The dark winter ends

The seasonal maximum extent of Arctic sea ice has passed, and with the passing of the vernal equinox, the sun has risen at the north pole. While there are plenty of cold days ahead, the long polar night is over. Arctic sea ice extent averaged for March 2021 was the ninth lowest in the satellite record. With little ice in the Gulf of St. Lawrence, harp seal pups are struggling. At month’s end, Antarctic sea ice extent was slightly above average.

Overview of conditions

Arctic sea ice extent March 2021

Figure 1. Arctic sea ice extent for March 2021 was 14.64 million square kilometers (5.65 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent averaged for March 2021 was 14.64 million square kilometers (5.65 million square miles). This was 350,000 square kilometers (135,000 square miles) above the record minimum set in 2017 and 790,000 square kilometers (305,000 square miles) below the 1981 to 2010 average. The average extent ranks ninth lowest in the satellite record, which began in 1979. Regionally, extent at the end of the month was below average on the Pacific side in the Bering sea and on the Atlantic side in the northern Barents Sea and well south of the Arctic in the Gulf of St. Lawrence. Elsewhere, extent was close to the average, though generally somewhat lower. Ice loss during March was primarily in the Sea of Okhotsk, the southern edge of the Bering Sea, east of Svalbard, and in the northern part of the East Greenland Sea. The ice edge expanded in the southern part of the East Greenland Sea and to the north of Svalbard.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of XXXXX XX, 20XX, along with daily ice extent data for four previous years and the record low year. 2020 to 2021 is shown in blue, 2019 to 2020 in green, 2018 to 2019 in orange, 2017 to 2018 in brown, 2016 to 2017 in magenta, and 2012 to 2013 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.||Credit: National Snow and Ice Data Center|High-resolution image

Figure 2a. The graph above shows Arctic sea ice extent as of April 5, 2021, along with daily ice extent data for four previous years and the 2012 record low. 2020 to 2021 is shown in blue, 2019 to 2020 in green, 2018 to 2019 in orange, 2017 to 2018 in brown, 2016 to 2017 in magenta, and 2011 to 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

average air temperature over Arctic

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for March 2021. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Average sea level pressure March 2021, Arctic

Figure 2c. This plot shows average sea level pressure in the Arctic in millibars March 2021. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

During March, sea ice extent tracked well below average, but as noted in our previous post, the seasonal maximum in extent, reached on March 21, one day after the vernal equinox, was only the seventh lowest in the passive microwave satellite record. Since ice extent in March increases through the first part of the month and then decreases thereafter, the daily average growth rate is not a very meaningful statistic.

Air temperatures at the 925 mb level (about 2,500 feet above sea level) in March were up to 5 degrees Celsius (9 degrees Fahrenheit) below average across northern Eurasia and extending east over Alaska. Temperatures were 1 to 3 degrees Celsius (2 to 5 degrees) Celsius above average over the Atlantic side of the Arctic, with a tongue of above-average temperatures extending into the Beaufort Sea (Figure 2b). The associated atmospheric circulation for March features low pressure over the northern North Atlantic, with the lowest pressure focused over the Barents Sea (Figure 2c). After remaining in a fairly persistent negative phase for much of the past winter, the Arctic Oscillation index in March was mostly positive, but with large fluctuations.

March 2021 compared to previous years

Trend line of sea ice decline for March

Figure 3. Monthly March ice extent for 1979 to 2021 shows a decline of 2.6 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

Through 2021, the linear rate of decline for March sea ice extent, relative to the 1981 to 2010 average extent, is 2.6 percent per decade, which corresponds to 39,700 square kilometers (15,300 square miles) per year, about the size of the US states of Maryland and Delaware combined or the country of Switzerland. The cumulative March ice loss over the 43-year satellite record is 1.67 million square kilometers (645,000 square miles), based on the difference in linear trend values in 2021 and 1979, which is equivalent in size to the state of Alaska.

Troubles in the Gulf of St. Lawrence

Figure 4. A harp seal pup rests on sea ice. Harp seal pups are born with long white fur that helps them absorb sunlight and stay warm while they’re still developing blubber. Pups shed their white fur after about three to four weeks old. Credit: Flickr/laika_ac | High-resolution image

Figure 4. A harp seal pup rests on sea ice. Harp seal pups are born with long white fur that helps them absorb sunlight and stay warm while they develop blubber. Pups shed their white fur after about three to four weeks old.

Credit: Flickr/laika_ac
High-resolution image

This winter ice extent was far below average in the Gulf of St. Lawrence, which is an outlet for the US Great Lakes located northeast of New Brunswick. The unusually low sea ice extent is leading to the death of many harp seal pups. In December, harp seals arrive at the Gulf of St. Lawrence from the Canadian Arctic and Greenland, and then give birth to pups under snow on the ice cover.  With so little sea ice, many pups were forced to cluster on shore where they are vulnerable to predators, leading to high pup mortality. It is widely viewed that with continued warming and loss of sea ice, harp seal populations will decline.

Antarctic sea ice on the rise

Antarctic sea ice extent for March 2021

Figure 5. Antarctic sea ice extent for March 2021 was 4.45 million square kilometers (1.72 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

After reaching its seasonal minimum extent on February 21, Antarctic sea ice extent climbed rapidly, passing the long-term average daily extent on March 1. The rate of growth was very rapid between February 25 and March 8, expanding by over one million square kilometers (386,000 square miles) in the 12-day period. This is the fastest expansion in the four-decade record of sea ice extent for this time of year, and was caused by a rapid refreezing of the western Amundsen Sea and eastern Ross Sea areas. Since early March, growth has slowed to a more typical, slightly below-average pace. The Amundsen and eastern Ross Seas remain well above the average extent for the season. Sea ice extent in the Bellingshausen Sea and Weddell Sea are slightly below average. At the end of the month, Antarctic ice extent neared 5.5 million square kilometers (2.1 million square miles).

Arctic sea ice reaches an uneventful maximum

Arctic sea ice appears to have reached its maximum extent on March 21, 2021, tying for seventh lowest in the 43-year satellite record. NSIDC will post a detailed analysis of the 2020 to 2021 winter sea ice conditions in our regular monthly post in early April.

Overview of conditions

Sea ice extent maximum for 2021

Figure 1. Arctic sea ice extent for March 21, 2021, was 14.77 million square kilometers (5.70 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

On March 21, 2021, Arctic sea ice likely reached its maximum extent for the year, at 14.77 million square kilometers (5.70 million square miles), tying for the seventh lowest extent in the satellite record with 2007. This year’s maximum extent is 870,000 square kilometers (336,000 square miles) below the 1981 to 2010 average maximum of 15.64 million square kilometers (6.04 million square miles) and 360,000 square kilometers (139,000 square miles) above the lowest maximum of 14.41 million square kilometers (5.56 million square miles) set on March 7, 2017. Prior to 2019, the four lowest maximum extents occurred from 2015 to 2018.

The date of the maximum this year, March 21, was nine days later than the 1981 to 2010 median date of March 12.

Table 1. Ten lowest maximum Arctic sea ice extents (satellite record, 1979 to present)

Rank Year In millions of square kilometers In millions of square miles Date
1 2017 14.41 5.56 March 7
2 2018 14.47 5.59 March 17
3 2016
2015
14.51
14.52
5.60
5.61
March 23
February 25
5 2011
2006
14.67
14.68
5.66
5.67
March 9
March 12
7 2007
2021
14.77
14.77
5.70
5.70
March 12
March 21
9 2019 14.82 5.72 March 13
10 2005 14.95 5.77 March 12

For the Arctic maximum, which typically occurs in March, the uncertainty range is ~34,000 square kilometers (13,000 square miles), meaning that extents within this range must be considered effectively equal.

Final analysis pending

Please note this is a preliminary announcement of the sea ice maximum. At the beginning of April, NSIDC scientists will release a full analysis of winter conditions in the Arctic, along with monthly data for March.

A lopsided January

Arctic sea ice extent for January 2021 tracked below average, with the monthly average finishing sixth lowest in the satellite record. While air temperatures were well above average on the Atlantic side of the Arctic, air temperatures were strongly below average over Siberia. A warm spell hit the Canadian Arctic, and rain fell on snow over Nunavut, Canada. According to NASA and the National Oceanic and Atmospheric Administration (NOAA), 2020 tied for the highest global annual temperature with 2016.

Overview of conditions

Arctic sea ice extent Jan 2021

Figure 1. Arctic sea ice extent for January 2021 was 13.48 million square kilometers (5.20 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent averaged for January 2021 was 13.48 million square kilometers (5.20 million square miles). This was 400,000 square kilometers (154,000 square miles) above the record low set in 2018 and 940,000 square kilometers (363,000 square miles) below the 1981 to 2010 average. Extent continued to track below average in the Barents Sea, Baffin Bay, Davis Strait, and the Labrador Sea. Extent was also below average on the Russian side of the Bering Sea, but elsewhere the ice edge was near its average location for this time of year. Ice extent expanded through the month on the Alaskan side of the Bering Sea and within the Sea of Okhotsk. Ice growth was also prominent in the northern Barents Sea west of Svalbard.

Conditions in context

Arctic sea ice extent compared to other years

Figure 2a. The graph above shows Arctic sea ice extent as of February 1, 2021, along with daily ice extent data for four previous years and the record low year. 2020 to 2021 is shown in blue, 2019 to 2020 in green, 2018 to 2019 in orange, 2017 to 2018 in brown, 2016 to 2017 in magenta, and 2012 to 2013 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Difference from average air temperature over Arctic for January 2021

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for January 2021. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Average Arctic sea level pressure, January 2021

Figure 2c. This plot shows average sea level pressure in the Arctic in millibars for January 2021. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

During January, sea ice extent tracked below measured values for most years except 2017 and 2016, but by the middle of the month, extent rose above the average for the last 10 years, from 2011 to 2020. Overall, in January the Arctic gained 1.42 million square kilometers (548,000 square miles) of ice.

