Sea ice extent increased at a faster than average pace through November and by the end of the month, extent was just within the interdecile range. Extent was above average in the Bering Sea, but Hudson Bay remained unusually ice free through the month.

Overview of conditions

Figure 1. Arctic sea ice extent for November 2021 was 9.77 million square kilometers (3.77 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

The November 2021 monthly average extent was 9.77 million square kilometers (3.77 million square miles), which ranked tenth lowest in the satellite record. The 2021 extent was 930,000 square kilometers (359,000 square miles) below the 1981 to 2010 long-term average. Extent was higher than average in the Bering Sea, but is extremely low in Hudson Bay.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of December 1 2021, along with daily ice extent data for four previous years and the record low year. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 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

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for November 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 Laboratory
High-resolution image

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

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

Air temperatures at the 925 millibar level (about 2,500 feet above the surface) were well above average north of the Canadian Archipelago, by as much as 6 degrees Celsius (11 degrees Fahrenheit). Conversely, temperatures over southwest Alaska and the eastern sector of the Bering Sea were as much as 6 degrees Celsius (11 degrees Fahrenheit) below average (Figure 2b).

The sea level pressure pattern for November featured widespread low pressure over the Atlantic side of the Arctic and extending into the Barents and Kara Seas, paired with a moderately strong Beaufort Sea High (Figure 2c). Strong low pressure over the Gulf of Alaska resulted in a circulation pattern in the eastern Bering Sea that brought cold air from the north. This pattern was favorable for sea ice growth, and can explain the above average ice extent in the region.

November 2021 compared to previous years

Figure 3. Monthly November ice extent for 1979 to 2021 shows a decline of 5.0 percent per decade.

Credit: National Snow and Ice Data Center
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The downward linear trend in November sea ice extent over the 43-year satellite record is 53,300 square kilometers (20,600 square miles) per year, or 5 percent per decade relative to the 1981 to 2010 average. Also based on the linear trend, since 1979, November has lost 2.2 million square kilometers (849,000 square miles). This is equivalent to about three times the size of Texas.

No freeze in Hudson Bay

Figure 4. This map of Hudson Bay shows sea ice extent as of November 30, 2021. The US National Ice Center/NSIDC Multisensor Analyzed Sea Ice Extent (MASIE) product provides the data for this map.

Credit: US National Ice Center and National Snow and Ice Data Center
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Typically, Hudson Bay begins freezing up by the beginning of November. By the end of the month, the northern half of the bay is usually completely iced over. However, as of the end of November 2021, only the far north has frozen over; the rest of the bay is ice free except for a narrow band of ice along the western coastline. According to the NSIDC Sea Ice Index, this is the second lowest extent in Hudson Bay at this time, above only 2010.

The USNIC/NSIDC Multisensor Analyzed Sea Ice Extent (MASIE) product provides a more detailed view (Figure 4). It also shows ice only in the far north of the region and along the western coast. The lack of ice has potential ramifications for polar bears in the region that must wait for the bay to freeze over to hunt. While the lack of ice in Hudson Bay at this time of year is extreme, the bay will eventually freeze over through the coming winter.

Frozen in the Northern Sea Route

An early freeze of sea-ice has led to logistical chaos on the Northern Sea Route.

Credit: Rosatomflot via The Independent Barents Observer
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The story on the opposite side of the Arctic stands in sharp contrast to Hudson Bay. Ice formed along the eastern part of the Siberian coast relatively early, at least compared to recent years. This caught ships transiting through the Northern Sea Route by surprise. Several have become frozen in and are awaiting icebreakers to free them. In addition to the surprisingly early freeze up, winds also pushed ice together into ridges (piled up ice) that are much more difficult to navigate through. Supplies to northern Siberian cities have been delayed.

Springtime in the South

Figure 5. This maps shows Antarctic sea ice concentration on December 1, 2021. The yellow area shows missing data. 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
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In the Antarctic, ice extent declined relatively rapidly during the austral spring. By the end of November, extent was the second lowest in the satellite record, bested only by the extreme low recorded in 2016. Extent was particularly low in the Bellingshausen and Weddell Seas as well as in the Indian Ocean sector, north of Enderby Land. The Maud Rise polynya has once again formed. This feature was not seen for many years after the 1970s, but has started to form in recent years.

ASINA team member Ted Scambos is currently on his way to Antarctica for field work.

Reference

US National Ice Center and National Snow and Ice Data Center. Compiled by F. Fetterer, M. Savoie, S. Helfrich, and P. Clemente-Colón. 2010, updated daily. Multisensor Analyzed Sea Ice Extent – Northern Hemisphere (MASIE-NH), Version 1. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi:10.7265/N5GT5K3K.

The sea ice extent has been quickly growing, and by the end of October, ice covered most of the Arctic Ocean. Overall, the ice extent remained below average for this time of year in the Barents and Kara Seas, as well as within northern Baffin Bay and the East Greenland Sea.

Overview of conditions

Figure 1. Arctic sea ice extent for October 2021 was 6.77 million square kilometers (2.61 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 monthly average extent for October 2021 was 6.77 million square kilometers (2.61 million square miles). This ranked eighth lowest in the long-term satellite data record, tied with 2017. It was 1.44 million square kilometers (556,000 square miles) greater than the record low of 5.33 million square kilometers (2.06 million square miles) recorded in 2020, and 1.58 million square kilometers (610,000 square miles) below the 1981 to 2010 long-term average. Ice growth was robust across the Eurasian side of the Arctic, including the East Greenland Sea, but there was little expansion of ice southwards within the eastern Beaufort Sea.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of November 1, 2021, along with daily ice extent data for four previous years and the record low year. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 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

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for October 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 Laboratory
High-resolution image

Figure 2c. This plot shows the departure from average sea level pressure in the Arctic at the 925 hPa level, in degrees Celsius, for October 2021. Yellows and reds indicate higher than average air pressures; blues and purples indicate lower than average air pressures.

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

As of October 31, sea ice extent is tracking higher than any year since 2015, as well as higher than observed in 2007, 2011, and 2012 (Figure 2a).

Average monthly air temperatures were well below freezing across much of the Arctic Ocean in October, the exceptions being along the coastal regions of the Barents Sea and across the North Atlantic region. Nevertheless, air temperatures at the 925 hPa level (about 2,500 feet above the surface) were above the 1981 to 2010 average, up to 8 degrees Celsius (14 degrees Fahrenheit) above average north of Greenland and the Canadian Archipelago (Figure 2b).

Above average temperatures were related in part to unusually low sea level pressure extending from Siberia across to Alaska, coupled with above average sea level pressure northeast of Greenland extending down towards Baffin Bay. In particular, the strong sea level pressure gradient between the low and high sea level pressure near the Canadian Arctic Archipelago helped to funnel winds from the south over Baffin Bay, which is still ice-free, northwards towards the central Arctic Ocean (Figure 2c).

Overall, ice extent increased by 99,700 square kilometers (38,500 square miles) per day during the month of October. This rate of increase was larger than the 1981 to 2010 average of 89,200 square kilometers (34,400 square miles) per day.

October 2021 compared to previous years

Figure 3. Monthly October ice extent for 1979 to 2021 shows a decline of 9.8 percent per decade.

Credit: National Snow and Ice Data Center
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The downward linear trend in October sea ice extent over the satellite record is 82,100 square kilometers (31,700 square miles) per year, or 9.8 percent per decade relative to the 1981 to 2010 average (Figure 3). While percentagewise, the overall long-term trend is largest in September, the actual amount (based on the linear trend) of ice lost per year is larger in October: 82,100 square kilometers (31,700 square miles) versus 81,200 square kilometers (31,400 square miles) in September.

Overall, since 1979, October has lost 3.45 million square kilometers (1.33 million square miles) of ice, based on the linear trend. This is equivalent to twice the size of the state of Alaska.

Last ice refuge continues to show signs of weakness

Figure 4. This NASA Moderate Resolution Imaging Spectroradiometer (MODIS) image from May 20, 2020, shows a large polynya, or open water region, that formed north of Ellesmere Island in Canada.

