A change of pace

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|High-resolution image

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
High-resolution image

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, 2015 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 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
High-resolution image

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|High-resolution image

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
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 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|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 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
High-resolution image

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| High-resolution image

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
High-resolution image

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. | High-resolution image

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

Credit: Mudryk et al., 2021.
High-resolution image

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|High-resolution image

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
High-resolution image

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.

Storms were the norm

A stormy May over the eastern Arctic helped to spread the sea ice pack out and keep temperatures relatively mild for this time of year. As a result, the decline in ice extent was slow. By the end of the month, several prominent polynyas formed, notably north of the New Siberian Islands and east of Severnaya Zemlya.

Overview of conditions

Figure 1. Arctic sea ice extent for May 2021 was 12.66 million square kilometers (4.89 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 May 2021 was 12.66 million square kilometers (4.89 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 continued the slow pace of seasonal decline observed in April, leading to an average extent for May 2021 of 12.66 million square kilometers (4.89 million square miles). This was 740,000 square kilometers (286,000 square miles) above the record low for the month set in 2016 and 630,000 square kilometers (243,000 square miles) below the 1981 to 2010 average. The average extent for the month ranks ninth lowest in the passive microwave satellite record. The ice edge is near its average location most everywhere in the Arctic Ocean except in the Labrador Sea and east of Novaya Zemlya. Nevertheless, large polynyas have formed, notably north of the New Siberian Islands and east of Severnaya Zemlya. Open water areas have also developed near the coast in the southern Beaufort Sea and west of Utqiaġvik, Alaska (formerly Barrow). Overall, ice retreat during May occurred primarily in the Bering and Barents Seas, the Sea of Okhotsk and within the Laptev Sea.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of June 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, 2015 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 2a. The graph above shows Arctic sea ice extent as of June 7, 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 average sea level pressure in the Arctic in millibars on May 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 average sea level pressure in the Arctic in millibars on May 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 2c. This plot shows average sea level pressure in the Arctic in millibars on May 24, 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 average sea level pressure in the Arctic in millibars on May 24, 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 2d. This plot shows average sea level pressure in the Arctic in millibars for May 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 2d. This plot shows average sea level pressure in the Arctic in millibars for May 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 2e. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for May 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 2e. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for May 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

The slow pace of sea ice loss this month (Figure 2a) can be explained in large part by a series of storms that migrated over the pole during May. The first storm split from a system over the Barents Sea and then slowly intensified over the central Arctic Ocean before reaching peak intensity (1007 hPa) north of Severnaya Zemlya on May 4. This was followed by another storm tracking northward from Europe, reaching peak intensity (sea level pressure of 987 hPa) over Severnaya Zemlya on May 12 and then joining with another storm that formed over Siberia on May 16 (Figure 2b). The strongest of the storms in terms of minimum central pressure (984 hPa) pressure, achieved on May 24, once again was located over Severnaya Zemlya and resulted from the merging of two systems moving in from the Barents Sea (Figure 2c).

As a result of the May storms, sea level pressure was lower than average by 6hPa centered just south of the pole at about 90 degrees E longitude. This was coupled with sea level pressure of 6 to 8 hPa above average over Greenland and the Canadian Arctic Archipelago extending into the northern Beaufort and Chukchi Seas (Figure 2d). Combined, this sea level pressure pattern fostered cold air spilling out of the Arctic Ocean into the North Atlantic and warm air flowing from the south over eastern Russia, leading to monthly averaged air temperatures at the 925 hPa level 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) above average for this time of year over much of the Arctic Ocean, but up to 6 degrees Celsius (11 degrees Fahrenheit) above average along the coast of the Laptev and East Siberian Seas (Figure 2e). By contrast, temperatures were below average east of Greenland and around Svalbard. Wind patterns also explain the opening of the ice cover around Franz Joseph Land, the New Siberian Islands, and in the southern Beaufort Sea.

May 2021 compared to previous years

Figure 3. Monthly May ice extent for 1979 to 2021 shows a decline of 2.7 percent per decade.||Credit: National Snow and Ice Data Center| High-resolution image

Figure 3. Monthly May ice extent for 1979 to 2021 shows a decline of 2.7 percent per decade.

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

Overall, the pace of ice loss was slower than average, leading to only the ninth lowest May extent during the satellite data record. Through 2021, the linear rate of decline for May sea ice extent, relative to the 1981 to 2020 average extent, is 2.7 percent per decade. This corresponds to 35,400 square kilometers (13,700 square miles) per year, about the size of the state of Maine. The cumulative May ice loss over the 43-year satellite record is 1.49 million square kilometers (575,000 square miles), based on the difference in linear trend values in 2021 and 1979. This is roughly twice the size of the state of Texas.

Capturing the break up in the Beaufort Sea

Visible wavelength imagery from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) provides the opportunity to track the ice breaking up in the southern Beaufort Sea this May; cloud cover was limited, offering decent views of the surface. Between April 25 and May 17, the pack ice started to move away from the landfast ice still attached to the coast, leading to open water and subsequent break up of the ice floes and partial break up of the landfast ice by mid-May. During the past winter, unusually high sea level pressure over the central Arctic Ocean resulted in unusually strong anticyclonic (clockwise) ice motion that drove a lot of fairly old ice from the central Arctic Ocean into the Beaufort Sea. Early break up of ice can enhance lateral and basal melt (at the underside of the ice) of the ice floes. This process can weaken the multiyear ice in the region and help to further deplete the Arctic of its multiyear ice. Large losses of multiyear ice in the region followed the unusually strong negative Arctic Oscillation winter of 2009 to 2010, which also featured a strong clockwise flow of the ice cover. More recently, analysis of Canadian ice charts by David Babb at the University of Manitoba suggests that between 2016 and 2020 on average 210,000 square kilometers (81,000 square miles) of multiyear ice now melts out each summer in the Beaufort Sea.

Are wavy jet stream winds wavier? Or not?

A new study takes a close look at an idea discussed several times in the Arctic Sea Ice News and Analysis (ASINA) reports—that Arctic Amplification, the observed strong warming in the Arctic region, driven in part by loss of Arctic sea ice, is affecting the shape and persistence of the jet stream. The polar front jet stream marks the boundary in the atmosphere between cold Arctic air and warmer mid-latitude air. Numerous studies have proposed that Arctic Amplification weakens the latitudinal temperature and atmospheric pressure gradient, manifested as a weaker and more sinuous jet stream. Since storms (low pressure systems) tend to form along the jet stream, weather in middle latitudes ought to become more variable, with large swings and more persistent patterns.

While the issue has long been controversial, the new study by James Screen, which was presented at the European Geophysical Union annual meeting in April, but has not yet been published, finds little evidence for this effect in climate model simulations and observations. In examining the past decade of observations, relationships that initially gave support to the idea have weakened. Even with far more open water conditions expected by 2050, the modeled effects of Arctic warming on the weather patterns at lower latitudes appear to be minor. The response is further obscured by the possibility of increased snowfall on Arctic land areas, creating cold regions that are not centered on the Pole. A separate new study by Jonathan Martin shows the polar jet has become slightly wavier and moved northward a bit, but maximum speeds in the jet are unchanged. The scientific debate on this issue is certain to continue.

Arctic sea ice thinning faster than expected

Figure 4. This plot shows mean sea ice thickness in the Beaufort, Chukchi, East Siberian, Laptev, Kara, and Barents seas in April 2021 from the Envisat and CryoSat-2 radar altimeters, processed with the conventional snow product (modified Warren (1999) or mW99) and a new, dynamic snow product (from SnowModel-LG). The rate of decline is more than doubled when processed with SnowModel-LG, as the sea ice thickness inferred from snow cover diminishes. ||Credit: R. Mallett. | High-resolution image

Figure 4. This plot shows average sea ice thickness in the Beaufort, Chukchi, East Siberian, Laptev, Kara, and Barents Seas in April 2004 to 2018 from the Environmental Satellite (Envisat) and CryoSat-2 radar altimeters, processed with the conventional snow product (modified Warren (1999) or mW99) and a new, dynamic snow product (from SnowModel-LG). The rate of decline is more than doubled when processed with SnowModel-LG, as the sea ice thickness inferred from snow cover diminishes.

Credit: R. Mallett, University College London.
High-resolution image

Satellites do not directly measure the thickness of sea ice. They measure the height of the ice surface above the ocean, termed the ice freeboard in the case of radar altimetry, or they measure the height of the ice plus the snow cover, in the case of laser altimetry. To convert these freeboards into total ice thickness requires knowledge of the depth and density of the snow cover atop the ice. Typically, a snow climatology based on snow depth observations collected several decades ago over multiyear ice is used. However, today’s Arctic mostly consists of smoother first-year ice, which tends to have a shallower snow pack than multiyear ice, allowing for deep snow accumulation around ridges. Further, delays in freeze-up and earlier melt onset in today’s warmer climate have reduced the time over which snow can accumulate on the ice. Both factors have resulted in a thinner snowpack than measured 20 years ago.

A new study published in The Cryosphere reveals that when using temporally varying snow depth and density estimates to convert ice freeboard to ice thickness, the ice is thinning at a faster rate in the Arctic marginal seas than previously believed (Figure 4). The time-varying snow depth is from a new data product, the SnowModel-LG, which is soon to be published at the NSIDC Distributed Active Archive Center (DAAC). It is based on coupling a sophisticated snow model with meteorological forcing data from atmospheric reanalysis systems and satellite-derived ice motion vectors. The study found that the rate of decline in ice thickness in the Laptev, Kara, and Chukchi seas was 70, 98 and, 110 percent faster, respectively, compared to previous estimates. As expected, the sea ice thickness variability also increased in response to interannually varying snow depth.

Antarctic notes

Figure 5a. The graph above shows Antarctic sea ice extent as of June 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, 2015 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

Figure 5a. The graph above shows Antarctic sea ice extent as of June 7, 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

Figure 5b. air temp as difference from average in Antarctic for May 2021||Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory|High-resolution image

Figure 5b. This plot shows the departure from average air temperature in the Antarctic at the 925 hPa level, in degrees Celsius, for May 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

Antarctic sea ice extent grew at a slightly below-average pace in May, moving the overall extent from slightly above average to tracking the 43-year satellite record daily-extent average line (technically, the ‘median’ line) quite closely (Figure 5a). Sea ice extent was below average in the Weddell and Ross Seas, and slightly above average in the Bellingshausen and Amundsen Seas. In keeping with the sea ice trends, air temperatures for the month were well above average over the west-central Weddell Sea, about 7 degrees Celsius (13 degrees Fahrenheit) above average for the month (Figure 5b).

An embayment, or notch, in the ice edge in the eastern Weddell suggests that the processes that create the Maud Rise polynya were active, but at month’s end, the sea ice edge in that area (near 0 degree longitude and 68 degrees S latitude) had not enclosed the potential polynya region.

Further reading

Liston, G. E., P. Itkin, J. Stroeve, M. Tschudi and J. S. Stewart. 2020. A Lagrangian snow-evolution system for sea-ice applications (SnowModel-LG): part I–model description. Journal of Geophysical Research.-Oceans. doi:10.1029/2019JC015913.

Mallett, R. D. C., J. C. Stroeve, M. Tsamados, J. C. Landy, R. Willatt, V. Nandan and G. E. Liston. 2021. Faster decline and higher variability in the sea ice thickness of the marginal Arctic seas. The Cryosphere. doi:10.5194/tc-15-2429-2021.