Air temperatures at the 925 mb level (about 2,500 feet above sea level) in January were considerably above average over the Atlantic side of the Arctic, especially in the Baffin Bay region (up to 8 degrees Celsius or 14 degrees Fahrenheit) above average. Temperatures were 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) above average over Canada and Alaska. By sharp contrast, air temperatures were between 6 and 8 degrees Celsius (11 and 14 degrees Fahrenheit) below average over Siberia. The atmospheric circulation associated with this lopsided pattern was dominated by high pressure over Siberia and low pressure over the Northern North Atlantic and Pacific Ocean.

January 2021 compared to previous years

Graph showing decline of sea ice for January from 1979 to 2021

Figure 3. Monthly January ice extent for 1979 to 2021 shows a decline of 3.1 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

Through 2021, the linear rate of decline for January sea ice extent is 3.1 percent per decade, which corresponds to 44,700 square kilometers (17,300 square miles) per year, about twice the size of New Jersey. The cumulative January ice loss over the 43-year satellite record is 1.88 million square kilometers (726,000 square miles), based on the difference in linear trend values in 2021 and 1979.

2020 ties for the warmest year on record

Time-series of global annual mean air temperatures from 1880 through 2020.

Figure 4a. This time-series shows global annual average air temperatures from 1880 through 2020.

Credit: NASA
High-resolution image

Figure 4b. The plot on the left shows annual air temperature departures in 2020 from the 1951 to 1980 average for the Arctic, while the plot on the right shows air temperature departures for Antarctica for the same time period. ||Credit: NASA | High-resolution image

Figure 4b. The plot on the left shows annual air temperature departures in 2020 from the 1951 to 1980 average for the Arctic, while the plot on the right shows air temperature departures for Antarctica for the same time period.

Credit: NASA
High-resolution image

According to the National Oceanic and Atmospheric Administration (NOAA) and the analysis of the NASA Goddard Institute for Space Studies (GISS), the global surface temperature for 2020 tied with 2016 as the highest in the instrumental record, at 1.02 degrees Celsius (1.84 degrees Fahrenheit) above than the baseline of 1951 to 1980 (Figure 4a). While both institutions use the same raw temperature record in their analysis, NOAA does not infer temperatures in the polar regions where observations are not as numerous. Whether travel restrictions may have opposed warming by reducing particulate air pollution and global CO2 emissions remains unclear. Year-to-year variability in global air temperatures is known to be partly tied to the phase of the El Niño-Southern Oscillation (ENSO). When ENSO is positive (El-Niño), more heat is exchanged between the ocean and the atmosphere, especially in the Pacific, leading to a higher global average temperature, such as in 1998 and 2016. While 2020 started in with modest El Niño conditions, it ended with La Niña conditions.

In the Arctic, NASA GISS analysis suggests that 2020 ranked as the warmest year on record, with extremely high temperatures relative to average over the Siberian Arctic; Temperatures were 6.4 degrees Celsius (11.5 degrees Fahrenheit) above the 1951 to 1980 average. The region around north central Siberia was especially warm (Figure 4b). The North Atlantic, east of Greenland, is an exception to the Northern Hemisphere warmth. Previous studies have linked relatively cool conditions in this area to weakening of the Atlantic Meridional Overturning Circulation (AMOC), related to an increase in freshwater input to the North Atlantic from Greenland’s melt water. A new study suggests other factors are also involved, including more low-level clouds that reduce the amount of incoming sunlight in that region.

Over the Antarctic, air temperatures were mostly above average during 2020, with particularly warm conditions over the West Antarctic Peninsula and the Bellingshausen Sea. This contrasts with below average temperatures over the Weddell Sea.

Leaky Arctic plug

Nares Strait on map

Figure 5a. This map shows the Nares Strait in relation to Greenland, Ellesmere Island (a northernmost Canadian Island). The ice arch forms at the entrance into Nares Strait from the Lincoln Sea.

Credit: Moore et al., 2021, Nature Communications
High-resolution image

collapse of north water polynya in summer 2020

Figure 5b. These two images show the collapse of the North Water Polynya between June 24 and July 4, 2020.

Credit: Moore et al., 2021, Nature Communications
High-resolution image

The amount of Arctic sea ice can be reduced through more summer melt, less winter growth, or export out of the Arctic Ocean through various passages, notably Fram Strait and the narrow passages in the Canadian Arctic Archipelago. Nares Strait, a passage between Ellesmere Island and Greenland that connects the Lincoln Sea with Baffin Bay, is one of the last refuges for old thick ice (Figure 5a). Most of the year, ice dams, or ice arches, prevent ice in the Lincoln Sea moving through Nares Strait. However, a recent study shows that the seasonal duration of the ice arch has fallen from typically 200 to 300 days annually between 1997 and 2001 to about 150 days or less since 2003. This allows some of the old and thick ice to move southwards where it melts out in Baffin Bay. An increased flow of thick, multiyear ice into northern Baffin Bay may also negatively impact the formation of the North Water Polynya, also called Pikialasorsuaq, which is an important biologically rich open water area that plays an essential role for Inuit communities (Figure 5b).

Warm winters, more rain

Climate models predict that in coming decades more Arctic precipitation will fall as rain instead of snow, both on sea ice and land. When rain falls on a snowpack in winter, it can refreeze, forming a hard icy layer. On land, caribou and muskoxen cannot break through this hard icy crust to forage. Icy layers can also form when air temperatures rise above freezing during winter and then fall below freezing. One such warm spell recently hit the Canadian Arctic in the area of Iqaluit, Nunavut, and local observers experienced rain. Unseasonably warm conditions lasted until the last week of January.

Further reading

Keil, P. et al. 2020. Multiple drivers of the North Atlantic warming hole. Nature Climate Change. doi:10.1038/s41558-020-0819-8.

Moore, G. W. K., Howell, S. E. L., Brady, M. et al. 2021. Anomalous collapses of Nares Strait ice arches leads to enhanced export of Arctic sea ice. Nature Communications 12, 1. doi:10.1038/s41467-020-20314-w.

Persistently peculiar

Entering December, which is the start of winter in the Northern Hemisphere, sea ice extent remains far below average, dominated by the lack of ice on both the Pacific and Atlantic sides of the Arctic Ocean. As was the case for October, air temperatures averaged for November were well above average over much of the Arctic Ocean, notably over open water areas. Averaged for the month, total ice extent for November 2020 was the second lowest in the satellite record.

Overview of conditions

sea ice extent for Nov 2020

Figure 1. Arctic sea ice extent for November 2020 was 8.99 million square kilometers (3.47 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

As reported in our previous post, sea ice extent averaged for October 2020 was the lowest in the satellite record. While extent increased through November as part of the annual cycle of autumn and winter growth, the November average extent of 8.99 million square kilometers (3.47 million square miles), ended up as second lowest in the satellite record for the month, just above 2016. This was 1.71 million square kilometers (660,000 square miles) below the 1981 to 2010 average and 330,000 square kilometers (127,000 square miles) above the record low of November 2016. Entering December, extent remains especially low over both the Barents and Kara Seas on the Atlantic side and the Chukchi Sea on the Pacific side of the Arctic Ocean.

Conditions in context

Arctic sea ice extent as of December 1, 2020 and several other years for comparison

Figure 2a. The graph above shows Arctic sea ice extent as of December 1, 2020, along with daily ice extent data for five previous years and the record low year. 2020 is shown in blue, 2019 in green, 2018 in orange, 2017 in brown, 2016 in magenta, and 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Arctic air temperatures, as a difference from average for November 2020

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for November 2020. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Average sea level pressure, November 2020

Figure 2c. This plot shows average sea level pressure in the Arctic in millibars for November 2020. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Arctic Oscillation Index from August 1 to November 30, 2020

Figure 2d. This graph shows the Arctic Oscillation (AO) index from August 1 to November 30, 2020.

Credit: National Centers for Environmental Prediction (NCEP) and National Oceanic and Atmospheric Administration (NOAA)
High-resolution image

Through the month of November 2020, sea ice grew by an average of 116,000 square kilometers (44,800 square miles) per day, which is the fastest daily average growth on record for the month, and 46,400 square kilometers (17,900 square miles) above the 1981 to 2010 average rate. However, growth rates varied greatly through the month. Continuing the pattern for late October, sea ice grew rapidly in the first week of November when the upper ocean lost its remaining summer heat back to the atmosphere and then to outer space. Thereafter, growth rates slowed, with a marked slowdown at the end of the month. Such temporary near pauses in ice growth, however, are not uncommon. As of early December, daily extents were the second lowest in the satellite record, behind 2016. Despite low extent for the Arctic as a whole, the Northern Sea Route along the Russian coast is now covered with ice.

Again continuing the pattern for October, air temperatures at the 925 hPa level (about 2,500 feet above the surface) averaged for November 2020 were above average over much of the Arctic Ocean (Figure 2b). Temperatures were 4 to 6 degrees Celsius (7 to 11 degrees Fahrenheit) above average over the Beaufort and Chukchi Seas, the northern Barents Sea, and the Laptev Sea. By contrast, temperatures at the 925 hPa level over the Canadian Arctic Archipelago were near average.

