Climate Science News
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 (9.9 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 (5.8 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.
After a quick initial freeze-up during the second half of September, ice growth slowed substantially during early October. On October 20, 2016, Arctic sea ice extent began to set new daily record lows for this time of year. After mid-October, ice growth returned to near-average rates, but extent remained at record low levels through late October. High sea surface temperatures in open water areas were important in limiting ice growth. October air temperatures were also unusually high, and this warmth extended from the surface through a considerable depth of the atmosphere.Overview of conditions
In October 2016, Arctic sea ice extent averaged 6.40 million square kilometers (2.5 million square miles), the lowest October in the satellite record. This is 400,000 square kilometers (154,400 square miles) lower than October 2007, the second lowest October extent, and 690,000 square kilometers (266,400 square miles) lower than October 2012, the third lowest. The average extent was 2.55 million square kilometers (980,000 square miles) below the October 1981 to 2010 long-term average.
As of early November, extent remains especially low within the Beaufort, Chukchi, East Siberian, and Kara Seas. Since the beginning of October, ice growth occurred primarily in the Laptev Sea, stretching from the New Siberian Islands towards the coast. Little ice growth occurred in the Kara and Barents Seas, while ice extent increased in the Chukchi and Beaufort Seas.Conditions in context
After an early rapid freeze-up in late September, the rate of ice growth slowed in the first half of October. From October 1 to 15, ice extent increased only 378,000 square kilometers (146,000 square miles), less than a third of the 1981 to 2010 average gain for that period. By October 31, Arctic sea ice extent stood at 7.07 million square kilometers (2.73 million square miles), the lowest extent in the satellite record for that date.
A primary culprit behind the slow growth is that sea surface temperatures in the Beaufort and Chukchi Seas, the Barents and Kara Seas along the Eurasian coast, as well as the East Siberian Sea, were above average. The open water areas in the highest latitudes at the date of the minimum in September had only recently formed and there was little input of solar radiation so far north. So those waters were just above the freezing point. When the atmosphere cooled in September, ice formed rapidly. However, further south, the sea ice had retreated far earlier in the season and a lot of solar energy was absorbed through the summer. This ocean heat inhibited the growth of ice in these regions. Finally toward the end of October, the surface ocean heat began to dissipate, triggering ice formation. However, even by October 25, sea surface temperatures were above average in these areas (Figure 2b).
The atmospheric circulation also played a role. October air temperatures at the 925 hPa level (about 2,500 feet above sea level) were unusually high over most of the Arctic Ocean (Figure 2c), especially over the Beaufort and Chukchi Seas and over the East Greenland Sea (up to 8 degrees Celsius or 14 degrees Fahrenheit above the 1981 to 2010 average). In part, these high temperatures resulted from high sea surface temperatures over the open water areas. However, unusually high sea level pressure centered over northern Scandinavia brought southerly winds from the East Siberian and Barents Seas, contributing to high air temperatures in these regions. In turn, unusually low pressure on the Pacific side centered roughly over the western Bering Sea brought southerly winds over the Beaufort and Chukchi Seas, contributing to unusually high air temperature there. The combined effects of the high sea surface temperatures and atmospheric circulation led to a pattern in which for the Arctic, unusual warmth in October extended from the surface through a deep layer of the atmosphere (Figure 2d).
Through 2016, the linear rate of decline for October is 66,400 square kilometers or (25,600 square miles) per year, or 7.4 percent per decade.Antarctic sea ice dropping
After a reaching its maximum extent unusually early and then following a period of relatively unchanging overall extent, Antarctic sea ice extent started to decline in earnest. Daily sea ice extent levels have been at second lowest in the satellite record since October 20 and below the two standard deviation range. Only the 1986 austral spring extent is lower. Ice extent is particularly low on both sides of the Antarctic Peninsula. The rapid early reduction in sea ice cover in this region may create favorable conditions for the break up of the eastern Peninsula ice shelves at the end of austral summer. Similar sea ice trends and weather conditions were present during the spring seasons preceding past ice shelf retreats (e.g., 2001 to 2002). Extensive open water, created by the downsloping fosters warmer air and surface melting, and allows longer-period ocean waves to reach the ice front of the ice shelves. Other areas of reduced sea ice cover are the Southern Ocean north of Dronning Maud Land, and the area west of the Ross Sea and north of Wilkes Land.