Martin, J. E. 2021. Recent trends in the waviness of the Northern Hemisphere wintertime polar and subtropical jets. Journal of Geophysical Research-Atmospheres. doi:10.1029/2020JD033668.

Stroeve, J. C., J. Maslanik, M. C. Serreze, I. Rigor and W. Meier. 2011. Sea ice response to an extreme negative phase of the Arctic Oscillation during winter 2009/2010. Geophysical Research Letters. doi: 10.1029/2010GL045662.

Stroeve, J., G. Liston, S. Buzzard, L. Zhou, R. Mallett, A. Barrett, M. Tsamados, M. Tschudi, P. Itkin and J. S. Stewart. 2020. A Lagrangian snow-evolution system for sea ice applications (SnowModel-LG): part II–analyses. Journal of Geophysical Research-Oceans. doi:10.1029/2019JC015900.

Warren, S. G., I. Rigor, N. Untersteiner, V. Radionov, N. Bryazgin, Y. Aleksandrov and R. Colony. 1999. Snow depth on Arctic sea ice. AMS Journey of Climate. doi:10.1175/1520-0442.

A step in our spring

The spring decline in Arctic sea ice extent continued at varying rates through the month of April, highlighted by a mid-month pause. Above average air temperatures and low sea level pressure dominated on the Atlantic side of the Arctic, while near average conditions ruled elsewhere.

Overview of conditions

Figure 1. Arctic sea ice extent for April 2021 was 13.84 million square kilometers (5.34 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 April 2021 was 13.84 million square kilometers (5.34 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 April 2021 was 13.84 million square kilometers (5.34 million square miles). This was 410,000 square kilometers (158,000 square miles) above the record low for the month set in 2019 and 850,000 square kilometers (328,000 square miles) below the 1981 to 2010 average. The average extent for the month ranks sixth lowest in the passive microwave satellite record. Extent was notably low in the Barents and Bering Seas as well as the Labrador Sea. Elsewhere, extent was close to or somewhat below average (Figure 1). The largest ice loss during April was in the Sea of Okhotsk and the Labrador Sea, with smaller losses along the southern edge of the Bering Sea, and in the eastern Barents Sea near the coast of Novaya Zemlya.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of May 4, 2021, along with daily ice extent data for four previous years and 2012, 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 2a. The graph above shows Arctic sea ice extent as of May 4, 2021, along with daily ice extent data for four previous years and 2012, 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 average sea level pressure in the Arctic in millibars from April 14 to 19, 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

Figure 2b. This plot shows average sea level pressure in the Arctic in millibars from April 14 to 19, 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

Figure 2c. This plot shows average sea level pressure in the Arctic in millibars for April 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

Figure 2c. This plot shows average sea level pressure in the Arctic in millibars for April 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

Figure 2d. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for April 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

Figure 2d. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for April 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

Sea ice extent remained below the tenth percentile range throughout the month of April. However, rate of decline was variable. Notably, the decline paused, and extent even slightly increased between April 14 and April 19 (Figure 2a). This was largely because of an increase in sea ice in the northern Barents Sea, particularly off the northwest coast of Novaya Zemlya.

This temporary ice expansion appears to have been primarily driven by low sea level pressure centered over the Laptev Sea (Figure 2b). This led to winds from the north in the northern Barents Sea, pushing ice southward. The sea level pressure pattern for the full month featured low pressure centered in the Barents Sea, north of the Scandinavian coast (Figure 2c); bringing warm winds from the south and above average monthly temperatures in the region. Elsewhere in the Arctic, conditions were more moderate with 925 mb temperatures 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) above average and weak high pressure (Figure 2d).

April 2021 compared to previous years

Figure 3. Monthly April 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

Figure 3. Monthly April 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 April sea ice extent, relative to the 1981 to 2010 average extent, is 2.6 percent per decade (Figure 3). This corresponds to 38,600 square kilometers (14,900 square miles) per year, about the size of the US states of New Hampshire and Connecticut combined. The cumulative April ice loss over the 43-year satellite record is 1.62 million square kilometers (625,000 square miles), based on the difference in linear trend values in 2021 and 1979, which is equivalent in size to 2.3 times the size of the state of Texas.

Sea ice age update

Figure 4. Sea ice age map for March 12 to 18 (a) 1985 and (b) 2021; (c) the 1985 to 2021 time series of percent coverage of the Arctic Ocean domain (inset map, purple shaded region). ||Credit: W. Meier, National Snow and Ice Data Center| High-resolution image

Figure 4. This figure compares sea ice age between March 12 to 18 for the years 1985 (a) and 2021 (b). The bottom graph (c) shows a time series from 1985 to 2021 of percent ice coverage of the Arctic Ocean domain. The Arctic Ocean domain is depicted in the inset map with purple shading. 

Credit: M. Tschudi, University of Colorado, and W. Meier and J.S. Stewart, National Snow and Ice Data Center/Image by W. Meier
High-resolution image

The sea ice continues to be far younger, and thus thinner, than in the 1980s. There is little change in the age distribution from last year. At the end of the ice growth season in mid-March, 73.3 percent of the Arctic Ocean domain was covered by first-year ice, while 3.5 percent was covered by ice 4+ years old. This compares to 70.6 percent and 4.4 percent respectively in March 2020. In March 1985, near the beginning of the ice age record, the Arctic Ocean region was comprised of nearly equal amounts of first-year ice (39.3 percent) and 4+ year-old ice (30.6 percent).

In 2021, the extremely high sea level pressure in February over the central Arctic Ocean produced a strong Beaufort Gyre sea ice circulation, as noted in our March post. This pushed a substantial amount of ice, including older ice, onto the northern Alaskan and Canadian coast in the Beaufort Sea. Some of this ice has now moved north and west into the Chukchi Sea–an isolated patch of older ice amidst first-year ice. This will bear watching through the summer to see the fate of that older ice.

Antarctica

Figure 5: Antarctic sea ice extent for April 2021 was 7.08 million square kilometers (2.73million 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 5: Antarctic sea ice extent for April 2021 was 7.08 million square kilometers (2.73million 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

In the Antarctic, autumn is now in full swing, but ice growth has been somewhat sluggish through the month. At the beginning of the month, extent was between the seventy-fifth and ninetieth percentile range of the 1981 to 2010 climatology. By the end of the month, extent was within the inner quartile range and just above the median.

Antarctic extent for April 2021 was 7.08 million square kilometers (2.73 million square miles), 230,000 square kilometers (88,800 square miles) above the 1981 to 2010 average (Figure 5). Extent was low in the northwestern Weddell Sea region and northern Ross Sea, and both areas had temperatures 3 to 8 degrees Celsius (5 to 14 degrees Fahrenheit) above the reference period. Sea ice extent was generally above average elsewhere, particularly in the Amundsen Sea, where rather cool conditions prevailed for April, at 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below average.

Seasonal predictability of Arctic sea ice from ocean heat transport

Figure 6. This figure shows correlations between ocean heat transport through the Bering strait and sea ice concentration in the Arctic Ocean. Heat transport anomalies in May are compared to June (left) and July (right) sea ice concentration anomalies. Red areas show regions of the Arctic Ocean where Pacific Ocean heat has the strongest influence on sea ice conditions. Significant correlations at the 95 percent significance level are outlined in black. Regions where the interannual variability in monthly sea ice concentration is larger than 10 percent are outlined in green. An anomaly refers to the deviation of ocean heat transports and sea ice concentrations from their linear trends. ||Credit: image adapted from Lenetsky et al. (2021). | High-resolution image

Figure 6. This figure shows correlations between ocean heat transport through the Bering strait and sea ice concentration in the Arctic Ocean. Heat transport anomalies in May are compared to June (left) and July (right) sea ice concentration anomalies. Red areas show regions of the Arctic Ocean where Pacific Ocean heat has the strongest influence on sea ice conditions. Significant correlations at the 95 percent significance level are outlined in black. Regions where the interannual variability in monthly sea ice concentration is larger than 10 percent are outlined in green. An anomaly refers to the deviation of ocean heat transports and sea ice concentrations from their linear trends.


Credit: image adapted from Lenetsky et al. (2021).
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As the Arctic summer nears, the Sea Ice Prediction Network team, which includes NSIDC scientists, is gearing up for another year of the Sea Ice Outlook. Participants in the Outlook and other researchers are investigating ways to better understand and improve seasonal predictability of Arctic September sea ice extent. One factor in sea ice predictability is ocean heat.

A recent study led by University of Colorado master’s student Jed Lenetsky, in collaboration with researchers at McGill University and the Massachusetts Institute of Technology, examined the influence of Pacific Ocean heat on sea ice conditions. Results show that Pacific Ocean heat entering the Arctic Ocean through the Bering Strait has the largest influence on sea ice conditions in the spring and early summer in the Chukchi Sea, fostering early opening of the pack ice and triggering the ice-albedo feedback (Figure 6). From August through October, the summer stratification of the Chukchi Sea reduces the influence of Pacific Ocean heat on sea ice conditions. At the same time, other processes, such as ocean heat uptake and wind-induced sea ice drift, become the dominant drivers of sea ice variability in the region. The influence of the Bering Strait heat transport re-emerges in November as a factor in the timing of freeze onset. These results have important implications for seasonal sea ice prediction in the Chukchi Sea, as predictions using Pacific Ocean heat are more skillful than predictions using more commonly used parameters such as sea ice concentration and sea ice thickness.

Further reading

Lenetsky, J. E., B. Tremblay, C. Brunette, and G. Meneghello. 2021. Subseasonal predictability of Arctic Ocean sea ice conditions: Bering Strait and Ekman-driven ocean heat transport.  J. Climate. doi:10.1175/JCLI-D-20-0544.1.

Fluctuating pressures

Sea ice extent for February 2021 tracked well below average, but at month’s end was still higher than levels recorded in several recent years. Extent grew at an average pace. For the first two weeks of the month, sea level pressure was extremely high over the central Arctic Ocean, driving a pronounced and enlarged Beaufort Gyre sea ice circulation. A strong negative phase of the Arctic Oscillation was a part of the overall Arctic pattern.

Overview of conditions

Figure 1. Arctic sea ice extent for February 2021 was 14.24 million square kilometers (5.50 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 February 2021 was 14.39 million square kilometers (5.56 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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Arctic sea ice extent averaged for the month of February 2021 was 14.39 million square kilometers (5.56 million square miles), placing it seventh lowest in the satellite record for the month. This was 910,000 square kilometers (351,000 square miles) below the 1981 to 2010 February average and 420,000 square kilometers (162,000 square miles) above the record low mark for February set in 2018. For the month of February, ice extent was near average in most regions of the Arctic except most notably in the Gulf of St. Lawrence, and to a lesser extent in the Bering Sea and the Sea of Okhotsk. The ice edge was also further north than average on the northern and western side of Svalbard.

Conditions in context

Figure2a. The graph above shows Arctic sea ice extent as of March 8, 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, 2015 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 2a. The graph above shows Arctic sea ice extent as of March 8, 2021, along with daily ice extent data for four previous winter seasons 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 2015 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
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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, for February 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

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for February 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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Figure 2c. This plot shows average sea level pressure in the Arctic in millibars for February 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

Figure 2c. This plot shows average sea level pressure in the Arctic in millibars for February 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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Throughout the month, sea ice grew by an average of 9,900 square kilometers (3,800 square miles) per day, roughly half the average rate over the period 1981 to 2010 of 20,300 square kilometers (7,800 square miles per day).

