NSIDC Artic Sea Ice News
Arctic sea ice appears to have reached its annual maximum extent on March 7. This is the lowest maximum in the 38-year satellite record. NSIDC will post a detailed analysis of the 2016 to 2017 winter sea ice conditions in our regular monthly post in early April.Overview of conditions
On March 7, 2017, Arctic sea ice likely reached its maximum extent for the year, at 14.42 million square kilometers (5.57 million square miles), the lowest in the 38-year satellite record. This year’s maximum extent is 1.22 million square kilometers (471,000 square miles) below the 1981 to 2010 average maximum of 15.64 million square kilometers (6.04 million square miles) and 97,000 square kilometers (37,000 square miles) below the previous lowest maximum that occurred on February 25, 2015. This year’s maximum is 100,000 square kilometers (39,000 square miles) below the 2016 maximum, which is now third lowest. (In 2016, we reported that year’s maximum as the lowest and 2015 the second lowest. An update to the Sea Ice Index last summer has changed our numbers slightly.)Conditions in context
It was a very warm autumn and winter. Air temperatures at the 925 hPa level (about 2,500 feet above sea level) over the five months spanning October 2016 through February 2017 were more than 2.5 degrees Celsius (4.5 degrees Fahrenheit) above average over the entire Arctic Ocean, and greater than 5 degrees Celsius (9 degrees Fahrenheit) above average over large parts of the northern Chukchi and Barents Seas. These overall warm conditions were punctuated by a series of extreme heat waves over the Arctic Ocean.
Data from the European Space Agency’s CryoSat-2 satellite indicate that this winter’s ice cover is slightly thinner compared to the past four years. An ice-ocean model at the University of Washington that incorporates observed weather conditions suggests the volume of ice in the Arctic is unusually low for this time of year.The Antarctic minimum
In the Southern Hemisphere, sea ice likely reached its minimum extent for the year on March 3, at 2.11 million square kilometers (815,000 square miles). This year’s minimum extent was the lowest in the satellite record, continuing a period of satellite-era record low daily extents that began in early November. However, the Antarctic system has been highly variable. As recently as 2015, Antarctic sea ice set record high daily extents, and in September 2014 reached a record high winter maximum.
The Antarctic minimum extent is 740,000 square kilometers (286,000 square miles) below the 1981 to 2010 average minimum of 2.85 million square kilometers (1.10 million square miles) and 184,000 square kilometers (71,000 square miles) below the previous lowest minimum that occurred on February 27, 1997.
Antarctic air temperatures during the autumn and winter were above average, but less so than in the Arctic. Air temperatures at the 925 hPa level (about 2,500 feet above sea level) near the sea ice edge have been about 1 to 2.5 degrees Celsius (2 to 4.5 degrees Fahrenheit) above the 1981 to 2010 average.Final analysis pending
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.
High air temperatures observed over the Barents and Kara Seas for much of this past winter moderated in February. Overall, the Arctic remained warmer than average and sea ice extent remained at record low levels.Overview of conditions
Arctic sea ice extent for February 2017 averaged 14.28 million square kilometers (5.51 million square miles), the lowest February extent in the 38-year satellite record. This is 40,000 square kilometers (15,400 square miles) below February 2016, the previous lowest extent for the month, and 1.18 million square kilometers (455,600 square miles) below the February 1981 to 2010 long term average.
Ice extent increased at varying rates, with faster growth during the first and third weeks, and slower growth during the second and fourth weeks. Most of the ice growth in February occurred in the Bering Sea, though extent in the Bering remained below average by the end of the month. Sea ice extent in the Sea of Okhotsk substantially decreased mid-month before rebounding to almost typical levels at the end of the month. Overall, however, the ice retreated in this region. Extent in the Barents and Kara Seas remained low through the month as is has all season, with little change in the ice edge location.Conditions in context
Air temperatures at the 925 hPa level (approximately 2,500 feet above sea level) remained 2 to 5 degrees Celsius (4 to 9 degrees Fahrenheit) above average over the Arctic Ocean. The high air temperatures observed over the Barents and Kara Seas for much of this past winter moderated in February. February air temperatures over the Barents Sea ranged between 4 to 5 degrees Celsius (8 to 9 degrees Fahrenheit) above average, compared to 7 degrees Celsius (13 degrees Fahrenheit) above average in January. Recall that these January temperature extremes were associated with a series of strong cyclones entering the Arctic Ocean from the North Atlantic, drawing in warm air. Sea level pressure in February was nevertheless lower than average over much of the Arctic Ocean. Sea level pressure was higher than average over the Bering Sea and just north of Scandinavia.February 2017 compared to previous years
The linear rate of decline for February is 46,900 square kilometers (18,100 square miles) per year, or 3 percent per decade.Antarctic minimum extent
Antarctic sea ice is nearing its annual minimum extent and continues to track at record low levels for this time of year. On February 13, Antarctic sea ice extent dropped to 2.29 million square kilometers (884,000 square miles), setting a record lowest extent in the satellite era. The previous lowest extent occurred on February 27, 1997. By the end of February, extent had dropped even further to 2.13 million square kilometers (822,400 square miles). The record lows are not surprising, given Antarctic sea ice extent’s high variability. Just a few years back, extent in the region set record highs (Figure 4b).