Credit: NASA
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In February 2018, a large polynya (open water region) formed northeast of Greenland. In May 2020, another large polynya formed north of Ellesmere Island (Figure 4). This region contains the oldest and thickest ice in the Arctic Ocean, a result of the Beaufort Gyre circulation, which pushes the ice towards the coasts of Greenland and the Canadian Archipelago, where it compresses along the coasts. However, during the polynya formation events, winds helped to push the ice away from the shores, leaving open water for several days. While such events have occurred before, they are rare. However, as the ice cover continues to thin, the ice will become more vulnerable to disruption by winds that can form such polynyas and seaward ridging and rafting of the ice.

Seeing daylight in the Antarctic

Figure 5. The graph above shows Antarctic sea ice extent as of November 1, 2021, along with daily ice extent data for four previous years and the record low year. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 in magenta, 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

Since the Antarctic maximum sea ice extent was reached on September 1, 2021, ice extent has been in a steep decline. Extent went from being above the interdecile (ninetieth percentile) range to being below the tenth percentile for most of October. As a result, sea ice extent in the Antarctic is currently tracking as the third lowest, behind only 2016 and 1986. Sea ice extent is particularly low along the western side of the Antarctic Peninsula, including the northern Weddell Sea and the central Indian Ocean sector. Air temperatures at the 925 hPa level (about 2,500 feet above the surface) were up to 6 degrees Celsius (11 degrees Fahrenheit) above average within the Weddell Sea. A strong low pressure feature in the Amundsen Sea and above average air pressure in the area south of Australia drove winds that led to the pattern of sea ice extent around the continent.

References

Moore, G. W. K., S. E. L. Howell, and M. Brady. 2021. First observations of a transient polynya in the Last Ice Area north of Ellesmere Island. Geophysical Research Letters. doi: 10.1029/2021GL095099

The summer melt season has come to a modest end. The summer of 2021 was relatively cool compared to the most recent years and September extent was the highest since 2014. It was nevertheless an eventful summer, with many twists and turns.

Overview of conditions

Figure 1a. Arctic sea ice extent for September 2021 was 4.92 million square kilometers (1.90 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 1b. The map above compares the annual minimum set on September 16, 2021, with October 3, 2021. Light blue shading indicates the region where ice occurred on both dates, while white and medium blue areas show ice cover unique to September 16, 2021 and October 3, 2021, respectively. Sea Ice Index data. About the data

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

Arctic sea ice extent for September averaged 4.92 million square kilometers (1.90 million square miles), the twelfth lowest in the 43-year satellite record. This is 1.35 million square kilometers (521,000 square miles) above the record low set in September 2012, and 1.49 million square kilometers (575,000 square miles) below the 1981 to 2010 average. The last 15 years (2007 to 2021) have had the 15 lowest September extents in the record.

The annual minimum extent occurred on September 16 and was the twelfth lowest minimum in the satellite record. Afterwards, ice extent increased primarily in the Beaufort Sea region, with the large irregular open water region that existed in mid-September filling in with ice (Figure 1b). The ice edge also expanded in the East Siberian Sea. The East Greenland Sea has been largely ice free for much of the summer, but sea ice is now expanding southward.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of October 5, 2021, along with daily ice extent data for four previous years and the record low year. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 in magenta, 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. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for September 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 Laboratory
High-resolution image

After the minimum set on September 16, extent began rising fairly rapidly as the scattered open water areas in the Beaufort and Chukchi Seas began to fill in (Figure 2a). Ocean temperatures remained low in this region because of the late ice retreat that limited the amount of solar insolation absorbed by the ocean. The cooler ocean allowed a quick freeze up as air temperatures dropped below freezing. Overall, extent increased 430,000 square kilometers (166,000 square miles) between the 16 and the end of the month, about the same as the increase for the 1981 to 2010 average.

During September, air temperatures at the 925 mb (about 2,500 feet above the surface) were higher than average over most of the Arctic Ocean (Figure 2b). Temperatures were up to 4 degrees Celsius (7 degrees Fahrenheit) above average in the East Greenland Sea, likely reflecting the unusual lack of ice in the region, allowing ocean heat to warm the lower atmosphere. The one notable cold region was in the East Siberian Sea; temperatures in the last two weeks of September were 3 to 4 degrees Celsius (5 to 7 degrees Fahrenheit) below average.

September 2021 compared to previous years

Figure 3. Monthly September ice extent for 1979 to 2021 shows a decline of 12.7 percent per decade.

Credit: National Snow and Ice Data Center
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The downward linear trend in September sea ice extent over the satellite records is 81,200 square kilometers (31,400 square miles) per year, or 12.7 percent per decade relative to the 1981 to 2010 average (Figure 3). September marks the month of the largest linear trend in ice extent, both in absolute terms and percentage loss. Overall, since 1979, September has lost 3.49 million square kilometers (1.35 million square miles) of ice, based on the linear trend values. This is equivalent to about twice the size of Alaska.

There was little net change in extent over the month of September—extent declined during the first half of the month and then increased in the second half. This year, extent was 5.17 million square kilometers (2.00 million square miles) on September 1 and 5.15 million square kilometers (1.99 million square miles) on September 30.

Antarctica’s unusual sea ice maximum

Figure 4a. The graph above shows Antarctic sea ice extent as of October 3, 2021, along with daily ice extent data for three previous years including the record low year. 2021 is shown in blue, 2016 in green, 2014 in black, and 2017 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
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Figure 4b. This map compares Antarctic sea ice extent for September 1, 2021, with October 3, 2021. Light blue shading indicates the region where ice occurred on both dates, while white and medium blue areas show ice cover unique to September 1, 2021 and October 3, 2021, respectively. Sea Ice Index data. About the data

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

As noted in our earlier posts, Antarctic sea ice extent has been above average for the past several months, culminating in late August when extent was the fifth highest in the satellite record (Figure 4a). However, since peaking on September 1, sea ice extent has declined steeply. At the beginning of October, Antarctic sea ice extent was nearly 600,000 square kilometers (232,000 square miles) lower than the beginning of the month (Figure 4a). The maximum observed on September 1 was 18.75 million square kilometers (7.24 million square miles) is very likely to be the annual maximum for the year, marking the second-earliest seasonal maximum in the 43-year satellite record. Sea ice loss since September 1 has been greatest in the Ross Sea, Bellingshausen Sea, and Weddell Sea sectors (Figure 4b).

For the interior of the Antarctic continent, specifically the region near the South Pole, the winter of 2021 was among the coldest on record. At the National Science Foundation’s Amundsen-Scott South Pole Station, temperatures for June, July, and August were 3.4 degrees Celsius (6.1 degrees Fahrenheit) lower than the 1981-to-2010 average at -62.9 degrees Celsius (-81.2 degrees Fahrenheit). This is the second coldest winter (June-July-August months) on record, behind only 2004 in the 60-year weather record at the South Pole Station. For the polar darkness period, from April through September, the average temperature was -60.9 degrees Celsius (-77.6 degrees Fahrenheit), a record for those months. The unusual cold was attributed to two extended periods of stronger-than-average encircling winds around the continent, which tend to isolate the ice sheet from warmer conditions. A strong upper-atmosphere polar vortex was observed as well, leading to a significant ozone hole. The ozone hole appears to have peaked as of this post, with initial measurements reporting that it is in the upper quartile (top 25 percent) of ozone reduction events since 1979.

2021 Arctic summer in review

Figure 5a. This graph shows daily sea ice extent in the Laptev Sea for May through September for 2021 (red) and the 1979 to 2020 minimum (dashed gray) as compared to the 1981 to 2010 average. At two periods in time the Laptev sea ice extent in 2021 fell to the lowest extent in the satellite record, as marked in red “record low.”

Credit: W. Meier, National Snow and Ice Data Center
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Figure 5b. This plot shows average sea level pressure in the Arctic in millibars for 2019, 2020, 2021, and the 1981 to 2010 average. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory
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Figure 5c. This graph shows the months of June, July, and August (JJA) at 925 mb air temperature averaged over 70 to 90 degrees N latitude for 1979 to 2021.

Credit: National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis
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Figure 5d. These maps show sea surface temperatures (SST) in mid-September for (a) 2021, (b) 2020, (c) 2019, and (d) 2018. SST data from are from the National Ocean and Atmospheric Administration (NOAA). Circles indicate buoy data points with SST or sea ice concentration.