These air temperature “hot spots” correspond to areas of open water, where the ocean is still releasing large amounts of heat to the lower atmosphere; temperatures at the surface in these areas are locally more than 12 degrees Celsius (22 degrees Fahrenheit) above long-term November averages. Recall that we addressed this issue in our previous post with the aid of vertical profiles of temperature. However, the prevailing atmospheric circulation pattern for November also played a role—sea level pressure was quite low over the Atlantic side of the Arctic, which coupled with high pressure over northern Eurasia, favored the transport of warm air into the Barents, Kara, and Laptev Seas (Figure 2c).

Particularly notable about this sea level pressure pattern is that it manifests a return to a strongly positive phase of the Arctic Oscillation (AO) (Figure 2d). Recall from a previous post that much of the 2019 to 2020 winter was characterized by a positive AO phase. As of late November 2020, the AO index had regressed back to a neutral phase; whether this is temporary remains to be seen.

November 2020 compared to previous years

November rate of sea ice decline from 1978 to 2020

Figure 3. Monthly November ice extent for 1978 to 2020 shows a decline of 5.1 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

Including 2020, the linear rate of decline for November sea ice extent is 5.1 percent per decade. This corresponds to a downward trend of 54,800 square kilometers (21,200 square miles) per year, or losing an area about the size of the state of West Virginia each year. Over the 42-year satellite record, the Arctic has lost about 2.30 million square kilometers (888,000 square miles) of ice in November, based on the difference in linear trend values in 2020 and 1978. This is comparable to about three times the size of Texas.

42 years of satellite data

Figure X. Monthly extent (thin lines) for Arctic (blue) and Antarctic (red) and 12-month trailing average (thick lines) for standardized anomalies (departure from the 1981 to 2010 average in each month divided by the 1981 to 2010 standard deviation for the month). The linear trend is overlaid in dashed lines. The trend values are provided below the plot, in # of standard deviations per decade with the +/- 95% confidence level; both trends are statistically significant. ||Credit: W. Meier, NSIDC|High-resolution image

Figure 4. This graph shows monthly extent (thin lines) for Arctic (blue) and Antarctic (red) and 12-month trailing average (thick lines) for standardized anomalies (departure from the 1981 to 2010 average in each month divided by the 1981 to 2010 standard deviation for the month). The linear trend is overlaid in dashed lines. The trend values are provided below the plot, in number of standard deviations per decade with the +/- 95 percent confidence level; both trends are statistically significant.

Credit: W. Meier, NSIDC
High-resolution image

The modern passive microwave satellite data started in late October 1978. November 2020 marks the start of 43 years of continuous and consistent observation of sea ice concentration and extent. The first 42 years of monthly extents from November 1978 through October 2020 provide a comparison of the trends and variability in the Arctic and Antarctic sea ice extent. By comparing each month’s departure from the 1981 to 2010 average for that month, the variability of sea ice extent becomes strongly evident (Figure 4). Here we remove the seasonal cycle of sea ice extent by dividing the departure from average of each month in the satellite record by the standard deviation of each month, both based on the climatological period of 1981 to 2010. The result is a time series of the number of standard deviations each month’s extent in the record is above or below the average. The plot for the Arctic reveals a clear downward trend with some monthly and annual variations. Overall, the Arctic ice extent has decreased by 0.97 standard deviations per decade. By contrast, the Antarctic ice extent is dominated by a lot of variation with a positive trend of 0.17 standard deviations per decade. The magnitude of the Arctic trend is hence roughly five times of the Antarctic trend. The large Antarctic variation is marked particularly by the dramatic reversal from record high extents in 2014 and 2015 to record low extents in 2016 and 2017. Since then, the extent has moderated to near-average conditions.

Antarctica: More ice, sparse ice, and Maud’s back

Sea ice concentration around Antarctica on Nov 30 2020

Figure 5. This map of Antarctica show sea ice concentration on November 30, 2020. The Japanese Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer-2 (AMSR2) shows a range from 0 percent (dark blue) to 100 percent (dark purple) in sea ice concentration. Several small shore polynyas, or openings in sea ice, are visible along the East Antarctic coast.

Credit: University of Bremen
High-resolution image

Antarctic sea ice extent for November 2020 continues to be well above the 1981 to 2010 average, a shift that began in August, with particularly above average extent in the Weddell Sea. However, low sea ice concentration dominates a large area of the Weddell Sea (Figure 5). Also notable is the retreat of ice along the eastern shore of the Antarctic Peninsula, a result of several warm chinook wind events off the Peninsula earlier in November. These strong winds blast warm and dry air downhill, pushing sea ice a tens of kilometers off the coast. On the western side of the Antarctic Peninsula, the reduced sea ice extent in the Bellingshausen Sea and its sharp ice edge add further evidence of strong winds from the northwest. The adjacent Amundsen Sea and Ross Sea have above average ice extent, while below average extent is the rule along the Wilkes, Adelie, and Enderby Land coasts. Numerous small shore polynyas, or openings in sea ice, typical for this time of year, are present along the East Antarctic coast.

There are also open water areas in the Maud Rise region, initiating a few degrees east of the prime meridian and around 64 degrees S latitude. This recurring polynya reopened, where sea ice concentration dropped below 15 percent, on November 26, as well as a second less common polynya several hundred kilometers to the north and west.

Lingering seashore days

Following the sea ice extent minimum on September 15, 2020, expansion of the ice edge has been most notable in the northern Chukchi and Beaufort Seas. The ice edge along the Laptev Sea continued to retreat farther. Antarctic sea ice has climbed to its highest extent since 2014; it may have reached its maximum on September 28, but it is too soon to say for sure.

Overview of conditions

September average sea ice extent in Arctic

Figure 1. Arctic sea ice extent for September 2020 was 3.92 million square kilometers (1.51 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent averaged for September 2020 was 3.92 million square kilometers (1.51 million square miles), the second lowest in the 42-year satellite record, behind only September 2012. This is 350,000 square kilometers (135,000 square miles) above that record low, and 2.49 million square kilometers (961,000 square miles) below the 1981 to 2010 average. Following the minimum seasonal extent, which occurred on September 15, ice growth quickly began along in the northern Beaufort, Chukchi, and East Siberian Seas (Figure 1). Expansion of the ice edge was also notable within the East Greenland Sea and within Canadian Arctic Archipelago. By contrast, the ice edge in the Kara and Barents Seas remained relatively stable until the end of the month when it started to expand, and within the Laptev Sea the ice edge retreated slightly. The Northern Sea Route remained open at the end of September whereas the Northwest Passage southerly route (Amundsen’s route) is now blocked by ice. Ten days after the minimum extent was reached, the total extent climbed above 4 million square kilometers (1.54 million square miles) and by the end of the month the ice extent was tracking at 4.25 million square kilometers (1.64 million square miles), still second lowest in terms of daily extent.

Conditions in context

Arctic sea ice extent as of October 4, 2020

Figure 2a. The graph above shows Arctic sea ice extent as of October 4, 2020, along with daily ice extent data for four previous years and the record low year. 2020 is shown in blue, 2019 in green, 2018 in orange, 2017 in brown, 2016 in purple, and 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

September 2020 Arctic air temperature, as difference from average (left) Average sea level pressure (right)

Figure 2b. The plot on the left shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for September 2020. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures. The plot on the right shows average sea level pressure in the Arctic in millibars (hPa) for September 2020. Yellows and reds indicate high air pressure; blues and purples indicate low pressure. The apparent high pressure over Greenland is an artifact of the high elevation there; errors are incurred in extrapolating from the surface of the ice to sea level.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Arctic air temperatures at the 925 hPa level (about 2,500 feet above the surface) remained overall above the 1981 to 2010 average during September. This warmth was primarily observed on the Eurasian side of the Arctic, where air temperatures along the coastal regions of the Laptev Sea reached up to 8 degrees Celsius (14 degrees Fahrenheit) above average. Below average temperatures prevailed over Greenland. Warm conditions over the Siberian side of the Arctic were driven by a strong high pressure ridge over Siberia coupled with a strong low-pressure trough centered over Svalbard. This is also manifested as a positive phase of the Arctic Oscillation (AO). A cyclonic (counterclockwise) circulation pattern set up over the Laptev Sea, bringing in warmer air from the south. At the same time, this circulation pattern enhanced ice drift out through Fram Strait and out of the Arctic Ocean. Winds from the south in the Kara and Barents Seas also kept the ice edge from expanding in that region, and led to retreat of the ice edge within the Laptev Sea.

September 2020 compared to previous years

Ice extent decline from 1979 to 2020 for September

Figure 3. Monthly September ice extent for 1979 to 2020 shows a decline of 13.1 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

The overall rate of sea ice decline in September is now at 83,700 square kilometers (32,300 square miles) per year, or a rate of ice loss of 13.1 percent per decade relative to the 1981 to 2010 average.

A look back at summer 2020

Ranking of Arctic Temperatures by month from 1979 to 2020

Figure 4a. This graphic ranks months based on their Arctic air temperature from 1979 to 2020 at 925 hPa from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis for all areas north of 70 degrees N. Dark reds indicate warmest months; dark blues indicate coldest months.

Credit: Z. Labe, Colorado State University, Colorado
High-resolution image

Arctic air temperatures for May through August 2020, difference from average

Figure 4b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for May, June, July, and August 2020. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Average sea level pressure for April, May, June, and July 2020

Figure 4c. These four plots show average sea level pressure in the Arctic in millibars (hPa) for May, June, July, and August 2020. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Sea surface temperatures (SST) in the Arctic Ocean

Figure 4d. These maps show sea surface temperature (SST) in degrees Celsius and sea ice concentration for August 23, 2020 on the left and September 13, 2020 on the right. SST data are from the University of Washington Polar Science Center Upper layer Temperature of the Polar Oceans (UptempO) buoys and satellite-derived values from the National Oceanic and Atmospheric Administration (NOAA), and ice concentration is from the NSIDC Sea Ice Index.

