Figure 1. Arctic sea ice extent for October 2010 was 7.69 million square kilometers (2.97 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 October 2010 was the third lowest over the satellite data record at 7.69 million square kilometers (2.97 million square miles). This was 1.60 million square kilometers (618,000 square miles) below the 1979 to 2000 average for October, but 920,000 square kilometers (355,000 square miles) above the record low for the month, which occurred in October 2007.

Figure 2. The graph above shows daily Arctic sea ice extent as of November 1, 2010, along with daily ice extents for years with the previous four lowest minimum extents. Light blue indicates 2010, dark blue shows 2009, purple shows 2008, dotted green indicates 2007, 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

Following the minimum ice extent on September 19, the ice cover quickly expanded as polar darkness returned to the Arctic and air temperatures dropped. Ice grew at an average daily rate for the month of October of 92,700 kilometers per day (35,800 square miles per day). This was similar to the growth rate in 2009, but slower than the growth rate following the 2007 and 2008 minimum ice extents. It was slightly faster than the 1979 to 2000 average rate of 82,200 square kilometers (31,700 square miles) per day.

At the end of October, ice growth slowed, and at the end of the month extensive open water areas remained in the Beaufort, Chukchi, Kara and Barents seas. This region had the warmest ocean surface temperatures at the end of the melt season.

Figure 3. Monthly October ice extent for 1979 to 2010 shows a decline of 6.2% per decade. —Credit: National Snow and Ice Data Center
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October 2010 compared to past years

Even with the rapid ice growth at the beginning of the month, October 2010 had the third-lowest ice extent for the month in the satellite record. The linear trend for October steepened slightly from -5.9% per decade to -6.2% per decade.

Figure 4. This map of Arctic air temperature anomalies shows warmer-than-usual conditions over much of the Arctic Ocean through the month of October.—Credit: NSIDC courtesy NOAA/ESRL PSD
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Warm air temperatures

While air temperatures were below freezing over much of the Arctic in October, they were 4 to 6 degrees Celsius (7 to 10 degrees Fahrenheit) higher than normal. The warm conditions resulted partly from regions of open water releasing heat to the atmosphere, and in part from an atmospheric circulation pattern that brought warm air from lower latitudes to the Arctic.

As noted in previous posts, open water in summer absorbs heat from the sun that would normally be reflected back to space by the bright sea ice cover. In order for the ocean to refreeze in autumn, it must first release the heat accumulated during summer in these open water areas to the atmosphere. While the unusually warm temperatures tend to be focused over areas of open water, winds can move this heat around, warming other regions of the Arctic.

Figure 5. The map of sea level pressure for October 1 to 30, 2010, shows a high-pressure system cenetered over the Beaufort and Chukchi sea and Greenland, and low pressure over the Kara and Barents seas. This pattern tends to bring warm air from lower latitudes into the Arctic.—Credit: National Snow and Ice Data Center courtesy NOAA/ESRL PSD
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Arctic circulation and mid-latitude weather

In addition to the effects from open water, weather patterns also contributed to warm conditions in some areas. For most of October, a high-pressure system sat over the Beaufort and Chukchi seas and Greenland, while unusually low pressure dominated the Kara and Barents seas. This pattern resembles the atmospheric pattern observed in October 2009, bringing warm air from lower latitudes to warm the Arctic.

The warming effects of open water, caused by the loss of summer sea ice cover, could add another twist to the warmer Arctic weather trends lately seen in the Arctic. NOAA researcher James Overland recently noted connections between warmer air temperatures in the lower Arctic atmosphere and atmospheric circulation at lower latitudes, in the 2010 NOAA Arctic Report Card.

Further Reading

Screen, J.A. and I. Simmonds, 2010. The central role of diminishing sea ice in recent Arctic temperature amplification. Nature, 464, 1334-1337. doi:10.1038/nature09051. (subscription required)

Serreze, M. C., Barrett, A. P., Stroeve, J. C., Kindig, D. N. & Holland, M. M., 2009. The emergence of surface-based Arctic amplification. Cryosphere 3, 11–19. doi:10.5194/tc-3-11-2009

Figure 1. Arctic sea ice extent for September 2010 was 4.90 million square kilometers (1.89 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data Center
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Overview of conditions

Average ice extent for September 2010 was 4.90 million square kilometers (1.89 million square miles), 2.14 million square kilometers (830,000 square miles) below the 1979 to 2000 average, but 600,000 square kilometers (230,000 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 near Svalbard.