Credit: Upper layer Temperature of the Polar Oceans (UpTempO), University of Washington
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Figure 5e. The top maps show sea ice age at the week of the minimum for 1984, on the left, and 2021, on the right. The bottom time series graph shows the total extent of age categories for 1984 to 2021, within the Arctic Ocean Domain (inset).

Credit: Tschudi et al., 2019a and Tschudi et al., 2019b
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The spring and summer of 2021 were notable for the extremely early melt and retreat of ice in the Laptev Sea, resulting in record low June sea ice extent in that region and much lower extent compared to average throughout the summer (Figure 5a). By contrast, sea ice retreat within the Beaufort and Chukchi Seas was slow and the ice edge remained near its long-term average position throughout summer. At least in part, this reflects the unusually strong transport of thick, old ice into the region during winter; thicker ice is more resistant to melting out in summer. Another interesting feature was the lack of summer ice in the East Greenland Sea. Transport of ice through Fram Strait southward generally feeds a tongue of ice along the eastern coast of Greenland through summer. The lack of summer ice this year can be tied to wind patterns inhibiting this southward flow of ice. Thinner ice encountering warm Atlantic waters may have also played a role.

The summer of 2021 was dominated by low sea level pressure over the Arctic Ocean and a lack of a strong Beaufort Gyre circulation (Figure 5b). Cyclone activity over the central Arctic Ocean tends to peak in summer, with cyclones forming over the Eurasian continent migrating into the region and cyclogenesis (cyclone formation) over the Arctic Ocean itself. However, the pattern is quite variable. While the summer of 2021 was characterized by frequent cyclone activity, other summers, like 2019 and 2020, had few cyclones in that region where high pressure prevailed (Figure 5b). Cyclones found over the central Arctic Ocean are of a type known as “cold cored,” which helps to account for the summer of 2021 being fairly cool (Figure 5c).

The ocean surface also remained relatively cool during summer 2021. Sea surface temperatures (SSTs) at summer’s end were lower than the three previous years, based on buoys and the National Oceanic and Atmospheric Administration satellite data (Figure 5d). The summer of 2021 had widespread areas of near-freezing SSTs near the ice edge; this is indicative of late season ice melt cooling the surface and little incoming solar radiation. Low SSTs enable rapid freeze up, as is occurring in those regions. Also, the area with SSTs greater than 5 degrees Celsius (9 degrees Fahrenheit), is much smaller and widespread than in recent years.

Despite September total ice extent being high compared to recent years, the amount of multiyear ice as assessed from ice age (Figure 5e) reached a near-record low, with an extent of only 1.29 million square kilometers (498,000 square miles), just slightly above the value of 1.27 million square kilometers (490,000 square miles) at the end of the 2012 melt season.

IceBird: Summer sea ice thickness north of Greenland and Fram Strait

Figure 6. This graph shows average, in red, and modal, in blue, sea ice thickness from the IceBird campaigns between 2001 and 2021. The average thickness is the average of all estimates; the modal thickness is the most frequently observed thickness estimate.

Credit: Belter et al. 2021
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In August 2021, the IceBird Summer campaign continued its observations of sea ice thickness north of Greenland and within northern Fram Strait by means of airborne electromagnetic sounding. Our colleagues J. Belter, T. Krumpen, S. Hendricks, and C. Haas at the Alfred Wegener Institute provided a summary of the campaign. The observed average sea ice thickness of 1.7 meters (5.6 feet) was among the lowest observed since 2001 (Figure 6). Ice motion tracking reveals that the sea ice in this area was originally first-year ice that formed in the shallow shelf in the central Laptev Sea. It was then transported across the Arctic Ocean via the Transpolar Drift Stream. Near the campaign’s base at Station Nord, the reoccurrence of the Wandel Sea polynya led to enhanced melting once the winds had dispersed the ice north.

Nansen Legacy: The northern Barents Sea before and during the 2021 melt season

Figure 7a. This graph shows sea ice extent in the Barents Sea from the Multisensor Analyzed Sea Ice Extent – Northern Hemisphere (MASIE-NH) product, with the periods of the four cruises highlighted in color.

Credit: Norwegian Polar Institute
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Figure 7b. Sea smoke in leads in between sea ice northeast of Svalbard in March 2021, during a Nansen Legacy research expedition with RV Kronprins Haakon, illustrating the heat exchange between the cold atmosphere and relatively warmer ocean. 

Credit: Sebastian Gerland, Norwegian Polar Institute
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During March to September 2021 a series of interdisciplinary research expeditions to the northern Barents Sea were conducted as part of the Norwegian “Nansen Legacy” project. A dedicated sea ice research team worked alongside researchers focused on ocean and ecosystem dynamics, with the aim of understanding the northern Barents Sea ocean, ice, and ecosystem interactions over the period from the regional sea ice maximum to seasonally ice-free conditions (Figure 7a). Our colleagues D. Divine, S. Gerland, A. Steer, and S. Lind at the Norwegian Polar Institute in Tromsø, Norway, provided a summary of the expeditions.

Observations during the voyages revealed a highly dynamic sea ice cover in the area. In March, the northern Barents Sea was covered with mainly level 0.4-to-0.6-meters (1.3-to-2.0-feet) thick sea ice, locally formed sea ice with a tendency towards a greater fraction of ridged ice north of Svalbard. This type of ice persisted in the central Barents Sea through April and May. Long-lasting, stable cold conditions in February to mid-March promoted the formation of large ice floes—often more than 1 square kilometer (0.39 square miles). This relatively thin ice cover experienced a rapid transformation during a single storm event from March 22 to 24, 2021, breaking into floes ranging from 20 to 100 meters (66 to 328 feet) length. At the shelf-break north of the Barents Sea in March 2021, the team observed strong heat losses from the ocean surface, seen as sea smoke (Figure 7b). Measurements also revealed upward oceanic heat fluxes from the deeper Atlantic layer, situated below about 100 meters (328 feet) depth. This likely limited local sea ice production in this region. The relatively warm water in the upper 100 meter (328 feet) likely prevented the ice from further thickening in this region, despite continuous cold atmospheric conditions in the area with air temperatures below -20 degrees Celsius (-4 degrees Fahrenheit), favorable for ice growth.

From May through July, the area northeast of Svalbard was dominated by 1.0 to 1.5 meters (3.3 to 4.9 feet) thick first-year ice that originated in the central Arctic Ocean. In July, sea ice was present only in the very north end of the research area, near the boundary with the Nansen Basin. By August and September, this part of the Barents Sea was ice free.

Acknowledgements

Thanks to Matthew Lazzara of the Antarctic Meteorological Research and Data Center at the University of Wisconsin-Madison, and to Kyle Clem of Victoria University in Wellington, New Zealand.

Further reading

Belter, H. J., T. Krumpen, L. V. Albedyll, T. A. Alekseeva, G. Birnbaum, S. V. Frolov, S. Hendricks, A. Herber, I. Polyakov, I. Raphael, R. Ricker, S. S. Serovetnikov, M. Webster, and C. Haas. 2021. Interannual variability in Transpolar Drift summer sea ice thickness and potential impact of Atlantification. The Cryosphere, 15, 6, 2575-2591, doi:10.5194/tc-15-2575-2021.

Krumpen, T., H. J. Belter, A. Boetius, et al. 2019. Arctic warming interrupts the Transpolar Drift and affects long-range transport of sea ice and ice-rafted matter. Scientific Reports 9, 5459, doi:10.1038/s41598-019-41456-y.

Mallett, R. D. C., J. C. Stroeve, S. B. Cornish, et al. 2021. Record winter winds in 2020/21 drove exceptional Arctic sea ice transport. Communications Earth & Environment 2, 149, doi:10.1038/s43247-021-00221-8

Erratum

On October 13, NSIDC scientists clarified the wording regarding the coldest winter on record for Antarctica: For the interior of the Antarctic continent, specifically the region near the South Pole, the winter of 2021 was among the coldest on record.

On September 16, Arctic sea ice likely reached its annual minimum extent of 4.72 million square kilometers (1.82 million square miles). The 2021 minimum is the twelfth lowest in the nearly 43-year satellite record. The last 15 years are the lowest 15 sea ice extents in the satellite record. The amount of multi-year ice (ice that has survived at least one summer melt season), is one of the lowest levels in the ice age record, which began in 1984.