Credit: University of Washington
High-resolution image

While average and below average air temperature characterized the Arctic Ocean in the winter of 2019 to 2020, exceptionally warm conditions prevailed this past summer. Indeed, the summer of 2020 appears to be the warmest since at least 1979. According to the NCEP/NCAR reanalyses, monthly averaged air temperatures (at the 925 hPa level) over the Arctic Ocean, north of 70 degrees N, were at record highs in May, July, and August. June ranked as the second warmest behind 2005 (Figure 4a). Exceptionally high temperatures in May led to early development of melt ponds along the Russian coast (Figure 4b). This, combined with exceptional warmth over Siberia in June and thin ice in the region, fostered by the strongly positive phase of the Arctic Oscillation (AO) in winter (see discussion below), resulted in early development of open water within the Laptev Sea. This led to record low ice extent in the region starting in mid-June. By mid-July, Arctic sea ice extent was tracking at record lows over the period of satellite observations, fueled by the early ice retreat along the Russian coast.

Sea level pressure patterns this melt season shifted from month to month (Figure 4c). For example, high air temperatures in May were linked to a high pressure ridge over Alaska that extended into the Beaufort and Chukchi Seas. Meanwhile, unusually low pressure was focused over the central Arctic Ocean and Scandinavia, driving winds from the south over to the Kara Sea. In June, the high pressure moved over to the western Arctic Ocean. High pressure also developed throughout the Canadian Arctic Archipelago, Greenland, and Scandinavia. This, combined with low sea level pressure near the pole and over the Kara Sea and Eurasia, spilled cold Arctic air into Eurasia and warm air over Siberia. In July, the high pressure ridge moved further east to the Kara and Laptev Seas. Coupled with low pressure over Siberia and Scandinavia, this circulation pattern funneled warm air from Scandinavia and Eurasia towards the pole, while pushing cold Arctic air from the Kara Sea over to Russia and from the central Arctic over to Alaska.

As August started, the pace of ice loss slowed and by the end of the month, total Arctic sea ice extent went from the lowest to the second lowest in the satellite record. This was despite August being the warmest August recorded since at least 1979.

By late August, sea surface temperatures showed large variations across the Arctic, with generally warm water to the south and colder, near-freezing water near the ice edge in most locations (Figure 4d). According to our colleague Mike Steele at the University of Washington, this cold water persists near the ice edge as the ocean gives up its heat to melt ice; this signals the last stage of summer ice retreat. The resulting new open water hardly warms up because there is little atmospheric heating late in the season from lack of solar energy. An exception is the eastern Beaufort Sea, where ice was swept southward this year into warm water along the northern coast of northwest Canada and Alaska. By mid-September, the cold northern band of sea surface temperatures expanded in response to continued ice retreat and weak atmospheric heating of the ocean. Many areas, such as the Beaufort and Chukchi Seas, Canada Basin, and Baffin Bay, had lower sea surface temperatures at this time relative to August. This surface cooling happens as the calm winds of summer  are replaced by windier conditions in the fall, which mixes the ocean heat downward. The date of maximum sea surface temperature is often earlier than the date of minimum sea ice extent. This is not so evident in the eastern Arctic Ocean, possibly because of the influence of warm ocean currents that continue to pump heat into the area through late summer.

Comment on the northernmost ice edge position in the Kara and Barents Seas

Three-month average Arctic Oscillation from 1950 to August 2020


Figure 5. These graphs show the 3-month average Arctic Oscillation (AO) index from 1950 through August 2020.

Credit: National Centers for Environmental Prediction (NCEP) and National Oceanic and Atmospheric Administration
High-resolution image

The near record minimum Arctic sea ice extent in September 2020, and particularly the loss of ice along the Russian margin of the Arctic Ocean, is consistent with wind patterns associated with the persistently strong positive phase of the Arctic Oscillation (AO) this past winter. During the positive phase of the winter AO, there tends to be a pattern of offshore winds along the Russian side of the Arctic, drawing ice out of the Siberian shelf seas (Kara, Laptev, East Siberian, and Chukchi Seas) and causing new ice formation in the openings left behind. The result is that the spring ice cover along the Siberian coast is thinner than usual and more likely to melt out in summer. The 2019 to 2020 winter AO was at a record or near record positive phase (Figure 5). According to our colleague Jamie Morrison at the University of Washington, this summer’s pronounced retreat of ice north of the Laptev-Kara-Barents-Seas region is consistent with the effects of the positive winter AO. Morison notes that the winter AO has been generally positive over the past 30 years, particularly so over the last 10 years. He speculates that the atmospheric circulation pattern associated with the AO may also favor a greater influence of Atlantic water heat on the sea ice cover through weakening the cold halocline layer—the cold, but low density water at the ocean surface.

Arctic sea ice age

Arctic sea ice age map at end of 2020 melt season

Figure 6. The upper left map shows sea ice age distribution toward the end of the melt season for 1985 and the upper left map shows the end of the 2020 melt season. The bottom time series of different age categories shows the minimum extent for 1985 to 2020. Note that the ice age product does not include ice in the Canadian Archipelago. Data from Tschudi et al., EASE-Grid Sea Ice Age, Version 3

Credit: W. Meier, National Snow and Ice Data Center and M. Tschudi et al.
High-resolution image

With the minimum reached, the remaining sea ice has had its “birthday,” aging one year. Assessing the ice age just before this birthday gives an indication of the health of the ice at the end of the melt season. The extent of the oldest ice (4+ years old) at that time in 2020 was 230,000 square kilometers (89,000 square miles). This is considerably higher compared to last year, when the 4+ year old ice extent stood at 55,000 square kilometers (21,000 square miles) at the 2019 minimum. The increase in 4+ year old ice in 2020 was compensated by a slight decrease in 2- to 3-year old ice and 3- to 4-year old ice (Figure 6). Overall, since the 1980s, when older ice covered over 2 million square miles (772,000 square miles) of the Arctic Ocean, sea ice has become much thinner and younger. The linear downward trend in 4+ year old ice extent at the sea ice minimum is 70,000 square kilometers (27,000 square miles) per year, equivalent to a decline of 6.1 percent per year relative to the 1984 to 2020 average.

Antarctica maximum may have been reached

Antarctic sea ice extent map for September 2020

Figure 7. Arctic sea ice extent for September 2020 was 18.77 million square kilometers (7.25 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Antarctic sea ice extent may have reached its maximum of 18.95 million square kilometers (7.32 million square miles) on September 28, but the extent could still expand in the coming days. As is typical this time of year, there are wide swings caused by winds and storms along the extensive ice edge. Ice extent is now well above the 1981 to 2020 median extent. This follows a remarkable transition from generally below median extent beginning in August 2016 to well above median extent just in the seven weeks preceding October 1, 2020. Ice extent is above the median extent along a broad area off the Wilkes Land coast and western Ross Sea, near the median extent from the Amundsen Sea clockwise to the Weddell Sea and above the median north of Dronning Maud Land, Enderby Land, and the Cosmonaut Sea. The only major area of below the median extent is in the Indian Ocean sector near the Amery Ice Shelf and eastward.

References

Morison, J. 2020. Workshop on observing, modeling, and understanding the circulation of the Arctic Ocean and Sub-Arctic Seas. Retrieved here.

Moore, G. W. K., Schweiger, A., Zhang, J., and M. Steele. 2019. Spatiotemporal variability of sea ice in the arctic’s last ice area. Geophysical Research Letters, 46, 11237– 11243. doi:10.1029/2019GL083722.

Polyakov, I. V., Pnyushkov, A. V., Alkire, M. B., Ashik, I. M., Baumann, T. M., Carmack, E. C., et al. 2017. Greater role for Atlantic inflows on sea-ice loss in the Eurasian Basin of the Arctic Ocean. Science, 356 (6335), 285. doi:10.1126/science.aai8204.

Rigor, I. G., Wallace, J. M., and R. L. Colony. 2002. Response of sea ice to the Arctic oscillation. Journal of Climate, 15(18), 2648-2663. doi:10.1175/1520-0442.

Steele, M., and T. Boyd. 1998. Retreat of the cold halocline layer in the Arctic Ocean. Journal of Geophysical Research Oceans, 103(C5), 10419-10435. doi:10.1029/98JC00580.

Steele, M., Zhang, J., and W. Ermold. 2010. Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt, Journal of Geophysical Research, 115, C11004. doi:10.1029/2009JC005849.

Steele, M., and S. Dickinson. 2016. The phenology of Arctic Ocean surface warming, Journal of Geophysical Research Oceans, 121, 6847– 6861. doi:10.1002/2016JC012089.

 

Arctic sea ice decline stalls out at second lowest minimum

On September 15, Arctic sea ice likely reached its annual minimum extent of 3.74 million square kilometers (1.44 million square miles). The minimum ice extent is the second lowest in the 42-year-old satellite record, reinforcing the long-term downward trend in Arctic ice extent. Sea ice extent will now begin its seasonal increase through autumn and winter. In the Antarctic, sea ice extent is now well above average and within the range of the ten largest ice extents on record, underscoring its high year-to-year variability. The annual maximum for Antarctic sea ice typically occurs in late September or early October.