Since reaching its seasonal minimum on September 10 of 4.14 million square kilometers (1.60 million square miles), Arctic sea ice extent has increased at a rapid rate. Antarctic ice extent saw a sharp decline during the first half of September.Overview of conditions
Arctic sea ice extent during September 2016 averaged 4.72 million square kilometers (1.82 million square miles), the fifth lowest in the satellite record. Average September extent was 1.09 million square kilometers (421,000 square miles) above the record low set in 2012, and 1.82 million square kilometers (703,000 square miles) below the 1981 to 2010 long-term average. Extent remains especially low in the Beaufort, Chukchi and East Siberian Seas. The Northern Sea Route along the Russian coast appears to still be open, but the southern Northwest Passage route (Amundsen’s route) appears to be closed.Conditions in context
As of October 1, Arctic sea ice extent stood at 5.19 million square kilometers (2.00 million square miles), which is an increase of 1.05 million square kilometers (405,000 square kilometers) from the seasonal minimum of 4.14 million square kilometers (1.60 million square miles) recorded on September 10. Compared to some other years, the growth rate since the seasonal minimum has been quite rapid. The ice growth has been predominantly in the central Arctic Ocean and the East Siberian Sea sector. There has been little ice growth in the Laptev and Kara Seas, and ice has actually retreated in the Barents Sea.
September saw a shift in weather patterns. The summer of 2016 was characterized by unusually low pressure over the central Arctic Ocean, west of the dateline. While low pressure was still a dominant feature of September, the center of low pressure shifted towards North America, and a center of high pressure strengthened over north central Eurasia (Figure 2b). Conditions under the high pressure region were quite warm; temperatures at the 925 hPa level were up to 6 degrees Celsius (11 degrees Fahrenheit) above the 1981 to 2010 average (Figure 2c).September 2016 compared to previous years
Through 2016, the linear rate of decline for September is 87,200 square kilometers (33,700 square miles) per year, or 13.3 percent per decade. While the absolute seasonal minimum for 2016 was tied with 2007 as second lowest, the average extent for the month of September 2016 of 4.72 million square kilometers (1.82 million square miles) ends up being fifth lowest in the satellite record, behind both 2012 and 2007. This reflects the rapid growth of ice following the seasonal minimum recorded on September 10.Antarctic sea ice reaches winter maximum on a record early date
Antarctic sea ice extent reached 18.44 million square kilometers (7.12 million square miles) on August 31, 2016, and this appears to be the maximum extent for this year. This is the earliest maximum in the satellite record since 1979, and the first time the maximum has occurred in August. The maximum was 240,000 square kilometers (93,000 square miles) greater than the average extent for this date of 18.20 million square kilometers (7.03 million square miles). It is the tenth lowest maximum extent on record. On average, the maximum occurs much later (September 23 to 24).
The early maximum appears to be the result of an intense wind pattern in September, spanning nearly half of the continent from the Wilkes Land area to the Weddell Sea, and centered on the Amundsen Sea. Stronger than average low pressure in this area, coupled with high pressure near the Falkland Islands, and near the southern tip of New Zealand in the Pacific Ocean, created two regions of persistent northwesterly winds. Sea ice extent decreased in the areas where the northwesterly winds reached the ice front.
A comparison of sea ice extent from the date of the maximum (August 31) and the last day of September (one month later) shows that sea ice extent decreased through the month along a broad region west and east of the Antarctic Peninsula. It also decreased on the other side of the continent north of Wilkes Land. By comparison, this was partly offset by increases in the northern Amundsen Sea and north of Dronning Maud Land.The 2016 Arctic melt season in review
The winter of 2015/2016 was extremely warm over the Arctic Ocean. The maximum sea ice extent in March set a new low in the satellite record, barely beating out March 2015. Extent for the month of March as a whole ended up second lowest on record. In April, problems with the F-17 sensor forced a temporary cessation of sea ice updates until data from the newer F-18 satellite could be brought online. Data from other sources documented that during this time, ice was still tracking very low. The months of May and June set more record lows in ice extent.