The U.S. National Ice Center declared both the Northwest Passage and the Northern Sea Route open for a period during September. Stephen Howell of Environment Canada reported a record early melt-out and low extent in the western Parry Channel region of the Northwest Passage, based on analyses of the Canadian Ice Service. Two sailing expeditions, one Norwegian and one Russian, successfully navigated both passages and are nearing their goal of circumnavigating the Arctic.

Figure 2. The graph above shows daily Arctic sea ice extent as of October 3, 2010, along with daily ice extents for years wtih the previous four lowest minimum extents. The solid light blue line indicates 2010; dark blue shows 2009, purple shows 2008; dashed green shows 2007; light green shows 2005; and solid gray indicates average extent from 1979 to 2000. 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

After the minimum extent of 4.60 million square kilometers (1.78 million square kilometers) on September 19, 2010, a rapid freeze-up has begun. On October 1, the 5-day average ice extent was 5.44 million square kilometers (2.10 million square miles).

Figure 3. Monthly September ice extent for 1979 to 2010 shows a decline of 11.5% per decade. 

—Credit: National Snow and Ice Data Center
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September 2010 compared to past years

Ice extent for September 2010 was the third lowest in the satellite record for the month, behind 2007 (lowest) and 2008 (second lowest). The linear rate of decline of September ice extent over the period 1979 to 2010 is now 81,400 square kilometers (31,400 square miles) per year, or 11.5% per decade relative to the 1979 to 2000 average. Sea ice extent at the end of the melt season is shaped by conditions in the atmosphere and ocean, as well as the condition of the ice cover itself.

Figure 4. These maps of sea level pressure for late summer show atmospheric conditions during August 2010 (left), and September 2010 (right). In August, high pressure over the Beaufort was paired with low pressure over Siberia. This pattern persisted through the first week of September, then broke down. —Credit: NSIDC courtesy NOAA/ESRL PSD
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The atmosphere
During the summer of 2010, atmospheric conditions shifted between warm conditions that favored melt, and stormy conditions that slowed the melt rate but helped break up the ice. The net effects of atmospheric conditions this season contributed to the low ice extent.

At the beginning of the melt season, ice extent was relatively high after a long winter dominated by an extreme negative phase of the Arctic Oscillation. Historically, these winter conditions would favor retention of ice through the summer. But in June, a combination of high pressure over the central Arctic Ocean and unusually low pressure over Siberia gave rise to warm conditions over much of the Arctic Ocean and strong westward ice motion off the Siberian Coast, favoring rapid ice melt. In contrast, a series of low-pressure systems moved into the central Arctic Ocean in July. While slowing the melt rate, the stormy conditions helped to break up the sea ice cover. August saw a return to the basic pattern seen in June, although not as prominent. This pattern persisted through the first week of September, helping to drive the sea ice toward what appeared to be its seasonal minimum on September 10. After ice extent started to climb, a change in atmospheric conditions caused it to fall again, to reach its final value of 4.60 million square kilometers (1.78 million square miles) on September 19.

Figure 5. This summer, sea surface temperatures were higher than average, but lower than in the last three years. The maps above show average sea surface temperatures and anomalies for August 2007 to 2010.—Credit: National Snow and Ice Data Center courtesy M. Steele, University of Washington
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The ocean

As in recent years, sea surface temperatures this summer were higher than normal in much of the Arctic Ocean, according to researchers at the University of Washington. Mike Steele, Wendy Ermold, and Ignatius Rigor found that temperatures in the Beaufort/Chukchi Seas and the region north of the Laptev Sea were particularly high. The high sea surrface temperatures resulted largely from the loss of sea ice: dark open water areas absorb more solar radiation than reflective ice. The warmer water in turn helps to melt more sea ice. This positive feedback likely contributed to the ice loss through summer 2010, especially late in the season when surface melt had largely ceased.