Sea ice extent was particularly low in the Amundsen Sea, which remained nearly ice-free throughout February. Typically, sea ice in February extends at least a couple hundred kilometers along the entire coastline of the Amundsen. Near-average ice extent persisted in the Weddell Sea and in several sectors along the East Antarctic coast.Continuity of the sea ice record
As noted last year, the sensor that NSIDC had been using for sea ice extent, the Special Sensor Microwave Imager and Sounder (SSMIS) on the Defense Meteorological Satellite Program (DMSP) F17 satellite, started to malfunction. In response, NSIDC switched to the SSMIS on the newer F18 satellite. Later, F17 recovered to normal function, though it recently started to malfunction again.
The DMSP series of sensors have been a stalwart of the sea ice extent time series, providing a continuous record since 1987. Connecting this to data from the earlier Scanning Multichannel Microwave Radiometer (SMMR) results in a continuous record starting in 1979 of high quality and consistency. However, with the issues of F17 and last year’s loss of the newest sensor, F19, grave concerns have arisen about the long-term continuity of the passive microwave sea ice record. Only two DMSP sensors are currently fully capable for sea ice observations: F18 and the older F16; these two sensors have been operating for over 7 and 13 years respectively, well beyond their nominal 5-year lifetimes.
The only other similar sensor currently operating is the Japan Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2), which is approaching its 5-year design lifetime in May 2017. NSIDC is now evaluating AMSR2 data for integration into the sea ice data record if needed. Future satellite missions with passive microwave sensors are either planned or proposed by the U.S., JAXA, and ESA, but it is unlikely that a successor to the DMSP series and AMSR2 will be operational before 2022. This presents a growing risk of a gap in the sea ice extent record. Should such a gap occur, NSIDC and NASA would seek to fill the gap as much as possible with other types of sensors (e.g., visible or infrared sensors).
Record low daily Arctic ice extents continued through most of January 2017, a pattern that started last October. Extent during late January remained low in the Kara, Barents and Bering Seas. Southern Hemisphere extent also tracked at record low levels for January; globally, sea ice cover remains at record low levels.Overview of conditions
Arctic sea ice extent for January 2017 averaged 13.38 million square kilometers (5.17 million square miles), the lowest January extent in the 38-year satellite record. This is 260,000 square kilometers (100,000 square miles) below January 2016, the previous lowest January extent, and 1.26 million square kilometers (487,000 square miles) below the January 1981 to 2010 long-term average.
Ice growth stalled during the second week of the month, and the ice edge retreated within the Kara and Barents Seas, and within the Sea of Okhotsk. After January 16, extent increased at a more rapid pace, but the rate of ice growth was still below average for January as a whole. For a few days towards the end of the month, the extent was slightly greater than recorded in 2006, a year which also saw many record low days in January, but by the 30th it was tracking below 2006. Through most of January the ice edge remained north of the Svalbard Archipelago, largely due to the inflow of warm Atlantic water along the western part of the archipelago. However, by the end of January, some ice was found to the northeast and northwest of Svalbard. At the end of January, ice extent remained well below average within the Kara, Barents, and Bering Seas.Conditions in context
January air temperatures at the 925 hPa level (approximately 2,500 feet above sea level) were above average over nearly all of the Arctic Ocean, continuing the pattern that started last autumn (Figure 2b). Air temperatures were more than 5 degrees Celsius (9 degrees Fahrenheit) above the 1981 to 2010 average over the northern Barents Sea and as much as 4 degrees Celsius (7 degrees Fahrenheit) above average in the northern Chukchi and East Siberian Seas. It was also unusually warm over northwestern Canada. Cooler than average conditions (up to 3 degrees Celsius, or 5 degrees Fahrenheit below average) prevailed over the northwest part of Russia and the northeast coast of Greenland.
