire series of ice age data based on a minimum of 15% concentration. The old version used a 40% minimum. The reprocessed ice age data is therefore more consistent with other measures of sea ice, including NSIDC sea ice extent data, which use a threshold of 15%.

Figure 1. Arctic sea ice extent on March 7 was 14.64 million square kilometers (5.65 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

On March 7, 2011, Arctic sea ice likely reached its maximum extent for the year, at 14.64 million square kilometers (5.65 million square miles). The maximum extent was 1.2 million square kilometers (471,000 square miles) below the 1979 to 2000 average of 15.86 million square kilometers (6.12 million square miles), and equal (within 0.1%) to 2006 for the lowest maximum extent in the satellite record.

Figure 2. The graph above shows daily Arctic sea ice extent as of March 22, 2011, along with daily ice extents for 2006, which had the previous lowest maximum extent, and 2007, the year with the lowest minimum extent in September. Light blue indicates 2011, green shows 2007, light green shows 2006, 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

As of March 22, ice extent has declined for five straight days. However there is still a chance that the ice extent could expand again. Sea ice extent in February and March tends to be quite variable, because ice near the edge is thin and often quite dispersed. The thin ice is highly sensitive to weather, moving or melting quickly in response to changing winds and temperatures, and it often oscillates near the maximum extent for several days or weeks, as it has done this year.

Since the start of the satellite record in 1979, the maximum Arctic sea ice extent has occurred as early as February 18 and as late as March 31, with an average date of March 6.

Figure 1. Arctic sea ice extent for February 2011 was 14.36 million square kilometers (5.54 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

Sea ice extent averaged over the month of February 2011 was 14.36 million square kilometers (5.54 million square miles). This was a tie with the previous record low for the month, set in 2005. February ice extent remained below normal in both the Atlantic and Pacific sectors, particularly in the Labrador Sea and the Gulf of St. Lawrence.

While ice extent has declined less in winter months than in summer, the downward winter trend is clear. The 1979 to 2000 average is 15.64 million square kilometers (6.04 million square miles). From 1979 through 2003, the February extent averaged 15.60 million square kilometers (6.02 million square miles). Every year since 2004 has had a mean February extent below 15 million square kilometers (5.79 million square miles).

Figure 2. The graph above shows daily Arctic sea ice extent as of February 28, 2011, along with daily ice extents for previous low-ice-extent years in the month of February. Light blue indicates 2011, green shows 2007, purple shows 2005 (the record low for the month was in 2005), 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 ice extent grew at average rates for February, the overall extent remained anomalously low. Air temperatures over most of the Arctic Ocean were between 2 and 4 degrees Celsius (4 and 7 degrees Fahrenheit) higher than normal. Over the East Greenland Sea and north towards the Pole, air temperatures were 5 to 7 degrees Celsius (9 to 13 degrees Fahrenheit) higher than normal. Colder conditions, 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) below average persisted over western Eurasia, east-central Eurasia and some of the Canadian Arctic.

As air temperatures dropped in the eastern Canadian Arctic in February, parts of the Labrador Sea started to freeze over. However, the Gulf of St. Lawrence remained mostly free of ice. As during winter 2010, when Environment Canada reported that sea ice in the Gulf of St. Lawrence was at the lowest level on record, the lack of ice will make it difficult for harp seals to give birth to their pups on the sea ice, as they normally do in February and March.

Figure 3. Monthly February ice extent for 1979 to 2011 shows a decline of 3.0% per decade. —Credit: National Snow and Ice Data Center
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February 2011 compared to past years

February 2011 tied February 2005 for the lowest ice extent for the month in the satellite record. Including 2011, the February trend is now at -3.0 percent per decade.

Through most of January, the Arctic Oscillation (AO) was generally in a strongly negative phase, similar to the pattern that dominated the winter of 2009 to 2010. This led to very warm temperatures over the eastern Arctic, helping to account for the low ice extents over the Labrador Sea and Gulf of Saint Lawrence. However, toward the end of January, the AO returned to a positive phase, and ice began to grow in the Labrador Sea and Gulf of St. Lawrence. For more information on current AO conditions, visit the NOAA Climate Prediction Center Web page.

