Arctic sea ice has reached its annual minimum for 2021, ranking 12th lowest on record, according to provisional data from the National Snow and Ice Data Center (NSIDC).
Although this is the highest summer minimum since 2014, the NSIDC notes that the amount of multi-year sea ice this year is “one of the lowest levels in the Ice Age record.”
Sea ice in the Arctic and Antarctic undergoes an annual cycle, increasing in thickness and coverage during the colder months, and thinning and retreating as temperatures rise. Arctic sea ice generally reaches its “summer minimum” in September, marking the time when it covers the smallest area.
Last year, arctic sea ice minimum hit the second lowest on record, in part due to an intense heat wave over Siberia. In contrast, this year was defined by storms and low pressure systems, which kept temperatures low and kept older multi-year ice moving to fill in sea ice gaps, limiting the reduction in extent. .
Meanwhile, at the South Pole, the extent of the Antarctic sea ice is “well above the long-term average”, according to the NSIDC, as it reaches its annual maximum, which is expected within weeks. future.
Minimum “not remarkable”
The extent of Arctic sea ice reached its lowest for the year at 4.72 m square kilometers (km2) on September 16, according to the NSIDC. This is the 12th lowest in a 43-year satellite record, according to the NSIDC, with the past 15 years seeing the 15 smallest sea ice minima.
It is also 1.50 m km2 smaller than the 1981-2010 average minimum extent, the NSIDC notes – equivalent to twice the size of Texas.
It’s official -> “The 2021 low is the twelfth lowest on the nearly 43-year satellite record. The past 15 years are the 15 lowest sea ice areas on the satellite record.”
– Zack Labe (@ZLabe) September 22, 2021
While the minimum extent does not break all records, NSIDC Director Dr Mark Serrezze notes that “the amount of old and thick sea ice is as low as it has ever been in our records. satellites ”. This means that the increase in the total extent of sea ice from last year’s low to this year’s low “is therefore made up of first-year ice,” the NSIDC notes.
Colorado State University postdoctoral researcher Dr Zack Labe points out that the non-exceptional minimum does not mark long-term recovery of the Arctic sea ice.
“The extent of sea ice in the Arctic shows significant year-to-year variability, despite a long-term trend of decreasing ice cover. This is due to changes in weather patterns and the natural variability of the climate system. While each year does not set new records, long-term trends show that human-made climate change will continue to warm the atmosphere and the ocean and reduce the amount of ice in the Arctic.
“Even in years like 2021, which haven’t set new records, the Arctic is a radically different place than it was in the 1980s and 1990s.”
A cool and stormy summer
Earlier this year, the Arctic sea ice reached an “uneventful maximum” in late March, ranking seventh among the lowest on record. The months that followed were largely defined by stormy and cloudy weather that kept temperatures low and limited sea ice loss, the NSIDC notes.
Serrezze told Carbon Brief that it had been “a very strange year in the Arctic,” adding that “in terms of extent, arctic sea ice cover has been suspended this year.”
However, records have still been set in parts of the Arctic in recent months. For example, Labe highlights the rapid loss of ice in the Laptev Sea, which began at the start of the melt season:
“The pack ice along the Siberian coast has once again set new records. The arctic pack ice in the Laptev Sea melted several weeks earlier than average. In fact, the average summer sea ice extent in the Laptev Sea has set new records for declines in both 2020 and 2021. “
Overall, the rate of decline of the Arctic sea ice in April was variable – and even increased slightly from April 14 to 19. This was caused by the low atmospheric pressure in the Laptev Sea, which drew northerly winds and pushed the ice south, according to the NSIDC.
Professor Julienne Stroeve, Professor of Polar Observation and Modeling at NSIDC and University College London, explains how the influx of older multi-year ice helped offset the loss of ice in the Laptev Sea:
“We had a very early ice retreat in the Laptev Sea region, but the multi-year ice that was transported into the Beaufort Sea last winter helped reduce ice loss in that region this summer – and we have more ice in the Chukchi Sea than we do. have had for a while.
Ice loss was slower than average during May as stormy weather over the eastern Arctic helped expand the pack ice and keep temperatures low, limiting the melt. The average extent of arctic sea ice during May ranked ninth among the lowest on record.
However, June brought with it a change of pace, as an “unusually strong” low near the North Pole and Western Europe brought northwesterly winds over the Arctic, pushing temperatures up to 2-5. ° C above average. High temperatures accelerated the ice loss and, a week after the start of July, arctic sea ice followed a record high for the time of year, according to the NSIDC.
During the first half of the northern hemisphere’s summer, a pattern of strong depression near the North Pole continued to dominate, pushing sea ice counterclockwise – away typical movement. During this time, the Arctic Ocean lost a total of 1.73 m km2 of sea ice. This is roughly equivalent in size to the state of Florida, according to the NSIDC:
“In early July, the extent of sea ice was above levels recorded in 2012, the year that ended with the lowest extent of September ice in satellite records. However, a fairly rapid loss of ice during the first week of July caused [the] measurement lower than 2012 levels. From July 4 to 9, the 2021 extent was the lowest of satellite records for this time of year. However, the wastage rate then slowed down and by the end of July 2021 the extent was greater than 2020, 2019, 2011 and 2007. “
In mid-July, the extent of Arctic sea ice was just below the record minimum extent observed in 2012 and “very close” to that of 2020 – the two years with the lowest minimum ice extent. and the second lowest in satellite records. On July 13, the Laptev Sea area was almost completely free of sea ice, according to the NSIDC.
The loss of sea ice “stalled” from August 8 to 11 before accelerating again. An “exceptionally strong” high pressure system dominated Siberia during the first half of August, coupled with low pressure over the Greenland ice sheet, favoring strong ice movement south from the central Arctic Ocean to the northern coasts -american and Siberian.
Extent of Arctic sea ice for each decade of the satellite era (dotted lines). Specific years are indicated by moving lines – 2007 (pink), 2012 (white), 2020 (blue) and 2021 so far (yellow). Graphic by Dr Zack Labe using data from the Japan Aerospace Exploration Agency.
It was a “strange summer” this year, according to the NSIDC. They note that although the summer melt was slow due to mild and stormy conditions, as of September 16, multi-year ice was at a “record low” – covering about a quarter of the 1980s area.
Antarctica recorded its annual minimum on February 21 of this year. After the low, there was a 12-day period in which the extent of sea ice increased at the fastest rate in the four-decade record for sea ice extent for the period. of the year. This was caused by a rapid refreezing of areas west of the Amundsen Sea and east of the Ross Sea.
However, from the second week of March, the expansion of sea ice in Antarctica slowed to a more “typical” rate, and by the end of July the extent of sea ice was the eighth most. high satellite recordings. At the end of August, the extent of the Antarctic sea ice was the fifth highest on record.
As of September 15, the extent of the Antarctic sea ice remains “well above the long-term average” as it reaches its annual maximum, which is expected in the coming weeks, according to the NSIDC.
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