Air temperatures at the 925 hPa level (about 2,500 feet above the surface) were from 1 to 6 degrees Celsius (2 to 11 degrees Fahrenheit) above average across much of the central Arctic Ocean, East Siberian Sea, Atlantic Sector, and Canadian Arctic Archipelago. By contrast, northern Alaska, Siberia, and the Beaufort Seas saw temperatures up to 8 degrees Celsius (14 degrees Fahrenheit)  below average (Figure 2b).

The first part of the month was characterized by extremely high sea level pressure over the central Arctic Ocean, driving an exceptionally strong clockwise Beaufort Gyre sea ice circulation. This is consistent with the strongly negative phase of the Arctic Oscillation observed over this time period, which is sometimes associated with a wavy jet stream pattern and cold air outbreaks in lower latitudes, such as was experienced in Texas during the middle of the month. While this pattern broke down later in the month, the average sea level pressure pattern for February still featured a strong Beaufort High, with peak surface pressures exceeding 1,030 (Figure 2c). This atmospheric circulation pattern, driving a pronounced clockwise Beaufort Gyre circulation, led to the transport of thick multiyear ice along the Canadian Arctic Archipelago towards the Alaskan coastline.

February 2021 compared to previous years

Figure 3. Monthly February ice extent for 1979 to 2021 shows a decline of 2.9 percent per decade.||Credit: National Snow and Ice Data Center| High-resolution image

Figure 3. Monthly February ice extent for 1979 to 2021 shows a decline of 2.9 percent per decade.

Credit: National Snow and Ice Data Center
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Including 2021, the linear rate of decline for February ice extent is 2.9 percent per decade. This corresponds to a trend of 43,800 square kilometers (16,900 square miles) per year, which is roughly twice the size of the state of New Hampshire. Over the 43-year satellite record, the Arctic has lost about 1.84 million square kilometers (710,000 square miles) of sea ice in February, based on the difference in linear trend values in 2020 and 1979. This is an area about two and a half times the size of Texas.

The minimum in the south

Figure 4. Antarctic sea ice extent for February 2021 was 2.83 million square kilometers (1.09 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 4. Antarctic sea ice extent for February 2021 was 2.83 million square kilometers (1.09 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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Antarctic sea ice extent reached its minimum around February 21, during the period of missing data of which we had notified data users. After February 21, sea ice began a rapid increase in extent caused by the early rapid sea ice growth in the Amundsen and eastern Ross Seas. Advanced Microwave Scanning Radiometer 2 (AMSR-2) data, which was not impacted by the outage, confirms that the minimum was reached on or near February 21.

Sea ice extent has trended below average again after several months in mid- to late 2020 above the 1981 to 2010 average. However, the 2021 minimum extent is twelfth lowest in the satellite record and far from the record low extent, which occurred in 2017. Below-average extents were present in the northern Weddell and eastern Ross Seas, while the Bellingshausen Sea and the Wilkes Land Coast were near average (Figure 4).

Sticking with our 30-year reference climatology

Figure 5. This graph shows the daily median Arctic sea ice extent for the calendar year from the 1981 to 2010 period and the 1991 to 2020 for comparison. NSIDC plans to maintain the 1981 to 2010 period as our standard climatology. ||Credit: National Snow and Ice Data Center| High-resolution image

Figure 5. This graph shows the daily median Arctic sea ice extent for the calendar year from the 1981 to 2010 period and the 1991 to 2020 for comparison. NSIDC plans to maintain the 1981 to 2010 period as our standard climatology.

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

A 30-year climatology is commonly used as a reference period in weather and climate to define “normal” conditions. Thirty years is long enough to average out most natural variations in climate, like El Niño, that can affect the average in the short term. At the same time, 30 years is short enough that it provides a window into recent experience for planning purposes, such as crop rotation. Weather forecast services update their climatology with each new decade. So, the US National Weather Service will soon update the period from 1981 to 2010 to 1991 to 2020.

However, a shifting baseline makes tracking long-term climate change more complicated. As the baseline shifts, anomalies (amount above or below “normal”) and relative (percent per decade) trends will change. For climate, it is better to use a fixed period with a good data record so that as new data is collected, there is a consistent baseline for decadal or longer evaluation of change. Ideally, this baseline period would be relatively stable and without much of a trend. This is particularly a problem for Arctic sea ice where the last 10 years have had several extremely low extents. Including these recent years hardly represents “normal” in terms of the long-term climate. For this reason, we plan to maintain the 1981 to 2010 period as our standard climatology. The period comprises the earliest three full decades in the continuous satellite record. The data for this period have been well validated and consistency has been maintained through careful calibrations between different sensors used in the time series. Figure 5 shows the daily median extent for the calendar year from the 1981 to 2010 period and the 1991 to 2020 for comparison. As expected, the 1991 to 2020 median extents are lower than the 1981 to 2010 values, particularly during summer. The annual minimum of the 1991 to 2020 median extent is about 800,000 square kilometers (309,000 square miles) lower than the 1981 to 2010 median. Additionally, 1991 to 2020 sea ice extents exhibit much greater variability compared to sea ice conditions between 1981 and 2010.

We will consider adding a 1991 to 2020 median line to our Charctic interactive sea ice graph. Our Sea Ice Analysis Tool allows users to customize the baseline period for anomaly calculations. A more thorough discussion of the issue of climate “normal” can be found in a recent Yale Climate Connections article.

Addressing the mid-February data gap

As previously posted, a gap occurred in our sea ice extent estimates from February 20 to 21 due to a data loss by our source of passive microwave sensor data used to derive our concentration and extent estimates. These data unfortunately do not appear to be recoverable. However, the sensor is still healthy and another outage is not expected. The data gap resulted in temporary outages of Sea Ice Index data and various tools, such as Charctic. Values for February 20 and 21 were derived by interpolating from surrounding days.

Ho, ho, ho-hum December

The Arctic climate was extraordinary in 2020, but the year ended with a less spectacular December. Ice growth was faster than average throughout the month, but extent at month’s end remained among the lowest in the satellite record. Air temperatures for the month were higher than average in most areas, but less so than in many previous months. Overall, it was an extremely warm 2020, especially over Siberia.

Overview of conditions

Figure 1. Arctic sea ice extent for December 2020 was 11.77 million square kilometers (4.54 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 December 2020 was 11.77 million square kilometers (4.54 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 December 2020 was the third lowest in the satellite record. The monthly average extent of 11.77 million square kilometers (4.54 million square miles) was 1.07 million square kilometers (413,000 square miles) below the 1981 to 2010 December average. Sea ice cover was below average in the Bering Sea on the Pacific side and the Barents Sea on the Atlantic side. Compared to 2016, which had the lowest December sea ice extent on record, the ice edge in 2020 is further south in the Barents and East Greenland Seas, but further north in Davis Strait and the Labrador Sea.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of January 4, 2020, along with daily ice extent data for five previous years and the record low year. 2019 to 2020 is shown in blue, 2018 to 2017 in green, 2017 to 2018 in orange, 2016 to 2017 in brown, 2015 to 2016 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

Figure 2a. The graph above shows Arctic sea ice extent as of January 4, 2021, along with daily ice extent data for five 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 record low year. 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 December 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 December 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

Sea ice extent increased by 2.71 million square kilometers (1.05 million square miles) during the month of December. This was greater than the 1981 to 2010 average gain in December of 1.99 square kilometers (780,000 square miles). However, after a rapid early and mid-month gain, the rate of extent increase slowed considerably (Figure 2a).

December air temperatures at the 925 mb level (about 2,500 feet about sea level) continued to be relatively high for this time of year over much of the Arctic Ocean, particularly north of the Laptev and East Siberian Seas, which saw temperatures of 5 degrees Celsius (9 degrees Fahrenheit) above the 1981 to 2010 average (Figure 2b). Average and below average temperatures prevailed in the Beaufort and eastern Chukchi Seas.

The Arctic Oscillation (AO), after being in a strong positive mode for most of November, flipped to a negative mode for most of December. As a result of the AO flipping to negative, a sea level pressure pattern formed in December with high pressure over the Arctic Ocean, a fairly strong  Beaufort Sea High pressure pattern, and low pressure over the Atlantic and Pacific subarctic. Earlier research (Rigor et al., 2002) argued that during winter, a negative mode tends to retain older and thicker ice within the Arctic Ocean, which potentially portends a more moderate ice loss the following summer. Conversely, when the AO is positive, the wind pattern helps to transport ice from the Siberian coast, across the pole and out of the Arctic Ocean via the Fram Strait, leaving more thin ice along the Siberian shore that melts out readily in summer. The strong positive AO during the winter of 2019 to 2020 may have played a role in this past summer’s low sea ice extent. However, this relationship between the AO and summer ice extent has not been strong in recent years.

December 2020 compared to previous Decembers

Figure 3. Monthly December ice extent for 1979 to 2020 shows a decline of 3.62 percent per decade.||Credit: National Snow and Ice Data Center| High-resolution image

Figure 3. Monthly December ice extent for 1979 to 2020 shows a decline of 3.6 percent per decade.

Credit: National Snow and Ice Data Center
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Through 2020, the linear rate of decline for December sea ice extent is 3.6 percent per decade, which corresponds to 46,500 square kilometers (18,000 square miles) per year, about twice the size of New Hampshire. The cumulative December ice loss over the 43-year satellite record is 1.97 million square kilometers (761,000 square miles), based on the difference in linear trend values in 2020 and 1978. This is equivalent to about three times the size of Texas.

Check in down south

Figure 4a. Antarctic sea ice extent (left) for December 2020 was 10.4 million square kilometers (4.02 million square miles). Antarctic sea ice concentration (right) for December 2020 was 6.5 million square kilometers (2.51 million square miles). The magenta line shows the 1981 to 2010 average extent (left) and concentration (right) for that month. Sea Ice Index data. About the data||Credit: National Snow and Ice Data Center|High-resolution image

Figure 4a. Antarctic sea ice extent (left) for December 2020 was 10.4 million square kilometers (4.02 million square miles). Antarctic sea ice concentration (right) for December 2020 was 6.5 million square kilometers (2.51 million square miles). The magenta line shows the 1981 to 2010 average extent (left) and concentration (right) for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Figure 4b. This figure shows the impact of the sudden decline of Antarctic sea ice extent in August 2016 on the ice extent for the rest of the year. This was due to a phase shift of the decline pattern. ||Credit: Handcock and Raphael, 2020 | High-resolution image

Figure 4b. This figure shows the impact of the sudden decline of Antarctic sea ice extent in August 2016 on the ice extent for the rest of the year. This was due to a phase shift of the decline pattern.

Credit: Handcock and Raphael, 2020
High-resolution image

After being above average for much of the austral winter and spring, Antarctic sea ice extent dropped below average in the last week of December. Ice extent tends to see a steep decline in December as the ice begins to disintegrate all around the continent. However, the decline in sea ice extent in the Weddell and Ross Seas has been unusually rapid this year and large regions of low-concentration ice are present at year’s end (Figure 4a).

In a recent study, Handcock and Raphael (2020) note that in the Antarctic, much of the departure from average extent depends on the timing of the ice loss. For example, when extent is dropping substantially each day, a few days difference in the timing of the beginning and end of ice loss and gain can result in relatively large departure in ice extent from average. The causes of earlier or later onsets of ice loss—weather or ocean forcings on the cyclical annual trend—have long-running effects if they adjust the phase of the cycle.

After an extended period of below-average ice extent since the second half of 2016, Antarctic sea ice expanded to above-average levels in August of 2020 and remained high until the last week of this month. Once again, the Maud Rise polynya was open, but only briefly in late November and early December, as sea ice retreat in the Weddell proceeded and the ice edge swept past the polynya.