In the Antarctic, sea ice extent is now falling rapidly, but it is still too early to assume that the maximum has been reached. The maximum for Antarctic sea ice typically occurs in late September or early October. However, Antarctic sea ice extent is highly variable near the maximum because of storms acting to expand or compact the extended ice edge.

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 16, 2021, was 4.72 million square kilometers (1.82 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 September 16, sea ice reached its annual minimum extent of 4.72 million square kilometers (1.82 million square miles) (Figure 1). In response to the setting sun and falling temperatures, ice extent has begun rising and will continue to rise through autumn and winter. However, a shift in wind patterns or a period of late season melt could still push the ice extent lower.

The minimum extent was reached two days later than the 1981 to 2010 median minimum date of September 14. The interquartile range of minimum dates is September 11 to September 19.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent on September 16, 2021, along with several other recent years and the record minimum set in 2012. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 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

This year’s minimum set on September 16 was 1.33 million square kilometers (514,000 square miles) above the record minimum extent in the satellite era, which occurred on September 17, 2012 (Figure 2). It is also 1.50 million square kilometers (579,000 square miles) below the 1981 to 2010 average minimum extent, which is equivalent to twice the size of Texas.

In the 43-year-satellite record, 15 of the lowest minimums have all occurred in the last 15 years.

Multiyear ice extent is one of the lowest on record. First-year-ice coverage increased dramatically since last year, jumping from 1.58 million square kilometers (610,000 square miles) to 2.71 million square kilometers (1.05 million square miles). The increase in total extent from last year’s minimum to this year’s is hence comprised of first-year ice.

The overall, downward trend in the minimum extent from 1979 to 2021 is 13.0 percent per decade relative to the 1981 to 2010 average. The loss of sea ice is about 80,600 square kilometers (31,100 square miles) per year, equivalent to losing the size of the state of South Carolina or the country of Austria annually.

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

Values within 40,000 square kilometers (15,000 square miles) are considered tied. The 2020 value has changed from 3.74 to 3.82 million square kilometers (1.47 million square miles) when final analysis data updated near-real-time data. The 2020 date of minimum also changed from September 15 to September 16. 

The Arctic sea ice minimum extent is imminent. After a cool and stormy summer, this year’s minimum extent will be one of the highest of the past decade, despite the amount of multiyear ice standing at a near-record low. A large area of low ice concentration persists in the Beaufort and Chukchi Seas, and some of this may still be compacted by winds or melt away because of the remaining heat in the upper ocean.

Overview of Conditions

Figure 1a. Arctic sea ice extent for September 15, 2021 was 4.73 million square kilometers (1.83 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. This map shows Arctic sea ice concentration based on data from the Advanced Microwave Scanning Radiometer 2 (AMSR2) data as of September 14, 2021. Yellows indicate sea ice concentration of 75 percent; dark purples indicate sea ice concentration of 100 percent.

Credit: University of Bremen
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As of September 15, Arctic sea ice extent stood at 4.73 million square kilometers (1.83 million square miles), placing it tenth lowest in the satellite record for the date. While extent continues to decline as of this post, the seasonal minimum is likely to occur soon, depending on how much heat remains in the upper ocean and on winds, which can compact the ice cover or spread it out. If the winds push the ice poleward, this may further reduce the total extent. Nevertheless, the seasonal minimum extent promises to be one of the highest of the past decade—only 2013, 2014, and 2018 are currently tracking above the 2021 sea ice extent.

It has been an odd summer. While fairly cool and stormy summer conditions limited summer melt, as discussed in our earlier post, the amount of multiyear ice is at a record low, roughly one-fourth of the amount seen in the early 1980s. Ice loss the first two weeks of September primarily occurred in the Beaufort and Chukchi Seas, and to a lesser extent also surrounding Severnaya Zemlya. As seen in Advanced Microwave Scanning Radiometer 2 (AMSR-2) imagery (Figure 1b), areas of low concentration ice persist in the Beaufort and Chukchi Seas; how much of this ice melts away largely depends on ocean heat. Satellite mapping of sea surface temperatures shows much of the open ocean surrounding the low ice concentration area is already near the freezing point. By contrast, the compact, well-defined ice edge along most of the Russian side of the Arctic Ocean indicates that freezing is already underway in this area.

Conditions in context

Figure 2a. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, between September 1 to 13, 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 Laboratory
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Figure 2b. This plot shows average sea level pressure in the Arctic in millibars from September 1 to 13, 2021. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory
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Air temperatures at the 925 hPa level (about 2,500 feet above the surface) as assessed over the first 13 days of September were near average over most of the Arctic Ocean. Temperatures from 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) above average were the rule along the coasts of the Kara and Laptev Seas (Figure 2a). In sharp contrast to the persistent pattern of low pressure over the Arctic Ocean characterizing this summer, the first 13 days of September saw high average air pressure (Figure 2b).

Focus on the Northwest Passage

Figure 3. These graphs show the total sea ice area along each Northwest Passage route (y axis) by day (x axis) dating back to 1981. The top graph shows the northern route and the bottom graph shows the southern route. 

Credit: Canadian Ice Service
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Data from the Canadian Ice Service compiled by colleague Steve Howell of Environment and Climate Change Canada allows for a closer look at sea ice conditions in the Northwest Passage. While there are multiple Northwest Passage routes, most attention is focused on the southern route, known as Amundsen’s route, entered from the Pacific side through Amundsen Gulf, and the northern route entered from the Pacific side via M’Clure Strait. This wide, deeper-water route is the one that might become a viable waterway for commercial shipping in the future. As of early to mid-September, the northern deep-water route is choked with ice and will not open this year; ice conditions are quite severe compared to the past couple of decades. By contrast, there is much less ice in the southern route, approximately 30,000 square kilometers (11,600 square miles). Most of this is located on Somerset and Prince of Wales Islands. On the other side of the Arctic, the Northern Sea Route is essentially open, though some areas of ice remain near Severnaya Zemlya.

Antarctic oddities

Figure 4. Antarctic sea ice extent for September 15, 2021 was 18.64 million square kilometers (7.20 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
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Antarctic sea ice extent is approaching its seasonal maximum, which typically occurs in late September. A surge in sea ice growth or outward transport in late August in the northeastern Weddell Sea and the area north of Dronning Maud Land brought sea ice extent to the fifth-highest level for the last day of the month. Since then, losses in the areas around the tip of the Antarctic Peninsula and the northeastern Ross Sea have reduced the total ice extent, although at this time of year, ice extent can change rapidly up or down as storms play havoc with thin, low concentration ice in the extended ice edge regions. As of this post, Antarctic ice extent remains well above the long-term average.

Arctic sea ice extent declined more slowly during August 2021 than most years in the past decade, and as a result, this year’s September minimum extent will likely be among the highest since 2007. Part of the reason for this is a persistent low pressure area in the Beaufort Sea, which tends to disperse ice and keep temperatures low. A remaining question is whether a large area of low concentration ice north of Alaska will melt away. Antarctic sea ice is nearing its seasonal maximum, and the monthly mean extent for August was the fifth highest in the satellite record.

Overview of conditions

Figure 1a. The graph above shows Arctic sea ice extent as of September 1, 2021, along with daily ice extent data for four previous years and the record low year. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 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
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Figure 1b. This map shows Arctic sea ice concentration based on data from the Advanced Microwave Scanning Radiometer 2 (AMSR2) data as of August 28, 2021. Yellows indicate sea ice concentration of 75 percent, dark purples indicate sea ice concentration of 100 percent.

Credit: University of Bremen
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Figure 1c. Arctic sea ice extent for August 2021 was 5.75 million square kilometers (2.22 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
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The decline in sea ice extent during August was relatively slow but steady after a pause in ice loss around August 9. The average daily loss was 33,000 square kilometers (12,700 square miles) per day, although by the end of the month the pace of ice loss increased to 51,000 square kilometers (19,700 square miles) per day as areas within the Beaufort and Chukchi Sea started to lose more ice. The monthly average extent for August 2021 is 5.75 million square kilometers (2.22 million square miles) (Figure 1a). This is 1.03 million square kilometers (398,000 square miles) above the record low for the month set in 2012 and 1.45 million square kilometers (560,000 square miles) below the 1981 to 2010 average. The average extent for the month ranks tenth lowest in the passive microwave satellite record.