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

Figure 1. Arctic sea ice extent for September 15, 2020

Figure 1a. Arctic sea ice extent for September 15, 2020 was 3.74 million square kilometers (1.44 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Figure 1b. The map above compares the 2012 Arctic sea ice minimum, reached on September 17, with the 2020 Arctic sea ice minimum, reached on September 15. Light blue shading indicates the region where ice occurred in both 2012 and 2020, while white and medium blue areas show ice cover unique to 2012 and to 2020, respectively. Sea Ice Index data. About the data||Credit: National Snow and Ice Data Center|High-resolution image

Figure 1b. The map above compares the 2012 Arctic sea ice minimum, reached on September 17, with the 2020 Arctic sea ice minimum, reached on September 15. Light blue shading indicates the region where ice occurred in both 2012 and 2020, while white and medium blue areas show ice cover unique to 2012 and to 2020, respectively. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

A sharp decline of Arctic sea ice at the beginning of September dropped the extent below 4.0 million square kilometers (1.54 million square miles) for only the second time since the beginning of the satellite record in 1979. After September 8, daily melt began leveling out, reaching its seasonal minimum extent of 3.74 million square kilometers (1.44 million square miles) on September 15 (Figure 1a). This appears to be the lowest extent of the year. In response to the setting sun and falling temperatures, ice extent will begin increasing through autumn and winter. However, a shift in wind patterns or a period of late season melt could still push the ice extent lower.

Compared to 2012, the minimum extent this year has more ice in the Beaufort Sea, but somewhat less ice in the Laptev and East Greenland Sea regions (Figure 1b). The minimum extent was reached one day later than the 1981 to 2010 median minimum date of September 14. The interquartile range of minimum dates is September 11 to September 19.

The 14 lowest extents in the satellite era have all occurred in the last 14 years.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent on September 18, 2019, along with 2007 and 2016—the years tied for second lowest minimum—and the record minimum for 2012. 2019 is shown in blue, 2016 in light brown, 2012 in dotted pink, and 2007 in dark brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.||Credit: National Snow and Ice Data Center|High-resolution image

Figure 2a. The graph above shows Arctic sea ice extent on September 15, 2020, along with several other recent years and the record minimum set in 2012. 2019 is shown in green, 2018 in orange, 2017 in brown, 2016 in magenta, and 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

14 year trends for Arctic sea ice loss

Figure 2b. This graph shows linear trends of Arctic sea ice extent for three 14-year periods for the day of the annual minimum. Trend percent values are relative to the 1981 to 2010 average minimum extent. On the right, the average (square) and range of highest and lowest extents at the minimum for each period are given.

Credit: W. Meier, NSIDC
High-resolution image

This year’s minimum set on September 15 was 350,000 square kilometers (135,000 square miles) above the record minimum extent in the satellite era, which occurred on September 17, 2012 (Figure 2a). It is also 2.51 million square kilometers (969,000 square miles) below the 1981 to 2010 average minimum extent, which is equivalent in size to roughly the states of Alaska, Texas, and Montana combined, or Greenland and Finland combined.

The 42-minimum-extent values in the satellite record can be broken down into three 14-year periods. Most notably, minimum extents in the last 14 years of the time series are the lowest 14 in the 42-year record (Figure 2b). All three periods show a downward trend. The middle period, 1993 to 2006, shows the steepest downward trend of 13.3 percent per decade, relative to the 1981 to 2010 average. The earliest period, 1979 to 1992, has a downward trend of 6.4 percent per decade, while the most recent period of low extents, 2007 to 2020, has a downward trend of 4.0 percent per decade.

The overall, downward trend in the minimum extent from 1979 to 2020 is 13.4 percent per decade relative to the 1981 to 2010 average.

Fourteen lowest minimum Arctic sea ice extents (satellite record, 1979 to present)

Table 1. Fourteen 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 2020 3.74 1.44 Sept. 15
3 2007
2016
2019
4.16
4.17
4.19
1.61
1.61
1.62
Sept. 18
Sept. 18
Sept. 10
6 2011 4.34 1.68 Sept. 11
7 2015 4.43 1.71 Sept. 9
8 2008
2010
4.59
4.62
1.77
1.78
Sept. 19
Sept. 21
10 2018
2017
4.66
4.67
1.80
1.80
Sept. 23
Sept. 13
12 2014
2013
5.03
5.05
1.94
1.95
Sept. 17
Sept. 13
14 2009 5.12 1.98 Sept. 13

Values within 40,000 square kilometers (15,000 square miles) are considered tied. The 2019 value has changed from 4.15 to 4.19 million square kilometers (1.62 million square miles) when final analysis data updated to near-real-time data.

Tapping the brakes

After a period of rapid sea ice loss extending into the last week of August, the rate has slowed with the onset of autumn in the Arctic. A region of low concentration ice persists in the Beaufort Sea. How much of this ice melts over in the next two weeks will strongly determine where the September sea ice minimum will stand in the record books. The Northwest Passage (Amundsen’s route) is largely open but some ice remains. The Northern Sea Route, along the Siberian coast, remains open.

Overview of conditions

Montly extent for August 2020

Figure 1. Arctic sea ice extent for August 2020 was 5.08 million square kilometers (1.96 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

August 2020 sea ice extent averaged 5.08 million square kilometers (1.96 million square miles), placing it at third lowest in the satellite record for the month. This was 360,000 square kilometers (139,000 square miles) above the record low set in 2012. As of September 1, Arctic sea ice extent stood at 4.26 million square kilometers (1.64 million square miles), the second lowest extent for that date in the satellite passive microwave record that started in 1979.

In our previous post, we noted the development of substantial openings of the sea ice north of Alaska within the Beaufort and Chukchi Seas, possibly related to the mid-July storm that spread out the ice cover. Since then, further melt has occurred in the area. Some of this ice appears to be multiyear, which tends to be resistant to melting away. Total sea ice extent at the September minimum will depend strongly on how much of the ice in this area melts from the remaining heat in the ocean, and on wind compaction or expansion of the overall ice edge (the line of 15 percent concentration). The Northwest Passage is largely open, but some ice remains. The Northern Sea route remains open.

Conditions in context

Arctic sea ice extent graph

Figure 2a. The graph above shows Arctic sea ice extent as of September 01, 2020, along with daily ice extent data for four previous years and the record low year. 2020 is shown in blue, 2019 in green, 2018 in orange, 2017 in brown, 2016 in purple, and 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Average air temperatures in Arctic from August 15 to 31, 2020

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, from August 15 to 31, 2020. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Average sea level pressure over Arctic from August 1 to 31, 2020

Figure 2c. This plot shows average sea level pressure in the Arctic in millibars (hPa) from August 15 to 31, 2020. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Following a period of slow August ice loss, the pace quickened during the middle of the month as areas of low ice concentration melted away, only to slow again towards the end of the month with the onset of autumn in the Arctic. Overall, from August 15 through September 1, 2020, extent declined by 1.1 million square kilometers (425,000 square miles), more than the average 1981 to 2020 extent loss of 800,000 square kilometers (309,000 square miles) during the same period (Figure 2a).

As assessed from August 15 to August 31, air temperatures at the 925 mb level (about 2,500 feet above sea level) were above average over much of the Arctic Ocean, continuing the basic pattern of warmth that prevailed through the first half of the month, most notably in the Kara Sea. Temperatures were below average over central Siberia (Figure 2b). The atmospheric circulation pattern shifted relative to the first half of the month to feature high pressure centered over the Laptev Sea and extending across the Beaufort and Chukchi Seas (Figure 2c). Low pressure has been the dominant feature of the Norwegian Sea region.

August 2020 compared to previous years

Average trend for August sea ice loss since 1979

Figure 3. Monthly August ice extent for 1979 to 2020 shows a decline of 10.7 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

The average sea ice extent for August 2020 as a whole is 5.08 million square kilometers (1.96 million square miles), placing it third lowest in the 42-year satellite record. Including 2020, the linear rate of decline for August sea ice extent is 10.7 percent per decade. This corresponds to a trend of 76,800 square kilometers (29,700 square miles) per year, or about the size of New Hampshire, Vermont, and Massachusetts combined. Over the satellite record, the Arctic Ocean has lost about 3.15 million square kilometers (1.22 million square miles) of ice in August, based on the difference in linear trend values in 2020 and 1979. This is comparable in size to about twice the size of the state of Alaska.

Atlantification continues

As discussed in a recent paper in the Journal of Climate led by colleague Igor Polyakov of the University of Alaska, the process of “Atlantification” of the Arctic Ocean, first noted in the Barents Sea, is continuing, with significant effects on the sea ice cover during the winter season in the Eastern Eurasian Basin. The relatively fresh surface layer of the Arctic Ocean is underlain by warm, salty water that is imported from the northern Atlantic Ocean. The cold fresh surface layer, because of its lower density, largely prevents the warm, salty Atlantic waters from mixing upwards. However, the underlying Atlantic water appears to have moved closer to the surface in recent years, reducing the density contrast with the water above it. Recent observations show this warm water “blob,” usually found at about 150 meters (492 feet) below the surface, has shifted within 80 meters (263 feet) of the surface. This has resulted in an increase in the upward winter ocean heat flow to the underside of the ice from typical values of 3 to 4 watts per square meter in 2007 to 2008 to greater than 10 watts per square meter from 2016 to 2018. Polyakov estimates that this is equivalent to a two-fold reduction in winter ice growth.

Other recent news

The RV Polarstern, which has been supporting the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, conducted an impromptu detour to the North Pole, taking advantage of fairly light ice conditions. Large openings in the sea ice were present north of Greenland, an area that would normally be very difficult to traverse. The United States’ medium-duty icebreaker Healy did not fare as well—a fire broke out in the engine compartment, and although it was quickly extinguished, the damage is extensive, and with the ship temporarily out of commission, a planned expedition to the Chukchi and Beaufort Seas has been cancelled.