Although the onset of surface melt was early over much of the Arctic Ocean, as the melt season progressed, a pattern of stormy weather set up. This ended up being a very persistent pattern; as averaged from June through August, sea level pressure was much lower than average over the central Arctic Ocean (Figure 5a), and air temperatures over most of the ocean were average or below average (Figure 5b). Such conditions have been previously shown to limit summer ice loss, and by the early August it became clear that a new record low for September extent was not in the offing. Two very strong storms crossed the central Arctic Ocean in August. In 2012, a strong storm contributed to accelerated ice loss, but this year, the overall influence of the storms remains unclear.
Despite the generally unfavorable weather conditions, the seasonal minimum of 4.14 million square kilometers (1.60 million square miles), reached on September 10, ended up in a statistical tie with 2007 as the second lowest in the satellite record. While previous analyses have shown that there is little correlation between the seasonal maximum extent and the season minimum extent, in large part because of the strong impacts of summer weather patterns, it is likely that the 2016 melt season started with a lot of fairly thin ice. This may help to explain why, despite summer weather unfavorable to sea ice loss, extent at the seasonal minimum ended up tied for second lowest.Sea ice age
Age is another indicator of the state of sea ice because older ice is generally thicker ice (Tschudi et al., 2016). As mentioned in previous posts, there has been an overall decline in ice age, particularly the oldest ice types—ice that has been in the Arctic for more than four years. Near-real-time updates (which are preliminary) indicate that at this year’s minimum, only 106,000 square kilometers (41,000 square miles) of 4+ year old ice remained, or 3.1 percent of the total ice extent. This is in stark contrast to the mid-1980s when over 2 million square kilometers (33 percent, or 772,000 square miles) of the summer minimum extent was composed of old ice that had survived at least four summer melt seasons.
Tschudi, M.A., J.C. Stroeve, and J.S. Stewart. 2016. Relating the age of Arctic sea ice to its thickness, as measured during NASA’s ICESat and IceBridge campaigns. Remote Sensing, 8, 457, doi:10.3390/rs8060457.
Arctic sea ice appears to have reached its seasonal minimum extent for 2016 on September 10. A relatively rapid loss of sea ice in the first ten days of September has pushed the ice extent to a statistical tie with 2007 for the second lowest in the satellite record. September’s low extent followed a summer characterized by conditions generally unfavorable for sea ice loss.
Please note that this is a preliminary announcement. Changing winds or late-season melt could still reduce the Arctic ice extent, as happened in 2005 and 2010. NSIDC scientists will release a full analysis of the Arctic melt season, and discuss the Antarctic winter sea ice growth, in early October.Overview of conditions
On September 10, Arctic sea ice extent stood at 4.14 million square kilometers (1.60 million square miles). This appears to have been the lowest extent of the year and is tied with 2007 as the second lowest extent on record. This year’s minimum extent is 750,000 square kilometers (290,000 square miles) above the record low set in 2012 and is well below the two standard deviation range for the 37-year satellite record. Satellite data show extensive areas of open water in the Beaufort and Chukchi seas, and in the Laptev and East Siberian seas.
During the first ten days of September, the Arctic lost ice at a faster than average rate. Ice extent lost 34,100 square kilometers (13,200 square miles) per day compared to the 1981 to 2010 long-term average of 21,000 square kilometers (8,100 square miles) per day. The early September rate of decline also greatly exceeded the rate observed for the same period in 2012 (19,000 square kilometers, or 7,340 square miles, per day). Recent ice loss has been most pronounced in the Chukchi Sea. This may relate to the impact of two strong cyclones that passed through the region during August.
