Category Archives: Analysis

Arctic sea ice reaches near-average extent in April

Arctic sea ice extent declined slowly through the first three weeks of April, compared to recent years. The slow decline through March and the first few weeks of April meant that by mid-April, ice extent was at near-average levels. However, much of the extensive ice cover is thin ice that will melt quickly once temperatures rise in the Arctic. Over the past week, extent has started to fall sharply.

Figure 1. Arctic sea ice extent for April 2012 was 14.73 million square kilometers (5.69 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 in April 2012 averaged 14.73 million square kilometers (5.69 million square miles). Because of the very slow rate of ice loss through the last half of March and the first three weeks of April, ice extent averaged for April ranked close to average out of 34 years of satellite data.  It was the highest average ice extent for the month since 2001, only 270,000 square kilometers (104,000 square miles) below the 1979 to 2000 average extent. April ice extent was 860,000 square kilometers (330,000 square miles) above the record low for the month, which happened in 2007.

In April, ice cover remained unusually extensive in the Bering Sea, continuing a pattern that persisted over the winter.  Ice extent was also slightly higher than average in Baffin Bay and part of the Sea of Okhotsk.  As in recent winters, ice extent was well below normal in the Barents Sea, compensating for the extensive ice in the Bering Sea.

As discussed in previous posts, the high Bering Sea ice extent this winter stemmed from unusually low air temperatures and persistent winds that helped to push ice southwards. During April, atmospheric conditions changed, warming the air to near-average temperatures for this time of year and slowing the strong southerly winds.

During April, air temperatures over most of the Arctic were higher than usual, particularly over the central Arctic Ocean.  Over the Bering Sea and parts of the East Greenland and Norwegian seas, temperatures ranged from average to slightly below average.

Figure 2. The graph above shows Arctic sea ice extent as of May 1, 2012, along with daily ice extent data for the previous five years. 2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy, 2008 in purple, and 2007 in green. 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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Note: That image originally published on May 3 contained an error in the climatology. The image has been replaced with the correct image. About the data

Conditions in context
Overall, the Arctic lost 1.07 million square kilometers (413,000 square miles) of ice during April, somewhat less than the 1979 to 2000 average April loss of 1.21 million square kilometers (467,000 square miles). The average daily rate of ice loss was 35,600 square kilometers (13,700 square miles) per day.  On April 24, ice extent was only 118,000 square kilometers (45,6000 square miles) below the 1979 to 2000 average for that day, although the difference has increased since then.

While ice conditions approached the 1979 to 2000 average levels for this time of year, the high ice extent will have little influence on how much ice melts this summer. Much of the ice cover is recently formed thin ice that will melt out quickly. Research has shown that sea ice extent in spring does not tell us much about ice extent the following summer. More important to the summer melt is the thickness of the ice cover, and summer weather.

Figure 3. Monthly April ice extent for 1979 to 2012 shows a decline of 2.6% per decade.

Credit: National Snow and Ice Data Center
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April 2012 compared to past years
Arctic sea ice extent for April 2012 was near average for the month in the satellite record, but was the highest since 2001. Including the year 2012, the linear rate of decline for April ice extent over the satellite record is 2.6% per decade.

Figure 4. This graph shows Antarctic sea ice extent as of May 1, 2012 (light blue line), along with the average ice extent and the ice extent from last year (dark blue). The average Southern Annular Mode (SAM) index number for each month is overlaid on the image. A stronger SAM correlates to stronger winds, which help to spread the sea ice and increase ice extent.

Credit: National Snow and Ice Data Center
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Antarctic sea ice spread by strong winds

The sea ice cover that surrounds the continent of Antarctica has been higher than average through most of the Southern Hemisphere summer (December to March). Ice extent declined much more slowly than usual in late November and remained above average through December and January, although it did not reach record highs for those months. At its minimum extent in March, Antarctic sea ice remained above average. Ice extent was the highest in the Weddell Sea and the northwestern Ross Sea.

The high ice extent likely stemmed from unusually strong winds that circled the continent of Antarctica during most the southern summer. These circumpolar winds tend to push the ice out from the continent, increasing the extent of the ice, although not necessarily the volume. Air temperatures in December and January were close to average over most of the sea ice-covered water. Researchers approximate the circumpolar wind intensity by an index called the Southern Annular Mode (SAM). A positive value for SAM indicates strong circumpolar winds around the continent; negative values indicate weaker winds. This index was at a record high for the two months of December 2011 and January 2012, at the same period of the higher-than-normal seasonal extents. For more information on Antarctic sea ice, see the NSIDC Icelights article: Sea ice down under: Antarctic sea ice and climate.

Figure 5. This map shows Arctic sea ice thickness, as well as the elevation of the Greenland Ice Sheet, for March 2011. The data come from the European Space Agency CryoSat-2 satellite. For the sea ice, green shades indicate thinner ice, while the yellows and oranges indicate thicker ice.