Figure 6. These images show the change in ice age from spring 2010 to fall 2010. The negative phase of the Arctic Oscillation this winter slowed the export of older ice out of the Arctic in the winter, but a large amount of older ice melted out during the summer.—Credit: National Snow and Ice Data Center ourtesy C. Fowler and J. Maslanik, CU Boulder
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The ice

Researchers often look at ice age as a way to estimate ice thickness. Older ice tends to be thicker than younger, one- or two-year-old ice. Last winter, the wind patterns associated with the negative phase of the Arctic Oscillation transported a great deal of multiyear ice from the coast of the Canadian Arctic into the Beaufort and Chukchi seas. Scientists speculated that much of this ice, some five years or older, would survive the summer melt period. Instead, it mostly melted away. At the end of the summer 2010, under 15% of the ice remaining the Arctic was more than two years old, compared to 50 to 60% during the 1980s. There is virtually none of the oldest (at least five years old) ice remaining in the Arctic (less than 60,000 square kilometers [23,000 square miles] compared to 2 million square kilometers [722,000 square miles] during the 1980s).

Whether younger multiyear ice (two or three years old) in the Arctic Ocean will continue to age and thicken depends on two things: first, how much of that ice stays in the Arctic instead of exiting into the North Atlantic through Fram Strait; and second, whether the ice survives its transit across the Beaufort and Chukchi Seas or instead melts away.

Further Reading

National Ice Center: Northwest Passage Opening

Northern Sea Route Opening

Borge Ousland: Northern Passage Expedition blog

Voice of Russia, 1 October 2010: Russian yacht circumnavigates North Pole

NSIDC Announcement: Arctic sea ice extent falls to third-lowest extent, downward trend persists

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

Figure 1. Daily Arctic sea ice extent on August 16 was 5.95 million square kilometers (2.30 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data Center
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Overview of conditions

As of August 16, 2010, Arctic ice extent was 5.95 million square kilometers (2.30 million square miles),1.68 million square kilometers (649,000 square miles) below the 1979 to 2000 average.

Figure 2. The graph above shows daily Arctic sea ice extent as of August 16, 2010. The solid light blue line indicates 2010; dashed green shows 2007; solid pink shows 2008; solid orange shows 2009; and solid gray indicates average extent from 1979 to 2000. 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 August 16, only 2007 and 2008 had lower extent. Approximately one month remains in the melt season.

High pressure has moved in over the central Arctic Ocean, replacing stormier, lower-pressure conditions that persisted during July. Paired with lower pressure on the Siberian side, this pattern generates winds that push the ice northward and reduce the total ice extent, especially since much of the ice pack is spread out.

Figure 3. Top: This image, from the Canadian Space Agency’s RADARSAT-2 satellite, shows the northern route of the Northwest Passage this August; although the passage is not completely open, sea ice cover is light. Bright, circular and other sharply defined shapes are sea ice; dark grey indicates calm ocean; white smudged regions are areas of ocean that have been roughened by winds. Bottom: The graph of ice area in the northern route of the Northwest Passage shows that ice retreated earlier than normal. The blue line tracks the area of sea ice for 2010, compared to average and to previous low ice years.—Credit: NSIDC courtesy Howell, Agnew, Wohlleben, and the Canadian Ice Service
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Early clearing in the Northwest Passage

Stephen Howell, Tom Agnew, and Trudy Wohlleben from Environment Canada report that sea ice conditions in the Northwest Passage are very light. Ice is still present at the mouth of the M’Clure Strait, in central Viscount-Melville Sound, and in Larsen Sound, as of early August. As a result, neither the northern route (Western Parry Channel) nor the southern route (Amundsen’s Passage) through the Northwest Passage are completely clear of ice. Sea ice area within the northern route is currently well below the 1968 to 2000 average and almost a month ahead of the clearing that was observed in 2007, according to ice chart data from the Canadian Ice Service. In the southern route, there is still a substantial amount of ice.

This year’s early clearing of sea ice probably resulted from record warm temperatures this past spring over the Western Canadian Arctic, as well as the decline in older, multiyear ice in the channel over recent years. Spring 2010 was the warmest in the region since 1948: some regions of the Western Canadian Arctic were more than 6°C (11°F) above normal. These warm conditions helped break the ice up early in the northern route. If winds push sea ice away from the entrance to M’Clure Strait, the northern route of the Northwest Passage could open completely this year. However, even scattered sea ice remains a significant threat to navigation.

Figure 4. This map shows ice concentration on August 16, 2010, from the NASA AMSR-E sensor on the Aqua satellite. Lines mark two well-known routes through the Northwest Passage: Amundsen’s route is yellow, and the northern route is red.—Credit: NSIDC courtesy University of Bremen IUP
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History of the Northwest Passage

Conditions in the Northwest Passage are quite variable and do not necessarily reflect overall conditions in the Arctic. However, today’s conditions in the Northwest Passage would likely astonish 19th century explorers such as McClure, Franklin, and Amundsen. In upcoming decades, the passage will be increasingly likely to open during summer.