Antarctic sea ice: looking up down below

Antarctic sea ice extent

Figure 4. The graph above shows Antarctic sea ice extent as of September 01, 2020, along with daily ice extent data for four previous years and the record maximum extent year. 2020 is shown in blue, 2019 in green, 2018 in orange, 2017 in brown, 2016 in purple, and 2014 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Antarctic sea ice growth in late winter has brought the ice extent substantially above average in late August for the first time in four years. Ice extent exceeded the 1981 to 2010 average over much of the Weddell Sea and off the Wilkes Land coast. A few areas of below-average extent persisted in the Davis Sea (south of Perth, Australia) and the northeastern Ross Sea. The cause appears to be persistent high air pressure in the western Weddell Sea and the Davis Sea that generate offshore cold winds on the eastern sides of the high-pressure areas. While Antarctica often has a trio of high pressure and low pressure areas surrounding it, for the second half of August there were just two such pairs.

Further reading

Polyakov, I. V., et al. 2020. Weakening of Cold Halocline Layer Exposes Sea Ice to Oceanic Heat in the Eastern Arctic Ocean. Journal of Climate, 33, 8107–8123, doi:10.1175/JCLI-D-19-0976.1.

Siberian downward slide

By July 15, 2020, Arctic sea ice extent was at a record low over the period of satellite observations for this time of year. The Siberian heat wave this past spring initiated early ice retreat along the Russian coast, leading to very low sea ice extent in the Laptev and Barents Seas. The Northern Sea route appears to be nearly open.

Overview of conditions

Figure 1. Arctic sea ice extent for XXXX XX, 20XX was X.XX million square kilometers (X.XX million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data||Credit: National Snow and Ice Data Center|High-resolution image

Figure 1. Arctic sea ice extent for July 15, 2020 was 7.51 million square kilometers (2.90 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

On July 15, Arctic sea ice extent stood at 7.51 million square kilometers (2.90 million square miles), 330,000 square kilometers (127,000 square miles) below the record for July 15, set in 2011. This places extent at the lowest level for this time of year on the satellite record. Low extent for the Arctic as a whole is largely driven by extensive open water in the Laptev and Barents Seas, continuing the pattern that began this spring and was discussed in the previous post. Ice concentrations are low in the East Siberian Sea; remaining ice in this area is likely to melt out soon. By contrast, extent north of Alaska is near the 1981 to 2010 average for this time of year. Such contrasts serve as prominent examples of the larger variations that occur for sea ice extent on the regional scale in comparison to the Arctic Ocean as a whole.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of XXXXX XX, 20XX, along with daily ice extent data for four previous years and the record low year. 2020 is shown in blue, 2019 in green, 2016 in orange, 2015 in brown, 20XX in purple, and 20XX in dashed red. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.||Credit: National Snow and Ice Data Center|High-resolution image

Figure 2a. The graph above shows Arctic sea ice extent as of July 15, 2020, along with daily ice extent data for four previous years and the record low year. 2020 is shown in blue, 2019 in green, 2018 in orange, 2017 in brown, 2016 in purple, and 2012 in dashed red. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Figure 2b.

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, from July 1 to 13, 2020. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Figure 2c

Figure 2c. This plot shows average sea level pressure in the Arctic in millibars (hPa) from July 1 to 13, 2020. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Figure 2b.

Figure 2d. This true-color composite image shows broken up sea ice on the Siberian coast, taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the NASA Terra satellite on July 12, 2020. Also visible is the smoke from wildfires surging in Siberia.

Credit: NASA Worldview
High-resolution image

Through the first half of July 2020, sea ice extent declined by an average of 146,000 square kilometers (56,400 square miles) per day, considerably faster than the 1981 to 2010 average rate of 85,900 square kilometers (33,200 square miles) per day  (Figure 2a).

Air temperatures at the 925 mb level (about 2,500 feet above sea level), as averaged over the first half of July, were unusually high over the central Arctic Ocean—up to 10 degrees Celsius (18 degrees Fahrenheit) (Figure 2b). These above average temperatures were associated with high sea level pressure, centered over the East Siberian and Chukchi Seas (Figure 2c). Arctic temperatures along the Russian coast were near to slightly above average. This is a sharp change from June, when, as part of the Siberian heat wave that has garnered much attention in the media, temperatures along the Siberian coast of the eastern Laptev Sea were 8 degrees Celsius (14 degrees Fahrenheit) above average. It is likely these high temperatures, combined with ice motion away from the coast, initiated early ice retreat along the Russian coast, leading to the present low ice extent (Figure 2d). Based on imagery from AMSR-2 processed by colleagues at the University of Bremen, the Northern Sea Route along the Russian coast appears to be largely open.

Greenland melting

For the first half of July, surface melt over the Greenland Ice Sheet has been above the 1981 to 2010 average, with a spike on July 10 when about 34 percent of the ice sheet experienced some melt. However, this spike pales in comparison to July 11, 2012, when nearly the entire ice sheet experienced some melt. Melt spikes are associated with warm air advection and cloud cover associated with the passage of weather systems. To date, the 2020 season has seen above average surface melt area, relative to 1981 to 2010, but somewhat lower melt extent than several recent years. A further analysis of the ongoing Greenland melt season will be forthcoming in early August in our Greenland Today analysis.

Antarctica freezing

Figure 2. The graph above shows Arctic sea ice extent as of XXXXX XX, 20XX, along with daily ice extent data for four previous years and the record low year. 2020 is shown in blue, 2019 in green, 2018 in orange, 2017 in brown, 2016 in purple, and 2012 in dashed red. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.||Credit: National Snow and Ice Data Center|High-resolution image

Figure 3. The graph above shows Antarctic sea ice extent as of July 15, 2020, along with daily ice extent data for four previous years and the record high year. 2020 is shown in blue, 2019 in green, 2018 in orange, 2017 in brown, 2016 in purple, and 2014 in dashed red. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Antarctic sea ice extent as of July 15 was slightly below the 1981 to 2010 average, continuing the trend for nearly every day this year. An effort is underway to use a combination of data from the NASA Ice Cloud and Elevation Satelite-2 (ICESat-2), a laser altimeter, and European Space Agency (ESA) CryoSat-2, a radar altimeter, to provide simultaneous snow surface and underlying sea ice surface heights. Generally, it is assumed that the ICESat-2 laser altimeter estimates the height of the top of the snow, while the radar altimeter on CryoSat-2 penetrates through the snow and obtains a measurement of the top of the ice surface beneath the snow. While there are many uncertainties in these characteristics, subtracting the two values—ICESat-2 height minus CryoSat-2 height—can potentially provide an estimate of snow thickness, a key variable needed to accurately determine sea ice thickness. A study by colleague Ron Kwok demonstrated the efficacy of the approach at cross-over point for the two satellite’s orbit tracks. Plans are now underway to align the satellite orbits such that they fly nearly overlapping profiles over long distances with a very short interval between sensor measurements. This longer comparison area and close time separation will be particularly important for assessing Antarctic sea ice, which has much more variability in ice floe age and origin than Arctic sea ice. It will allow the first careful assessment of Antarctic sea ice mass, and over time, the trend in mass, if any.

Further reading

Kwok, R.Kacimi, S.Webster, M. A.Kurtz, N. T., and A. A. Petty. 2020Arctic snow depth and sea ice thickness from ICESat‐2 and CryoSat‐2 freeboards: A first examinationJournal of Geophysical Research: Oceans125, e2019JC016008. doi:10.1029/2019JC016008.

Holey ozone

The seasonal decline of Arctic sea ice extent proceeded at a near-average pace in May. Extent did not approach record lows but remained well below the 1981 to 2010 average. Sea ice extent was notably below average in the Barents and Chukchi Seas, but less so than in recent years. Western Russia and the central Arctic Ocean were unusually warm. Recent research demonstrates a strong link between the persistently positive Arctic Oscillation of last winter and early spring and the record stratospheric Arctic ozone hole. The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) ice floe is breaking up and a new one will most likely have to be found to continue the scientific expedition.

Overview of conditions

Sea ice extent for May 2020

Figure 1. Arctic sea ice extent for May 2020 was 12.36 million square kilometers (4.77 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Sea ice extent averaged for May 2020 was 12.36 million square kilometers (4.77 million square miles), placing it in the fourth lowest extent in the satellite record for the month. This was 930,000 square kilometers (359,000 square miles) below the 1981 to 2010 May average and 440,000 square kilometers (170,000 square miles) above the record low mark for May set in 2016. Ice retreat was predominantly in the Bering, Chukchi, Barents and Kara Seas, whereas more modest retreats prevailed in Baffin Bay/Davis Strait, northern Hudson Bay, and the southeastern Greenland Sea. The North Water Polynya also opened up during May. As May came to a close, the ice extent was below average in the Barents and Chukchi Seas, but less so than in recent years. Areas of low extent also included southeastern Greenland, northern Hudson Bay, and northern Baffin Bay. Several coastal polynyas began opening along the Russian coast, a pattern which has been common in recent years. A somewhat larger-than-average opening north of Svalbard appeared in May.

Conditions in context

Arctic Sea Ice extent for 2020 and five other years

Figure 2a. The graph above shows Arctic sea ice extent as of June 1, 2020, along with daily ice extent data for four previous years and the record low year. 2020 is shown in blue, 2019 in green, 2018 in orange, 2017 in brown, 2016 in purple, and 2012 in dashed red. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Figure 2X. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for XXXmonthXX 20XX. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.||Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division| High-resolution image

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for May 2020. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Through the month, sea ice declined by an average of 54,100 square kilometers (20,900 square miles) per day, slightly faster than the 1981 to 2010 average of 47,000 square kilometers (18,000 square miles) per day. The total sea ice loss during May 2020 was 1.68 million square kilometers (649,000 square miles).