Figure 4. Ice motion charts for December 2009 and December 2010 show mean sea ice drift, with the size and direction of the arrows indicating average speed and direction of ice motion. December 2010 saw stronger anticyclonic (clockwise) motion that transported ice towards the southern Beaufort and Chukchi seas.—Credit: NSIDC courtesy James Maslanik and Chuck Fowler, CU Boulder
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Ice motion

Typically during a negative AO phase, weather patterns favor the retention of thick ice in the central Arctic and Canada basin, where it can better survive the summer. The negative AO also typically leads to a stronger Beaufort Gyre, which helps move ice from the western to eastern Arctic. There the ice thickens, ridging and rafting against the Siberian coast.

Last winter, the AO was in its most negative phase since at least 1951. However, slight differences from the typical AO pattern in the location of the sea level pressure anomalies had a significant impact on how the ice moved within and out of the Arctic Basin. During winter 2009 to 2010 the peak pressure anomalies were shifted towards the Barents and Kara seas, which helped transport ice from the Canadian Arctic towards the southern Beaufort and Chukchi seas. Since some of the oldest and thickest ice in the Arctic is found north of the Canadian Archipelago, this atmospheric pattern ended up further depleting the Arctic of its store of old, thick ice as that old ice melted during summer in these southerly locations.

This winter also saw a relatively strong negative AO index during December and January.  However, as we discussed in our January 5, 2011 post, the positive sea level pressure anomalies were centered near Iceland. This led to a more extensive anticyclonic (clockwise) transport pattern than last winter.  This may help keep a more extensive distribution of multiyear ice cover as summer approaches.

Figure 5. The maps of January and February 2011 snow cover data show the extent of snow cover over the Northern Hemisphere (top), and the percent difference from average snow cover extent from 1971 to 2000 (bottom). Strong positive departures can be seen over the midwestern U.S., western China, and Mongolia.—Credit: NSIDC courtesy Dave Robinson and Thomas Estilow, Rutgers University
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January and February Northern Hemisphere snow cover

Sea ice extent is only one of a number of data sets scientists use to understand how climate is changing. Rutgers University and NOAA have compiled a 45-year record of Northern Hemisphere snow cover extent from NOAA snow charts. These data show that much of northern North America, Scandinavia and northern Eurasia are snow covered between 90 and 100 percent of the time in January and February. High elevation plains and mountains at lower latitudes, such as the southern Rocky Mountains in the U.S. and Hindu Kush in Asia, also have extensive snow cover.

Over this record, in January, Northern Hemisphere snow cover averages 47 million square kilometers (18.1 million square miles), and in February it averages 46 million square kilometers (17.8 square miles)—approximately 45 to 46 percent of the land area in the region. While sea ice extent was below average for January 2011, this month had the sixth-largest snow cover extent since the record started in 1966, at 49 million square kilometers (18.9 million square miles). Snow was unusually widespread over the mid-western and eastern United States, eastern Europe, and western China. Snow cover in February remained above average at 47.4 million square kilometers (18.3 million square miles), with more snow than usual in the western and central U.S., eastern Europe, Tibet and northeastern China.

Reduced sea ice extent and extensive snow cover are not contradictory, and are both linked to a strong negative phase of the Arctic Oscillation (see our January 5, 2011 post). A strongly negative AO favors outbreaks of cold Arctic air over northern Europe and the U.S., as many people experienced first-hand these last two winters. Whether this is a trend, or in any way linked to ongoing climate warming in the Arctic, remains to be seen.

Figure 1. Arctic sea ice extent for January 2011 was 13.55 million square kilometers (5.23 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

Arctic sea ice extent averaged over January 2011 was 13.55 million square kilometers (5.23 million square miles). This was the lowest January ice extent recorded since satellite records began in 1979. It was 50,000 square kilometers (19,300 square miles) below the record low of 13.60 million square kilometers (5.25 million square miles), set in 2006, and 1.27 million square kilometers (490,000 square miles) below the 1979 to 2000 average.