By the end of the month, large areas of the Beaufort and Chukchi Seas were covered by low concentration ice (25 to 75 percent; Figure 1b); some of this ice may yet melt away or fall below the 15 percent concentration threshold adopted for calculating ice extent. Many other areas have unusually low extent, such as Fram Strait and north of Svalbard and Franz Josef Land. As noted in our July post, open water persists north of Greenland in the Wandel Sea, an area that has rarely been open in past years. A small area of ice persists in the eastern Kara Sea (Figure 1c). At this time of year, any remaining sea ice loss is primarily driven by melt from heat absorbed in the ocean mixed layer. Compaction from northward winds may also reduce ice extent.

Conditions in context

Figure 2. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, between August 1 to 30, 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 Laboratory
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A pair of monthly-averaged high and low air pressure regions governed the weather in the high Arctic in August, centered in the northernmost Laptev and the central Beaufort Seas, respectively. These patterns created strong winds from the north over the Alaska and Bering Sea region, leading to temperatures at the 925 hPa level (approximately 2,500 feet above the surface) that were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below the 1981 to 2010 average. Warm conditions prevailed over northern Siberia; temperatures there were as much as 4 to 5 degrees Celsius (7 to 9 degrees Fahrenheit) above average. A persistent area of low pressure between Hudson Bay and Baffin Island drove winds from the south over Greenland, which were responsible for several above-average temperature events in Greenland during the month.

August 2021 compared to previous years

Figure 3. Monthly August ice extent for 1979 to 2021 shows a decline of 10.4 percent per decade.

Credit: National Snow and Ice Data Center
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The pace of ice loss for the month was much slower than in recent years but still near the average pace for the reference period of 1981 to 2010, leading to the tenth lowest August of the satellite data record. Through 2021, the linear rate of decline for monthly mean August sea ice extent is 10.4 percent per decade (Figure 3). This corresponds to 75,000 square kilometers (29,000 square miles) per year. The cumulative August ice loss over the 43-year satellite record is 3.15 million square kilometers (1.22 million square miles), based on the difference in linear trend values in 2021 and 1979. The loss of ice since 1979 in August is equivalent to about twice the size of the state of Alaska.

Buoy oh buoy

Figure 4. This graph shows data from one ice mass balance (IMB) monitoring buoy in the Chukchi Sea off the northwest coast of Alaska from April through August. The data demonstrate that bottom ice growth continued into May. Surface snow melt started in June, and by July, bottom melt began. Surface freeze-up occurred in early August while bottom melt continued through mid-August.

Credit: The Cold Regions Research and Engineering Laboratory-Dartmouth Mass Balance Buoy Program
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Ice mass balance (IMB) monitoring buoys drifting in the Arctic Ocean provide data on both surface melting and sub-surface thinning of the ice by warm ocean water. The IMB buoys include a downward-looking acoustic sounder above the ice to obtain snow depth on sea ice, temperature sensors (thermistor string) through the ice, and an upward-looking underwater acoustic sensor to measure the depth of the bottom of the ice. Putting these measurements together provides a profile of ice thickness and snow depth. Real-time data are provided, but are subject to errors. Data are later corrected to provide a high-quality climate record.

New buoys are regularly deployed to replace those that have ceased operation or have drifted out of the Arctic Ocean into the Atlantic. Data from one buoy in the Chukchi Sea off the northwest coast of Alaska is shown in Figure 4 for April through August. The data demonstrate that bottom ice growth continued into May. Surface snow melt started in June, and by July, bottom melt began in earnest. Surface freeze-up occurred in early August while bottom melt continued through mid-August. This is typical for sea ice—ocean heat continues to melt ice from the bottom (and sides) even as the surface air temperatures drop below 0 degrees Celsius (32 degrees Fahrenheit) and the top of the ice cover begins to refreeze. Overall, the ice thickness dropped from about 1.5 meters (4.9 feet) in late June to about 0.5 meters (1.6 feet). As of the end of August, thickening of the ice through bottom freezing has begun.

Northern passages

Figure 5. In this image, a Coast Guard Cutter HEALY crewmember prepares to retrieve an oceanographic research mooring in the Chukchi Sea on August 2, 2021.

Credit: Janessa Warschkow, U.S. Coast Guard
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A persistent tongue of ice has remained along the coast of the Severnya Zemlya islands. However, ice has pulled away from the Siberian coast, opening a narrow channel with little or no ice. Regardless of the ice, there have been icebreaker-supported transits through the passage through the summer. And in fact, there was even a winter transit in January through February.

The Northwest Passage (NWP) through the channels of the Canadian Archipelago still has ice blocking all routes, although concentration and extent are low in some areas. Nevertheless, this past week, the U.S. Coast Guard icebreaker, the Healy, left port in Seward, Alaska, to begin a transit through the NWP. The mission is focused on conducting scientific research, including mapping of the seafloor and providing experience in navigating through the passage.

Icebergs in the Arctic Ocean

Figure 6. These images from Planet image data show the break-up of the Milne Ice Shelf located in northern Ellesmere Island; the large pieces seen in the 31 July image are now drifting in the Beaufort, and are much thicker than multi-year sea ice. The large iceberg labeled “Arctic ‘ice Island'” is about 10 kilometers by 8 kilometers in size. The Canadian Ice Service is tracking the larger pieces.

Credit: Planet, and Chris Shuman
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The break up of the Milne Ice Shelf in June 2020 spawned several tabular icebergs that are now drifting in the Arctic Ocean (Figure 6). While not unprecedented, these ‘ice islands,’ as they were called in the 1950s, are now quite rare. The icebergs are a result of the calving retreat and demise of several small Arctic-style ice shelves (much smaller than Antarctic ice shelves) that formerly occupied several of the fjords along the northern coast of Ellesmere Island. Calving and loss of most of the Milne Ice Shelf (the setting for a work of fiction, “Deception Point” by Dan Brown) in late July 2020 marked the break-up of the last relatively intact ice shelf of a fringe of shelves that once spanned several thousand square kilometers along the Ellesmere coast. The Canadian Ice Service is tracking the bergs.

Antarctic Notes

Figure 7. The graph above shows Antarctic sea ice extent as of September 1, 2021, along with daily ice extent data for four previous years and the record high year. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 in magenta, 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
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Sea ice in the Southern Ocean surrounding Antarctica was well above the 1981 to 2010 average extent in August, rising above the ninetieth percentile of the satellite record period near the end of the month (Figure 7). As of this post, Antarctic sea ice extent is fifth highest for the day in the satellite record, a sharp contrast from the several years of persistent below-average ice extent following an abrupt change in September 2016. Antarctica’s sea ice is highly variable. Sea ice extent is slightly above average in nearly all sectors, in particular in the Weddell and Cosmonaut Seas and the region north of eastern Wilkes Land.

Further Reading

Crary, A. P., R. D. Cotell, and T. F. Sexton. 1952. Preliminary Report on Scientific Work on “Fletcher’s Ice Island.” Arctic, 5(4), pp.211-223.

Koenig, L. S., K. R. Greenaway, M. Dunbar, and G. Hattersley-Smith. 1952. Arctic ice islands. Arctic, 5(2), pp.66-103.

Brown, D. 2001. Deception Point, Simon and Schuster, 372 pp.

Sea ice loss during the first half of August stalled, though ice in the Beaufort Sea is finally starting to weaken. The Northern Sea Route appears closed off in 2021, despite being open each summer since 2008.

Overview of conditions

Figure 1a. Arctic sea ice extent for August 17, 2021 was 5.77 million square kilometers (2.23 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
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Figure 1b. This satellite image of the Arctic Ocean on August 8, 2021, shows sea ice break up in the Northern Chukchi and Beaufort Seas. The magenta outline depicts smoke from Siberian fires moving over Arctic sea ice. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra and Aqua satellites took this image.