Atmospheric circulation over the Arctic during the first three weeks of January was characterized by a broad area of below average sea level pressure extending over almost the entire Arctic Ocean. Higher-than-average sea level pressure dominated over the Gulf of Alaska and the North Atlantic Ocean south of Iceland. This set up warm southerly winds from both the northern North Atlantic and the Bering Strait areas, helping to explain the high January air temperatures over the Arctic Ocean. According to the analysis of NASA scientist Richard Cullather, the winter of 2015 to 2016 was the warmest ever recorded in the Arctic in the satellite data record. Whether the winter of 2016 to 2017 will end up warmer remains to be seen; conditions are typically highly variable. For example, during the last week of January, the area of low pressure shifted towards the Siberian side of the Arctic. In the northern Laptev Sea, pressures fell to more than 20 hPa below the 1981 to 2010 average. This was associated with a shift towards cooler conditions over the Arctic Ocean, which may explain why ice extent towards the end of the month rose above levels recorded in 2006.January 2017 compared to previous years
Through 2017, the linear rate of decline for January is 47,400 square kilometers (18,300 square miles) per year, or 3.2 percent per decade.Amundsen Sea nearly free of ice
Extent is tracking at records low levels in the Southern Hemisphere, where it is currently summer. As shown in this plot for February 5, this is primarily due to low ice extent within the Amundsen Sea, where only a few scattered patches of ice remain. By contrast, extent in the Weddell Sea is now only slightly below average. This pattern is consistent with persistent above average air temperatures off western Antarctica.Further reading
Cullather, R. I., Y.-K. Lim, L. N. Boisvert, L. Brucker, J. N. Lee, and S. M. J. Nowicki. 2016. Analysis of the warmest Arctic winter, 2015-2016. Geophysical Research Letters,43, doi:10.1002/2016GL071228.
Sea ice in the Arctic and the Antarctic set record low extents every day in December, continuing the pattern that began in November. Warm atmospheric conditions persisted over the Arctic Ocean, notably in the far northern Atlantic and the northern Bering Sea. Air temperatures near the Antarctic sea ice edge were near average. For the year 2016, sea ice extent in both polar regions was at levels well below what is typical of the past several decades.Overview of conditions
Arctic sea ice extent for December 2016 averaged 12.10 million square kilometers (4.67 million square miles), the second lowest December extent in the satellite record. This is 20,000 square kilometers (7,700 square miles) above December 2010, the lowest December extent, and 1.03 million square kilometers (397,700 square miles) below the December 1981 to 2010 long-term average.
The rate of ice growth for December was 90,000 square kilometers (34,700 square miles) per day. This is faster than the long-term average of 64,100 square kilometers (24,700 square miles) per day. As a result, extent for December was not as far below average as was the case in November. Ice growth for December occurred primarily within the Chukchi Sea, Kara Sea, and Hudson Bay—areas that experienced a late seasonal freeze-up. Compared to the record low for the month set in 2010, sea ice for December 2016 was less extensive in the Kara, Barents, and East Greenland Seas, and more extensive in Baffin and Hudson Bays.Conditions in context
Air temperatures at the 925 hPa level (approximately 2,500 feet above sea level) were more than 3 degrees Celsius (5 degrees Fahrenheit) above the 1981 to 2010 average over the central Arctic Ocean and northern Barents Sea, and as much as 5 degrees Celsius (9 degrees Fahrenheit) above average over the Chukchi Sea. Repeated warm air intrusions occurred over the Chukchi and Barents Seas, continuing the pattern seen in November.
In contrast, central Russia and northern British Columbia experienced temperatures 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) below average (Figure 2b). Atmospheric circulation over the Arctic in December was characterized by a broad area of lower-than-average pressure over Greenland and the North Pole, extending across the Arctic Ocean to eastern Siberia, and another region of low pressure over the Ural Mountains. Higher-than-average pressure dominated Europe and the Gulf of Alaska. This set up the very warm southerly winds from both the northern North Atlantic and the Bering Strait areas, pushing Arctic air temperatures to unusually high levels for brief periods in early December and near Christmas.December 2016 compared to previous years
Through 2016, the linear rate of decline for December is 44,500 square kilometers (17,200 square miles) per year, or 3.4 percent per decade.
