According to the US Snow and Ice Data Center, the Arctic sea ice extent 2021 at December’s end was the highest in recent decades and the 2nd highest for 18 years. The rapid increase in sea-ice this year was due to a cool summer and autumn in the western Arctic Ocean. The Hudson Bay was almost completely free at the end November, but this was a significant negative anomaly. It froze in the last two weeks, despite being delayed for more than a month.
ARCTIC SEA ICE AT 2021’S END
In fact, the Arctic sea ice extent grew faster than it did in the recent years. By the end of December, its extent is 12.95 million square kilometers (5.00 million square miles) which is just within the interdecile range according to the National Snow & Ice Data Center of Boulder, Colorado (US).
The interdecile range measures statistical dispersion among data values. This means that, although it is lower than average, it is still within the normal sea-ice annual variability. The Greenland Sea and the Sea of Okhotsk have sea ice extents that are significantly higher than the average.
November was a surprise for cargo ships traveling through the Northern Sea Route. Many of them were frozen in and had to wait weeks for icebreakers. It was an Arctic adventure for many ships and crews that got trapped in the sea-ice along the remote Northern Sea Route.
A convoy of nine ships finally made it to safety in Kara Sea after a month of icy captivity, rescue by icebreakers, and a month of imprisonment. The Russian nuclear icebreaker completed the escort of ships, which began in the far eastern Arctic, nearly six thousand kilometers away, on the 7th December.
Photo courtesy ESL shipping
According to the Barents Sea Observer Sea Ice grew quickly to 30 cm across most of the Laptev Sea, East Siberian and other seas. The eastern portions of the sea route were already ice-covered in late October, which was several weeks earlier than usual.
The sea ice extent reached 9.77 millions square kilometers (3.77million sq mi) by November 31st. Sea ice expanded by approximately 3.20 million square km (1.24 million sq mi) in the past 30 days. Sea ice grew rapidly in the Greenland Sea, the Sea of Okhotsk and the Hudson Bay. The Hudson Bay was unusually ice-free throughout November, with sea ice exceptionally low in November.
Below is a video showing the Arctic sea ice extent. It is updated every 5 working days, starting on the 29th Nov and ending on the 29th Dec.
SEA ICE
Sea ice refers to all types of ice formed when seawater freezes. Sea ice that isn’t fast ice is called drift ice. If the concentration is greater than 70%, it’s called pack ice. If sea ice concentration falls below 15%, it is considered open water. The boundary between open and ice is known as the ice border.
The Arctic’s sea ice cover increases throughout the winter, peaking in March. The sea ice extends to its minimum in September. This is typically around one-third its winter maximum. To get a complete picture of the sea-ice state, it is necessary to determine both the extents and the volumes. These numbers generally include the ice thickness which is often linked to the age.
Below is an image of Arctic sea ice climate from 1981 to 2010. It was taken by the Snow and Ice Data Center at the University of Colorado, Boulder.
The image below shows that the 2021 blue line continued to reduce the negative anomaly between the 1981-2010 median and December. Since August, the 2021 sea ice extent was above the average 2011-2020. The sea ice extent for this year is 12.953 kilometers, the highest in 7 years.
On December 29, sea ice extent was roughly 0.399million square kilometers higher than 2020. This corresponds to a 3% difference. The 2021 sea ice extent is 4.4% lower than the average 1981-2010, which corresponds to a 0.603million square kilometers decrease.
The current situation is primarily caused by the rapidly increasing Sea Ice in the western Arctic sections, namely the Bering Sea and the Chukchi Sea in November.
HUDSON BAY & REGIONAL DIFFERENCES
Other sectors were much lower than average in November, including the Greenland Sea, Barents Sea and Hudson Bay. The Hudson Bay was particularly low in sea ice, which remained unusually uniced through November. Hudson Bay typically freezes in November. The northern portion of the basin is typically completely iced over by December.