Ice extent in January 2011 remained unusually low in Hudson Bay, Hudson Strait (between southern Baffin Island and Labrador), and Davis Strait (between Baffin Island and Greenland). Normally, these areas freeze over by late November, but this year Hudson Bay did not completely freeze over until mid-January. The Labrador Sea remains largely ice-free.

Figure 2. The graph above shows daily Arctic sea ice extent as of January 31, 2011, along with daily ice extents for previous low-ice-extent years in the month of January. Light blue indicates 2010-2011, green shows 2005-2006 (the record low for the month was in 2006), 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

Air temperatures over much of the Arctic were 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) above normal in January. Over the eastern Canadian Arctic Archipelago, Baffin Bay/Davis Strait and Labrador Sea, temperatures were at least 6 degrees Celsius (11 degrees Fahrenheit) higher than average. Temperatures were near average over the western Canadian Arctic Archipelago and Scandinavia.

As in December 2010, the warm temperatures in January came from two sources: unfrozen areas of the ocean continued to release heat to the atmosphere, and the wind patterns accompanying the negative phase of the Arctic oscillation brought warm air into the Arctic. Near the end of January the negative Arctic oscillation pattern broke down and turned positive, which usually favors ice growth. It is unclear how long it will remain in a positive mode.

Figure 3. Monthly January ice extent for 1979 to 2011 shows a decline of 3.3% per decade. —Credit: National Snow and Ice Data Center
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January 2011 compared to past years

January 2011 had the lowest ice extent for the month since the beginning of satellite records. The linear rate of decline for the month is –3.3% per decade.

Ice extent for the Arctic as a whole increased at an average of 42,800 square kilometers (16,500 square miles) per day through the month of January, which is about average.

Figure 4. This graph shows the ice extent in Hudson Bay from late November to the end of January, for the last five years. This year, Hudson Bay froze up substantially later than in previous years. MASIE data.—Credit: NSIDC /NIC MASIE Product
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Slow regional ice growth

In contrast, regional ice growth has been particularly slow compared to past years. Hudson Bay did not completely freeze up until mid-January, about a month later than normal according to Canadian Ice Service analyses. The Labrador Sea region is still largely free of ice, except in protected bays along the coast. Normally at this time of year, ice extends a few hundred kilometers from the coast all the way from Hudson Strait to Newfoundland.

Figure 5. These images show high and low atmospheric pressure patterns for January 2011 (left) and the January 1968-1996 average (right). Yellows and reds show higher pressures; blues and purples indicate lower pressures, as indicated by the height of the 850 millibar pressure level above the surface, called the pressure surface. Normally, the pressure surface is nearer to the surface around the pole, winds follow the pressure contours around the pole (the polar vortex), and cold air is trapped in the Arctic. This year, the pressure surface is allowing cold air to spill out of the Arctic into the mid-latitudes. —Credit: NSIDC courtesy NOAA/ESRL PSD
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Potential links with mid-latitude weather

While the Arctic has been warm, cold and stormy weather has affected much of the Northeast U.S. and Europe. Last winter also paired an anomalously warm Arctic with cold and snowy weather for the eastern U.S. and northern Europe. Is there a connection?

Warm conditions in the Arctic and cold conditions in northern Europe and the U.S. are linked to the strong negative mode of the Arctic oscillation. Cold air is denser than warmer air, so it sits closer to the surface. Around the North Pole, this dense cold air causes a circular wind pattern called the polar vortex , which helps keep cold air trapped near the poles. When sea ice has not formed during autumn and winter, heat from the ocean escapes and warms the atmosphere. This may weaken the polar vortex and allow air to spill out of the Arctic and into mid-latitude regions in some years, bringing potentially cold winter weather to lower latitudes.