While daily extents for December 2016 were at record lows, based on the method employed by NSIDC, the monthly average extent for December 2016 was slightly higher than that recorded for December 2010, the record low December in the satellite record. The monthly average extent for the month of December is higher than the month’s average of daily extents because of the way in which the Sea Ice Index algorithm calculates the monthly extent. The algorithm calculates the monthly average total extent from the monthly average gridded concentration field. Thus, when sea ice is retreating or advancing at a high rate over the course of the month, as was the case for December 2016, the Sea Ice Index monthly average can yield a larger extent than from simply averaging daily extent values. See the Sea Ice Index documentation for further information.
Average annual sea ice extent in both polar regions was low in 2016. Throughout the year, a wave of new record lows were set for both daily and monthly extent. Record low monthly extents were set in the Arctic in January, February, April, May, June, October, and November; and in the Antarctic in November and December.
For the Arctic, the year opened with daily sea ice extent at near record low levels. Sea ice extent in March tied with 2015 for the lowest maximum in the 37-year satellite period. Ice extent was as much as 500,000 square kilometers (193,000 square miles) below any previous year in the record through most of mid-May to early June. However, the pace of decline returned to near-average rates by July, and the end-of-summer minimum sea ice extent, recorded on September 10, eventually tied for second lowest with 2007 (2012 remains the lowest in the satellite time series by more than 600,000 square kilometers or 232,000 square miles).
That September 2016 did not see a new record low is likely due to the unusually stormy atmospheric pattern that set up over the Arctic Ocean in the summer. Storm after storm moved into the central Arctic Ocean, including a pair of very deep low pressure systems in late August. While a stormy pattern will tend to chew up the ice cover, it also spreads the ice out to cover a larger area and typically brings cloudy and, in summer, relatively cool conditions, inhibiting melt. Sometimes these deep lows act to reduce extent by mixing warm ocean waters upwards, but at present there is no compelling evidence that this occurred in 2016.
In October, a pattern of warm air intrusions from the North Atlantic began. This pattern combined with unusually high sea surface temperatures over the Barents and Kara Seas and helped to keep Arctic sea ice extent at low levels for November and December. In the middle of November there was even a several-day period when Arctic sea ice extent decreased. Unusually warm conditions and record low daily sea ice extent levels continued through the end of the year. The unusually high sea ice surface temperatures reflect a shift in ocean circulation, enhancing the import of warm, Atlantic-derived waters into the Arctic Ocean.
In the Southern Hemisphere, overall sea ice extent shifted from near-average over the first half of the year to sharply below average in mid-August. This initiated a period of near-record, and then extreme record low extents that persisted until late in the year. While the Antarctic seasonal sea ice minimum was unremarkable (slightly earlier, and slightly lower, than the 37-year average), the sea ice maximum occurred early (August 31), followed by a period of rapid ice extent decline. By November, extent was more than 2 million square kilometers (772,000 square miles) below the 1981 to 2010 average extent. In combination with the low Arctic sea ice extent for November, this produced a remarkably low global sea ice total.
The cause of the rapid drop in Antarctic sea ice in the second half of 2016 remains elusive. Significant changes in Southern Ocean wind patterns were observed in August, September, and November, but air temperatures and ocean conditions were not highly unusual.Sea ice cover in Chukchi Sea depends on Bering Strait inflow
A recent study by NSIDC scientists Mark Serreze, Julienne Stroeve, and Alexander Crawford, along with University of Washington scientist Rebecca Woodgate, demonstrates strong links between seasonal sea ice retreat and advance in the Chukchi Sea and the inflow of ocean heat into the region through the Bering Strait. The Chukchi Sea region is important as a focus for resource exploration, and vessels transiting the Arctic Ocean must inevitably pass through it. The Chukchi Sea is also part of the seasonal migration route for Bowhead whales that supports subsistence hunting by local indigenous communities.