The Arctic sea ice year in review

Figure 5a. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for the full calendar year 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 5a. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for the full calendar year 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 5b. This figure shows the average January, February, March Arctic Oscillation (AO) Index for 1950 to 2020. ||Credit: NSIDC courtesy, with data from the NOAA NCEP Climate Prediction Center. |High-resolution image

Figure 5b. This figure shows the average January, February, March Arctic Oscillation (AO) Index for 1950 to 2020.

Credit: NSIDC courtesy, with data from the NOAA NCEP Climate Prediction Center.
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The year 2020 was extreme for the Arctic, even compared to the past 20 years. Notable was the extreme heat over Siberia. The annual average temperature at the 925 mb level (about 2,500 feet above sea level) was over 3.5 degrees Celsius (6 degrees Fahrenheit) above the 1981 to 2010 annual average over a broad area of North Central Siberia extending over the Kara and Laptev Seas (Figure 5a). Temperatures were particularly high in the region through the first six months of the year, culminating in a 100-degree Fahrenheit (38-degrees Celsius) temperature reading in June in Verkhojansk, Russia. This was the first recorded temperature of over 100 degrees Fahrenheit north of the Arctic Circle.

These very warm conditions, coupled with winds from the south, led to early melt onset and ice retreat in the Laptev Sea. By mid-June, ice in the Laptev Sea had reached record low extent for that time of year. The strong positive mode of the Arctic Oscillation (AO) during the 2020 winter from January through March may have contributed to thin ice in the region that melted out easily once melt started. The average 2020 winter AO index was the most positive in the National Centers for Environmental Prediction (NCEP) record, dating back to 1950. Only 1989 and 1990 rivaled 2020 (Figure 5b).

The winter and spring conditions and early sea ice melt onset and retreat led to the second lowest September minimum extent in the satellite record, above only 2012. While Arctic air temperatures ranked as the highest recorded during both July and August, changes in the winds likely prevented extent from falling below the 2012 record low. There was a remarkably long open water shipping season along the Northern Sea Route (NSR) along the Russian coast. The relatively thin winter ice along the Russian coast (relative to the Central Arctic Ocean) allows for Russian icebreakers to maintain a channel for ships to navigate the passage throughout the year. However, as the summer ice extent has decreased, the NSR has become ice free for a longer period of time. In many recent years, the NSR was ice free for several weeks. A recent report indicates that this year’s ice-free season was the longest on record.

While the Arctic sea ice story largely centered on the Russian side of the Arctic Ocean, eyes also shifted toward the Atlantic in late summer with the retreat of the ice edge towards the pole. During late summer, the ice edge retreated to within about 500 kilometers (300 miles) of the North Pole north of the Barents and Kara Seas. Along that ice edge, the ice was not very compact. This allowed the German icebreaker, R.V. Polarstern, to easily cruise to the pole in early August as part of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition.

Initial results from MOSAiC

Figure 6. The left side of this figure shows the agreement between snow depth derived from the Ku-Ka radar sensor (x-axis) and in situ measurements (y-axis) by a magnaprobe snow depth instrument across two transects (red and blue dots). The radar measurements have a correlation with the in situ measurements of 0.66, demonstrating the utility of the radar for estimating snow depth. The right side shows the data along a transect across the snow and ice with the radar and the magnaprobe. The colors in the plot correspond to the strength of radar signal and the lines demarcate snow/air and snow/ice boundaries. For further details on the analysis and the figures, see Stroeve et al. (2020). ||Credit: Julienne Stroeve, National Snow and Ice Data Center|High-resolution image

Figure 6. The left side of this figure shows the agreement between snow depth derived from the Ku-Ka radar sensor (x-axis) and in situ measurements (y-axis) by a magnaprobe snow depth instrument across two transects (red and blue dots). The radar measurements have a correlation with the in situ measurements of 0.66, demonstrating the utility of the radar for estimating snow depth. The right side shows the data along a transect across the snow and ice with the radar and the magnaprobe. The colors in the plot correspond to the strength of radar signal and the lines demarcate snow/air and snow/ice boundaries. For further details on the analysis and the figures, see Stroeve et al. (2020).

Credit: R. Willatt, University of College London
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As discussed in earlier posts, the MOSAiC expedition was the most notable scientific Arctic event of 2020. The expedition involved freezing an icebreaker into Arctic sea ice for one year beginning in September 2019. Scientists collected data on all aspects of the Arctic environment, including sea ice, atmosphere, ocean, biology, chemistry, and more. It will take years to fully assess the data, but initial analyses are already being published. This includes a new paper (Stroeve et al., 2020) analyzing data from a ground-mounted radar, an effort led by NSIDC senior research scientist and MOSAiC participant, Julienne Stroeve. This radar has the same frequencies as used on current satellite systems to monitor ice thickness and snow depth. However, satellites do not directly retrieve sea ice thickness; it is inferred based on assumptions as to where the radar return is coming from as well as assumptions on depth of the snowpack, and densities of the ice, snow and water. To better understand how snowpack properties influence radar backscatter at these frequencies, Stroeve and colleagues deployed a fully polarimetric, dual frequency radar with both Ku radar (12 to 18 gigahertz) and Ka radar (27 to 40 gigahertz). The instrument operated in a scanning mode, sweeping above the surface at different azimuth and incidence angles, as well as an altimeter mode, looking straight down while being towed with a skidoo. Observations were supported by detailed snow pit observations, snow depth and ice thickness, as well as laser scans of the surface to provide estimates of surface roughness.

Initial results based on data collected between October 2019 and January 2020 show that a combination of frequencies can provide estimates of snow depth. Further, the data illustrate the radar backscatter sensitivity to snow pack temperature and surface roughness, affecting the retrieved height of the sea ice freeboard, or sea ice thickness calculations.

Further reading

Handcock, M. S. and M. N. Raphael. 2020. Modeling the annual cycle of daily Antarctic sea ice extent. The Cryosphere. doi:10.5194/tc-14-2159-2020.

Rigor, I. G., Wallace, J. M., and R. L. Colony. 2002. Response of Sea Ice to the Arctic Oscillation. Journal of Climate. doi:10.1175/1520-0442(2002)015<2648:ROSITT>2.0.CO;2.

Stroeve, J., Nandan, V., Willatt, R., Tonboe, R., Hendricks, S., Ricker, R., Mead, J., Mallett, R., Huntemann, M., Itkin, P., Schneebeli, M., Krampe, D., Spreen, G., Wilkinson, J., Matero, I., Hoppmann, M., and M. Tsamados. 2020. Surface-based Ku- and Ka-band polarimetric radar for sea ice studies. The Cryosphere. doi:10.5194/tc-14-4405-2020.

Ocean waves in November—in the Arctic

A vast area of the Arctic Ocean remains ice free as November begins, far later in the season than is typical. The monthly average ice extent for October is the lowest in the satellite record. On October 24, a record difference was set in daily ice extent relative to the 1981 to 2010 average. Large heat transfers from the open water to the atmosphere have manifested as above-average air temperatures near the surface of the ocean.

Overview of conditions

Figure 1. Arctic sea ice extent for October 2020 was 5.28 million square kilometers (2.04 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 October 2020 was 5.28 million square kilometers (2.04 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 for October 2020 was 5.28 million square kilometers (2.04 million square miles), placing it lowest in the satellite record for the month. This was 3.07 million square kilometers (1.19 million square miles) below the 1981 to 2010 October average and 450,000 square kilometers (173,700 square miles) below the record low mark for October set in 2019. October 2020 is the largest departure from average conditions seen in any month thus far in the satellite record, falling 3.69 standard deviations below the 1981 to 2010 mean. Ice extent is far below average in all of sectors of the Eurasian side of the Arctic Ocean and in Baffin Bay.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of November 3, 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

Figure 2a. The graph above shows Arctic sea ice extent as of November 3, 2020, along with daily ice extent data for four previous years and the 2012 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

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for October 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 October 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. This plot shows average sea level pressure in the Arctic in millibars (hPa) for October 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 2c. This plot shows average sea level pressure in the Arctic in millibars (hPa) for October 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

Throughout the month, sea ice grew by an average of 71,200 square kilometers (27,500 square miles) per day, which is close to the average rate for 1981 to 2010. For the first three weeks of October, however, growth rates were well below average, around 51,600 square kilometers (19,900 square miles) per day. Following the pattern of recent years, growth became very rapid late in the month, averaging around 134,000 square kilometers (51,700 square miles) per day. From October 13 into early November, the daily sea ice extent was the lowest for that day in the satellite record. Sea ice growth in the last 10 days of the month was mostly along the Siberian coast, extending northward, and along the Eurasian side of the sea ice pack, extending southward. Based on passive microwave data, the Northern Sea Route remained open through nearly all of October.

Air temperatures at the 925 hPa level (about 2,500 feet above the surface) were 4 to 5 degrees Celsius (7 to 9 degrees Fahrenheit) above average for the month across much of the Central and Western Arctic Ocean and the Siberian Arctic coast, as well as over Northern Greenland. Elsewhere in the Arctic and the northernmost Atlantic regions, temperatures were near average to slightly below average. Temperatures in Central Canada were 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) below average (Figure 2b).

The average sea level pressure pattern for October was characterized by below-average pressure over the Northern Atlantic Ocean and Laptev and Bering Seas, driving winds northward toward the Lena River region, Barents Sea, and Novaya Zemlya. Below-average pressure also occurred over the Hudson Bay (Figure 2c).

October 2020 compared to previous years

Figure 3. Monthly October ice extent for 1979 to 2020 shows a decline of 10.11 percent per decade.||Credit: National Snow and Ice Data Center| High-resolution image

Figure 3. Monthly October ice extent for 1979 to 2020 shows a decline of 10.1 percent per decade.

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

Including 2020, the linear rate of decline for October sea ice extent is 10.1 percent per decade. This corresponds to a downward trend of -84,400 square kilometers (32,600 square miles) per year, or losing an area about the size of South Carolina each year. Over the 42-year satellite record, the Arctic has lost about 3.45 million square kilometers (1.33 million square miles) of ice in October, based on the difference in linear trend values in 2019 and 1979. This is comparable to twice the size of the state of Alaska.

Increasing departures from average in autumn

Figure 4a. With longer periods of open water during spring and summer, more solar energy is absorbed within the upper part of the ocean. This delays sea ice formation because before ice can form, the ocean must lose this heat to the atmosphere and then to space. This excess heat transferred to the atmosphere can be seen in a vertical profile of temperature by latitude along longitude 140 to 170 degrees E, which is shown in this plot.||Credit: NCEP/NCAR Reanalysis| High-resolution image

Figure 4a. This figure shows a profile of temperature (in color) for the lower half of the atmosphere (500 to 1,000 millibars, or about 18,000 feet to the surface) versus latitude, averaged along a swath of longitudes from 140 to 170 degrees E. With longer periods of open water during spring and summer, more solar energy is absorbed within the upper part of the ocean. This delays sea ice formation because before ice can form, the ocean must lose this heat to the atmosphere and then to space. This excess heat transferred to the atmosphere can be seen as the warm (red) layer over the open water region.