Some scientists have speculated that more frequent episodes of a negative Arctic Oscillation, and the stormy winters that result, are linked to the loss of sea ice in the Arctic. Dr. James Overland of NOAA Pacific Marine Environmental Laboratory (PMEL) recently noted a link between low sea ice and a weak polar vortex in 2005, 2008, and the past two winters, all years with very low September sea ice extent. Earlier work by Jennifer Francis of Rutgers University and colleagues also suggested a relationship between autumn sea ice levels and mid-latitude winter conditions. Judah Cohen, at Atmospheric and Environmental Research, Inc., and his colleagues propose another idea—a potential relationship between early snowfall in northern Siberia, a negative phase of the Arctic Oscillation, and more extreme winters elsewhere in the Northern Hemisphere. More research on these ideas may shed light on the connections and have the potential to improve seasonal weather forecasting.

Further reading

Francis, J.A., Chan, W-H., Leathers, D.J., Miller, J.R., Veron, D.E., 2009. Winter Northern Hemisphere weather patterns remember summer. Geophys. Res. Lett. 36, L07503, doi:10.1029/2009GL037274.

Overland, J.E., Wang, M-Y., 2010. Large-scale atmospheric circulation changes are associated with the recent loss of Arctic sea ice. Tellus 62A, 1-9.

Cohen, J., J. Foster, M. Barlow, K. Saito, and J. Jones, 2010. Winter 2009-2010: A case study of an extreme Arctic Oscillation event. Geophys. Res. Lett., 37, L17707, doi:10.1029/2010GL044256.

Figure 1. Arctic sea ice extent for December 2010 was 12.00 million square kilometers (4.63 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

Arctic sea ice extent averaged over December 2010 was 12.00 million square kilometers (4.63 million square miles). This is the lowest December ice extent recorded in satellite observations from 1979 to 2010, 270,000 square kilometers (104,000 square miles) below the previous record low of 12.27 million square kilometers (4.74 million square miles) set in 2006 and 1.35 million square kilometers (521,000 square miles) below the 1979 to 2000 average.

As in November, ice extent in December 2010 was unusually low in both the Atlantic and Pacific sides of the Arctic, but particularly in Hudson Bay, Hudson Strait (between southern Baffin Island and Labrador), and in Davis Strait (between Baffin Island and Greenland). Normally, these areas are completely frozen over by late November. In the middle of December, ice extent stopped increasing for about a week, an unusual but not unique event.

Figure 2. The graph above shows daily Arctic sea ice extent as of January 2, 2011, along with daily ice extents for previous low-ice-extent years in the month of November. Light blue indicates 2010-2011, pink shows 2006-2007 (the record low for the month was in 2006), green shows 2007-2008, 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 low ice conditions in December occurred in conjunction with above-average air temperatures in regions where ice would normally expand at this time of year. Air temperatures over eastern Siberia were 6 to 10 degrees Celsius (11 to 18 degrees Fahrenheit) above normal in December. Over the eastern Canadian Arctic Archipelago, Baffin Bay/Davis Strait and Hudson Bay, temperatures were at least 6 degrees Celsius (11 degrees Fahrenheit) higher than average. Southern Baffin Island had the largest anomalies, with temperatures over 10 degrees Celsius (18 degrees Fahrenheit) higher than normal. By sharp contrast, temperatures were lower than average (4 to 7 degrees Celsius, 7 to 13 degrees Fahrenheit) over the Alaska-Yukon border, north-central Eurasia, and Scandinavia.

The warm temperatures in December came from two sources: unfrozen areas of the ocean continued to release heat to the atmosphere, and an unusual circulation pattern brought warm air into the Arctic from the south. Although the air temperatures were still below freezing on average, the additional ocean and atmospheric heat slowed ice growth.

Figure 3. Monthly December ice extent for 1979 to 2010 shows a decline of 3.5% per decade. —Credit: National Snow and Ice Data Center
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December 2010 compared to past years

December 2010 had the lowest ice extent for the month since the beginning of satellite records. The linear rate of decline for the month is –3.5% per decade.