Serreze and colleagues looked at time series of the date of retreat and advance in which linear trends related to general warming were removed. They found that 68 percent of the variance in the date that ice retreats from the continental shelf break in the Chukchi Sea in spring can be explained by fluctuations in the April through June Bering Strait oceanic heat inflow. The Bering Strait heat inflow data comes from a mooring located within the strait maintained by the University of Washington. They also found that 67 percent of the variance for the date at which ice advances back to the shelf break in autumn and winter can be related to the combined effects of the July through September Bering Strait inflow and the date of ice retreat. When seasonal ice retreat occurs early, low-albedo open water areas are exposed early, which gain a lot of energy from the sun. With more heat in the upper ocean, autumn ice growth is delayed. These relationships with the Bering Strait inflow and ocean heat uptake are superimposed upon the overall trends due to a warming climate. While these relationships lay a path forward to improving seasonal predictions of ice conditions in the region, developing an operational prediction scheme would require more timely acquisition of Bering Strait heat inflow data than is presently possible.Global sea ice tracking far below average
Global sea ice (Arctic plus Antarctic) continues to track at record low levels in the satellite record, but the deviation from average has moderated compared to what was observed in November. This reflects a December pattern of faster-than-average growth in the Arctic, and slightly slower-than average sea ice extent decline in the Southern Ocean. The gap between the 1981 to 2010 average and the 2016 combined ice extent for December now stands at about 3.0 million square kilometers (1.16 million square miles), down from a peak difference of just over 4 million square kilometers (1.50 million square miles) in mid-November. This globally combined low ice extent is a result of largely separate processes in the two hemispheres.Changes to our graphics for 2017
NSIDC is transitioning the sea ice extent time series graphs to show interquartile and interdecile ranges, with the median extent value, in place of standard deviations and the average values. Standard deviations are most useful with data that are clustered towards the average, or “normally distributed” like a bell curve, with few outliers. Sea ice extent data, however, has become skewed due to the strong downward trend in ice extent, with a wider spread of values and more values falling at the low end of the range. Interquartile and interdecile ranges, along with the median value, are better for presenting data with these characteristics. The interquartile and interdecile ranges more clearly show how the data are distributed and can better distinguish outliers, and so provide a better view of the variability of the data.Further reading
Serreze, M. C., A. Crawford, J. C. Stroeve, A. P. Barrett, and R. A. Woodgate. 2016. Variability, trends and predictability of seasonal sea ice retreat and advance in the Chukchi Sea. Journal of Geophysical Research, 121, doi:10.1002/2016JC011977.
Average Arctic sea ice extent for November set a record low, reflecting unusually high air temperatures, winds from the south, and a warm ocean. Since October, Arctic ice extent has been more than two standard deviations lower than the long-term average. Antarctic sea ice extent quickly declined in November, also setting a record low for the month and tracking more than two standard deviations below average during the entire month. For the globe as a whole, sea ice cover was exceptionally low.Overview of conditions
In November 2016, Arctic sea ice extent averaged 9.08 million square kilometers (3.51 million square miles), the lowest November in the satellite record. This is 800,000 square kilometers (309,000 square miles) below November 2006, the previous lowest November, and 1.95 million square kilometers (753,000 square miles) below the 1981 to 2010 long-term average for November. For the month, ice extent was 3.2 standard deviations below the long-term average, a larger departure than observed in September 2012 when the Arctic summer minimum extent hit a record low.
At this time of year, air temperatures near the surface of the Arctic Ocean are generally well below freezing, but this year has seen exceptional warmth. The overall rate of ice growth this November was 88,000 square kilometers (34,000 square miles) per day, a bit faster than the long-term average of 69,600 square kilometers (26,900 square miles) per day. However, for a brief period in the middle the month, total extent actually decreased by 50,000 square kilometers, or 19,300 square miles—an almost unprecedented occurrence for November over the period of satellite observations. A less pronounced and brief retreat of 14,000 square kilometers (5,400 square miles) occurred in 2013.
Ice growth during November as a whole occurred primarily within the Beaufort, Chukchi and East Siberian Seas, as well as within Baffin Bay. Ice extent slightly retreated in the Barents Sea for the month. Compared to the previous record low for the month set in 2006, sea ice was less extensive in the Kara, Barents, East Greenland, and Chukchi Seas, and more extensive in Baffin Bay this year.Conditions in context
Continuing the warm Arctic pattern seen in October, November air temperatures were far above average over the Arctic Ocean and Canada. Air temperatures at the 925 hPa level (about 2,500 feet above sea level) were above the 1981 to 2010 average over the entire Arctic Ocean and, locally up to 10 degrees Celsius (18 degrees Fahrenheit) above average near the North Pole. This is in sharp contrast to northern Eurasia, where temperatures were as much as 4 to 8 degrees Celsius (7 to 14 degrees Fahrenheit) below average (Figure 2b). Record snow events were reported in Sweden and across Siberia early in the month.