Credit: NSIDC courtesy CPOM/UCL/Leeds/ESA/PVL
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Cryosat provides new ice thickness data

NSIDC data provide a long-term record of the Arctic and Antarctic sea ice cover. But researchers also want to know how thick the ice cover is, since thinner ice melts faster than thicker ice. Ice thickness measurements are more limited than ice extent, because researchers can only sample small regions in person, and there have only been a few satellite sensors that can measure ice thickness. For example, the NASA ICESat satellite recorded Arctic sea ice thickness between 2003 and 2008, but the mission ended in 2009, and the follow-on mission is not expected to begin until 2016. In the meantime, NASA is filling some of the data gap with airplane-borne instruments as part of Operation IceBridge.

The European Space Agency (ESA) has released initial data from the radar altimeter on their CryoSat-2 satellite. Last week, ESA released the first calibrated maps of Arctic sea ice thickness capturing thickness changes through the winter from October 2010 through March 2011. In the coming years, CryoSat-2 will provide monthly fields of thickness that will allow scientists to track the evolution of the ice cover. For more information on CryoSat-2 and an animation of the thickness maps, see: http://www.esa.int/SPECIALS/Cryosat/SEMU55NW91H_0.html.

Further Reading

Kwok, R., G. F. Cunningham, M. Wensnahan, I. Rigor, H. J. Zwally, and D. Yi. 2009. Thinning and volume loss of the Arctic Ocean sea ice cover: 2003–2008, J. Geophys. Res., 114, C07005, doi:10.1029/2009JC005312.

Kwok, R., G. F. Cunningham, S. S. Manizade, and W. B. Krabill. 2012. Arctic sea ice freeboard from IceBridge acquisitions in 2009: Estimates and comparisons with ICESat, J. Geophys. Res., 117, C02018, doi:10.1029/2011JC007654.

Kwok, R., and G. F. Cunningham. 2008. ICESat over Arctic sea ice: Estimation of snow depth and ice thickness, J. Geophys. Res., 113, C08010, doi:10.1029/2008JC004753.

Laxon, S., N. Peacock, and D. Smith. 2003. High interannual variability of sea ice thickness in the Arctic region, Nature, 424, 947-950, October, doi:10.1038/nature02063.

Daily Graph Changes

Update, April 19, 2012: The nine-day trailing average climatology on the daily data graph has been changed to a five-day trailing average, to be consistent with the five-day trailing average for the daily data.

Figure 1. The graph above shows sea ice extent data graphed using the old method, a five-day centered mean (orange line), and the new method, a five-day trailing mean (blue line). The black line shows the raw daily data. In the old averaging method, extrapolated data sometimes changed values when sea ice extent was changing trajectory. The new method solves this problem by averaging only observed values.
Click for Animation

NSIDC has updated our processing of the daily sea ice extent graph. NSIDC calculates daily extent using a five-day average of the data. Previously, this average was a five-day centered mean, meaning that the final two days of data in the series were extrapolated from the previous three days.

The new method takes the average of the previous five days, so that readers will see fewer “wiggles” in the tail end of the data series (see animation, left). The value of the trailing mean lags the actual data values, so sea ice values will appear lower when ice extent is increasing, but will appear larger when ice is decreasing. The climatology is a 9-day running mean rather than a 5-day, so the climatology line also shifts slightly with this change.

While the averaging changes the data points on the graph,  the underlying data remain unchanged. This change does not affect the monthly average data, which scientists use for longer climate comparisons.

NSIDC will be making further improvements to the Sea Ice Index graphs and images in the coming months. Sea ice data processing methods are described in detail in the Sea Ice Index Documentation.

 

Arctic sea ice enters the spring melt season

Arctic sea ice reached its annual maximum extent on March 18, after reaching an initial peak early in the month and declining briefly. Ice extent for the month as a whole was higher than in recent years, but still below average.

As the melt season begins, researchers look at a variety of factors that may contribute to summer ice melt. While the maximum extent occurred slightly later than average, the new ice growth is very thin and likely to melt quickly. Ice age data indicate that despite the higher extent compared to recent years, the winter sea ice continues to be dominated by younger and thinner sea ice.

Figure 1. Arctic sea ice extent for March 2012 was 15. 21 million square kilometers (5.87 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 in March 2012 averaged 15.21 million square kilometers (5.87 million square miles). Ice extent this March ranked ninth lowest out of the 34 years of satellite data for the month, but it was the highest March average ice extent since 2008 and one of the higher March extents in the past decade. Ice extent was 530,000 kilometers (205,000 square miles) below the 1979 to 2000 average extent, and 780,000 square kilometers (301,000 square miles) above the record low for the month, which happened in 2006.

Ice cover remained extensive in the Bering Sea, where it has been above average all winter. Ice extent was also higher than average in Baffin Bay, between Greenland and Canada, and the Sea of Okhotsk, east of Russia. These conditions stemmed from a combination of wind patterns and low temperatures. Air temperatures were 6 to 8 degrees Celsius (11 to 14 degrees Fahrenheit) below average over the Bering Sea, Baffin Bay, and parts of the Sea of Okhotsk, at the 925 millibar level (about 3,000 feet above sea level). View a map of Arctic regions.

In the Kara Sea, where ice extent had been below average during January and February, ice extent rebounded to near-average levels in March. Winds that had been pushing the ice cover back shifted, allowing areas of open water in the Kara Sea to freeze over and the ice to spread out. Ice extent in the Barents Sea remained well below normal. In both the Barents and Kara seas, temperatures remained above normal by 4 to 6 degrees Celsius (7 to 11 degrees Fahrenheit).

