August 2021 has featured the second-lowest Arctic sea ice loss in the past 20 years. The main reason behind it was the colder than normal weather in the western Arctic Ocean, slowing down the sea ice melt in the Canadian and Alaskan regions.
We will look at the current interesting sea ice conditions in high resolution. How/where the temperatures were colder than normal, why the sea-ice melt was weaker in the western Arctic, and look at the predictions for the grand minimum in September, which looks to be far from the record low values.
ARCTIC SEA ICE – 2021 MELT SEASON
The Arctic region is actually just one large ocean and has no true large-scale landmass. It is the smallest and shallowest of the world’s five major oceans, and it is also the coldest. This is also the only ocean, which is smaller than the largest country in the world by area (Russia).
The image below shows the Arctic ocean, as it would look without water, revealing a very complex underwater terrain. You can see the main regions of the Arctic ocean, each with its own set of unique weather and oceanic properties. The graphic is from one of the more recent Arctic ocean studies.
The Arctic sea ice has its own seasonal cycle and it can be seen in the image below from the Arctic-ROOS system. It shows the sea ice extent change over a one-year period. The melt season usually starts in late March, lasting well into September where a minimum is reached.
The graph above shows the last few years of data, where we can see the 2020 Arctic ice extent (black line) was second-lowest, only behind 2012, which still holds the record for the lowest ice extent since satellite measurements began.
The seasonal sea ice melt cycle is driven by seasonal temperature changes. When the days start to get longer and the solar radiation over the Northern regions gets strong enough, the temperatures rise and the melting process slowly starts on the outer edges first.
During Summer, the Arctic region has sunlight full 24 hours a day, which means a near-constant sea ice melt process. The image below shows the tilt of the Earth’s axis and the angle of the incoming sun rays during a North Hemisphere Summer Solstice.
We produced a high-resolution video, which shows the 2021 sea ice melt season since April, with a faster melt in July and a slowdown in August. Take notice of the constant strong movement of the icecap, influenced by the ocean currents and also strong weather/wind dynamics.
Below we can see the sea ice maximums over the last 17 years, and how the 2021 sea ice maximum compares. It was actually higher than some of the recent years, and around the average for the 2010-2019 period. Note that this is from the JAXA dataset, which can be slightly different than the data used on the previous graphic.
Looking at current conditions from NSIDC, we can see the extent of the sea ice, compared to the long-term average (orange lines). The largest deficits can be found in the Siberian regions of the Laptev Sea, Kara Sea, and also in the Barents Sea. There is actually some sea ice reaching out of the long-term average lines in the Beaufort Sea and the Chukchi Sea in the western Arctic.
Looking at the sea ice extent in the Chukchi Sea, we can see the abrupt stop of daily melt in early August. Daily sea ice melt was very slow, and almost at zero, with no sea ice melt going on.
A similar story can be seen in the Beaufort Sea, as the Weather pattern change in early August reduced the daily sea ice melt. There was actually some re-freezing of the ocean water in week 2 of August.
The line graph below shows the latest total Arctic sea ice extent, which is running below the long-term average. The dashed line is the 2012 melt season, which in September ended up with the record lowest sea ice extent. After being close to the 2012 trends, the 2021 melt season broke away in late July. The melt pace since then was steady and much slower than last year.
The current sea ice extent is around 5.1 million square kilometers in area, which is around 1.5 million square kilometers below the long-term average. It is currently running a full million square kilometers larger than this time last year. The biggest difference occurred in the second half of August when the sea ice melt rate this year did not accelerate as in the past years.
The main reason for that was a specific Weather pattern in the Arctic. Below we have the geopotential height anomaly for the second half of August over the Northern Hemisphere. We can see a strong negative height anomaly in the western Arctic Ocean, and a high-pressure zone over the North Atlantic.
looking at sea level pressure anomalies below, we can see a strong low-pressure zone over the western half of the Arctic. This has counter-clockwise circulation, transporting colder air from the central Arctic into the Canadian and Alaskan sectors.
The surface temperature anomaly analysis for August 2021 shows colder than normal surface temperatures in the western Arctic. Warmer than normal temperatures were dominating most of the Siberian Arctic.
The global temperature anomaly for August 2021 shows colder than normal temperatures in the western Arctic sectors. We can also see colder temperatures over Europe and warmer than normal conditions over the central and eastern United States.
Not only air temperatures, but ocean temperatures are also colder than normal in the west Arctic sector. Warmer ocean temperatures can contribute to faster and earlier sea ice melt, especially on the outside edges, where waters are above the melting point earlier. But currently, the sea temperatures are also normal to colder-than-normal in the western regions.
SEA ICE CONDITIONS AND WEATHER FORECAST
Arctic sea ice is much more than just extent and area. Below you can see our graphic, which shows the sea ice concentration. It tells us what is the fraction of the sea ice in the ocean. We can see the strongest concentration is in the central regions, reducing towards the outer regions which are going to melt first.
We can compare it to last year below. It is clear right away that there was less sea ice last year in the western sector and on the eastern edges. But there was more sea ice in the Greenland sea. Overall the central Arctic sea ice concentration was higher, while this year the concentrations look less healthy, despite a lower area loss.