Credit: National Snow and Ice Data Center/NASA Worldview
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As of August 17, sea ice extent stood at 5.77 million square kilometers (2.23 million square miles), tracking above the last six years, as well as 2011, 2012, and 2007 (Figure 1a). Sea ice loss stalled between August 8 and 11 before picking up the pace again. While overall decline in total ice extent has slowed, the ice cover is becoming more diffuse within the northern Chukchi Sea and the western Beaufort Sea. Further reductions are likely in that region (Figure 1b). Ice motion during the first week of August pushed sea ice in the Beaufort Sea southwards, and ice within the Chukchi Sea moved towards the East Siberian Sea. While sea ice in the western Arctic has been more extensive than in recent summers, the Laptev Sea has lost more sea ice thus far than at any other time in the satellite record. However, ice remains south of Severnaya Zemlya in the Kara Sea, blocking the Northern Sea Route. Further south in the East Greenland Sea, there is only 119,000 square kilometers (45,900 square miles) of sea ice, the second least amount of ice for this time of year following 2002.

Conditions in context

Figure 2a. Arctic sea ice extent for August 17, 2021 was 5.77 million square kilometers (2.23 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
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Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, between August 1 to 15, 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 Laboratory
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An unusually strong high-pressure system dominated over Siberia during the first half of August, extending towards the pole. This high pressure was coupled by low pressure over the Greenland Ice Sheet, promoting strong southwards ice motion from the center of the Arctic Ocean towards the North American and Siberian coastlines. Overall, air temperatures at the 925 millibar level (about 2,500 feet above the surface) were about 2 to 5 degrees Celsius (4 to 9 degrees Fahrenheit) above average over most of the Arctic Ocean, with air temperatures up to 7 degrees Celsius (13 degrees Fahrenheit) above average in the Kara Sea near Severnaya Zemlya (Figure 2b). However, while temperatures have mostly been higher than average, this is the time of the year when air temperatures start to drop as the sun dips lower on the horizon. Surface melting ends and melt ponds begin to refreeze, and thus remaining ice loss is primarily from below the sea ice, melting out the bottom from heat in the upper layer of the ocean.

Timing of melt onset is a mixed bag

Figure 3. This map shows the date of sea ice melt onset in the Arctic for the 2021 melt season compared to the 1981 to 2010 average. Shades in red depict sea ice melt up to 30 days earlier than average, while shades in blue depict melt up to 30 days later than average.

Credit: Walt Meier, NSIDC; data courtesy J. Miller, NASA Goddard
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This summer sea ice retreated early within the Laptev Sea. This was in part a result of earlier melt onset, starting more than a month earlier than the 1981 to 2010 average over parts of the Laptev Sea (Figure 3). Earlier melt onset allows for earlier loss of the winter snow cover and earlier development of melt ponds that reduce the surface reflectivity, known as albedo. A lower surface albedo enhances summer ice melt by absorbing more of the sun’s energy. Melt this summer was also unusually early within Hudson Bay and Davis Strait, on average 16 days earlier. The sea ice within the Barents Sea near Franz Josef Land and within the Kara Sea around Novaya Zemlya also started to melt more than a month earlier than average. On the other hand, melt was about two to three weeks later than average in the northern Beaufort Sea, despite earlier melt observed near the coast. This later melt onset may have helped to reduce ice loss in the region this summer. Overall, pan-Arctic melt onset was five days earlier than average.

Multiyear ice near record low

Figure 4a. This graph shows the near record-low amount of multiyear ice in the Arctic as of week 31 (July 30 to August 5) of the 2021 melt season, comparing this year to the same week in previous years of the satellite record that began in 1979. Historical data through 2020 are provided by Tschudi et al., 2019a and quicklook data for 2021 by Tschudi et al., 2019b

Credit: Robbie Mallett
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Figure 4b. This graph compares the area of multiyear ice in the Arctic between 2021, 2020, and the average from 2008 to 2019 as it melts out throughout the spring and summer. The grey lines depict previous years for general comparison. The area is calculated by adding all pixels in the Arctic that are older than one year based on the NSIDC ice age data product, and multiplying by the area per pixel of each grid cell. Historical data through 2020 are provided by Tschudi et al., 2019a and quicklook data for 2021 by Tschudi et al., 2019b

Credit: Robbie Mallett
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While the multiyear ice that advected into the Beaufort Sea has helped to stabilize ice loss in that region, multiyear ice for 2021 in the Arctic as a whole is at a record low. Based on ice age classification, the proportion of multiyear ice in the Arctic during the first week of August is at 1.6 million square kilometers (618,000 million square miles). The loss of the multiyear ice since the early 1980s started in earnest after the 2007 record low minimum sea ice cover that summer, and while there have been slight recoveries since then, it has not recovered to values seen in the 1980s, 1990s, or early 2000s. This loss of the oldest and thickest ice in the Arctic Ocean is one of the reasons why the summer sea ice extent has not recovered, even when weather conditions are favorable for ice retention.

2021 Arctic sea ice minimum forecasts

Figure 5. This figure shows Arctic sea ice extent projections for the 2021 minimum using data through August 1, 2021. The projections are based on the average loss rates for the 1981 to 2010 average in red, the 2007 to 2020 average in green, 2012 rates in dotted purple, and 2006 rates in dotted teal.

Credit: Walt Meier, National Snow and Ice Data Center
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In about three or four weeks, Arctic sea ice will reach its minimum extent for the 2021 melt season. A community effort, called the Sea Ice Prediction Network (SIPN), each years runs the Sea Ice Outlook. The Outlook is a forum for researchers and other interested people to provide a seasonal forecast of the September monthly average extent and the daily seasonal minimum. One submission by Arctic Sea Ice News & Analysis (ASINA) team member Walt Meier uses ice extent loss rates from previous years to project this year’s ice loss through the end of September (Figure 5). Projections of the minimum and September average extent are initially submitted using data through the beginning of May as starting points and updated Outlooks can be provided in following months as conditions evolve. Figure 5 shows the latest projection starting with observations on August 1, submitted to the August Outlook. The projections are based on the average loss rates for four different rates using data from previous years. The August Outlook report will be published later this month.

Further reading

Babb, D. G., J. C. Landy, D. G. Barber, and R. J. Galley. 2019. Winter sea ice export from the Beaufort Sea as a preconditioning mechanism for enhanced summer melt: A case study of 2016. Journal of Geophysical Research: Oceans, 124, 6575– 6600. doi:10.1029/2019JC015053.

Mallett, R. D. C., J. C. Stroeve, S. B. Cornish, et al. 2021. Record winter winds in 2020/21 drove exceptional Arctic sea ice transport. Communication Earth Environment 2, 149. doi:10.1038/s43247-021-00221-8.

The rate of Arctic sea ice loss was somewhat slow through much of July, lowering prospects for a new record low minimum extent in September. The month as a whole was marked by widespread low pressure over most of the Arctic Ocean, which was much more extensive than recorded for June.

Overview of conditions

Figure 1. Arctic sea ice extent for July 2021 was 7.69 million square kilometers (2.97 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
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The seasonal decline in Arctic sea ice extent was fairly rapid during the first week of July, but slowed later in the month. The monthly average extent for July 2021 was 7.69 million square kilometers (2.97 million square miles). This was 400,000 square kilometers (154,000 square miles) above the record low for the month set in 2020 and 1.78 million square kilometers (687,000 square miles) below the 1981 to 2010 average. The average extent for the month ranks fourth lowest in the passive microwave satellite record. The rapid ice loss in the Laptev Sea early in the melt season has slowed, but extent in the Laptev remains well below average. Ice extent in the Beaufort and Chukchi Seas continues to be near the long-term average.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of August 2, 2021, along with daily ice extent data for four previous years and the record low year. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 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
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Figure 2b. This plot shows average sea level pressure in the Arctic in millibars from July 1 to 31, 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
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Figure 2c. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for July 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
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At the start of July, sea ice extent was above the levels recorded in 2012, the year that ended up with the lowest September ice extent in the satellite record. However, fairly rapid ice loss during the first week of July brought extent below 2012 levels. From July 4 to July 9, the 2021 extent was the lowest in the satellite record for that time of the year. However, the loss rate then slowed, and by late July, 2021 extent was tracking above 2020, 2019, 2011, and 2007 (Figure 2a). Overall, sea ice extent decreased by 2.96 million square kilometers (1.14 million square miles) during July 2021. This corresponds to an average loss of 95,300 square kilometers (36,800 square miles) per day, slightly faster than the 1981 to 2010 July average daily loss.