Figure 2. The graph above shows daily Arctic sea ice extent as of April 2, 2012, along with the ice extents for the previous four years. The current year is shown in light blue, 2010-11 is in pink, 2009-10 in dark blue, 2008-09 is in purple, and 2006-2007, the year with the record low minimum, is dashed green. 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
Overall, the Arctic gained 140,000 square kilometers (54,000 square miles) of ice during March. Typically, March has been a month of net ice loss (an average of 260,000 square kilometers [100,000 square miles] for 1979 to 2000), but the last three Marches have had net ice growth. At its maximum extent on March 18, Arctic sea ice extent was within two standard deviations of the average, a measure that scientists look at as an estimate of the natural range of variability for the data.

Over the past thirty years of satellite data, the day of the maximum has varied by over six weeks, occurring as early as mid-February and as late as the end of March. However, even with so much variability, there is a small trend towards later maximum ice extents. This year’s maximum ice extent continued that trend, occurring 12 days later than average.

It is not clear why the maximum ice extent would happen later, given that in general, ice extent is decreasing. One possibility is that the lower winter ice extents might make it easier for ice to continue growing later in the season. With lower winter extents, a late cold snap or northerly wind could spread ice southward over ocean that would normally be ice-covered at that point. Researchers do not expect the late maximum ice extent to strongly influence summer melt. The ice that grew late this winter is quite thin, and will melt rapidly as the sun rises higher in the sky and the air and water get warmer.

Figure 3. Monthly March ice extent for 1979 to 2012 shows a decline of 2.6% per decade.

Credit: National Snow and Ice Data Center
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March 2012 compared to past years
Arctic sea ice extent for March 2012 was the 9th lowest in the satellite record, but the highest since 2008 and one of the highest March extents in the past decade. Including the year 2012, the linear rate of decline for March ice extent over the satellite record is 2.6% per decade.

Figure 4. This image, from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS), shows extensive sea ice cover in the Bering Sea on March 18, 2012. For more details and a full-resolution image, visit the NASA Earth Observatory Web site.
Credit:NASA image by Rob Simmon based on data from Jeff Schmaltz, NASA GSFC.
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High ice extent in the Bering Sea
In the Bering Sea, off Alaska, ice extent reached a record high for the month of March. Persistent winds pushed the sea ice southward and froze more seawater into ice.

As winds from the north pushed Arctic ice southward through the Bering Strait, the ice locked together and formed a structurally continuous band known as an ice arch, which acts a bit like a keystone arch in a building. The ice arch temporarily held back the ice behind it, but as the winds continued, the arch failed along its southern edge, and ice cascaded south through the strait into the Bering Sea. Sea ice also piled up on the northern coast of St. Lawrence Island, streaming southward on either side of it.

Figure 5. Ice age data show that first-year ice made up 75% of the Arctic sea ice cover this March. Thicker multiyear ice used to make up around a quarter of the Arctic sea ice cover. Now it constitutes only 2%.

Credit: NSIDC courtesy J. Maslanik and M. Tschudi, University of Colorado
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Ice age data shows thin ice cover
One key predictor for summer ice melt is the amount of old, thick ice in the Arctic at the end of the winter. Some ice thickness data are available from satellites, but these records are short and discontinuous. Data from the NASA ICESat satellite covers only 2003 to 2009, and the new European Space Agency CryoSat satellite began collecting data in 2011. So researchers look at ice age data as one indicator of Arctic sea ice thickness. Older ice that has survived multiple melt seasons tends to be thicker than newly formed ice.

Ice age data this year show that the ice cover remains much thinner than it was in the past, with a high proportion of first-year ice, which is thin and vulnerable to summer melt. After the record low minimum of 2007 the Arctic lost a significant amount of older, thicker ice, both from melting and from movement of ice out of the Arctic the following winter. In the last few years, the melt and export of old ice was less extreme than in 2007 and 2008, and multiyear ice started to regrow, with second and third-year ice increasing over the last three years.

After the near-record melt last summer, second-year ice declined again, but some of the ice that had survived the previous few summers made it through another year, increasing the proportion of third- and fourth-year ice. However the oldest, thickest ice, more than four years old, continued to decline. Ice older than four years used to make up about a quarter of the winter sea ice cover, but now constitutes only 2%. First-year ice (0 to 1 years old) this year makes up 75% of the total ice cover, the third highest at this time of year in the satellite record. In 2008 the proportion of first-year ice was 79%, and in 2009 it was 76%.

Figure 6. The top image shows a decline in upper-atmosphere winds (solid line) over the last 30 years that mirrors the decline in sea ice over the same time period (dashed line). The bottom image shows the expected change in trajectory of the jet stream (dotted line) compared to the current jet stream trajectory (solid line).

Credit: Jennifer Francis, Rutgers University
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Rapid Arctic warming and mid-latitude weather
The Arctic has warmed about twice as fast as the rest of the Northern Hemisphere in recent decades. Summer Arctic sea ice has declined by 40%, and snow is melting earlier in spring on the surrounding land. This dramatic change in the climate system is expected to affect weather patterns well beyond the confines of the Arctic—but researchers are working to understand exactly how those changes are affecting other regions.