Last month, Canadian investigators located the wreckage of the HMS Investigator, which sank on an expedition led by Captain Robert McClure in the 1850s. The McClure expedition had set out to rescue the Franklin Expedition, which had gone missing after leaving Baffin Bay for the Northwest Passage in 1845. McClure attempted to enter the passage from the west through what is now called M’Clure Strait, but quickly became trapped in the ice. They remained trapped through two winters before being rescued by another ship. The Franklin Expedition was not so fortunate: all 128 men perished. It was another fifty years before Norwegian Roald Amundsen and a small crew successfully navigated the passage. Their trek, by the southern route, took over two years.

Figure 5. This image shows melt onset anomalies in the Arctic Ocean for 2010, compared to the 1979 to 2000 average. Green, red, and yellow indicate areas of earlier melt onset, while blue and violet show regions of later melt onset. White and black indicate regions with no data.—Credit: NSIDC courtesy Thorsten Markus, NASA GSFC/data from DMSP SSM/I and NASA AMSR-E
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Melt onset

Despite a late spurt in ice growth this past winter, air temperatures remained higher than normal during spring and early summer, leading to an early melt onset over parts of the Arctic Ocean, though onset was later in other areas. Compared to the 1979 to 2000 average onset date, melt began one to two weeks earlier in the eastern Arctic. The central Arctic melt onset date was about average. In contrast, melt started about a week later than average in the western Arctic, including the Beaufort, Chukchi and East Siberian seas, and in the Bering Sea, one of the regions that experienced a surge in ice growth late in the winter.

Recent work by Thorsten Markus at NASA Goddard Space Flight Center shows that date of melt onset got steadily earlier from 1979 to 2008, in all regions of the Arctic except for the Sea of Okhotsk. Although this year showed some areas of later melt onset, compared to normal, the overall trend remains towards earlier melt. The largest trend is in the Barents Sea, where ice melt has begun about seven days earlier each decade since 1979.

Figure 1. Arctic sea ice extent for July 2010 was 8.39 million square kilometers (3.24 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data Center
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Overview of conditions

Average ice extent for July was 8.39 million square kilometers (3.24 million square miles), 1.71 million square kilometers (660,000 square miles) below the 1979 to 2000 mean, but 260,000 square kilometers (100,000 square miles) above the average for July 2007, the lowest July in the thirty-two-year satellite record.

Stormy, cloudy, and relatively cool weather persisted through the month, which helped slow the rate of ice loss. The daily rate of decline for July was 77,000 square kilometers (29,700 square miles) per day, close to the 1979 to 2000 average of 84,400 square kilometers (32,600 square miles).

Figure 2. The graph above shows daily Arctic sea ice extent as of August 3, 2010. The solid light blue line indicates 2010; dashed green shows 2007; solid pink shows 2006, and solid gray indicates average extent from 1979 to 2000. 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

Cool, stormy weather this July has made it less likely that the upcoming 2010 sea ice minimum will set a new record. It would take a very unusual set of conditions in August to create a new record low.

If the daily rate of decline this August follows the average August rate of decline for 1979 to 2000, the daily sea ice minimum in September would be 5.00 million square kilometers (1.93 million square miles), considerably higher than the record minimum of 4.13 million square kilometers (1.59 million square miles) observed for September 16, 2007. A daily rate of decline identical to 2007 would yield a September minimum of 4.43 million square kilometers (1.71 million square miles); while daily decline rates similar to 2008 (the largest ever observed for August), would yield a September minimum of 4.08 million square kilometers (1.58 million square miles). If the daily rate of decline is similar to 2006, the slowest in recent years, the minimum would be 5.27 million square kilometers (2.03 million square miles).

Figure 3. Monthly July ice extent for 1979 to 2010 shows a decline of 6.4% per decade. —Credit: National Snow and Ice Data Center
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July 2010 compared to past years

Ice extent for July 2010 was the second lowest in the satellite record for the month. The linear rate of decline of July ice extent over the period 1979 to 2010 is now 6.4% per decade.