Air temperatures at the 925 hPa level (about 2,500 feet above the surface) were above average over almost all of the Arctic Ocean, with departures as much as 7 degrees Celsius (13 degrees Fahrenheit) over the central Arctic Ocean (Figure 2b). Temperatures were also up 7 degrees Celsius (13 degrees Fahrenheit) over the western portion of Russia. Far northern Canada had temperatures on the order of 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) below average.

Sea level pressures were especially low over Scandinavia, driving winds from south to north toward the Ob River estuary and Kara Sea region was unusually warm. Pressures were quite high over the Canadian Arctic Archipelago.

May 2020 compared to previous years

Average sea ice extent for May 1979 t0 2020

Figure 3. Monthly May ice extent for 1979 to 2020 shows a decline of 2.7 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

Including 2020, the linear rate of decline for May sea ice extent is 2.7 percent per decade. This corresponds to a trend of 36,400 square kilometers (14,100 square miles) per year, or about the size of the state of Indiana. Over the 42-year satellite record, the Arctic has lost about 1.36 million square kilometers (525,000 square miles) of ice in May, based on the difference in linear trend values in 2019 and 1979. This is comparable to about twice the size of the state of Alaska.

Arctic ozone hole and Arctic Oscillation

Arctic Ozone Hole

Figure 4. Arctic stratospheric ozone reached its record low level of 205 Dobson units, shown in blue and turquoise, on March 12, 2020.

Credit: NASA
High-resolution image

As noted in our previous post, the Arctic Oscillation (AO), a key pattern of atmospheric variability over the Arctic and northern Atlantic, was in a persistently positive (cyclonic) phase from mid-December through early spring. Such persistence, which ended only in early May, is highly unusual, and appears to be linked to a strong, cold stratospheric polar vortex and the largest Arctic stratospheric ozone hole observed to date (Figure 4). Scientists have learned there are two-way relationships—what happens in the stratosphere (high in the atmosphere) influences what happens in the lower atmosphere (the troposphere), and vice versa. A study by University of Colorado researcher Zac Lawrence and National Oceanic and Atmospheric Administration (NOAA) researchers Judith Perlwitz and Amy Butler, submitted recently to the Journal of Geophysical Research, took a close look at these connections. They find that the winter of 2019 to 2020 featured an exceptionally strong and cold stratospheric polar vortex. In general, atmospheric waves generated in the troposphere spread both outward and upward into the stratosphere where they can disturb and weaken the stratospheric polar vortex. But this wave activity was fairly weak this past winter, so the vortex remained largely undisturbed. The vortex was also configured in a way such that upward propagating waves were “reflected” back downwards, which further enabled the vortex to remain strong and cold. The end result is that the cyclonic (counterclockwise) circulation at the surface associated with the positive AO was tied closely to the cyclonic circulation of the strong, cold stratospheric vortex. The cold conditions in the stratosphere and its persistence into spring in turn provided favorable conditions to form polar stratospheric clouds, which foster ozone loss through well-understood chemical processes.

MOSAiC turns into a mosaic

Ice breaks up surrounding the RV Polarstern ship

Figure 5a. Before the RV Polarstern left its ice floe location to exchange crew and scientists for the next leg of the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition, ice break ups around the ship intensified.

Credit: C. Rohleder
High-resolution image

Tent collapsed under Arctic sea ice ridging

Figure 5b. A tent compresses under the pressure of Arctic sea ice ridging, showing increased instability in the region surrounding the RV Polarstern. Surface melt appears at the forefront of the image.

Credit: J. Schaffer
High-resolution image

Scientists on leg three of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition left their ice floe, which was specifically selected for having survived one summer melt season, on May 16 to exchange crew and scientists and pick up cargo from transport vessels in Svalbard. Before the RV Polarstern ship actually departed, scientists hoped to leave behind several instruments that began monitoring ice, ocean, and atmospheric conditions back in October 2019 when the Central Observatory around the ship was initially established. Some of these instruments included autonomous light stations that measure the amount of light under the ice and changes in water color caused by phytoplankton growth. However, as the scientists were getting ready to leave, the ice floe began to break apart, rendering the MOSAiC floe into a true mosaic of ice blocks (Figure 5a and 5b). With such unstable conditions, all of the instrumentation used to provide calibration and validation data for overflights of satellites and aircraft were removed temporarily. It is not clear how many of the instruments left behind will survive, including the light stations. The warming and power hut from the remote sensing site, for instance, was left on the ice and was in a precarious situation as cracks in the ice opened nearby. In more recent days, images from cameras left behind indicate that the surface is melting which will likely make the floe more unstable. Given these conditions, it remains unclear whether or not the MOSAiC expedition will need to find a new floe to continue the experiment through September 2020.

Effects of cyclones on sea ice

Change in Arctic Sea Ice Concentration Four Days after Cyclonic Storm, Four Seasons

Figure 6. These maps of the Arctic Ocean compare sea ice concentration changes four days after cyclonic storms were present to changes that occur when no storms are present. MAM stands for March-April-May; JJA stands for June-July-August; SON is September-October-November; and DJF is December-January-February. Blue tint indicates greater sea ice concentration after a cyclone; the dots indicate areas where the change is different than random variations in sea ice conditions.

Credit: E. Schreiber, University of Colorado Boulder
High-resolution image

A recently-published study by University of Colorado Boulder doctoral candidate Erika Schreiber considered the effects of the passage of Arctic low pressure systems (extratropical cyclones) on sea ice concentration. In earlier studies, a range of effects has been attributed to storms. Some point to increasing sea ice concentration locally, while others argue that winds associated with cyclones disperse the ice. Schreiber’s research shows that, overall, the thermodynamic effects (cold air, snow, and cloudiness) associated with storms increase sea ice concentration in impacted areas days after the storm hit (Figure 6). In warm months, cyclones slow down melt, while in cold months they tend to speed up freezing. The effects are greatest in summer and autumn, when the ice pack is already changing rapidly, but do still occur along the ice margin in spring and winter. The result has implications for short- and medium-term forecasting of sea ice conditions.

Further reading

Schreiber, E. A. P. and M. C. Serreze. 2020. Impacts of synoptic-scale cyclones on Arctic sea ice concentration: a systematic analysis. Annals of Glaciology, 1–15. doi:10.1017/aog.2020.23.

Polar sunrise

After reaching its annual maximum on March 5, Arctic sea ice extent remained stable for several days before it started clearly declining. Continuing the pattern of this past winter, the Arctic Oscillation was in a persistently positive phase. Scientists participating in the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition finally reached shore after being held at sea for three weeks from a combination of logistical challenges and COVID-19 concerns.

Overview of conditions

Figure 1. Arctic sea ice extent for XXXX 20XX was X.XX million square kilometers (X.XX million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data||Credit: National Snow and Ice Data Center|High-resolution image

Figure 1. Arctic sea ice extent for March 2020 was 14.78 million square kilometers (5.71 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

The March 2020 Arctic sea ice extent was 14.78 million square kilometers (5.71 million square miles). This was the eleventh lowest in the satellite record, 650,000 square kilometers (251,000 square miles) below the 1981 to 2020 March average and 490,000 square kilometers (189,000 square miles) above the record low March extent in 2017.

At the end of the month, extent was particularly low in the Bering Sea after a rapid retreat during the second half of the month. Ice loss was also prominent in the Sea of Okhotsk and Gulf of St. Lawrence.

Conditions in context

Figure 2. Figure 2. The graph above shows Arctic sea ice extent as of XXXX X, 20XX, along with daily ice extent data for four previous years and the record low year. 2018 to 2019 is shown in blue, 2017 to 2018 in green, 2016 to 2017 in orange, 2015 to 2016 in brown, 2014 to 2015 in purple, and 2011 to 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.||Credit: National Snow and Ice Data Center|High-resolution image

Figure 2a. The graph above shows Arctic sea ice extent as of April 1, 2020, along with daily ice extent data for four previous years and the record low year. 2019 to 2020 is shown in blue, 2018 to 2017 in green, 2017 to 2016 in orange, 2016 to 2017 in brown, 2015 to 2016 in purple, and 2011 to 2012 in dashed red. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for March 1 to 30, 2020. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.||Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division| High-resolution image

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for March 1 to 30, 2020. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

The plot shows the values of the Arctic Oscillation Index, which is a weather phenomenon indicating the state of the atmospheric circulation over the Arctic. ||Credit: NCEP/NOAA | High-resolution image

Figure 2c. The plot shows the values of the Arctic Oscillation Index, which is a weather phenomenon indicating the state of the atmospheric circulation over the Arctic.

Credit: National Centers for Environmental Prediction/National Oceanic and Atmospheric Administration
High-resolution image

After reaching its maximum on March 5, extent declined slowly until March 19 after which it declined rapidly for the next ten days. The decrease was most pronounced in the Bering Sea, where extent went from slightly above average at the time of the maximum to well below average by the end of the month. Overall, sea ice extent decreased 750,000 square kilometers (290,000 square miles) between March 5 and March 31, with 590,000 square kilometers (228,000 square miles) of this decrease occurring between March 19 and March 29.