Only the Hudson Bay’s far north was affected by the ice melt at the end of November 2021. The NSIDC reported this was Hudson Bay’s second-lowest level of sea ice, after only 2010.
Despite this, the Greenland Sea, Sea of Okhotsk and Hudson Bay experienced an unusually rapid increase in Sea Ice extent through December. Below is a map showing the Hudson Bay sea ice extent as of November 30th (left), and December 29th, respectively, thanks to the Multisensor Analyzed Sea Ice Extent products of the NSIDC.
The Hudson Bay Sea Ice Extent grew slowly but steadily over the first 10 days, increasing from 0.0.3 million square kilometers to 0.75million square kilometers on December 12. It remained stable until December 18, but then it increased abruptly by about 0.4million square kilometers in 5 days.
Sea Ice extent reached 1.15 million km on December 22nd and is slowly approaching the complete freeze of the bay’s 1.25 million km2. The Hudson Bay’s 2021 green line for Sea Ice Growth is clearly visible in the image below. This is far below the trend over the last few years.
After the unusually rapid growth that was observed through November, the Bering Sea’s Sea Ice Extent has stabilized and is now well above the long-term average. After peaking at around 440 000 square kilometers in mid December, it dropped to 350 000 square kilometers.
Below is an image showing that the 2021 green line for Sea Ice growth in Bering Sea is quite different from the trend seen in the last years. There is nevertheless a positive anomaly in the current extent compared to the one in 2017 and 2020.
The Sea of Okhotsk saw a steady increase in Sea Ice, as was the case in recent years. The ice growth was steady and accelerated in the second month. The present extent of the ice is about 400 thousand kilometers. This is similar to what was observed in recent years.
The 2021 green line of Sea Ice Growth in the Sea of Okhotsk can be seen in the image below. This is consistent with the trend that has been observed over the last few years.
According to the NSIDC, the December 29 sea ice extent was the highest since 2014. It was 12964 millions square kilometers that day. The extent at the end of December was close to the 2021’s values from 2004 to 2014, except 2010 when it was much lower. In 2016, it dropped to less 12300 million square km.
We observe a brief 4-year-long trend of increasing sea ice extent since 2017. However, the trend over 20 years is clearly negative, as shown in the image below, which we obtained data from the National Snow and Ice Data Center Boulder, Colorado (USA).
Below is an image by Zachary Labe showing the current Arctic sea ice extents. We can see clearly how the Chucky Sea (and the Bering Sea) froze earlier this year than usual.
On the other side, the Greenland Sea and the Laptev Sea, Beaufort Seas, the Canadian Archipelago and the Hudson Bay all froze late. The Kara Sea and East Siberian Sea experienced rapid increases in November and December.
The image below, created by Zachary Labe, shows more detail about the current Arctic Sea Ice anomalies. The plot is calculated using the 5-day running mean of a climatological baseline from 1981-2010. The yellow line indicates the year 2020. The red line is for the year 2021 (updated 12/27/2021).
This plot clearly shows that Arctic Sea Ice is in a positive phase, which has led to a decrease of the negative anomaly over the last five months. After a rapid melt in late May and early juillet, the anomaly decreased through August and then rose again in September or October.
Sea ice reached its lowest extent this year on September 16th, but it was far from the lowest and was only the 12th lowest in the last decade. This was due to the fact that the western Arctic Ocean had received colder than average temperatures, which prevented sea ice from melting in Alaska and Canada.
The 2021 minimum sea-ice extent was approximately 4.724million square kilometers. This is roughly 1.6 million more than the long-term average. A northern hemisphere’s strong negative height anomaly in the geopotential in late summer kept the western Arctic cooler and reduced the ice from melting.
Last summer, the western Arctic sector saw a drop in air temperature and sea temperatures. This was certainly a positive trigger, contributing to faster and earlier freezing in the Arctic sector when the autumn season began.