Satellite passive microwave data and images from the Moderate Resolution Imaging Spectroradiometer (MODIS) suggest that the southern Northwest Passage routes are still open. While the passive microwave data show that the Northern Sea route is open, MODIS data reveal a narrow band of scattered sea ice blocking the passage near the Taymyr Peninsula.Conditions in context
Weather in early September was warm along the Siberian coast (up to 9 degrees Celsius or 16 degrees Fahrenheit above average), with high pressure over the same region and strong winds across the central Arctic. However, as discussed in previous posts, weather over the Arctic Ocean this past summer has been generally stormy, cool, and cloudy—conditions that previous studies have shown to generally limit the rate of summer ice loss. That September ice extent nevertheless fell to second lowest in the satellite record is hence surprising. Averaged for July through August, air temperatures at the 925 hPa level (about 2,500 feet above sea level) were 0.5 to 2 degrees Celsius (1 to 4 degrees Fahrenheit) below the 1981 to 2010 long-term average over much of the central Arctic Ocean, and near average to slightly higher than average near the North American and easternmost Siberian coasts. Reflecting the stormy conditions, sea level pressures were much lower than average in the central Arctic during these months.
Why did extent fall to a tie for second lowest with 2007? The 2016 Arctic melt season started with a record low maximum extent in March, and sea ice was measured at record low monthly extents well into June. Computer models of ice thickness, and maps of sea ice age both indicated a much thinner ice pack at the end of winter. Statistically, there is little relationship between May and September sea ice extents after removing the long-term trend, indicating the strong role of summer weather patterns in controlling sea ice loss. However, the initial ice thickness may play a significant role. As noted in our mid-August post, the upper ocean was quite warm this summer and ocean-driven melting is important during late summer. The science community will be examining these issues in more detail in coming months.Ice loss primarily in the northern Chukchi Sea
The late season ice loss appears to have been greatest in an extended area of patchy ice reaching from the eastern Beaufort Sea to the northern Chukchi Sea. This is in the area influenced by the two strong cyclones discussed in our August posts—the strong winds appear to have compacted the ice cover and may have led to an upward mixing of warm ocean water.
The Defense Meteorological Satellite Program (DMSP) F-17 satellite, which NSIDC ceased to use in May as its primary source for sea ice extent due to erratic data, has since re-stabilized and is providing more consistent day-to-day readings. While NSIDC will continue to use the DMSP F-18 satellite for data processing, it is instructive to examine the F-17 record. Early September extent from the F-17 record is slightly higher than from F-18. Both sensors indicate that the minimum extent for 2016 is slightly lower than the 2007 minimum, which was 4.15 million square kilometers (1.60 million square miles) and reached on September 18. However, the measurement accuracy is about ±25,000 square kilometers (±9,600 square miles) for a five-day trailing average daily extent measurement. This means that at the present levels, 2016 is a statistical tie for second lowest sea ice extent.Previous minimum Arctic sea ice extents Table 1. Previous minimum Arctic sea ice extents YEAR MINIMUM ICE EXTENT DATE IN MILLIONS OF SQUARE KILOMETERS IN MILLIONS OF SQUARE MILES 2007 4.15 1.60 Sept. 18 2008 4.59 1.77 Sept. 20 2009 5.12 1.98 Sept. 13 2010 4.62 1.78 Sept. 21 2011 4.34 1.67 Sept. 11 2012 3.39 1.31 Sept. 17 2013 5.06 1.95 Sept. 13 2014 5.03 1.94 Sept. 17 2015 4.43 1.71 Sept. 9 2016 4.14 1.60 Sept. 10 1979 to 2000 average 6.70 2.59 Sept. 13 1981 to 2010 average 6.22 2.40 Sept. 15 Ten lowest minimum Arctic sea ice extents (satellite record, 1979 to present) Table 2. Ten lowest minimum Arctic sea ice extents (satellite record, 1979 to present) RANK YEAR MINIMUM ICE EXTENT DATE IN MILLIONS OF SQUARE KILOMETERS IN MILLIONS OF SQUARE MILES 1 2012 3.39 1.31 Sept. 17 2
1.60 Sept. 10
Sept. 18 3 2011 4.34 1.67 Sept. 11 4 2015 4.43 1.71 Sept. 9 5 2008 4.59 1.77 Sept. 20 6 2010 4.62 1.78 Sept. 21 7 2014 5.03 1.94 Sept. 17 8 2013 5.06 1.95 Sept. 13 9 2009 5.12 1.98 Sept. 13 10 2005 5.32 2.05 Sept. 22
Note that the dates and extents of the minima have been re-calculated from what we posted in previous years. In June 2016, NSIDC transitioned to using data from the DMSP F-18 satellite, due to issues with the F-17 satellite. Data beginning April 1, 2016 are from F-18. In July 2016, Sea Ice Index data were updated to Version 2. These changes do not significantly affect sea ice trends and year-to-year comparisons, but in some instances users may notice small changes in values from the previous version of the data. Details on the changes are discussed in the Sea Ice Index documentation.