New research by Jennifer Francis of Rutgers University and Steve Vavrus of the University of Wisconsin suggests that warming in the Arctic is causing weather patterns in mid-latitudes to become more persistent. This persistence can lead to conditions like heat waves, cold spells, drought, flooding, and heavy snows. The researchers found that as temperatures in the Arctic warm and become closer to temperatures in lower latitudes, the waves of the jet stream tend to spread out, and west-to-east winds slow down in the upper level of the atmosphere (where storm tracks form). Both of these effects tend to slow the progression of weather patterns, which means that a weather pattern, whether hot or cold, is more likely to stick around.

References

Francis, J.A. and S.J. Vavrus. 2012. Evidence linking Arctic amplification to extreme weather in mid-latitudes. Geophysical Research Letters, 39, L06801, doi:10.1029/2012GL051000.

Francis, J.A. 2012. Linking weird weather to rapid warming of the Arctic. Yale Environment 360, http://e360.yale.edu/feature/linking_weird_weather_to_rapid_warming_of_the_arctic/2501/

Kwok, R., T. Pederson, P. Gudmandsen, S. Pang. 2010. Large sea ice outflow in the Nares Strait in 2007. Geophysical Research Letters, 37, L03502, doi:10.1029/2009GL041872.

Sodhi, D. S. 1977. Ice arching and the drift of pack ice through restricted channels, Rep. 77‐18, Cold Reg. Res. and Eng. Lab., Hanover, N. H.

Arctic sea ice maximum marks beginning of melt season

On March 18, 2012, Arctic sea ice extent reached its annual maximum extent, marking the beginning of the melt season for Northern Hemisphere sea ice. This year’s maximum extent was the ninth lowest in the satellite record.

Figure 1. Arctic sea ice extent on March 18 was 15.24 million square kilometers (5.88 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 18, 2012 Arctic sea ice likely reached its maximum extent for the year, at 15.24 million square kilometers (5.88 million square miles). The maximum extent was 614,000 square kilometers (237,000 square miles) below the 1979 to 2000 average of 15.86 million square kilometers (6.12 million square miles). The maximum occurred this year 12 days later than the 1979 to 2000 average date of March 6.

This year’s maximum ice extent was the ninth lowest in the satellite record, slightly higher than the 2008 maximum (15.24 million square kilometers or 5.88 million square miles) Last year, 2011, was the lowest maximum on record, 14.64 million square kilometers (5.65 million square miles). Including this year, the nine years from 2004 to 2012 are the nine lowest maximums in the satellite record.

The graph above shows daily Arctic sea ice extent as of March 25, 2012, along with the ice extents for the previous four years. 2011-12 is shown in light blue, 2010-11 is in pink, 2009-10 in dark blue, 2008-09 is in purple, and 2006-2007, the year with the record low minimum, is dashed green. 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 23, ice extent has declined for five 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.

Arctic sea ice extent is declining in winter as well as in summer months, although the decline is not as steep in the winter months. At the beginning of April, NSIDC scientists will release a full analysis of winter conditions, along with monthly data for March. For more information about the maximum extent and what it means, see the NSIDC Icelights post, the Arctic sea ice maximum.

February ice extent low in the Barents Sea, high in the Bering Sea

As in January, sea ice extent in February was low on the Atlantic side of the Arctic, but unusually high on the Pacific side of the Arctic, remaining lower than average overall. At the end of the month, ice extent rose sharply, as winds changed and started spreading out the ice cover.

Sea ice extent in late winter can go up and down very quickly, getting pushed together or dispersed by strong winds. Ice extent usually reaches its annual maximum sometime in late February or March, but the exact date varies widely from year to year.

Arctic sea ice extent for February 2012 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.

Credit: National Snow and Ice Data Center
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Overview of conditions
Arctic sea ice extent in February 2012 averaged 14.56 million square kilometers (5.62 million square miles). This is the fifth-lowest February ice extent in the 1979 to 2012 satellite data record, 1.06 million square kilometers (409,000 square miles) below the 1979 to 2000 average extent.

Continuing the pattern established in January, conditions differed greatly between the Atlantic and Pacific sides of the Arctic. On the Atlantic side, especially in the Barents Sea, air temperatures were higher than average and ice extent was unusually low. February ice extent for the Barents Sea was the lowest in the satellite record.  Air temperatures over the Laptev, Kara and Barents seas ranged from 4 to 8 degrees Celsius (7 to 14 degrees Fahrenheit) above average at the 925 hectopascal (hPa ) level (about 3000 feet above sea level).  In contrast, on the Pacific side, February ice extent in the Bering Sea was the second highest in the satellite record, paired with air temperatures that were 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) below average at the 925 hPa level.

graph showing years and ice extent

The graph above shows daily Arctic sea ice extent as of March 5, 2012, along with the ice extents for the previous four years. 2011 is shown in light blue, 2010 is in pink, 2009 in dark blue, 2008 is in purple, and 2007, the year with the record low minimum, is dashed green. 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

Overall, the Arctic gained 956,000 square kilometers (369,000 square miles) of ice during the month. This was 486,000 square kilometers (188,000 square miles) more than the average ice growth for February 1979 to 2000. The overall low ice extent for the month stemmed mostly from the low ice extent in the Barents Sea: the extensive ice in the Bering Sea was not enough to compensate. On average, the Barents Sea has 865,000 square kilometers (334,000 square miles) of ice for the month of February. This year there were only 401,000 square kilometers (155,000 square miles) of ice in that region, the lowest recorded in the satellite data record.