Credit: NCEP/NCAR Reanalysis
High-resolution image

Figure 4b. A delay in Arctic sea ice growth in autumn tends to lead to large departures from average in sea ice extent after the summer minimum and particularly in the month of October. The five lowest September extent minima (2007, 2012, 2016, 2019, and 2020) all show large departures in October extent compared to the reference period. This plot shows Arctic sea ice extent anomalies for those five years from June to December compared with the 1981 to 1990 average, 1991 to 2000 average, and the 2001 to 2010 average.||Credit: NSIDC| High-resolution image

Figure 4b. A delay in Arctic sea ice growth in autumn tends to lead to large departures from average in sea ice extent after the summer minimum and particularly in the month of October. The five lowest September extent minima (2007, 2012, 2016, 2019, and 2020) all show large departures in October extent compared to the reference period. This plot shows Arctic sea ice extent anomalies for those five years from June to December compared with the 1981 to 1990 average, 1991 to 2000 average, and the 2001 to 2010 average.

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

Figure 4c. This chart shows monthly sea ice extent anomaly (difference from the 1981 to 2010 average) for 1979 to October 2020. Low sea ice extent in autumn is shown as deep blue periods in several years beginning in 2007.||Credit: NSIDC| High-resolution image

Figure 4c. This chart shows monthly sea ice extent anomaly (difference from the 1981 to 2010 average) for 1979 to October 2020. Deep blue colors depict low autumn sea ice extent over the past 15 years.

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

On October 24, Arctic sea ice extent had its largest departure from the 1981 to 2010 average of daily sea ice extent in the 42-year continuous satellite record, at 3.4 million square kilometers (1.31 million square miles). With longer periods of open water during spring and summer, more solar energy is absorbed within the upper few tens of meters of the ocean. This has the effect of delaying sea ice formation—before ice can form, the ocean must lose this heat to the atmosphere and then to space (Figure 4a).

The delay in ice regrowth leads to large departures from average in sea ice extent in the time after the summer minimum and particularly in the month of October. The five lowest September extent minima (2007, 2012, 2016, 2019, and 2020) all show large departures in October extent compared to the reference period (Figure 4b).

This excess heat transferred to the atmosphere can be seen in a vertical profile of temperature by latitude along longitude 140 to 170 degrees E, which cuts though the open water area along the Eurasian coast (Figure 4a). In the past two decades, high autumn temperatures over the open water here have strongly contributed to Arctic Amplification—the larger rise in air temperatures over the Arctic compared to the rest of the globe. However, the anomalous warmth is largely limited to near the surface of the ocean.

Northern Sea Route shipping rises as sea ice falls

Figure 5. This chart shows Northern Sea Route (NSR) shipping traffic for August 2020 and other shipping information for that region. Track color legend is shown in the lower right. Transits through the NSR are shown in red, departing or arriving at the Arctic coastal ports in blue and green, and port-to-port within the Arctic is shown in yellow. The increase in August activity between 2018, 2019, and 2020 is shown in the bar chart at upper left. ||Credit: CHNL Information Office at Nord University| High-resolution image

Figure 5. This chart shows Northern Sea Route (NSR) shipping traffic for August 2020 and other shipping information for that region. Track color legend is shown in the lower right. Transits through the NSR are shown in red, departing or arriving at the Arctic coastal ports in blue and green, and port-to-port within the Arctic is shown in yellow. The increase in August activity between 2018, 2019, and 2020 is shown in the bar chart at upper left.

Credit: Center for High North Logistics Information Office at Nord University
High-resolution image

Commercial shipping along the Northern Sea Route of the Russian north coast is increasing. This includes complete transits from Europe to East Asia, local shipping within the Arctic Ocean, and deliveries of liquefied natural gas from gas fields in the Yamal Peninsula to ports in both Europe and East Asia. The years 2019 and 2020 saw significantly increased shipping activity compared with 2018. 2020 had slightly more shipping than 2019 when comparing August shipping from both years. The shipping traffic map shows the importance of passages just north of the Taymyr Peninsula and near the New Siberian Islands on either side of the Laptev Sea; these are generally the last areas to clear of ice, and only in the warmest years. However, in 2020, the Northern Sea Route was essentially ice free from mid-July through about October 25. Icebreaker and ice-hardened tankers made several voyages within the route as early as June.

Looking to the south

Figure 6. This figure shows the Japanese Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) sea ice concentration for Antarctic sea ice on October 31, 2020. Antarctic sea ice extent reached its seasonal sea ice extent maximum of 18.95 million square kilometers (7.32 million square miles) on September 28, 2020. Sea Ice Index data. About the data||Credit: University of Bremen|High-resolution image

Figure 6. This figure shows the Japanese Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) sea ice concentration for Antarctic sea ice on October 31, 2020. Antarctic sea ice extent reached its seasonal sea ice extent maximum of 18.95 million square kilometers (7.32 million square miles) on September 28, 2020. Sea Ice Index data. About the data

Credit: University of Bremen
High-resolution image

Antarctic sea ice extent reached its seasonal maximum of 18.95 million square kilometers (7.32 million square miles) on September 28, as was tentatively reported in the October post. The maximum extent was the eleventh highest in the satellite record. Since then, Antarctic sea ice has declined by 1.30 million square kilometers (502,000 million square miles), but at a rate slightly slower than the average, resulting in a slight increase in the difference between the daily sea ice extent and the 1981 to 2010 average. Sea ice extent is above average along a wide area of the Ross Sea and Wilkes Land coast, and in the Eastern Weddell Sea. It is slightly below average in the Bellingshausen and Amundsen Seas. Notably, in the last few days of the month, sea ice concentration dropped in the area of the Maud Rise and in an area near the front of the Amery Ice Shelf.

Suddenly in second place

In the first week of September, sea ice extent took a sharp downward turn, exceeding the pace of decline for any previous year during that period, and placing the 2020 sea ice minimum firmly as second lowest—after 2012—in the 42-year continuous satellite record. Pulses of warm air from north-central Siberia are responsible for the late downward trend. Sea ice decline has slowed in the past few days, and the annual minimum is imminent.

Overview of conditions

Figure 1a. Arctic sea ice extent for September 15, 2020 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 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. This figure shows daily Arctic sea ice extent as of September X, 2020, as well as the 1981 to 2010 median and 2007, 2012, 2016, 2019, and 2020.||Credit: National Snow and Ice Data Center|High-resolution image

Figure 1b. The graph above shows Arctic sea ice extent as of September 15, 2020, along with daily extent data for several low sea ice extent years and the record low year. 2020 is shown in blue, 2019 in dark green, 2018 in purple, 2007 in light green, 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 1c. This figure shows the Japanese Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) sea ice concentration for Arctic sea ice on September 12, 2020. ||Credit: University of Bremen|High-resolution image

Figure 1c. This map shows sea ice concentration for Arctic sea ice on September 12, 2020, using data collected from the Japanese Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2).

Credit: University of Bremen
High-resolution image

Figure 1d. This figure compares Arctic sea ice extent on September 1, 2020 (in white), and September 14, 2020 (in blue), showing recent areas of retreat. ||Credit: National Snow and Ice Data Center|High-resolution image

Figure 1d. This figure compares Arctic sea ice extent on September 1, 2020 (in white), and September 14, 2020 (in blue), showing recent areas of retreat.

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

Sea ice extent stood at 3.74 million square kilometers (1.44 million square miles) on September 15, already well below 2007, 2016, and 2019 and within 400,000 square kilometers (154,400 square miles) of the record low extent set in 2012 (Figure 1a). Sea ice extent has dropped below 4 million square kilometers (1.54 million square miles) only once before, in 2012 (Figure 1b). Between August 31 and September 5, 2020, sea ice extent decreased by an average of 79,800 square kilometers (30,800 square miles) per day. This is a greater loss rate than any other year for these six days in the sea ice record. Ice retreat during this period was along the ice front in the northern Barents, Kara, and Laptev seas. A remaining tail of multiyear ice extends into the southern Beaufort Sea north of the Mackenzie River Delta and the Alaskan North Slope. North of Scandinavia and Russia, a very broad sea-ice-free area exists with the ice edge lying near 85 degrees N, far to the north of Svalbard, Franz Josef Land, and Severnaya Zemlya (Northern Land) (Figure 1c). The sharply defined ice edge in this area, between about 0 degrees and 100 degrees longitude, indicates strong compaction of the ice by winds coming from the south and is the furthest north the ice edge has been in this location over the satellite data record (Figure 1d).

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, from September 1 to 14, 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 2a. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, from September 1 to 14, 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 average sea level pressure in the Arctic in millibars (hPa) from September 1 to 14, 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. This plot shows average sea level pressure in the Arctic in millibars (hPa) from September 1 to 14, 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

As assessed over the first two weeks of September, air temperatures at the 925 mb level (about 2,500 feet above sea level) were above average over much of the Eurasian side of the Arctic Ocean. Air temperatures were up to 6 degrees Celsius (11 degrees Fahrenheit) above the 1981 to 2010 average near the Taymyr Peninsula of north-central Siberia. Temperatures were 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) below average in easternmost Siberia and western Alaska, 4 degrees Celsius (7 degrees Fahrenheit) below average in central Canada, and 5 degrees Celsius (9 degrees Fahrenheit) below average in northern Greenland (Figure 2a). The atmospheric circulation over the first two weeks of the month was characterized by generally high pressure in eastern Siberia and low pressure over the Atlantic side of the Arctic, driving winds from the south over much of the Eurasian side of the Arctic Ocean (Figure 2b). The Arctic Oscillation index has cycled between slightly negative and moderately positive values. Pulses of warm air have been observed to migrate across the Arctic Ocean and then break down over a scale of several days.

Late summer sea ice drift and sea surface temperature

Figure 3a. This figure shows sea ice motion determined from National Snow and Ice Data Center EASE-Grid passive microwave data from August 26, 2020, to September 1, 2020.||Credit: National Snow and Ice Data Center|High-resolution image

Figure 3a. This figure shows sea ice motion determined from National Snow and Ice Data Center EASE-Grid passive microwave data from August 26 to September 1, 2020.

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

Figure 3b. This map shows sea surface temperature and ice concentration for September 13, 2020. The locations of three Upper layer Temperature of the Polar Oceans (UpTempO) drifting buoys are marked as 1, 2, and 7. Sea surface temperature data are from the National Oceanic and Atmospheric Administration daily Optimum Interpolation Sea Surface Temperature (OISST), and ice concentration from the NSIDC Sea Ice Index. Download data from UptempO drifting buoy locations. ||Credit: University of Washington|High-resolution image

Figure 3b. This map shows sea surface temperature (SST) in degrees Celsius and ice concentration for September 13, 2020. 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

Ice motion in late August drifted northward along the Eurasian side of the Arctic Ocean, while the multiyear sea ice region north of western Canada and Alaska drifted rapidly westward toward the Chukchi Sea (Figure 3a). Ice motion was determined by tracking patterns in the sea ice using passive microwave and other data. Both the motion and the compaction of the loose sea ice pack are responsible for the strong decline in ice extent seen in this period and the following week. Warm waters in the Chukchi Sea may induce some late melting of the multiyear ice from the heat in the ocean, but much of the water in the region is already near freezing from more recent ice loss (Figure 3b).

Sailing across the top of the world in a “new Arctic” soon

Figure 4. This map shows the potential transpolar shipping route discussed in Bennett et al., 2020. The orange line shows the approximate September 2020 ice edge overlaid on the September 2019 Arctic sea ice extent. ||Credit: Bennett et al., 2020|High-resolution image

Figure 4. This map shows the potential transpolar shipping route discussed in Bennett et al., 2020. The orange line shows the approximate September 2020 ice edge overlaid on the September 2019 Arctic sea ice extent.

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

A recent paper by an international group led by political geographer Mia Bennett at the University of Hong Kong discusses the potential impacts of the near-future emergence of a transpolar shipping route as sea ice retreat continues to open a very wide shipping lane along the Eurasian side of the Arctic Ocean (as it has this year). The route would pass over the North Pole as a way of avoiding an extensive Russian exclusive economic zone (EEZ) and still-contended continental shelf claim.