Figure 4. This map of ice age for the end of July, 2010, shows a region of open water north of Alaska, where old, thick ice has melted out. —Credit: NSIDC courtesy J. Maslanik and C. Fowler, CU Boulder
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Older, thicker ice melting in the southern Beaufort Sea

This past winter’s negative phase of the Arctic Oscillation transported old ice (four, five, and more years old) from an area north of the Canadian Archipelago. The ice was flushed southwards and westward into the Beaufort and Chukchi seas, as noted in our April post. Ice age data show that back in the 1970s and 1980s, old ice drifting into the Beaufort Sea would generally survive the summer melt season. However, the old, thick ice that moved into this region is now beginning to melt out, which could further deplete the Arctic’s remaining store of old, thick ice. The loss of thick ice has been implicated as a major cause of the very low September sea ice minima observed in recent years.

Figure 5. This image from NASA’s MODIS sensor on the Aqua satellite on July 25, 2010 shows an individual floe of old ice, which broke away from the main ice pack and is melting away.—Credit: National Snow and Ice Data Center courtesy NASA/GSFC MODIS Rapid Response
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High-resolution images from MODIS

High-resolution (250-meter) visible imagery from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) sensor vividly shows the loss of the old, thick ice. A region of mostly old ice has become separated from the main pack along the north coast of Alaska, east of Point Barrow, where it has begun to melt in the warm shallow shelf waters. While cloud cover obscures some areas, it is clear that the old ice floe has broken up into many smaller floes. Whether this old ice will completely melt out by the end of summer will depend to some extent on weather conditions. However, smaller floes melt more easily than consolidated ice. This behavior is becoming more typical of the ice pack as the ice thins.

Figure 1. Daily Arctic sea ice extent on July 15 was 8.37 million square kilometers (3.23 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

From July 1 to 15, Arctic sea ice extent declined an average of 60,500 square kilometers (23,400 square miles) per day, 22,500 square kilometers (8,690 square miles) per day slower than the 1979 to 2000 average and substantially slower than the rate of decline in May and June.

Ice extent remained lower than normal in all regions of the Arctic, with open water developing along the coasts of northwest Canada, Alaska and Siberia.

Figure 2. The graph above shows daily Arctic sea ice extent as of July 15, 2010. The solid light blue line indicates 2010; dashed green shows 2007; solid pink shows 2006, and solid gray indicates average extent from 1979 to 2000. 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 July 15, total extent was 8.37 million square kilometers (3.23 million square miles), which is 1.62 million square kilometers (625,000 square miles) below the 1979 to 2000 average for the same date, but 360,000 square kilometers (139,000 square miles) above July 15, 2007, the lowest extent for that date in the satellite record.

Figure 3. This map of sea level pressure for July 1 to 15, 2010 shows low pressure over the central Arctic Ocean, a pattern that brought cooler and cloudier conditions.—Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences Division
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A change in circulation

Through much of May and June, high pressure dominated the Beaufort Sea with low pressure over Siberia. Winds associated with this pattern, known as the dipole anomaly, helped speed up ice loss by pushing ice away from the coast and promoting melt.

However, the dipole anomaly pattern broke down in early July. In the first half of July, cyclones (low pressure systems) generated over northern Eurasia tracked eastward along the Siberian coast and then into the central Arctic Ocean, where they tend to stall. This cyclone pattern is quite common in summer. The low-pressure cells have brought cooler and cloudier conditions over the Arctic Ocean. They have also promoted a cyclonic (anticlockwise) sea ice motion, which acts to spread the existing ice over a larger area. All of these factors likely contributed to the slower rate of ice loss over the past few weeks.

In the last few days, high pressure has started to build again in the Beaufort Sea, but whether this will continue remains to be seen.

Figure 4. In mid-summer, the NASA Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E) (left) may show areas of low ice concentration which are actually melt ponds or weather effects. Visible band images from the NASA Moderate Resolution Imaging Spectroradiometer (right) confirm areas of low-concentration sea ice in the interior pack ice. Both images are from July 12, 2010.—Credit: National Snow and Ice Data Center
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Areas of diffuse ice

Satellite images provided by the University of Bremen, from the NASA Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E), show areas of low ice concentration over the central Arctic pack ice. While we normally report on the extent of area covered by at least fifteen percent sea ice, a more reliable measurement, it is also valuable to look at ice concentration values, which can reveal conditions in more detail. However, it can be difficult to interpret AMSR-E concentration data during the summer, because microwave signals associated with low ice concentration look very much like signals associated with surface melt. Weather effects can also cause false concentration signals.