At the end of February, ice extent rose sharply. Data from the NSIDC Multisensor Analyzed Sea Ice Extent (MASIE) showed that the rise came mainly from the Bering Sea and Baffin Bay. In the Bering Sea and Baffin Bay, winds pushed the ice extent southward. Ice growth in the Kara Sea also contributed to the rise in ice extent. In the Kara Sea, westerly winds that had been keeping the area ice-free shifted, allowing the open water areas to freeze over. During late winter, ice extent can change quickly as winds push extensive ice cover together, or spread out ice floes over a greater area.

Monthly February ice extent for 1979 to 2012 shows a decline of 3.0% per decade.

Credit: National Snow and Ice Data Center
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February 2012 compared to past years
Arctic sea ice extent for February 2012 was the fifth lowest in the satellite record. Including the year 2012, the linear rate of decline for February ice extent over the satellite record is 3.0% per decade. Based on the satellite record, through 2003, average February ice extent had never been lower than 15 million square kilometers (5.79 million square miles). February ice extent has not exceeded that mark eight out of the nine years since 2003.

This photograph of sea ice near Greenland was taken on March 18, 2011 from the NASA P3 aircraft. The IceBridge mission is collecting data on ice thickness, an important measure of the health of sea ice.

Credit: NASA/ATM automatic Cambot system
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IceBridge thickness data
Measuring ice thickness is critical to assessing the overall health of Arctic sea ice. The passive microwave data that NSIDC presents here provide only ice extent, a two-dimensional measure of ice cover. But ice can vary in thickness from a few centimeters to several meters, and scientists want to know if the ice pack is thinning overall as well as declining in extent. A new study by NASA scientist Ron Kwok compared ice thickness data collected by airplanes during the ongoing Operation IceBridge with thickness data from the NASA Ice, Cloud and Land Elevation Satellite (ICESat), which ended its mission in 2009. IceBridge is an airborne data-collection mission that started in 2009, in order to bridge the data gap between the first ICESat and ICESat-2, which is scheduled to launch in 2016.

Kwok found good agreement between simultaneous IceBridge and ICESat freeboard measurements made in 2009. Freeboard is the elevation of sea ice above the ocean surface, and provides a measure of ice thickness. These results show that IceBridge measurements will be able to bridge the gap between the ICESat and ICESat-2 satellite missions and add to other ice thickness data from the European Space Association (ESA) Cryosat-2. Satellite measurements of ice thickness provide a third dimension of information on the changing sea ice cover, helping scientists to more accurately assess the amount of sea ice in the Arctic.

Data collected by the IceBridge mission is archived and distributed by the NSIDC IceBridge Data program.

These images show the general effects of the positive phase (left) and negative phase (right) of the NAO. Red dots show the location of harp seal breeding grounds.

Credit: Johnston, et. al., 2012
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Regional ice conditions and harp seals
Many animals rely on sea ice as part of their habitat. Harp seals, for example, give birth to and care for their young on floes of sea ice. Recent research by David Johnston and colleagues at Duke University showed that harp seals in the northwest Atlantic have higher mortality rates during years when the North Atlantic Oscillation (NAO) is in its negative phase, a pattern that favors low ice cover in the Labrador Sea and Gulf of St. Lawrence, where harp seals breed. 

This winter, the NAO has mostly been in a positive phase and ice conditions in the Labrador Sea and Gulf of St. Lawrence have been at near-normal levels. However, in recent years, ice conditions in the region have been very low. The study showed a longer-term decline in sea ice cover of up to 6% per decade across all North Atlantic harp seal breeding grounds since 1979. While harp seals are well-suited to deal with natural short-term shifts in ice conditions, they may not be able to adapt to the combined effects of both short-term variability and long-term climate change.

Further reading
Friedlaender, A.S., D.W. Johnston and P.N. Halpin. 2010. Effects of the North Atlantic Oscillation on sea ice breeding habitats of harp seals (Pagophilus groenlandicus) across the North Atlantic, Progress in Oceanography, 86, 261-266. 

Johnston DW, Bowers MT, Friedlaender AS , Lavigne DM. 2012. The Effects of Climate Change on Harp Seals (Pagophilus groenlandicus). PLoS ONE, 7(1): e29158. doi:10.1371/journal.pone.0029158.

Kwok, R., G.F. Cunningham, S.S. Manizade and W.B. Krabill. 2012. Arctic sea ice freeboard from IceBridge acquisitions in 2009: Estimates and comparisons with ICESat, Journal of Geophysical Research, Vol. 117, C02018, doi:10.1029/2011JC007654.

Arctic ice extent low overall, high in the Bering Sea

Overall, Arctic sea ice extent remained lower than average in January. However, in the Bering Sea, ice extent was much greater than normal. The heavy ice cover caused problems for fishermen and made for an arduous late-season resupply mission to Nome, Alaska. The Arctic Oscillation, which had been in its positive phase most of the winter so far, switched to a negative mode, bringing cold weather to Europe and changing the direction of sea ice movement.