This emerging transpolar route reflects a fundamentally changed Arctic environment. Another recent paper by researchers Laura Landrum and Marika Holland at the National Center for Atmospheric Research found that the Arctic has indeed entered into a “new Arctic climate” state. This new climate is one characterized by warmer temperatures, more open water, less sea ice, more rain, and less snow. In the Arctic, weather that used to be considered extreme is becoming the norm. The summer of 2020 is clearly representative of this new Arctic.

Further reading

Bennett, M. M. et al. 2020. The opening of the Transpolar Sea Route: Logistical, geopolitical, environmental, and socioeconomic impacts. Marine Policy. doi.10.1016/j.marpol.2020.104178.

Landrum, L., and Holland, M. M. 2020. Extremes become routine in an emerging new Arctic. Nature Climate Change. doi.10.1038/s41558-020-0892-z.

Summer’s last stand

While the Arctic summer is waning, sea ice extent continues to drop. In early August, ice-free pockets began to develop in the Beaufort and Chukchi Seas and expanded steadily through the first half of the month.

Overview of conditions

Figure 1a. Arctic sea ice extent for August 17, 2020 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 1a. Arctic sea ice extent for August 17, 2020 was 5.15 million square kilometers (1.99 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 Japan Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) image shows sea ice concentration in the Arctic Ocean on August 17, 2020, highlighting the openings of sea ice north of Alaska within the Beaufort and Chukchi Seas. ||Credit: University of Bremen |High-resolution image

Figure 1b. This Japan Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) image shows sea ice concentration in the Arctic Ocean on August 17, 2020, highlighting the openings of sea ice north of Alaska within the Beaufort and Chukchi Seas.

Credit: University of Bremen
High-resolution image

Sea ice extent stood at 5.15 million square kilometers (1.99 million square miles) on August 17, essentially tied with 2007 for the third lowest extent for the date since the satellite record began in 1979 (Figure 1a). The August 17 extent was lower only in 2012 and 2019. The most notable feature during the first half of August was the development of substantial openings of the sea ice north of Alaska within the Beaufort and Chukchi Seas. This may be related to the mid-July storm that passed and spread out the ice cover, creating openings in the sea ice.

The reduced concentration patches and initial openings were first observed in higher-resolution Japan Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) fields from the University of Bremen (Figure 1b). By the middle of the month, the ice-free areas had greatly expanded. Meanwhile, another open water patch developed north of the Mackenzie River delta. Persistent offshore winds have also moved the pack ice edge northward from the northern Greenland and Ellesmere coasts.

The Northern Sea Route has been open for a few weeks. The Northwest Passage appears to be mostly ice-free with a little ice remaining within Victoria Strait. The deeper Parry Channel still contains a substantial amount of sea ice and will likely not open this year.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of August 17, 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 2a. The graph above shows Arctic sea ice extent as of August 17, 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

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, from August X to XX, 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, from August 1 to 15, 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. This plot shows average sea level pressure in the Arctic in millibars (hPa) from August 1, 2020 to August 15, 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 2c. This plot shows average sea level pressure in the Arctic in millibars (hPa) from August 1, 2020 to August 15, 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

From July 27 through August 8, 2020, extent declined 470,000 square kilometers (181,000 square miles), which is less than half of the average 1981 to 2020 extent loss of 950,000 square kilometers (367,000 square miles) during the same period (Figure 2a). After August 8, the rate of loss increased again due in part to melt in the Beaufort and Chukchi Seas, though the loss rate was still slower than average.

As assessed from August 1 to 15, air temperatures at the 925 mb level (about 2,500 feet above sea level) were above average over much of the Arctic Ocean, with air temperatures up to 7 degrees Celsius (13 degrees Fahrenheit) above average over the North Pole. Temperatures were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below average in the East Siberian Sea region (Figure 2b). The atmospheric circulation was characterized by generally high pressure on the Eurasian side of the Arctic and low pressure on the North American side (Figure 2c).

2020 Arctic sea ice minimum forecasts

Figure 3. This figure show Arctic sea ice extent projections using data through August 17, 2020. These projections include the 2020 minimum and September 2020 average extent. These are based on the average loss rates for the years 2007 to 2019. The variation in the projection decreases for later dates because there is less time for variation before the end of the melt season. ||Credit: National Snow and Ice Data Center|High-resolution image

Figure 3. This figure show Arctic sea ice extent projections using data through August 17, 2020. These projections include the 2020 minimum and September 2020 average extent. These are based on the average loss rates for the years 2007 to 2019. The variation in the projection decreases for later dates because there is less time for variation before the end of the melt season.

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

Table 1. This table shows a projection of Arctic sea ice extent for the September average and the daily minimum starting from June 1, July 1, August 1, and August 17, 2020. The projection in based on the average of the 2007 to 2019 estimates and the standard deviation range is in parentheses. Units are in millions of square kilometers. ||Credit: National Snow and Ice Data Center|High-resolution image

Table 1. This table shows a projection of Arctic sea ice extent for the September average and the daily minimum starting from June 1, July 1, August 1, and August 17, 2020. The projection is based on the average of the 2007 to 2019 estimates and the standard deviation range is in parentheses. Units are in millions of square kilometers.

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

The end of the summer melt season, when the Arctic sea ice extent reaches its seasonal minimum, is likely about three to four weeks away. Over the last several years, there has been a community effort, called the Sea Ice Outlook, to submit seasonal projections 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 summer. Projections of the minimum and September average extent are submitted using data through the beginning of June, July, and August as starting points. Another projection with data through August 17 is included here to provide a further update (Figure 3 and Table 1). The projections are based on the average loss rates for the years 2007 to 2019. The variation in the projection decreases for later dates because there is less time before the end of the melt season. Note how the projections have seesawed up and down from June through mid-August. This is a result of the changes in the extent loss rates from one period to the next; it highlights how strongly weather conditions affect the ice loss through the summer, as well as the influence of thickness on how fast ice is melted away.

Another projection from National Snow and Ice Data Center scientist Andy Barrett, using a probabilistic method developed by our former colleague Drew Slater, projects a September average extent of 4.48 million square kilometers (1.73 million square miles), which is slightly higher than the Meier method prediction.

Past ice-free Arctic Oceans

Climate models are projecting that under continued warming trends, the Arctic Ocean may become substantially ice-free during the summer within the next 30 years. Such a state would be unprecedented for at least thousands of years. However, such conditions may have existed during the Last Interglacial (LIG) period, about 130,000 to 116,000 years before present, when summer Arctic air temperatures were 4 to 5 degrees Celsius (7 to 9 degrees Fahrenheit) above pre-industrial levels. Previous model simulations were unable to capture the reconstruction of LIG Arctic temperatures, and a likely cause was a simplified treatment of sea ice that did not represent the influence of melt ponds on summer sea ice loss. The latest version of the UK Hadley Centre Global Environment Model version 3 (HadGEM3) climate model includes more complex characterization of melt ponds. In a recent paleoclimate study, this model was able to reproduce the reconstructed estimates of summer Arctic air temperatures during the LIG. This supports previous studies showing that melt pond formation is a key factor in the loss of summer sea ice because formation of melt ponds earlier in the season results in more absorption of solar energy through the summer and therefore more ice melt. ASINA team member Julienne Stroeve is a co-author on the study.

Farewell to the Milne Ice Shelf

Figure 4. This NASA Landsat 8 true color image shows the former extent of the Milne Ice Shelf on Ellesmere Island in Nunavut, Canada, on July 23, 2018. It was acquired with off-nadir pointing of the satellite. The shelf is covered with linear blue lakes of meltwater that collect in the gently folded (corrugated) surface. In the upper left is the Arctic Ocean covered by perennial sea ice. ||Credit: NASA |High-resolution image

Figure 4. This NASA Landsat 8 true color image shows the former extent of the Milne Ice Shelf on Ellesmere Island in Nunavut, Canada, on July 23, 2018. It was acquired with off-nadir pointing of the satellite. The shelf is covered with linear blue lakes of meltwater that collect in the gently folded (corrugated) surface. In the upper left is the Arctic Ocean covered by perennial sea ice.

Credit: NASA
High-resolution image

Another recent notable event in the Arctic was the calving of a large area of the Milne Ice Shelf off Ellesmere Island in Nunavut, Canada, in late July. The Milne Ice Shelf had been Canada’s last intact Arctic ice shelf. A piece of the shelf measuring about 81 square kilometers (31 square miles), which made up about 43 percent of the total ice shelf area, broke off on July 30 and 31. Warm air temperatures and offshore winds likely triggered the ice shelf collapse. Offshore winds move the perennial sea ice cover north from the coast, reducing the compressive forces that hold the shelf in, and potentially contribute to basal melting of the ice by allowing solar energy to warm the upper ocean layer. Polar explorer Robert Peary discovered the Canadian Arctic ice shelves, once a single 9,000-square kilometer (3,475-square mile) sheet, in 1902. Although evidence from seal remains and driftwood suggests they were thousands of years old, they have dwindled dramatically and now comprise of only a few small ice-covered fragments in inlets along the northernmost coast of Canada.

Rest in peace, Koni Steffen

Former CIRES Director Konrad Steffen. (Courtesy of CIRES/CU Boulder)

Former Cooperative Institute for Research in Environmental Sciences director Konrad Steffen passed away on August 8, 2020, while conducting field work on the Greenland Ice Sheet. He will be missed. Photo courtesy of CIRES/CU Boulder.

As has been widely reported, the polar climate community suffered a huge loss in the tragic death of our colleague and former Cooperative Institute for Research in Environmental Sciences director, Konrad (Koni) Steffen on the Greenland Ice Sheet. He was an outstanding researcher, science communicator, and friend. He is most remembered for his research on the Greenland Ice Sheet, including an invaluable 30-plus-year climate record of station data spanning the island that he instituted and maintained. Earlier in his career, he conducted substantial research on sea ice, visiting both polar regions. Early papers of his (e.g., Steffen and Schweiger, 1991; Steffen et al., 1992) helped provide key validation of the sea ice concentration and extent products that we employ in our analyses here. He will be missed.

Further reading

Guarino, M., L. C. Sime, D. Schröeder, et al. Sea-ice-free Arctic during the Last Interglacial supports fast future loss. Nature Climate Change. (2020). doi.10.1038/s41558-020-0865-2.

Steffen, K., J. Key, D. J. Cavalieri, J. Comiso, P. Gloersen, K. St. Germain, and I. Rubinstein. 1992. The estimation of geophysical parameters using passive microwave algorithms. American Geophysical Monograph Series. doi:10.1029/GM068p0201.

Steffen, K., and A. Schweiger. 1991. NASA team algorithm for sea ice concentration retrieval from Defense Meteorological Satellite Program special sensor microwave imager: comparison with Landsat satellite data. Journal of Geophysical Research: Oceans. doi:10.1029/91JC02334.

Steep decline sputters out

The fast pace of ice loss observed in the beginning of July continued through the third week of July, after which the ice loss rates slowed dramatically. Above-average air temperatures and extensive melt pond development helped to keep the overall sea ice extent at record low levels, however, leading to a new record low for the month of July. Toward the end of the month, a strong low pressure system moved into the ice in the Beaufort Sea region. Antarctic sea ice extent remains below average levels as it climbs towards its seasonal maximum, which is typically reached in early October.