By comparing AMSR-E data with data from other satellites, we can determine which areas of apparent low-concentration ice are real, and which appear to be low because of melt or atmospheric effects. Visible-band images from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) sensor show that some of the areas of apparent low ice concentration within the central pack ice are actually melt and atmospheric effects. However, the MODIS data also confirm that there are substantial areas of open water within the pack ice, such as near the North Pole and in the Beaufort Sea.

Open water in the interior pack ice is not unprecedented. Winds can push the ice apart, creating openings in the pack ice. These areas of open water may close up quickly if the wind changes, but since the dark areas of open water readily absorb solar energy, they can also lead to more extensive melt.

Further Reading

Serreze, M., and A. P. Barrett. 2007. The Summer Cyclone Maximum over the Central Arctic Ocean. Journal of Climate 21, pp. 1048-1065. doi: 10.1175/2007JCLI1810.1

Figure 1. Arctic sea ice extent for June 2010 was 10.87 million square kilometers (4.20 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 10.87 million square kilometers (4.20 million square miles) for the month of June, 1.29 million square kilometers (498,000 square miles) below the 1979 to 2000 average and 190,000 square kilometers (73,000 square miles) below the previous record low for the month of 11.06 million square kilometers (4.27 million square miles), set in 2006. In June, ice extent declined by 88,000 square kilometers (34,000 square miles) per day, more than 50% greater than the average rate of 53,000 square kilometers (20,000 square miles) per day. This rate of decline is the fastest measured for June.

During June, ice extent was below average everywhere except in the East Greenland Sea, where it was near average.

Figure 2. The graph above shows daily Arctic sea ice extent as of July 5, 2010. The solid light blue line indicates 2010; dashed green shows 2007; solid pink shows 2006, and solid gray indicates average extent from 1979 to 2000. 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

At the end of May 2010, daily ice extent fell below the previous record low for May, recorded in 2006, and during June continued to track at record low levels. By the 30th of June, the extent was 510,000 square kilometers (197,000 square miles) below the same day in 2006.

Weather conditions, atmospheric patterns, and cloud cover over the next month will play a major role in determining whether the 2010 sea ice decline tracks at a level similar to 2007, or more like 2006. Although ice extent was greater in June 2007 than June 2006, in July 2007 the ice loss rate accelerated. That fast decline led up to the record low ice extent of September 2007.

However, it would not be surprising to see the rate of ice loss slow in coming weeks as the melt process starts to encounter thicker, second and third year ice in the central Arctic Ocean. Loss of ice has already slowed in the Beaufort and Chukchi Seas due to the tongue of thicker, older ice in the region noted in our April update.

Figure 3. Monthly June 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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June 2010 compared to past years

Average ice extent for June 2010 was190,000 square kilometers (73,000 square miles) less than the previous record low for June, observed in 2006; 620,000 square kilometers (240,000 square miles) below that observed in 2007; and 1.29 million square kilometers (498,000 square miles) below the average extent for the month.

The linear rate of monthly decline for June over the 1979 to 2010 period is now 3.5% per decade. This year’s daily June rate of decline was the fastest in the satellite record; the previous record for the fastest rate of June decline was set in 1999. This rapid decline was in part driven by ice loss in Hudson Bay.

Figure 4. This map of sea level pressure for June 2010 shows a return of the Arctic dipole anomaly pattern, with unusually high pressure (yellow and orange) over the northern Beaufort Sea and unusually low pressure (purple and blue) over the Eurasian coast.—Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences Division
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The Arctic dipole anomaly

The record low ice extent of September 2007 was influenced by a persistent atmospheric pressure pattern called the summer Arctic dipole anomaly (DA). The DA features unusually high pressure centered over the northern Beaufort Sea and unusually low pressure centered over the Kara Sea, along the Eurasian coast. In accord with Buys Ballot’s Law, this pattern causes winds to blow from the south along the Siberian coast, helping to push ice away from the coast and favoring strong melt. The DA pattern also promotes northerly winds in the Fram Strait region, helping to flush ice out of the Arctic Ocean into the North Atlantic. The DA pattern may also favor the import of warm ocean waters from the North Pacific that hastens ice melt.