In autumn and winter, the typical cyclone path is from Iceland, across the Norwegian Sea and into the Barents Sea. This November, an unusual jet stream pattern set up, and storms instead tended to enter the Arctic Ocean through Fram Strait (between Svalbard and Greenland). This set up a pattern of southerly wind in Fram Strait, the Eurasian Arctic and the Barents Sea and accounts for some of the unusual warmth over the Arctic Ocean. The wind pattern also helped push the ice northwards and helps to explain why sea ice in the Barents Sea retreated during November.
Sea surface temperatures in the Barents and Kara Seas remained unusually high, which also helped prevent ice formation. These high sea surface temperatures are a result of warm Atlantic water circulating onto the Arctic continental shelf seas.November 2016 compared to previous years
Through 2016, the linear rate of decline for November is 55,400 square kilometers (21,400 square miles) per year, or 5.0 percent per decade.Warm Arctic delays ice formation in Svalbard’s fjords
In the Svalbard archipelago, sea ice usually begins to form in the inner parts of the fjords in early November. This November, however, no sea ice was observed. Throughout autumn, the wind pattern transported warm and moist air to Svalbard, leading to exceptionally high air temperatures and precipitation, which fell as rain.
Atmospheric and oceanic conditions in the fjord system were assessed by students from the University Centre in Svalbard. They noted an unusually warm ocean surface layer about 4 degrees Celsius (7 degrees Fahrenheit) above the salinity-adjusted freezing point (Figure 4a). Coinciding with exceptionally high air temperatures over Svalbard during autumn, the water has hardly cooled at all, and it is possible that no sea ice will form this winter.
The above average ocean temperatures arose in part from changes in ocean currents that bring warm and salty Atlantic Water into the fjords. As the warm Gulf Stream moves east, it becomes the branching North Atlantic Drift. One small branch is named the West Spitsbergen Current (Figure 4b). This current flows along the continental shelf on the west coast of Svalbard and is one mechanism for transporting heat towards the fjords. Since 2006, changes in atmospheric circulation have resulted in more Atlantic water reaching these fjords, reducing sea ice production in some and stopping ice formation entirely in others.Antarctic sea ice continues to track well below average
This year, Antarctic sea ice reached its annual maximum extent on August 31, much earlier than average, and has since been declining at a fairly rapid pace, tracking more than two standard deviations below the 1981 to 2010 average. This led to a new record low for the month of November over the period of satellite observations (Figure 5a). Average extent in November was 14.54 million square kilometers (5.61 million square miles). This was 1.0 million square kilometers (386,000 square miles) below the previous record low of 15.54 million square kilometers (6.00 million square miles) set in 1986 and 1.81 million square kilometers (699,000 square miles) below the 1981 to 2010 average.
For the month, Antarctic ice extent was 5.7 standard deviations below the long-term average. This departure from average was more than twice as large as the previous record departure from average, set in November 1986.
Ice extent is lower than average on both sides of the continent, particularly within the Indian Ocean and the western Ross Sea, but also to a lesser extent in the Weddell Sea and west of the Antarctic Peninsula in the eastern Bellingshausen Sea. Moreover, several very large polynyas (areas of open water within the pack) have opened in the eastern Weddell and along the Amundsen Sea and Ross Sea coast.
Air temperatures at the 925 mbar level were 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) above average near the sea ice edge during late October and early November, corresponding to the period of rapid sea ice decline (Figure 5b).