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 July 2020 was 7.28 million square kilometers (2.81 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 July 2020 was 7.28 million square kilometers (2.81 million square miles), the lowest extent in the satellite record for the month. This was 2.19 million square kilometers (846,000 square miles) below the 1981 to 2010 July average and 310,000 square kilometers (120,000 square miles) below the previous record low mark for July set in 2019.

Arctic sea ice extent continued to track at record low levels through the end of July, dominated by extensive open water in the East Siberian, Laptev, and Kara Seas. As of July 31, sea ice was tracking 187,000 square kilometers (72,200 square miles) below 2019, which held the previous record for least amount of sea ice on that date, and 396,000 square kilometers (153,000 square miles) below 2012, the year of the record low. The ice edge was further north than average everywhere except the southeastern Beaufort Sea, the Canadian Archipelago and the East Greenland Sea.

Because of the unusually early retreat of sea ice on the Siberian side of the Arctic, the Northern Sea Route appears ice-free in the satellite passive microwave data record in the second half of the month. This is the earliest in the year that the route has been free of ice, according to this data record. However, the MASIE sea ice product, which relies on data from several satellite sources and is provided through collaboration with the U.S. National Ice Center, shows some ice remaining south of Severnaya Zemlya. While ice chart data tend to be conservative, it appears that the route likely will be open for the next two to three months.

While ice retreated at a fast pace through the first three weeks of July, it started to slow around July 23 as the retreating ice edge approached areas of higher-concentration ice that does not melt out as readily. Nevertheless, July 2020 set a new record low sea ice extent over the satellite time-period.

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 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 2a. The graph above shows Arctic sea ice extent as of August 3, 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. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, from July 1 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

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 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

Through the month, sea ice declined by an average of 116,000 square kilometers (44,800 square miles) per day, faster than the 1981 to 2010 average of 86,800 square kilometers (33,500 square miles) per day. This corresponds to a total loss of 3.59 million square kilometers (1.39 million square miles) of ice extent during July 2020.

The average near-surface air temperatures at the 925 hPa level (about 2,500 feet above sea level) for July was up to 8 degrees Celsius (14 degrees Fahrenheit) above average over the central Arctic Ocean centered near the pole. Coastal regions experienced temperatures between 2 and 4 degrees Celsius (4 to 7 degrees Fahrenheit) above average. Above-average air temperatures also stretched further south through Baffin Bay and Davis Strait. The exception was the southern Beaufort Sea which was 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) cooler than average. The warm conditions of the first half of July continued through the third week of July. This temperature pattern reflects unusually high sea level pressure over the Laptev, East Siberian, and Chukchi Seas and Greenland, coupled with unusually low sea level pressure over the Central Arctic Ocean and over the North Atlantic Ocean, centered north of Iceland. This pattern has brought warm air over Siberia, extending to the coastal regions while allowing cold Arctic air to spill out into Russia.

July 2020 compared to previous years

Figure 3. Monthly XXXXX ice extent for 1979 to 20XX shows a decline of X.X percent per decade.||Credit: National Snow and Ice Data Center| High-resolution image

Figure 3. Monthly July sea ice extent for 1979 to 2020 shows a decline of 7.48 percent per decade.

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

Including 2020, the linear rate of decline of July sea ice extent is 7.48 percent per decade, or 70,800 square kilometers (27,300 square miles) per year. This corresponds to about the size of the state of North Dakota. Over the 42-year satellite record, the Arctic has lost about 2.90 million square kilometers (1.12 million square miles) of ice in July, based on the difference in linear trend values in 2020 and 1979. This is comparable to about the size of the states of Alaska, Texas, and California combined.

Cyclone in the Beaufort Sea

Figure 4. This figure shows four images that depict an Arctic cyclone from July 27 to 30, 2020. Image a in the upper left-hand corner is a NASA Moderate Resolution Imaging Spectroradiometer (MODIS) composite image that shows the cyclone in Beaufort Sea region on July 29. Image b in the upper right-hand corner shows a NASA Advanced Microwave Scanning Radiometer 2 (AMSR-2) sea ice concentration map for July 29 that shows the same area as in a. Image c in the lower left-hand corner shows the surface pressure from Climate Reanalyzer for July 29. Image d in the lower right-hand corner shows the wind speed for July 29 from Climate Reanalyzer.||Credit: National Snow and Ice Data Center| High-resolution image

Figure 4. This figure shows four images that depict an Arctic cyclone from July 27 to 30, 2020. Image a in the upper left-hand corner is a NASA Moderate Resolution Imaging Spectroradiometer (MODIS) composite image from NASA Worldview that shows the cyclone in Beaufort Sea region on July 29. Image b in the upper right-hand corner shows a Japan Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) sea ice concentration map from the University of Bremen for July 29 that shows the same area as in a. Image c in the lower left-hand corner shows the surface pressure from Climate Reanalyzer for July 29. Image d in the lower right-hand corner shows the wind speed for July 29 from Climate Reanalyzer.

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

A strong, but not exceptional, cyclone with a minimum sea level pressure of 975 hPa on July 28 entered the Beaufort Sea from Alaska in late July. Winds along the sea ice edge reached about 12 meters per second (23 knots). While the cyclone gradually weakened through the next few days, it appears to have forced some ice divergence within the East Siberian Sea such that the ice edge expanded slightly southwards. The storm temporarily caused atmospheric and surface effects on the passive microwave signal due to emission from the thick clouds and changes in the snow and sea ice surface properties (Figure 4). This is illustrated in the sea ice concentration fields (Figure 4b), where concentrations are reduced, particularly in the “eye” of the storm—the small circular region near the center of the image north of Utqiagvik that has much lower concentration ( the green color corresponds to about 50 percent concentration). The spiral circulation pattern is also quite clear in the Bremen sea ice concentrations, which is an atmospheric and surface effect due to the storm, not a real pattern of concentration. However, early indications are that some spreading of the ice pack occurred, and this may permit somewhat faster sea ice decline in the coming weeks in this area. A similar storm in 2012—the record low sea ice extent year—led to effects that augmented the decline in that year.

Melt onset and melt ponds

Figure 5a. This figure shows the melt onset anomaly (left) and mean melt onset dates (right) for 2020. Anomaly is computed relative to the 1981 to 2010 average. Melt detection is based on passive microwave brightness temperatures following the algorithm described in Markus et al. 2008. ||Credit: National Snow and Ice Data Center| High-resolution image

Figure 5a. This figure shows the melt onset anomaly (left) and mean melt onset dates (right) for 2020. Anomaly is computed relative to the 1981 to 2010 average. Melt detection is based on passive microwave brightness temperatures following the algorithm described in Markus et. al. 2009.

Credit: Linette Boisvert and Jeffrey Miller, NASA Goddard Space Flight Center
High-resolution image

Figure 5b. This figure shows melt pond fractional area anomalies for May (left) and June (right). Red colors show more extensive melt ponds relative to the 2002 to 2020 average, whereas blue colors show less melt ponds than average. ||Credit: Markus et. al., 2009| High-resolution image

Figure 5b. This figure shows melt pond fractional area anomalies for May (left) and June (right). Red colors show more extensive melt ponds relative to the 2002 to 2020 average, whereas blue colors show fewer melt ponds than average.

Credit: Sanggyun Lee, University College London
High-resolution image

The timing of melt onset and melt pond development influences how much sea ice will melt during the summer. This is because early melt onset and early melt pond development lowers the surface albedo, which allows more of the sun’s energy to be absorbed by the ice. In turn, early development of open water allows the ocean to readily absorb solar energy, heating the ocean mixed layer, fostering more bottom and lateral ice melt.

This summer, melt onset was earlier than average over almost all of the Arctic Ocean, the exceptions being the southern portions of the Beaufort, Chukchi, and parts of the East Siberian Seas as well as the southern Hudson Bay. Melt onset was as much as 30 days earlier than average in the Laptev and Kara Seas (Figure 5a). This early melt onset was linked in part to persistent high sea level pressure over Siberia throughout April and May and a record warm spring in that region. Early melt onset on the Siberian side of the Arctic is reflected in more extensive melt pond development over the East Siberian, Laptev, and parts of the Kara Seas already in May (Figure 5b). By June, melt ponds were more extensive than average over much of the Arctic Ocean and, most prominently, north of Greenland and the Canadian Archipelago. Extensive early season melt pond development in the East Siberian and Laptev Seas likely played a role in earlier open water development in the region. At the same time, this region likely had relatively thin ice at the start of the melt as a result of the strong positive Arctic Oscillation over winter. A general spring and early summer offshore atmospheric circulation also contributed to early ice retreat in this region.

Ice melt and phytoplankton

Figure 6. This image shows a phytoplankton bloom in the Barents Sea on July 26, 2020, from a Moderate Resolution Imaging Spectroradiometer (MODIS) True Color composite in NASA Worldview. The phytoplankton show up in the visible imagery as a light blue and teal swirling pattern against the dark blue ocean. The northern part of the Finnoscandian peninsula is in the lower right corner. ||Credit: NASA Worldview|High-resolution image

Figure 6. This image shows a phytoplankton bloom in the Barents Sea on July 26, 2020, from a Moderate Resolution Imaging Spectroradiometer (MODIS) True Color composite in NASA Worldview. The phytoplankton show up in the visible imagery as a light blue and teal swirling pattern against the dark blue ocean. The northern part of the Finnoscandian peninsula is in the lower right corner.

Credit: NASA Worldview
High-resolution image

As sea ice retreats and melt ponds form, more light can enter the Arctic Ocean, increasing the time-period over which phytoplankton can grow. This may increase overall net primary productivity, which is the rate at which the full metabolism of phytoplankton produces biomass, as light plays a strong role in initiating phytoplankton growth. Other factors may counteract the positive influence of more light availability, namely reduced mixing of deep nutrients to the surface waters. Mixing is reduced due to increased sea ice melt, precipitation and river outflow, which can increase surface stratification, or inhibit mixing, and hence inhibit nutrients from reaching the surface.

A new study analyzed 20 years of phytoplankton and net primary productivity over the Central Arctic Ocean. Researchers examined these competing effects using a combination of direct observations on light and phytoplankton biomass together with satellite-derived estimates of chlorophyll a (Chl a) and sea ice concentration. Overall, Chl a concentrations have increased for the Arctic Ocean as a whole, but there are large regional differences, with increases in Chl a observed in the Chukchi and Barents inflow shelves, and no significant changes elsewhere.

The study was able to determine that increases in net primary productivity from 1998 to 2018 were not only a result of changes in open water fraction, but also a result of changes in nutrient availability. In particular, Pacific water inflow through Bering Strait has brought more nutrients into the Chukchi Sea to support summer phytoplankton blooms. Similarly, on the Atlantic side, weakening of the mixed layer ocean stratification increased nutrient availability to surface waters. Chl a increases on shelfbreaks appears to be a result of increased vertical mixing as sea ice melts back and exposes surface waters to winds. This vertical mixing overcomes the stratification effects of the added freshwater. Overall, primary production of the Arctic Ocean has increased 57 percent between 1998 and 2018.

Antarctic check-in

Figure 7. This figure shows the Japanese Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) sea ice concentration for Antarctic sea ice on July 30, 2020. The Cosmonaut Sea polynya is the oblong low-concentration region near 35° East longitude. ||Credit: University of Bremen|High-resolution image

Figure 7. This figure shows the Japanese Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) sea ice concentration for Antarctic sea ice on July 30, 2020. The Cosmonaut Sea polynya is the oblong low-concentration region near 35° East longitude.