October 19, 2016: We revised the title for Table 2 from “Ten lowest minimum Arctic sea ice extents (1981 to 2010 average)” to “Ten lowest minimum Arctic sea ice extents (satellite record, 1979 to present)”
Throughout August, Arctic sea ice extent continued to track two or more standard deviations below the long-term average. The month saw two very strong storms enter the central Arctic Ocean from along the Siberian coast. In the Antarctic, ice extent remained near average.Overview of conditions
Average sea ice extent for August 2016 was 5.60 million square kilometers (2.16 million square miles), the fourth lowest August extent in the satellite record. This is 1.03 million square kilometers below the 1981 to 2010 average for the month and 890,000 square kilometers (344,000 square miles) above the record low for August set in 2012. As of September 5, sea ice extent remains below average everywhere except for a small area within the Laptev Sea. Ice extent is especially low in the Beaufort Sea and in the East Siberian Sea. With about two weeks of seasonal melt yet to go, it is unlikely that a new record low will be reached. However, since August 26, total sea ice extent is already lower than at the same time in 2007 and is currently tracking as the second lowest daily extent on record. In addition, during the first five days of September the ice cover has retreated an additional 288,000 square kilometers (111,000 square miles) as the tongue of sea ice in the Chukchi Sea has started to disintegrate.Conditions in context
The average ice loss rate through August was 75,000 square kilometers per day (29,000 square miles), compared to the long-term 1981 to 2010 average of 57,300 square kilometers per day (22,100 square miles per day), and a rate of 89,500 square kilometers per day for 2012 (34,500 square miles per day). Total ice extent loss in August was 2.34 million square kilometers (904,000 square miles).
Air temperatures at the 925 hPa level were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below average for a large area stretching from the northern Kara Sea, through the Laptev Sea, and into north-central Eurasia. Temperatures elsewhere over the Arctic Ocean were near average. Reflecting the generally stormy pattern through the month, sea level pressures were well below average (as much as 10 hPa) over the central and eastern Arctic Ocean. Two very strong cyclones entered the central Arctic Ocean in August from along the Siberian coast, bringing strong winds. On August 16, the central pressure of the first cyclone dropped to 968 hPa, nearly rivaling the storm in early August 2012 that attained a minimum central pressure of 966 hPa. On 22 August, the second storm started moving to the central Arctic Ocean along a similar track, and on August 23, attained a central pressure of 970 hPa.
Past studies have shown that stormy summers tend to end up with more sea ice at the end of the melt season than summers with high pressure over the central Arctic Ocean, primarily because stormy summers are both fairly cool and the wind pattern tends to spread the ice out. However, the impact of strong individual storms may be different—the 2012 event appears to have temporarily boosted ice loss by breaking up the ice cover, with the wave action tending to mix warmer waters from below to hasten melt. It may also be that, as the ice cover thins, its response to storms is changing.
It indeed appears that the August 2016 storms helped to break up the ice and spread it out, contributing to the development of several large embayments and polynyas. Some of this ice divergence likely led to fragmented ice being transported into warmer ocean waters, hastening melt. Whether warmer waters from below were mixed upwards to hasten melt remains to be determined, but as discussed below, these storms were associated with very high wave heights.August 2016 compared to previous years
Arctic sea ice extent averaged for August 2016 was the fourth lowest in the satellite data record. Through 2016, the linear rate of decline for August is 10.4 percent per decade.Cyclones, ocean wave heights, and ice retreat
Large waves are common at high latitudes; 10-meter wave heights (33 feet) are not unusual for the Nordic Seas, and 15-meter wave heights (49 feet) can occur in the high latitudes of the Southern Ocean. However, large waves are a relatively new feature of the western Arctic Ocean. The height of waves is in part determined by surface wind speed, as well as the fetch (distance over open water that the wind can travel) and the duration of a wind event. A moderate sea ice cover damps ocean waves by absorbing and dispersing the wave energy through jostling of the ice floes against one another. A dense ice pack cover acts as a shield between the ocean and the surface wind, preventing wave formation.