June 2010 saw the return of the DA, but with the pressure centers shifted slightly compared to summer 2007. As a result, winds along the Siberian coastal sector are blowing more from the east rather than from the south. Whether or not the DA pattern persists through the rest of summer will bear strongly on whether a new record low in ice extent is set in September 2010.

Figure 5. This satellite image, acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the NASA Terra satellite on June 30, 2010, shows that Nares Strait was open and sea ice was flowing through it. Normally Nares Strait remains plugged by an “ice arch” through early July, but this year it was clear by May.—Credit: National Snow and Ice Data Center courtesy NASA/GSFC MODIS Rapid Response
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Nares Strait

Ron Kwok of the Jet Propulsion Laboratory (JPL) reports that Nares Strait, the narrow passageway between northwest Greenland and Ellesmere Island is clear of the ice “arch” that usually plugs southward transport of the old, thick ice in the Lincoln Sea. Typically the ice arch forms in winter and breaks up in early July. This year the arch formed around March 15th and lasted only 56 days, breaking up in May. In 2007 the ice arch did not form at all, allowing twice as much export through Nares Strait than the annual mean. Although the export of sea ice out of the Arctic Ocean through Nares Strait is very small in comparison to the export through Fram Strait, the Lincoln Sea contains some of the Arctic’s thickest ice. For the ice flux rates out of Nares strait, see Figure 5a.

Figure 6. The graph above shows daily Antarctic sea ice extent as of July 5, 2010. The solid light blue line indicates 2010; dashed green shows 2007, and solid gray indicates average extent from 1979 to 2000. 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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Meanwhile, in Antarctica

At the end of June, Southern Hemisphere mid-winter, the sea ice surrounding Antarctica was more than two standard deviations greater than normal. On June 30, Antarctic sea ice extent was15.88 million square kilometers (6.13 million square miles), compared to the 1979 to 2000 average of 14.64 million square kilometers (5.65 million square miles) for that day.

While recent studies have shown that wintertime Antarctic sea ice has a weak upward trend, and substantial variability both within a year and from year to year, the differences between Arctic and Antarctic sea ice trends are not unexpected. Climate models consistently project that the Arctic will warm more quickly than the Antarctic, largely due to the strong climate feedbacks in the Arctic. Warming is amplified by the loss of ice cover in the Arctic Ocean in areas that had been ice-covered for decades, and by the warming of Arctic lands as snow cover is lost earlier and returns later than in recent decades.

Moreover, rising levels of greenhouse gases and the loss of stratospheric ozone appear to be affecting wind patterns around Antarctica. Shifts in this circulation are referred to as the Antarctic Oscillation (AAO). As greenhouse gases have increased, and especially when ozone is lost in spring, there is a tendency for these winds to strengthen (a positive AAO index). The net effect is to push sea ice eastward, and northward, increasing the ice extent. As the current sea ice anomaly has developed, the AAO index has been strongly positive. See the NOAA AAO Index Web site. For more information about the differences between sea ice dynamics in the Arctic and Antarctic, see the NSIDC All About Sea Ice Web site.

References

Arblaster, J. M., and G. A. Meehl. 2006. Contributions of External Forcings to Southern Annular Mode Trends. Journal of Climate, 19: 2896-2905.

Hall, A., and M. Visbeck. 2002. Synchronous Variability in the Southern Hemisphere Atmosphere, Sea Ice, and Ocean Resulting from the Annular Mode. Journal of Climate, 15: 3047-3053.

Kwok, R. 2005. Variability of Nares Strait ice flux. Geophys. Res. Lett., 32, L24502, doi:10.1029/2005GL024768

Kwok, R., L. Toudal Pedersen, P. Gudmandsen, and S. S. Pang. 2010. Large sea ice outflow into the Nares Strait in 2007. Geophys. Res. Lett., 37, L03502, doi:10.1029/2009GL041872.

Thompson, W. J., and S. Solomon. 2002. Interpretation of Recent Southern Hemisphere Climate Change. Science. 296, 895-899, doi:10.1126/science.1069270

Wang, J., J. Zhang, E. Watanabe, M. Ikeda, K. Mizobata, J. E. Walsh, X. Bai, and B. Wu. 2009. Is the Dipole Anomaly a major driver to record lows in Arctic summer sea ice extent? Geophys. Res. Lett., 36, L05706, doi:10.1029/2008GL036706.