Low pressure continued to dominate the Arctic Ocean region in July, becoming more widespread than in June, with some indications that the pattern was breaking down late in the month. Monthly mean sea level pressures were below 1,004 millibars over most of the Arctic Ocean (Figure 2b). The low pressure brought generally cloudy conditions. Air temperatures at the 925-millibar level (about 2,500 feet above the surface) were within about two degrees Celsius (4 degrees Fahrenheit) of average over nearly all of the Arctic Ocean (Figure 2c).

July 2021 compared to previous years

Figure 3. Monthly July ice extent for 1979 to 2021 shows a decline of 7.5 percent per decade.

Credit: National Snow and Ice Data Center
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Through 2021, the linear rate of decline for July sea ice extent is 7.5 percent per decade. This corresponds to 70,500 square kilometers (27,200 square miles) per year. The cumulative July ice loss over the 43-year satellite record is 2.96 million square kilometers (1.14 million square miles) based on the difference in linear trend values in 2021 and 1979. The loss of ice in July since 1979 is equivalent to about ten times the size of Arizona.

Northern routes across the Arctic

Figure 4. This image shows potential navigational routes through the Arctic from Mudryk et al., 2021.

Credit: Mudryk et al., 2021.
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In recent years, the trans-Arctic Northern Sea Route corridor along the Russian coast has become ice free, or nearly so, in summer, with significant commercial shipping transport (in general, with icebreaker escort). Things are looking different this year. While sea ice receded from the coast in the Laptev Sea several weeks ago, the Kara Sea coastline still remains locked in ice. In the Eastern Siberian Sea, ice remains near the coast. Whether these areas will clear of ice by the end of summer remains to be seen.

The southern route of the Northwest Passage through the channels of the Canadian Archipelago (Figure 4) is still locked in ice and seems unlikely to open in any significant way this year. However, more open summer conditions are likely in the future as temperatures continue to increase, according to a recent study in Nature Climate Change. Led by Lawrence Mudryk at Environment and Climate Change Canada, the study examines ice conditions under future warming scenarios. Based on climate model projections, the authors found that under 2 degrees Celsius (4 degrees Fahrenheit) of global warming, the target of the Paris Agreement, there is a 100 percent probability that the Northwest Passage will be navigable for at least some period by the end of summer. A caveat is that the current climate models do not necessarily capture processes that result in thick ice piling up due to winds and currents pushing ice from the Arctic Ocean into the archipelago’s channels.

Rising in the south

Figure 5. Antarctic sea ice extent for July 2021 was 16.38 million square kilometers (6.32 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
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In the Antarctic, sea ice extent increased faster than average during July, particularly in the latter half of the month. By the end of the month, extent was above the ninetieth percentile and was eighth highest in the satellite record. Extent was higher than average in the northeastern Ross Sea and in the Southern Ocean south of Africa, extending north from the coast of Dronning Maud Land and Enderby Land. Sea ice was below average in the area west of the Peninsula (the Bellingshausen Sea). Through 2021, the linear rate of increase for July sea ice extent is 0.6 percent per decade, but the uncertainty on this trend is ±0.7 percent. While this corresponds to 9,000 square kilometers (3,500 square miles) per year, the low level of certainty on the trend means that no clear pattern has yet emerged for Southern Ocean sea ice.

Further reading

Mudryk, L. R., J. Dawson, S. E. L. Howell, C. Derksen, T. A. Zagon, and M. Brady. 2021. Impact of 1, 2 and 4 °C of global warming on ship navigation in the Canadian Arctic. Nature Climate Change. doi:10.1038/s41558-021-01087-6.

As of July 13, Arctic sea ice extent was tracking just below the 2012 record and very close to 2020, the years with the lowest and second lowest (tied with 2007) minimum ice extent in the satellite record. The Laptev Sea is essentially ice free. Multiyear ice persists close to the Alaskan shoreline near Utqiaġvik (formerly Barrow), and low atmospheric pressure persists over the central Arctic Ocean, forcing a pronounced cyclonic (counterclockwise) ice motion pattern.

Overview of conditions

Figure 1. Arctic sea ice extent for July 13, 2021 was 7.95 million square kilometers (3.07 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. This map shows Arctic sea ice concentration based on data from the Advanced Microwave Scanning Radiometer 2 (AMSR2) data. Yellows indicate sea ice concentration of 75 percent, dark purples indicate sea ice concentration of 100 percent.

Credit: University of Bremen
High-resolution image

Sea ice loss continued at a brisk pace through the first two weeks of July. On July 13, Arctic sea ice extent stood at 7.95 million square kilometers (3.07 million square miles). This is 1.98 million square kilometers (764,000 square miles) below the 1981 to 2010 average. This extent is also just below the 2012 record and very close to 2020, the years with the lowest and second lowest (tied with 2007) minimum in the satellite record, respectively. By July 13, the Laptev Sea area, which began melting out much earlier than is typical for this time of year, was almost completely free of sea ice. This is broadly similar to last summer’s pattern, which holds the record for the lowest sea ice extent within the Laptev Sea at this time of year. The Northern Sea Route along the Russian coast is not yet ice free, and not really even close; as shown in the Advanced Microwave Scanning Radiometer 2 (AMSR-2) imagery from the University of Bremen (Figure 1b), a substantial area of high concentration ice persists north of the Taymyr Peninsula and west of the Severnaya Zemlaya islands (the traditional “choke point”). The Northwest Passage through the channels of the Canadian Arctic Archipelago also remains choked with ice. Continuing the pattern discussed in our previous post, sea ice remains close to the shore north of Utqiaġvik, AK.

Conditions in context

Figure 2a. This plot shows average sea level pressure in the Arctic in millibars from July 1 to 12, 2021. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

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

Figure 2b. This plot shows the direction of sea ice motion for the period between June 25 and July 1, 2021. Data are from the Quicklook Arctic Weekly EASE-Grid Sea Ice Motion Vector, a NASA NSIDC DAAC data product.

Credit: M. Tschudi, W. Meier, and Stewart/NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC)
High-resolution image

Figure 2c. This plot shows the departure from average sea level pressure in the Arctic at the 925 hPa level, in degrees Celsius, from July 1 to 12, 2021. Yellows and reds indicate higher than average air pressures; blues and purples indicate lower than average air pressures.

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

A pattern of unusually strong low pressure near the North Pole continued to dominate the average atmospheric circulation pattern for the first 12 days of July (Figure 2a). The pressure at the center of the system was up to 15 millibars below average. It is not unusual to see such a persistent pattern of low pressure set up near the pole in summer, but the center of low pressure is usually located towards the Bering Strait side of the central Arctic. Past research has shown that the low-pressure region is maintained by cyclones moving into the region from Eurasia and as well as the generation of lows (cyclogenesis) over the Arctic Ocean itself.

This persistent low pressure pattern has had a pronounced effect on sea ice motion based on NSIDC DAAC data (Figure 2b).  Since winds blow counterclockwise around low pressure centers (in the Northern Hemisphere) the sea ice motion has taken on the same counterclockwise pattern, the opposite of the long-term average. This may have an effect on the compaction and survival of multiyear ice later this season.

Compared to averages over the 1981 to 2010 period, air temperatures at the 925 level (about 2,500 feet above the surface) are mostly below average over most of the Arctic Ocean, particularly over north central Russia, part of the Kara Sea, northeastern Russia, Alaska, and the Canadian Arctic Archipelago (Figure 2c). Scandinavia has seen record high temperatures this summer; for the first half of July, 925 hPa temperatures in this area were up to 6 degrees Celsius (11 degrees Fahrenheit) above the 1981 to 2010 average, and relatively warm conditions extended into the largely ice-free Barents Sea. The extreme warmth that has plagued the Pacific Northwest has also influenced much of western Canada and has been linked to a string of forest fires in British Columbia.

Comparison to previous years

Figure 3. The graph above shows Arctic sea ice extent as of July 13, 2021, along with daily ice extent data for five previous years and the record low year. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 in magenta, 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

The brisk pace of ice loss for the first half of July was at 124,000 square kilometers (47,900 square miles) per day, exceeding the long-term average of 80,000 square kilometers (30,900 square miles) per day. From June 1 through July 13, the Arctic Ocean lost a total of 1.73 million square kilometers (668,000 square miles) of sea ice. This is roughly equivalent in size to the state of Florida.