Air temperatures in March at the 925 hPa level (approximately 2,500 feet above the surface) over the Arctic Ocean were near average to slightly below average (Figure 2b). Temperatures over the central Arctic Ocean were 2 to 3 degrees Celsius (4 to 5 degrees Fahrenheit) below average, but as much as 6 degrees Celsius (11 degrees Fahrenheit) below average in the region around Svalbard. Only in the Sea of Okhotsk and the Bering Sea were temperatures above average (2 to 5 degrees Celsius or 4 to 9 degrees Fahrenheit). Sea level pressure was very low over the Arctic Ocean, reflecting the strong positive mode of the Arctic Oscillation (AO) that has persisted through most of the past winter (Figure 2c). The AO index became more neutral by the end of March but has been positive through all of 2020 so far.

March 2020 compared to previous years

Figure 3. Monthly XXXXX ice extent for 1979 to 201X shows a decline of X.X percent per decade.||Credit: National Snow and Ice Data Center| High-resolution image

Figure 3. Monthly March ice extent for 1979 to 2020 shows a decline of 2.6 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

Through 2020, the linear rate of decline for March extent is 2.6 percent per decade. This corresponds to a trend of 40,500 square kilometers (15,600 square miles) per year, which is roughly the size of Massachusetts and Connecticut combined. Over the 42-year satellite record, the Arctic has lost about 1.66 million square kilometers (641,000 square miles) of sea ice in March, based on the difference in linear trend values in 2020 and 1979. This is comparable in size to the size of the state of Alaska.

Thickness data from CryoSat-2

Figure 4b. This maps shows sea ice thickness for February 22, 2020. Light green depicts ice under a meter thin; dark blue depicts ice up to 4 meters thick. NASA Goddard (Kurtz and Harbeck, 2017) produces the thickness product and the NASA NSIDC Distributed Active Archive Center distributes it.||Credit: W. Meier, NSIDC | High-resolution image

Figure 4a. This maps shows sea ice thickness for February 22, 2020. Light green depicts ice under a meter thin; dark blue depicts ice up to 4 meters thick. NASA Goddard (Kurtz and Harbeck, 2017) produces the thickness product and the NASA NSIDC Distributed Active Archive Center distributes it.

Credit: W. Meier, NSIDC
High-resolution image

Figure 4a. This graph shows sea ice volume from European Space Agency (ESA) CryoSat-2 thickness for February 22, 2020. Ice volume is tracked between mid-October and mid-May. Ice volume is estimated from the NASA CryoSat-2 Sea Ice Elevation, Freeboard, and Thickness, Version 1 product (Kurtz and Harbeck, 2017). ||Credit: B. Raup, NSIDC | High-resolution image

Figure 4b. This graph shows sea ice volume from European Space Agency (ESA) CryoSat-2 satellite from October 20, 2010 through February 22, 2020. Ice volume is tracked between mid-October and mid-May. Ice volume is estimated from the NASA CryoSat-2 Sea Ice Elevation, Freeboard, and Thickness, Version 1 product (Kurtz and Harbeck, 2017).

Credit: B. Raup, NSIDC
High-resolution image

NASA Goddard produces sea ice thickness estimates based on data from the European Space Agency CryoSat-2 radar altimeter. The altimeter sends out radar pulses that reflect from the surface back to the satellite. By measuring the time it takes for the pulses to transmit to the surface and reflect back to the satellite, the elevation of the surface can be estimated. For sea ice, this corresponds to the freeboard—the part of the ice above the waterline. Using information about snow depth, and snow and sea ice density, total thickness can be estimated.

Maps of ice thickness are produced daily with about a 40-day lag, necessary to carefully process the data (Figure 4a). CryoSat-2 has been operating since 2010, providing nearly a decade long record of sea ice thickness and sea ice volume. Ice volume roughly triples from mid-October to mid-May due to the increase in extent and thickness through the winter (Figure 4b). However, the radar altimeter cannot obtain reliable estimates over sea during summer as surface melt contaminates the radar signal.

The future of pollutant transport via sea ice drift

Figure 5. . Map of exclusive economic zones (EEZs) within the Arctic: Canada (purple), Greenland (orange), Iceland (green), Norway (turquoise), Russia (light blue), and USA (dark blue). As sea ice reduces there will be less opportunity for ice to drift from one EEZ to another, which has implications for the potential spread of pollutants. Image from DeRepentigny et al. (2020) courtesy American Geophysical Union (CC BY-NC-ND 4.0).

Figure 5. This map show the exclusive economic zones (EEZs) within the Arctic: Canada (purple), Greenland (orange), Iceland (green), Norway (turquoise), Russia (light blue), and USA (dark blue). As sea ice reduces there will be more opportunity for ice to drift from one EEZ to another, which has implications for the potential spread of pollutants.

Credit: DeRepentigny et al., 2020
High-resolution image

As the Arctic sea ice cover becomes less extensive, thinner, and more mobile, ice floes are able to travel longer distances in a shorter amount of time. Patricia DeRepentigny, a PhD candidate at the University of Colorado, led a study that uses the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) to assess how the transport of sea ice across the Arctic Ocean will likely change throughout the twenty-first century. She performed CESM experiments with two different greenhouse gas emissions scenarios to assess the impact of societal choices. The area of sea ice exchanged between the different countries bordering the Arctic more than triples between the end of the twentieth century and the middle of the twenty-first century, with the Central Arctic Ocean joining the Russian coast as a major ice exporter. At the same time, the sea ice that drifts over long distances is predicted to diminish in favor of shorter drifts between neighboring Arctic countries. By the end of the twenty-first century, there are large differences between the two CESM experiments: in the high-emissions scenario, the proportion of sea ice leaving each region starts to reduce, whereas it continues to increase in the low-emissions scenario. This is because the Arctic Ocean goes completely ice free every summer under the high-emissions scenario, allowing ice floes less than a year to travel. The study raises concerns regarding risks associated with contaminants transported on distributed ice floes, especially in light of increased shipping and offshore development in the Arctic.

The return: MOSAiC update

Figure 6a. The German icebreaker Polarstern drifts with the sea ice, where it has been lodged since September 2019 as part of the MOSAiC project. As the project heads into spring, a perpetual sunrise eclipses the horizon. ||Credit: J. Stroeve, NSIDC | High-resolution image

Figure 6a. The German icebreaker Polarstern drifts with the sea ice, where it has been lodged since September 2019 as part of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) project. As the project heads into spring, a perpetual sunrise eclipses the horizon.

Credit: J. Stroeve, NSIDC
High-resolution image

Figure 6b. The radiometer instrument is strapped to its tow-sled to measure snow depth. || Credit: J. Stroeve, NSIDC | High-resolution image

Figure 6b. The Ka/Ku radar is strapped to a tow-sled, looking straight down to simulate what a satellite altimeter would see when towed along the transects. This instrument was built by ProSensing specifically for the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition.

Credit: J. Stroeve, NSIDC
High-resolution image

After delays related to logistical challenges and the COVID-19 pandemic, the science crew of the second leg of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC), including NSIDC scientist Julienne Stroeve, is finally back on shore. Stroeve and colleagues embarked on a supporting icebreaker on November 27, reaching the German Polarstern icebreaker—the basecamp for MOSAiC—on December 13. On leg two, Stroeve’s research focused on remote sensing of sea ice using various instruments, including a dual frequency Ka/Ku band polarimetric radar. This instrument was deployed at the remote sensing site, which consisted of a refrozen melt pond, and hourly measurements were collected. At the beginning of the instrument set up in October, the ice floe was about 80 centimeters (2.6 feet) thick but grew to nearly 2 meters (6.6 feet) thick by the end of February. The instrument was also towed along several kilometer-long transects using a sled that fixed the instrument position in a nadir (“stare”) mode to simulate returns seen by a radar altimeter (Figure 6b). The radar backscatter data will be useful to better understand how snowpack properties influence radar penetration and if a satellite radar altimeter mission using Ka- and Ku-bands can allow scientists to simultaneously map snow depth and ice thickness.

An update from the south

Figure 7: This map compares sea ice extent in Antarctica on March 1 and March 31, 2020. ||Credit: National Snow and Ice Data Center | High-resolution image

Figure 7. This map compares sea ice extent in Antarctica on March 1 and March 31, 2020.

Credit: National Snow and Ice Data Center
High-resolution image

In the Antarctic, sea ice extent has increased sharply since early March and at the end of the month is near the 1981 to 2010 average. This ends a 41-month period of below-average monthly sea ice extent. Ice growth has occurred all along the Antarctic coast, but most notably in the Ross Sea and eastern Weddell Sea regions. Air temperatures over most coastal areas for the month were near average within 1 degree Celsius (2 degrees Fahrenheit) of the 1981 to 2010 average, slightly above average near the southern Peninsula area at 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit), and notably below average in the Wilkes Land area of the ice sheet at 5 to 7 degrees Celsius (9 to 13 degrees Fahrenheit). The atmospheric circulation patterns were somewhat unusual, dominated by extensive low pressure in the Amundsen Sea and Ross Sea region, and another area of low pressure north of Dronning Maud Land. Offshore winds guided by these low-pressure areas correlate with the two areas of more rapid ice growth. Consistent with the strong low pressure in the Ross and Amundsen Seas, the Southern Annular Mode index was positive for the month.

References

DeRepentigny, P., A. Jahn, L. B. Tremblay, R. Newton, and S. Pfirman. 2020. Increased transnational sea ice transport between neighboring Arctic states in the 21st century. Earth’s Future, 8, e2019EF001284, doi.org:10.1029/2019EF001284.

Kurtz, N. and J. Harbeck. 2017. CryoSat-2 Level-4 Sea Ice Elevation, Freeboard, and Thickness, Version 1. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi:10.5067/96JO0KIFDAS8.