Figure 4. Air temperatures were higher than normal over Baffin Island, Hudson Bay, and eastern Siberia for the month of December, which was associated with low sea ice extent in those areas. The temperature pattern resulted from a negative phase of the Arctic Oscillation.—Credit: NSIDC courtesy NOAA/ESRL PSD
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Negative phase of the Arctic Oscillation

As in December 2009, a strongly negative phase of the Arctic Oscillation dominated the middle and high latitudes of the Northern Hemisphere in December 2010, bringing higher-than-normal pressures to the Arctic region, with lower-than-normal pressures in middle latitudes. However, unlike 2009, when higher-than normal pressures centered near the central Arctic , in December 2010 higher pressures centered near Iceland and the eastern tip of the Aleutians in the Pacific, and yielded a different pattern of winds. As a result, different areas experienced warm anomalies in 2010, and a different pattern of ice extent emerged.

Our January 5, 2010 post discussed the connection between very warm temperatures over much of the high Arctic in December 2009 and a strongly negative phase of the Arctic Oscillation.

Figure 5. This full-year graph puts 2010 sea ice extent in context. The gray line shows the 1979 to 2000 climatology, thick blue-gray indicates the 1979 to 2008 (30-year) climatology, dashed green shows 2007, and 2009 is shown in sky blue. Sea Ice Index data.—Credit: National Snow and Ice Data Center
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2010 year in review

Despite a late date of the maximum in winter sea ice extent, the minimum sea ice extent for September 2010 was third lowest in the 1979 to 2010 satellite record, above only 2007 (the record low) and 2008. The late summer of 2010 saw an open Northwest Passage: this year, the deep water channel (the northern route) from M’Clure Strait to Lancaster Sound was navigable. The Northern Sea Route along the Siberian coast also became briefly navigable.

2010 started out with a highly negative phase of the Arctic Oscillation, an atmospheric pattern that in the past has favored the survival of old ice through the winter, and more ice at the end of this summer. But this tendency seems to be changing. A recent study led by Julienne Strove of NSIDC showed that while wind patterns linked with the strongly negative Arctic Oscillation winter of 2009-2010 transported much old ice into the southern Beaufort and Chukchi Seas, most of this ice later melted. It may be that with a warmer Arctic, old rules regarding links between the atmospheric pressure patterns and sea ice extent no longer hold. So far the winter of 2010-2011 has also had a strongly negative Arctic Oscillation, but it is not yet clear how this pattern will affect summer sea ice.

Figure 6. The graph of Antarctic sea ice extent as of January 3, 2011. Light blue indicates 2010-2011, dark blue shows 2009-2010, 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—Credit: National Snow and Ice Data Center
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A note on Antarctica

While sea ice is growing in the Arctic, it is early summer in the Antarctic and sea ice is melting. For the past four months, Antarctic sea ice extent has remained well above average. The high ice extent around Antarctica appears to relate to a persistently positive phase of the Southern Annular Mode—an Antarctic counterpart to the Arctic Oscillation—and to the mild La Niña conditions in the Pacific. In December 2010, the monthly mean Southern Annular Mode index was lower, and Antarctic sea ice extent had dropped back to within about standard deviation of the mean.

For more information about Antarctic sea ice, see the Frequently Asked Questions section.

Antarctic sea ice data is available on the Sea Ice Index.

New sea ice data

NSIDC has recently released a new sea ice extent product, called the Multisensor Analyzed Sea Ice Extent (MASIE). The MASIE project is a collaborative effort with the U.S. National Ice Center to provide a daily high-resolution sea ice extent estimate based on the NOAA Interactive Mapping System (IMS) product. This new product is considered more accurate for tracking the current position of the ice edge; for climate studies, the passive microwave product (on which Arctic Sea Ice News & Analysis is based) is preferred for a more consistent, long-term average. For more information, read an article about the product at the NSIDC Monthly Highlights Web site.

Further reading

Stammerjohn, S. E., D. G. Martinson, R. C. Smith, X. Yuan, and D. Rind, 2008. Trends in Antarctic annual sea ice retreat and advance and their relation to El Nino — Southern Oscillation and Southern Annular Mode variability. Journal of Geophysical Research, 113, C03S90, doi: 10.1029/2007JC004269.

Stroeve, J.C., J. Maslanik, M. C. Serreze, I. Rigor, W. Meier, and C. Fowler. 2010. Sea ice response to an extreme negative phase of the Arctic Oscillation during winter 2009/2010. Geophysical Research Letters. In Press.

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