Thick ice in the Beaufort Sea

Figure 4a. This map shows the age of Arctic sea ice for the June 25 to July 1 period. Note the lingering multiyear ice north of the Alaskan coast.

Credit: M. Tschudi, W. Meier, and Stewart, NASA NSIDC DAAC
High-resolution image

Figure 4b. This true-color image shows sea ice off the coast of Alaska in the Beaufort Sea, taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the NASA Terra satellite on June 26, 2021. The more bluish ice—toward the right side of the image, with the bigger visible floes—is the multiyear ice. The grayish ice, more towards the coast is first-year ice.

Credit: NASA Worldview
High-resolution image

While ice extent is very low for the Arctic Ocean as a whole, with a nearly ice-free Laptev Sea, ice extent in the Beaufort Sea remains extensive and in areas extends to the Alaskan shores. This is explained by the presence of a tongue of fairly thick multiyear ice in the region that is resistant to melting out (Figure 4a). Some of this ice is at least four years old. As shown in a study in press led by R. Mallett and colleagues, winds associated with a period of strong high pressure transported this tongue of ice into the Beaufort Sea this past winter from the central Arctic Ocean and the shores of the Canadian Arctic Archipelago. The image from the NASA Moderate Resolution Imaging Spectroradiometer for June 26, shows the difference between first-year ice close to the shore and the high concentration of multiyear ice farther north (Figure 4b). Whether this thick ice melts away through the remainder of this summer in the fairly warm waters of the Beaufort Sea remains to be seen; if it does, it will reduce the Arctic’s remaining store of multiyear ice.

Further Reading

Serreze, M. C. and A.P. Barrett. 2008. The summer cyclone maximum over the central Arctic Ocean. Journal of Climate, 21, 1048-1065, doi:10.1175/2007JCLI1810.1.

At the end of the first week of July, Arctic sea ice extent was tracking at record low for this time of year. July is the month with most rapid sea ice decline. As in most of the years in the past decade, June saw rapid ice loss in Hudson Bay, Baffin Bay, the Siberian coast, and the Chukchi Sea. However, ice remains extensive north of Alaska.

Overview of conditions

Figure 1. Arctic sea ice extent for June 2021 was 10.71 million square kilometers (4.14 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

Loss of Arctic sea ice in June was relatively steady and rapid. The monthly average extent for June 2021 was 10.71 million square kilometers (4.14 million square miles). This was 300,000 square kilometers (116,000 square miles) above the record low for the month set in 2016 and 1.05 million square kilometers (405,000 square miles) below the 1981 to 2010 average. The average extent for the month ranks sixth lowest in the passive microwave satellite record. Large open-water areas developed in the Laptev and East Siberian Seas, and warm winds pushed the ice edge north in the Kara and Barents Seas near Novaya Zemlya. The Fram Straight region and the area to the north of northeastern Greenland had an unusually low ice concentration as the month drew to a close because of both pre-existing thin ice and unusually warm weather. By contrast, by June’s end, sea ice still persisted along the northern coast of Alaska.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of July 6, 2021, along with daily ice extent data for five previous years and the record low year. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 in magenta, 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. This plot shows average sea level pressure in the Arctic in millibars for June 2021. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

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

Figure 2c. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for June 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 Laboratory
High-resolution image

Unusually strong low pressure (up to 10 hPa below average) near the North Pole dominated the average atmospheric circulation pattern for June (Figure 2b). High pressure also hovered over western Europe, driving winds northeastward over the Norwegian Sea and into the Barents and Kara Seas. Temperatures at the 925 hPa level over Scandinavia were high as a result, averaging 2 to 5 degrees Celsius (4 to 9 degrees Fahrenheit) above average (Figure 2c). Above average temperatures were also present over northeastern Siberia along the Laptev and East Siberian Sea coast, but cool conditions prevailed over central Alaska and central Siberia. Most of the Arctic Ocean was 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) above average, although a region near the Severnaya Zemlya islands was near average. Air temperatures near strong low pressure areas over the Arctic Ocean have historically been associated with relatively cool conditions. However, June temperatures in the vicinity of the low-pressure pattern were near the long-term average.

June 2021 compared to previous years

Figure 3. Monthly June ice extent for 1979 to 2021 shows a decline of 4.0 percent per decade.

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

The pace of ice loss for the month was faster than average; the Arctic lost a total of 2.39 million square kilometers (923,000 square miles) during the month of June. This corresponds to an average ice loss of 79,600 square kilometers (30,700 square miles) per day compared to the 1981 to 2010 average loss of 56,200 square kilometers (21,700 square miles) per day. Through 2021, the linear rate of decline for June sea ice extent is 4.0 percent per decade. This corresponds to 47,000 square kilometers (18,000 square miles) per year. The cumulative June ice loss over the 43-year satellite record is 1.99 million square kilometers (768,000 square miles), based on the difference in linear trend values in 2021 and 1979. The loss of ice since 1979 in June is equivalent to about three times the size of Texas.

“Last Ice Area” not lasting all that well

Figure 4. This map and graph shows sea ice conditions in the Wandel Sea during the summer of 2020. The top map includes a locator map and a map of sea ice concentration in the northern Greenland area in August 2020 as the RV Polarstern transited the area (marked by the red line). The bottom graph shows sea ice concentration for the area marked by the black outline over the course of the 2020 summer, derived from NSIDC Climate Data Record for sea ice. In most years since 1978, sea ice concentration average is above 90 percent (solid blue line) throughout the summer.

Credit: Schweiger et al. 2021
High-resolution image

The area north of Greenland and the Canadian Archipelago has recently been referred to as the “Last Ice Area” (LIA) because ice has persisted there in late summer decades while in other regions ice largely melts away. In the LIA, ice is the thickest and oldest in the Arctic, and ice circulation tends to keep ice pressed against the northern coasts of these islands. However, in the summer of 2020, the easternmost portion of the LIA, know as the Wandel Sea, had record low sea ice concentration (Figure 4). This provided easy access to the interior Arctic ice pack for the icebreaker RV Polarstern last summer as it returned to complete research associated with the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition.

A recent paper by colleagues from University of Washington in Seattle, and the University of Toronto Mississauga explains that the record low ice concentration in the Wandel Sea was caused by both thinning of the thick multi-year sea ice and unusual wind-forced ice motion away from the area, particularly in mid- to late August. Changes in the winds replaced the old ice with thinner first-year ice. The authors note that the unusual winds were a significant factor, likely a result of natural variability but that persistent long-term thinning trends in the LIA multi-year sea ice pack were also partly to blame. Winds would not have had as large of an impact in previous decades when the pack was thicker on average.

Antarctic notes

Figure 5. The graph above shows Antarctic sea ice extent as of July 6, 2021, along with daily ice extent data for five previous years and the record low year. 2021 is shown in blue, 2020 in green, 2019 in orange, 2018 in brown, 2017 in magenta, 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

Sea ice in the Southern Ocean surrounding Antarctica was well above the 1981 to 2010 average extent in June, rising above the ninetieth percentile near the end of the month. Areas north of Dronning Maud Land, Wilkes Land, and the Ross and Amundsen Seas were above average in extent, while regions on either side of the Antarctic Peninsula—the Bellingshausen Sea and the northwestern Weddell Sea—were below average.

The atmospheric circulation pattern for the month was characterized by a strong Amundsen Sea low pressure area (10 to 15 millibars lower than the average for the month) and a weak “wave-3 pattern” around the rest of the Southern Ocean. A wave-3 pattern consists of three high-pressure areas (in this case, the Weddell Sea, Indian Ocean, and southwest Pacific) interspersed with three low-pressure regions (the Amundsen Sea, the areas south of South Africa, and the area south of Australia).

Further reading

Schweiger, A. J., M. Steele, and J. Zhang et al. 2021. Accelerated sea ice loss in the Wandel Sea points to a change in the Arctic’s Last Ice Area. Communications Earth & Environment 2, 122 (2021), doi:10.1038/s43247-021-00197-5.