Credit: University of Bremen
High-resolution image

Antarctic sea ice grew at a slower-than-average pace in July, resulting in a monthly mean ice extent of 15.65 million square kilometers (6.04 million square miles), or ninth lowest in the continuous satellite record. Regionally, the Bellingshausen and eastern Ross Seas, as well as a wide area south of the Indian Ocean, had below-average extents relative to the 1981 to 2010 average, and the western Weddell Sea had above-average extent. Despite the below-average extent in the Indian Ocean region, the Cosmonaut Sea once again featured a large closed polynya of about 20,000 square kilometers (7,700 square miles) at month’s end, similar to the feature we reported on in the August 2019 ASINA summary. The feature transitioned from an embayment in the ice edge to a closed polynya around July 20. The cause of the polynya is upwelling of deeper warmer water, which suppresses sea ice growth (see references below).

Further reading

Comiso, J. C. and A. L.  Gordon. 1987. Recurring polynyas over the Cosmonaut Sea and the Maud Rise. Journal of Geophysical ResearchOceans. doi: 10.1029/JC092iC03p02819.

Lee, S., S. Stroeve, M. Tsamados, and A. Khan. 2020. Machine learning approaches to retrieve pan-Arctic melt ponds from visible satellite imagery. Remote Sensing of Environment. doi.10.1016/j.rse.2020.111919.

Lewis, K. M., G. L. van Dijken, and K. R. Arrigo. 2020. Changes in phytoplankton concentration now drive increased Arctic Ocean primary production. Science. doi:10.1126/science.aay8380.

Markus, T., J. C. Stroeve, and J. Miller. 2009. Recent changes in Arctic sea ice melt onset, freeze-up, and melt season length. Journal of Geophysical Research: Oceans. doi:10.1029/2009JC005436.

Prasad, T. G., J. L. McClean, E. C. Hunke, A. J.  Semtner, and D. Ivanova. 2005. A numerical study of the western Cosmonaut polynya in a coupled ocean–sea ice model. Journal of Geophysical Research: Oceans. doi: 10.1029/2004JC002858.

 

Laptev Sea lapping up the heat in June

The Siberian heat wave continued into June with a record high temperature in Verkhoyansk, just north of the Arctic Circle. The heat also affected the Laptev Sea, where ice extent dropped to a record low for this time of year. Sea ice extent was low overall in the Arctic Ocean, though not at record levels. Late June into early July is the period of most rapid ice loss in the Arctic.

Overview of conditions

Figure 1. Arctic sea ice extent for June 2020 was 10.58 million square kilometers (4.08 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 June 2020 was 10.58 million square kilometers (4.08 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

June 2020 sea ice extent averaged 10.58 million square kilometers (4.08 million square miles), placing it at third lowest in the satellite record for the month. This was 170,000 square kilometers (65,600 square miles) above the record low set in 2016. Ice loss during June was particularly pronounced in the Kara and Laptev Seas, where extent was well below average. In other areas of the Arctic Ocean, extents were near or slightly below average. Since June 19, sea ice extent in the Laptev Sea has been at a record low for this time of year.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of July 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 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 July 1, 2020, along with daily ice extent data for four previous years and 2012, 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

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for June 1 to 28, 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|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 June 1 to 28, 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 extent declined by an average of 64,300 square kilometers (40,000 square miles) per day—about 20 percent faster than the 1981 to 2010 average (Figure 2a).

Air temperatures at the 925 mb level (about 2,500 feet above sea level) were 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) above average over most of the Arctic Ocean (Figure 2b). Along the Siberian coast of the eastern Laptev Sea, temperatures were 8 degrees Celsius (14 degrees Fahrenheit) above average. After persisting in a winter-long strong positive phase, the Arctic Oscillation has been in a mostly neutral phase since early May.

June 2020 compared to previous years

Figure 3. Monthly June ice extent for 1979 to 2020 shows a decline of 4.06 percent per decade.||Credit: National Snow and Ice Data Center| High-resolution image

Figure 3. Monthly June ice extent for 1979 to 2020 shows a decline of 4.06 percent per decade.

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

Through 2020, the linear rate of decline for June sea ice extent is 4.06 percent per decade, which corresponds to 47,700 square kilometers (18,400 square miles) per year, about twice the size of the state of Vermont. The cumulative June ice loss over the 42-year satellite record is 1.96 million square kilometers (757,000 square miles), based on the difference in linear trend values in 2020 and 1979. This is about 12 percent larger than the state of Alaska.

Record set in the Laptev Sea

Figure4a. This graph shows Laptev Sea ice extent for May 1 through July 31 for the 1979 to 2019 median (black) as well as the sea ice extent for May 1 through June 30, 2020 (red). Extent is shown in thousands of square kilometers. The graph also includes the 25 percent and 75 percent quartiles (gray), and the minimum and maximum sea ice extent (dashed black). ||Credit: National Snow and Ice Data Center| High-resolution image

Figure 4a. This graph shows Laptev Sea ice extent for May 1 through July 31 for the 1979 to 2019 median (black) as well as the sea ice extent for May 1 through June 30, 2020 (red). Extent is shown in thousands of square kilometers. The graph also includes the 25 percent and 75 percent quartiles (gray), and the minimum and maximum sea ice extent (dashed black).

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

Figure 4b. This map shows sea surface temperature and ice concentration for June 28, 2020. The locations of three Upper layer Temperature of the Polar Oceans (UpTempO) drifting buoys are marked as 1, 2, and 7. Sea surface temperature data are from the National Oceanic and Atmospheric Administration daily Optimum Interpolation Sea Surface Temperature (OISST), and ice concentration from the NSIDC Sea Ice Index. Download data from UptempO drifting buoy locations.||Credit: University of Washington|High-resolution image

Figure 4b. This map shows sea surface temperature and ice concentration for June 28, 2020. The locations of three Upper layer Temperature of the Polar Oceans (UpTempO) drifting buoys are marked as 1, 2, and 7. Sea surface temperature data are from the National Oceanic and Atmospheric Administration daily Optimum Interpolation Sea Surface Temperature (OISST), and ice concentration from the NSIDC Sea Ice Index. Download data from UptempO drifting buoy locations.

Credit: University of Washington
High-resolution image

As noted above, northern Siberia and the Laptev Sea have seen particularly high temperatures compared to average. This contributed to early ice loss in the Laptev Sea. The strongly positive phase of the Arctic Oscillation (AO) over winter likely also played a role; studies have shown that strong offshore motion of the sea ice along the coast of Siberia during the positive AO fosters new ice growth, which is thinner and easier to melt out once summer arrives. Sea ice extent in the Laptev Sea was at record low from June 19 through the end of the month. With the early opening of the Laptev Sea, ocean sea surface temperatures (SST) have already risen up to 4 degrees Celsius (7 degrees Fahrenheit) above freezing, according to NOAA SST data provided by the Upper layer Temperature o the Polar Oceans (UpTemp0) buoy site (Figure 4b). River runoff may also be contributing to the warm surface waters in the region.

News from the South Pole

Figure 5a. Antarctic sea ice extent for June 2020 was 13.20 million square kilometers (5.10 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 5a. Antarctic sea ice extent for June 2020 was 13.20 million square kilometers (5.10 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 5b. The top figure shows a map of Antarctica as seen from space with the mechanisms discussed in Clem et al., 2020, overlain onto the map. Stronger westerlies driven by warming combined with tropical teleconnections from the negative phase of the Interdecadal Pacific Oscillation produce enhanced cyclonic activity in the Weddell Sea (illustrated with dark blue arrows). This increases the advection of warm moist air into the high Antarctic interior (illustrated with red arrows), but shifts wind direction over the Peninsula, slowing the warming there. The bottom figure shows mean annual air temperatures at Faraday/Vernadsky Station in the Antarctic Peninsula and at Amundsen-Scott South Pole Station, the locations of which are shown in top image. This figure illustrates near-record lows from the 1980s to late-1990s followed by a series of record and near-record highs since about 2000.||Credit: Stammerjohn and Scambos, 2020 |High-resolution image

Figure 5b. The top figure shows a map of Antarctica as seen from space with the mechanisms discussed in Clem et al., 2020, overlain onto the map. Stronger westerlies driven by warming at lower latitudes combined with changes in the storm track due to the Interdecadal Pacific Oscillation produce enhanced cyclonic activity in the Weddell Sea (illustrated with dark blue arrows). This increases the advection of warm moist air into the high Antarctic interior (illustrated with red arrows), but shifts wind direction over the Peninsula, slowing the warming there. The bottom figure shows mean annual air temperatures at Faraday/Vernadsky Station in the Antarctic Peninsula and at Amundsen-Scott South Pole Station, the locations of which are shown in top image. This figure illustrates near-record lows from the 1980s to late-1990s followed by a series of record and near-record highs since about 2000.

Credit: Stammerjohn and Scambos, the Institute of Alpine and Arctic Research and the Cooperative Institute for Research in Environmental Sciences, 2020
High-resolution image

Antarctic sea ice extent tracked slightly below the 1981 to 2010 average extent for the month of June, as it has for all but a few days since August 2016. Areas of below average ice extent are west of Enderby Land and the Bellingshausen Sea. Ice growth during the month was near average, and ice extent increased primarily in the eastern Weddell Sea, Ross Sea, and Bellingshausen Sea, as winter growth continued rapidly towards the maximum, which generally occurs in early October. An indentation in the sea ice edge in the Cosmonaut Sea region—near 50 degrees E longitude—suggests that a polynya may form there in July or August as the ice edge advances outward. At this time, there is no indication of the Maud Rise Polynya forming near 0 degrees longitude.

Air temperatures at the South Pole are climbing rapidly, according to a recent study led by our colleague, Kyle Clem. During the past 30 years, temperatures there have risen at three times the global average rate—0.6 degrees Celsius (1.1 degree Fahrenheit) per decade at the South Pole versus about 0.2 degrees Celsius per decade (0.4 degrees Fahrenheit) for the recent global average. The warming is tied to atmospheric circulation patterns, the positive trend of westerly winds around Antarctica as represented by the Southern Annular Mode (SAM) and its index, and the Interdecadal Pacific Oscillation (IPO), an El Niño-La Niña-like multi-decadal pattern of surface temperatures in the Pacific. Since the late 1990s, warming in the western tropical Pacific, which is associated with the ‘negative’ or La Niña-like phase of the IPO and climate trends of warmer sea surface temperatures, combined with the long-term trend of faster westerly winds around Antarctica has led to an increase in cyclone activity, i.e. more low- pressure systems, in the Weddell Sea, which tend to drive warm air towards the pole.

An earlier study of 50 years of weather data at South Pole by our colleague Matt Lazzara and others noted the trend towards warming beginning in the mid-1990s, although the larger causes of the warming were not clear at that time.

All of that said, the South Pole is still the South Pole, and that means cold. Following the rapid warming that Clem and his colleagues describe, average annual temperatures set a record in 2018 of -47 degrees Celsius (-53 degrees Fahrenheit).

Further reading

Clem, K. R., R. L. Fogt, J. Turner, B. R. Lintner, G. Marshall, J. R. Miller, and J. A. Renwick. 2020. Record warming at the South Pole during the past three decades. Nature Climate Change. doi:10.1038/s41558-020-0815-z.

 Lazzara, M. A., L. M. Keller, T.  Markle, and J. Gallagher. 2012. Fifty-year Amundsen–Scott South Pole station surface climatology. Atmospheric Researchdoi:10.1016/j.atmosres.2012.06.027.

Stammerjohn, S., and T. Scambos. 2020. Warming reaches the South Pole. Nature Climate Change. doi: 10.1038/s41558-020-0827-8.