Figure 1. Arctic sea ice extent for January 2012 was 13.73 million square kilometers (5.30 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
Arctic sea ice extent in January 2012 averaged 13.73 million square kilometers (5.30 million square miles). This is the fourth-lowest January ice extent in the 1979 to 2012 satellite data record, 1.10 million square kilometers (425,000 square miles) below the 1979 to 2000 average extent.

As in December, ice extent was lower than normal on the Atlantic side of the Arctic, especially in the Barents Sea. However, on the other side of the Arctic, ice extent in the Bering Sea was much greater than average, reaching the second-highest levels for January in the satellite record. The greater-than-normal ice extent in the Bering Sea partly compensated for low ice extent on the Atlantic side of the Arctic Ocean, but ice extent as a whole remained far below average.

Figure 2. The graph above shows daily Arctic sea ice extent as of February 5, 2012, along with the ice extents for the previous four years. 2011 is shown in light blue, 2010 is in pink, 2009 in dark blue, 2008 is in purple, and 2007, the year with the record low minimum, is dashed green. 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 growth rate for Arctic sea ice in January was the slowest in the satellite record. After growing relatively quickly early in January, ice extent declined briefly in the middle of the month, and then grew more slowly than normal for the rest of the month. The slow growth likely stemmed from winds from the south and west that compressed the sea ice in the Barents Sea, and above-average temperatures and winds that limited ice growth in the Sea of Okhotsk.

Overall, the Arctic gained 765,000 square kilometers (295,000 square miles) of ice during the month. This was 545,000 square kilometers (210,000 square miles) less than the average ice growth rate for January 1979 to 2000.

Figure 3. Monthly January ice extent for 1979 to 2012 shows a decline of 3.2% per decade.

Credit: National Snow and Ice Data Center
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January 2012 compared to past years
Arctic sea ice extent for January 2012 was the fourth lowest in the satellite record. Including the year 2012, the linear rate of decline for January ice extent over the satellite record is 3.2% per decade.
Based on the satellite record, before 2005 average January ice extent had never been lower than 14 million square kilometers (5.41 million square miles). January ice extent has now fallen below that mark six out of the last seven years.

Figure 4. Monthly average sea ice motion for December 2011 (top) and January 2012 (bottom), derived from the DMSP Special Sensor Microwave Imager and Sounder (SSMIS) shows how the changing Arctic Oscillation (AO) phase affects the movement of ice. In January, the AO switched from a positive phase to a negative phase.

Credit: National Snow and Ice Data Center
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The Arctic Oscillation turns negative
From November through the first part of January, the Arctic Oscillation (AO) was in a generally positive phase, which tends to bring warm conditions to the United States and Europe, and colder conditions to the Arctic. However, in the middle of the month, the AO shifted back to a negative phase. This shift helped bring cold air outbreaks over middle latitudes, notably a record cold snap throughout much of Europe.

The Arctic Oscillation also affects how sea ice moves in the Arctic, which can affect how much ice melts in the summer months. In December, when the AO was in its positive phase, ice was flowing from Siberia toward North America, and also south out of the Arctic through Fram Strait. That pattern favors a thinner, younger ice cover in the summer. In mid-January, the AO switched to its negative phase. In general, the negative phase of the AO tends to retain ice in the Arctic Ocean, leading to a stronger, more resilient summer sea ice cover. Ice motion charts for January confirm that in January, there was less motion across the pole and through Fram Strait but a stronger clockwise motion in the Beaufort Sea called the Beaufort Gyre.

For background on the Arctic Oscillation, see the NSIDC Icelights post: The Arctic Oscillation, winter storms and sea ice.

Figure 5. This NASA Moderate Resolution Imaging Spectroradiometer (MODIS) image, acquired in mid-January, shows heavy sea ice conditions in Bristol Bay and the Bering Sea, off the western coast of Alaska.

Credit: NASA Earth Observatory courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC.
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Ice-covered Bering Sea
Arctic sea ice extent in the Bering Sea was the second highest in the satellite record for the month of January. Ice extent in the Bering Sea was 562,000 square kilometers (217,000 square miles), which is 104,600 square kilometers (40,400 square miles) above the 1979 to 2000 average. The record high ice extent for the month occurred in January 2000, at 629,000 square kilometers (242,900 square miles).

The above-average sea ice extent in the Bering Sea stemmed from a weather pattern that brought cold air from the Arctic into the Bering Sea, driving sea ice southwards. The weather pattern, which has persisted since November, features unusually low surface pressure south and east of the Alaskan coast, which leads to winds from the north or northeast that blow into the Bering Sea region. This weather pattern also brought moist air from the Pacific Ocean to the southern Alaska coast, helping to explain record snowfalls in towns such as Cordova, Alaska, which received over 15 feet of snow between early November and mid-January.

The extensive sea ice impeded winter fishing in the Bering Sea and slowed an important fuel resupply mission to Nome, on the west coast of Alaska. More information on sea ice conditions off southwestern Alaska, and a full-resolution version of the image at left, are available on the NASA Earth Observatory Web site.

Positively Arctic: Arctic Oscillation switches phase

Arctic sea ice extent remained unusually low through December, especially in the Barents and Kara seas.  In sharp contrast to the past two winters, the winter of 2011 has so far seen a generally positive phase of the Arctic Oscillation, a weather pattern that helps to explain low snow cover extent and warmer than average conditions over much of the United States and Eastern Europe.  In Antarctica, where summer is beginning, sea ice extent is presently above average.