The entire austral autumn and winter (since March 2016) was characterized by generally strong west to east winds blowing around the continent. This was associated with a positive phase of the Southern Annular Mode, or SAM. This pattern tends to push the ice eastward, but the Coriolis force acting in the ice adds a component of northward drift. During austral spring (September, October and November), the SAM index switched from strongly positive (+4 in mid-September, a record) to negative (-2.8 in mid-November). When the westerly wind pattern broke down in November, winds in several areas of Antarctica started to blow from the north. Over a broad area near Wilkes Land, the ice edge was pushed toward the continent. Areas with southward winds were also located between Dronning Maud Land and Enderby Land, and near the Antarctic Peninsula. This created three regions where ice extent quickly became much less extensive than usual (Figure 5c), reflected in the rapid decline in extent for the Antarctic as a whole. Interspersed with the areas of compressed sea ice and winds from the north, areas of south winds produced large open water areas near the coast, creating the polynyas.Arctic sea ice loss linked to rising anthropogenic CO2 emissions
A new study published in the journal Science links Arctic sea ice loss to cumulative CO2 emissions in the atmosphere through a simple linear relationship (Figure 6). Researchers conducting the study, including NSIDC scientist Julienne Stroeve, examined this linear relationship based on observations from the satellite and pre-satellite era since 1953, and in climate models. The observed relationship is equivalent to a loss of 3 square meters (32 square feet) for every metric ton of CO2 added to the atmosphere, compared the average from all the climate models of 1.75 square meters (19 square feet). This smaller value, or lower sensitivity, from the models is consistent with findings that the models tend to be generally conservative relative to observations in regard to how fast the Arctic has been losing its summer ice cover. The observed rate of ice loss per metric ton of CO2 allows individuals to more easily grasp their contribution to Arctic sea ice loss.Global sea ice far below average
As a result of both Arctic and Antarctic sea ice currently tracking at record low levels, global ice extent near November’s end stood at 7.3 standard deviations below average (Figure 7). However, the processes governing the evolution of sea ice in both hemispheres is a result of different atmospheric and oceanic processes and geographies and it unlikely that record low conditions in the two hemispheres are connected. Also, it is not especially instructive to assess a global sea ice extent because the seasons are opposite in the two hemispheres. In November the Arctic is in its ice growth season while Antarctic is losing ice. Antarctic sea ice as a whole has slightly increased over the past four decades (but with the last two austral winters having average and below average extent, respectively). The slight overall increase in Antarctic ice over the satellite record can be broadly linked to wind patterns that have helped to expand the ice cover towards the north (towards the equator).NASA Operation IceBridge completes its 2016 Antarctic campaign
In October, four NSIDC personnel accompanied the NASA Operation IceBridge campaign on its airborne surveys over Antarctica. The campaign completed a total of 24 flights over the continent in October and November, covering sea ice, land ice, ice shelves, and glaciers as Antarctica headed into its austral summer. Missions surveyed sea ice in the Weddell and Bellinghausen Seas with instruments that measure both sea ice extent and thickness. These measurements add to a time series of data that measures changes in sea ice and helps researchers assess the future trajectory of the ice pack and its impact on the climate. Visual observations from the flights confirmed that areas in the Bellingshausen Sea that are typically covered in sea ice were open water this year.
One of this year’s missions flew over a massive rift in the Antarctic Peninsula’s Larsen C Ice Shelf. Ice shelves are the floating parts of ice streams and glaciers, and they buttress the grounded ice behind them; when ice shelves collapse, the ice behind accelerates toward the ocean, where it then adds to sea level rise. Larsen C neighbors a smaller ice shelf that disintegrated in 2002 after developing a rift similar to the one now growing in Larsen C.
The IceBridge scientists measured the Larsen C fracture to be about 70 miles long, more than 300 feet wide and about a third of a mile deep. The crack completely cuts through the ice shelf but it does not go all the way across it. Once it does, it will produce an iceberg roughly the size of the state of Delaware.
The mission of Operation IceBridge is to collect data on changing polar land and sea ice and maintain continuity of measurements between NASA’s Ice, Cloud and Land Elevation Satellite (ICESat) missions. The original ICESat mission ended in 2009, and its successor, ICESat-2, is scheduled for launch in 2018. Operation IceBridge, which began in 2009, is currently funded until 2019. The planned overlap with ICESat-2 will help scientists validate the satellite’s measurements.Further reading
Nilsen, F., Skogseth, R., Vaardal-Lunde, J., and Inall, M. 2016. A simple shelf circulation model: Intrusion of Atlantic Water on the West Spitsbergen Shelf. J. Physical Oceanography, 46, 1209-1230. doi:10.1175/JPO-D-15-0058.1
Notz, D. and J. Stroeve. 2016. Observed Arctic sea-ice loss directly follows anthropogenic CO2 emission. Science, 11 Nov 2016: Vol. 354, Issue 6313, pp. 747-750. doi:10.1126/science.aag2345.
Parkinson, C. 2014. Global sea ice coverage from satellite data: Annual cycle and 35-year trends. Journal of Climate, December 2014. doi:10.1175/JCLI-D-14-00605.1.References
Fetterer, F., K. Knowles, W. Meier, and M. Savoie. 2016, updated daily. Sea Ice Index, Version 2. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi:10.7265/N5736NV7.