The Arctic’s sea-ice extent has important implications on global climate and weather in North America as well as Europe. It has been shown, for example that decreasing Arctic sea ice has a strong effect on precipitation in northern Europe.
In a paper published in the Journal Environmental Research Letters, scientists state that wet summer months in northern Europe are caused by the jet stream being displaced to its south. They simulate that Arctic sea-ice loss leads to a southward shift by the summer jetstream over Europe and an increase in northern European precipitation.
The image shows the average summer precipitation anomalies over northern Europe (% from 1981-2010 average). The inset map shows the precipitation anomalies in the period 2007–2012 relative to the period 1979–2006. (b) Time series of summer precipitation anomalies for England and Wales (% from 1981 through 2010 average). The black curves represent 5-year-old running means.
It will be interesting to watch the changes in sea ice extent over time, especially as global warming accelerates. By now, the Arctic continues to increase its sea ice extent at a steady pace, and if this trend continues in the coming months, there may be important repercussions for next spring’s synoptic and meteorological conditions.
The Arctic Sea Ice Extent is much lower than what is currently happening globally. In particular, the Antarctic sea-ice is in rapid decline. Although the Antarctic Sea Ice is stable above the long term average from March to August, the rapid decline of the Antarctic Sea Ice began in September. The anomaly covers approximately 2 million square kilometers.
The global anomaly hovers around 2.5 million square km due to both the Arctic Sea Ice extent and the Antarctic Sea Ice extent. The opposite trend between Antarctica and Arctica is clearly visible in the graphic Zachary Labe and source NOAA data NSIDC (1981-2010 baseline).
Sea Ice Extent is less than in recent years but 2020 in Arctic saw the 7th highest air temperature in instrumental records. The Arctic’s average temperature in 2021 is shown in the image. Redder colors indicate areas of greater warmth. The bottom half shows how Arctic temperatures differ from global temperatures since 2000. (Climate.gov)
The extremely high anomaly that was recorded in the Laptev Sea North of Siberia can be seen, as well the strong to moderate anomaly around Greenland. The Last Ice Area north Greenland, Ellesmere is included in the positive temperature anomaly.
This is the only part of the Arctic where thick and old ice can still be found. It is located in Nunavut, Canada. The area is the projected summer sea-ice extent for the year 2040 and beyond.
Climate projections project that the Arctic will see the complete disappearance of summer sea-ice by 2040. The Last Ice Area could be the last refuge for ice-dependent animals as the world heats.
But why is the Arctic heating at an accelerated rate? This is largely due to the Arctic Amplification.
Arctic Amplification is the increase in Arctic near-surface temperature change relative to lower latitudes. These mechanisms include both local feedbacks as well as changes in poleward energy transport. Arctic Amplification is particularly dependent on temperature and sea-ice-related feedbacks. They are significantly greater at Arctic Latitudes than they are at lower latitudes.
Wintery top-down aerial view showing cracked ice around Helsinki in the Baltic Sea. Miemo Penttinen – miemo.net / Getty Images
The Arctic’s extreme temperatures can be affected by changes in albedo, which can range from a dark sea surface with a frozen surface to a lighter sea surface with no ice.
In the Image above, annual mean surface air temperature anomalies for the Arctic (67-90°N) and for the Global average (90°S-90°N) from 1950 to 2020. Also shown are linear trend lines (dashed), for the period 1990 to 2020. GISS Surface Temperature Analy (GISTEMPv4) can be accessed at data GISS NASA from 1880 to 2020.
The image above shows the changes in Arctic sea ice extent over the past decade (NSIDC Sea Ice Index v3) as well as air temperature anomalies (Berkeley earth surface Temperature; BEST). The Arctic sea-ice reduction is the primary driver of temperature increases, rather than the other way around, as one might imagine.
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SEE ALSO
A warming wave will begin in the stratosphere. The Polar Vortex will temporarily be displaced as it heads towards North America.
Source: Severe Weather