Figure 1. Arctic sea ice extent for December 2011 was 12.38 million square kilometers (4.78 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
Arctic sea ice extent in December 2011 averaged 12.38 million square kilometers (4.78 million square miles). This is the third lowest December ice extent in the 1979 to 2011 satellite data record, 970,000 square kilometers (375,000 square miles) below the 1979 to 2000 average extent.

Ice extent was particularly low on the Atlantic side of the Arctic, most notably in the Barents and Kara seas. The eastern coast of Hudson Bay did not freeze entirely until late in the month: normally, Hudson Bay has completely frozen over by the beginning of December. In the Bering Sea, ice extent was slightly above average.

Figure 2. The graph above shows daily Arctic sea ice extent as of January 3, 2012, along with the ice extents for the previous four years. 2011 is shown in light blue, 2010 is in pink, 2009 in dark blue, 2008 is in purple, and 2007, the year with the record low minimum, is dashed green. 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
For the Arctic as a whole, ice extent for the month remained far below average. The Arctic sea ice cover grew slightly faster than average, but December started out with a lower-than-average ice extent.

Overall, the Arctic gained 2.37 million square kilometers (915,000 square miles) of ice during the month. The average ice gain for December was 1.86 million square kilometers (718,000 square miles). On December 31, Arctic sea ice extent was 13.25 million square kilometers (5.12 million square miles), 561,000 square kilometers (217,000 square miles) more than the ice extent on December 31, 2010, the lowest extent on December 31 in the satellite record.

Figure 3. Monthly December ice extent for 1979 to 2011 shows a decline of 3.5% per decade.

Credit: National Snow and Ice Data Center
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December 2011 compared to past years
Arctic sea ice extent for December 2011 was the third lowest in the satellite record. The five lowest December extents in the satellite record have occurred in the past six years. Including the year 2011, the linear rate of decline ice December ice extent over the satellite record is -3.5% per decade.

Figure 4. This map of air temperature anomalies at the 925 hPa level (approximately 3000 feet) for December 2011 shows near-normal or lower-than-average temperatures over much of the Arctic basin, while air temperatures over the Kara and Barents seas were warmer than normal.

Credit: NSIDC courtesy NOAA/ESRL PSD
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Arctic temperatures
Air temperatures in December were lower than average over much of the Arctic Ocean, but higher than average over the Kara and Barents seas. Higher-than-average temperatures in these regions stemmed from two major factors. First, where sea ice extent is low, heat can escape from areas of open water, warming the atmosphere. Second, surface winds in the Kara and Barents Sea ice blew persistently from the south, bringing in heat from lower latitudes. This imported heat also helped to keep sea ice extent low in this area. Conditions over Canada were also unusually warm during December, but conditions over southeast Greenland have been 6 to 8 degrees Celsius (11 to 14 degrees Fahrenheit) colder than average, partly because of northerly winds in the area.

Figure 5. This graph shows daily Arctic Oscillation Index values from the NOAA Climate Prediction Center for early September 2011 to early January 2012. The index is a normalized (unitless) index of relative pressure anomalies between polar and mid-latitude regions.

Credit: NSIDC courtesy NOAA NWS Climate Prediction Center
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Positive phase of the Arctic Oscillation
The past two Arctic winters were dominated by a negative phase of the Arctic Oscillation, a large-scale weather pattern that brings generally warm conditions to the Arctic and colder conditions to Europe and North America. In contrast, the winter of 2011 has so far seen a mostly positive phase of the Arctic Oscillation. While temperatures were above normal in the Kara and Barents seas, the positive phase of the Arctic Oscillation tends to keep the coldest winter air locked up in the Arctic, which keeps the middle latitudes free of frigid Arctic temperatures and strong snowstorms. This weather pattern helps to explain the low snow cover and warm conditions over much of the United States and Eastern Europe so far this winter.

Several studies have shown that during the positive phase of the Arctic Oscillation, thick ice tends to move out of the Arctic through Fram Strait, leaving the Arctic with thinner ice that melts out more easily in summer. Scientists will be watching closely for this connection if the positive phase of the Arctic Oscillation continues through the winter.

Some scientists have speculated that the negative Arctic Oscillation pattern of the last two winters was in part driven by low sea ice extent. The recurrence of the positive phase of the Arctic Oscillation so far this winter, following a near-record low summer sea ice extent, suggests that other factors play an important role.

Figure 6. This full-year graph puts 2011 sea ice extent in context. The gray line shows the 1979 to 2000 climatology, thick blue-gray indicates the 1981 to 2010 (30-year) climatology. NOAA this year switched to using the period 1981 to 2010 for their thirty-year climate comparison period. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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2011 year in review
Arctic sea ice extent fell to its seasonal minimum on September 9, 2011, falling just short of the record low set in September 2007, when summer weather conditions were extremely favorable for ice loss. This summer, the weather was not as extreme as 2007, so it was surprising that ice extent dropped so low. The low ice extent, along with data on ice age, suggests that the Arctic ice cover remains thin and vulnerable to summer melt.