In the latter half of the twentieth century, 4 to 6 meter waves (13 to 20 feet) rarely occurred in the western Arctic Ocean, but with more open water they have become more frequent, especially when strong storms enter the Arctic Ocean in late summer or early autumn. During the first of the two August cyclones discussed above, waves up to 5.9 meters (19 feet) were predicted. This occurred during the early part of the cyclone’s lifecycle (1800 UTC August 14), in the eastern Kara Sea. Further east, north of the New Siberian Islands, wave heights were estimated as high as 4.3 meters (14 feet) late on August 15. In this region, the waves were directly incident on the ice edge. In response, the ice edge retreated following the 4.3 meter waves on August 15.Northwest Passage update
The Northwest Passage refers to the fabled shortcut between the Atlantic and Pacific through the Canadian Archipelago. However, it is not one route. There is a northern, deep-water route through the Parry Channel, entered from the west through the M’Clure Strait and a shallower southern route, known as Amundsen’s route. Sea ice in the Parry Channel route has shown a sharp decline since the middle of July, but the channel is still not entirely ice free. Considerable ice remains in the western (M’Clure Strait) region and there are lesser amounts in the eastern regions. This is mostly (~80 percent) multiyear ice. Low ice years in the Parry Channel are typically the result of early summer breakup associated with high sea level pressure over the Beaufort Sea and Canada Basin that displace the Arctic Ocean pack ice away from the western entrance. Conversely, low sea level pressure anomalies over the Beaufort Sea and Canada Basin keep the Arctic Ocean pack ice up against the western entrance. This has been the case for much of the 2016 melt season. The southern (Amundsen’s) route is open but it is still uncertain whether the northern route will open in the coming weeks.
Even during mild ice years, thick multiyear ice is typically advected into these routes during the summer months. Multiyear ice is a significant obstacle for ships. Nevertheless, taking advantage of mild sea ice conditions, the 68,000-ton Crystal Serenity set sail from Anchorage, Alaska on August 16 for its 32-day journey through the Northwest Passage via Amundsen’s route. This is the largest ship thus far to navigate the Northwest Passage and is accompanied by an icebreaker ship and two helicopters. The ship sailed through the Northwest Passage in less than three weeks—52 times faster than Amundsen’s nearly three-year voyage.
On the other side of the Arctic, the Northern Sea Route appears mostly ice free.Further reading
Collins, C. O., W. E. Rogers, A. Marchenko and A. V. Babanin. 2015. In situ measurements of an energetic wave event in the Arctic marginal ice zone. Geophysical Research Letters, 42, doi:10.1002/2015GL063063.
Haas, C., and S. E. L. Howell. 2015. Ice thickness in the Northwest Passage. Geophysical Research Letters, 42, 7673–7680, doi:10.1002/2015GL065704.
Hogan, T., et al. 2014. The Navy Global Environmental Model, Oceanography, 27(3), 116-125.
Howell, S. E. L., T. Wohlleben, M. Dabboor, C. Derksen, A. Komarov and L. Pizzolato. 2013. Recent changes in the exchange of sea ice between the Arctic Ocean and the Canadian Arctic Archipelago. Journal of Geophysical Research, 118, 3595–3607, doi:10.1002/jgrc.20265.
Thomson, J., and W. E. Rogers. 2014. Swell and sea in the emerging Arctic Ocean, Geophysical Research Letters 41, doi:10.1002/2014GL059983.
Thomson, J. et al. 2016. Emerging trends in the sea state of the Beaufort and Chukchi seas, Ocean Modelling 105, doi:10.1016/j.ocemod.2016.02.009.
Monthly mean of Sea Level Anomalies (annual and seasonal cycles removed)measured by altimetry over the Pacific for August 1997 (left) and August 2015 (right). Credits CNES/CLS.Further information:
- Indicators: ENSO
- Applications: Climate, ENSO
- Image of the month, July 2015 "El Niño's return, west side story".
- ENSO current conditions on CPC/NCEP website
- Météo France (2015/08/28): Vers un épisode El Niño de forte intensité (in french)