Figure 1. Arctic sea ice extent on August 14, 2011 was 5.56 million square kilometers (2.15 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data Center
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Overview of conditions

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

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

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

Figure 2. The graph above shows daily Arctic sea ice extent as of August 14, 2011, along with daily ice extents for previous low-ice-extent years. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, purple shows 2008, and dark gray shows the 1979 to 2000 average. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data Center
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Conditions in context

Arctic sea ice loss slowed down in late July through early August; then over the past week, the rate of ice loss sped up. At present there is more ice than at the same time in 2007, which saw the record minimum September extent.

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

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

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

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

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

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

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

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

References

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

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

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

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

Figure 1. Arctic sea ice extent for July 2011 was 7.92 million square kilometers (3.06 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data Center
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Overview of conditions

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

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

Figure 2. The graph above shows daily Arctic sea ice extent as of August 2, 2011, along with daily ice extents for previous low-ice-extent years. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, purple shows 2008, and dark gray shows the 1979 to 2000 average. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data Center
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Conditions in context

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

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

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

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

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

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

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

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

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

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

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

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

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