Northern Hemisphere snow cover retreated very rapidly last spring, with record and near-record low snow cover extents in May and June despite higher-than-average winter snow extent as of February and March.

Figure 7. This graph shows Antarctic sea ice extent as of January 3, 2011. This year’s sea ice extent is shown in light blue, and 2010 is shown in dark blue. 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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A quick look at Antarctica
After a particularly slow ice loss rate at the beginning of the month, Antarctic sea ice extent was unusually high through much of December, in particular in the northern Ross Sea and the eastern Weddell Sea. December and November have had a markedly strong Amundsen Sea Low, an atmospheric pressure pattern that tends to spread the sea ice cover northward in the Ross Sea. Low pressure over the eastern Weddell Sea later in the month had the same effect there. Sea ice for the Antarctic in December 2011 was the fifth-highest for that month in the satellite record; the highest December extent occurred in 2007. Overall though, Antarctic sea ice extent remained below or near normal for most of 2011. Antarctic sea ice data are available on the Sea Ice Index Web site.

References
Rigor, I. G., and J. M. Wallace. 2004. Variations in the age of Arctic sea-ice and summer sea-ice extent, Geophys. Res. Lett., 31, L09401, doi:10.1029/2004GL019492.

Winter in the Arctic: Ice and storms

Arctic sea ice continued its winter expansion, although ice growth slowed briefly in early November. The slowdown may have been related to a strong Arctic storm that tracked from the Bering Sea into the Beaufort and Chukchi seas. In the Southern Hemisphere, Antarctic sea ice is tracking near average for this time of year.

map from space showing sea ice extent, continentsFigure 1. Arctic sea ice extent for November 2011 was 10.01 million square kilometers (3.86 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 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.

graph with months on x axis and extent on y axis Figure 2. The graph above shows daily Arctic sea ice extent as of December 1, 2011, along with the ice extents for the previous four years. 2011 is shown in light blue, 2010 is in pink, 2009 in dark blue, 2008 is in purple, and 2007, the year with the record low minimum, is dashed green. 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 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.

graph with months on x axis and extent on y axis Figure 3. Monthly November ice extent for 1979 to 2011 shows a decline of 4.7% per decade.

—Credit: National Snow and Ice Data Center
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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.

graph with months on x axis and extent on y axis 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?

graph with months on x axis and extent on y axis Figure 5. This map shows snow cover this November, compared to the 1971 to 2000 average. Areas in orange and red had lower snow cover than usual, while areas in blue had more snow than normal during November.

—Credit: NSIDC courtesy David Robinson, Rutgers University Snow Cover Laboratory
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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.

graph with months on x axis and extent on y axis Figure 6. This graph shows Antarctic sea ice extent as of December 1, 2011. This year’s sea ice extent is shown in light blue, and 2010 is shown in dark blue. 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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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.

Further Reading

Cohen, J., and J. Jones, 2011. A new index for more accurate winter predictions, Geophysical Research Letters, vol. 38, L21701, doi:10.1029/2011/GL049626.

NOAA has released their annual Arctic Report Card, an annual compilation of scientific observations of the changing Arctic region. NSIDC scientist Walt Meier contributed to the sea ice section of the report.

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

A rapid freeze-up

Arctic sea ice extent increased rapidly through October, as is typical this time of year. Large areas of open water were still present in the Beaufort and Chukchi seas at the end of the month. The open water contributed to unusually warm conditions along the coast of Siberia and in the Beaufort and Chukchi seas.

map from space showing sea ice extent, continentsFigure 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.

graph with months on x axis and extent on y axis 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).

graph with months on x axis and extent on y axis 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.

graph with months on x axis and extent on y axis 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.

graph with months on x axis and extent on y axis 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.

Further ReadingOvereem, I., R.S. Anderson, C.W. Wobus, G.D. Clow, F.E. Urban, and N. Matell. 2011: Sea ice loss enhances wave action at the Arctic coast. Geophysical Research Letters, 38, L17503, doi:10.1029/2011GL048681.

Serreze, M.C., and R.G. Barry. 2011: Processes and impacts of Arctic Amplification: A research synthesis. Global and Planetary Change, 77,85-96.

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

Summer 2011: Arctic sea ice near record lows

The summer sea ice melt season has ended in the Arctic. Arctic sea ice extent reached its low for the year, the second lowest in the satellite record, on September 9. The minimum extent was only slightly above 2007, the record low year, even though weather conditions this year were not as conducive to ice loss as in 2007. Both the Northwest Passage and the Northern Sea Route were open for a period during September.

map from space showing sea ice extent, continentsFigure 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.

graph with months on x axis and extent on y axis 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).

graph with months on x axis and extent on y axis 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)

graph with months on x axis and extent on y axis 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.

graph with months on x axis and extent on y axis 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.

ice age image 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.

Table 1. Previous Arctic sea ice extents
for the month of September
Year Average Arctic Sea Ice Extent for September Trend, in % per decade (relative to 1979-2000 avg.)
in millions of square kilometers in millions of square miles
2007 4.30 1.66 -10.2
2008 4.67 1.80 -11.1
2009 5.36 2.07 -11.2
2010 4.90 1.89 -11.6
2011 4.61 1.78 -12.0
1979 to 2000 average 7.04 2.72
1979 to 2010 average 6.52 2.52

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