Another important parameter of the Arctic sea ice is of course its thickness. It reveals where the icecap is thicker, and where it is thinner and thus much more prone to melting. The central regions are remaining quite thick this season, but the maximum thickness is somewhat lower.
If we look at the same day last year, we can see that the icecap was smaller in the area. But, the ice was much thicker in the coastal areas of northern Canada and Greenland. While the sea ice might seem healthier at the moment due to its larger size, it is actually weaker in the long term, as it is quite thinner this year (image above).
Another important parameter that can affect the melting process is the movement of the ice. The graphic below shows the latest sea-ice velocities and directions. We can see that the icecap has a counter-clockwise spin, which is mostly a result of a low-pressure system over the North Pole and wind forcing the ice movement.
Looking ahead for the next few days, we can see a strong high-pressure area building into the central Arctic. Low-pressure systems will remain over the far western Arctic, keeping the cooler air over the western region.
Looking at the air mass temperature anomaly forecast below, we can see the colder airmass in the western Arctic, which will try to hold back the melting process as much as it can, but this does not mean that no melt will occur. We can also see a cold air intrusion into eastern Europe, and some cooler weather into the northeastern United States.
Looking at the surface temperature anomalies, we can see the colder than normal central Arctic and the western region in the Beaufort Sea and the Chukchi Sea. Warmer temperatures will be present in the Siberian region, but those regions are already nearly ice-free this time of year.
Knowing the weather forecast and the state of the ocean, we can look at the forecasted changes of the Arctic icecap in the first third of September 2021.
The Arctic sea ice concentration change forecast does show the reduction in concentrations around most of the icecap (yellow-red colors). But strong dynamics and sea ice movement does create a lot of noise in the western regions. Overall the concentrations are forecast to reduce there, but the sea ice redistributions will be strong.
Overall, not every reduction in concentration over the central regions is melt, as the icecap is constantly moving, changing its concentrations. We can see the blue/red area of increased/reduced concentrations in the western edge, where strong weather dynamics are quickly changing the concentrations.
Looking at the Arctic sea ice thickness forecast below, you can see most of the icecap is actually increasing in thickness. You can nicely see the “stripes” across the icecap, which are due to the movement of the sea ice. They show where the sea ice compacts together or moves away, increasing/decreasing thickness and concentrations across the icecap.
SEA ICE CONDITIONS IN CONTEXT
The typical numbers and maps do not mean much if we don’t put them in some context. We will look at some images below, that will help to understand where exactly the sea ice stands this year compared to the recent past. All graphics in this segment are provided on the great Arctic sea ice page by Zachary Labe.
Currently, the 2021 Arctic sea ice extent is ranked as the 5th highest in the past 15 years. It is also the highest sea ice extent in the past 7 years. The data shown is for August 30th. At this point, the 2012 extent was already at record low values for this time of year, and last year trailing behind as 2nd lowest.
The current sea ice extent anomaly shows the deviation from the 1980-2010 average extent. In mid-July, the sea ice extent anomaly actually dropped to the second-lowest deficit in modern records. But since then the sea ice melt season has slowed down, reducing the negative (deficit) anomalies.
Looking at the Arctic basin sea ice, where the main seas are included, the melt is progressing at a decent pace, but holding more to the low-mid part of the group. You can see on the graph how the older years (violet) started the melt much later and melted way less than recent (white-blue) years.
The one exception is of course the Laptev Sea, which was melting at a record pace this season. Last year (yellow line) it melted entirely for only the second time in known records. This year the Laptev sea ice melt began early and is currently ice-free for only the third time in the past 42 years, as modern satellite observations began.
Overall, you can see the daily sea ice extent change on the graph below. This is useful to see if on average the Arctic icecap is melting or also gaining some ice area. Strong overall melt was ongoing since April, with a few days in between where the ice extent has still increased, due to weather conditions and ice movement, rather than actual new ice being formed.
But you can see that since mid-July, the daily sea ice melt has actually decreased almost every day. There were some strong melt days in early August, but overall the melt rate was reducing at a decent rate.
Looking closely at August we can see the slowing rate of the sea ice melt in the second half of the month. August 2021 ended with the second lowest sea ice melt rate in the past 20 years.
Despite having the second-lowest August ice melt rate, the month has still finished low, as the sea ice loss in previous months was not as slow. It still ended up with the largest extent of the past 6 years.
In the last 5 days, most Arctic regions experienced melting at a low pace. The fastest melt was observed in the Beaufort Sea, while some increase was observed in the Canadian Archipelago.
ARCTIC SEA ICE VOLUME AND TRENDS
During winter 2020/2021, the Arctic sea ice volume was running below normal, continuing from the low volume in Autumn 2020. The peak episode in April was decent, holding for over a month. But currently, the sea ice volume is just slightly below the long-term average, and quite larger than last year. The red square outlines the latest sea ice volume data for 2021 (black line).
Looking at the past 40 years, we can see a strong negative trend in the Arctic sea ice volume. The sea ice volume is decreasing quite rapidly, but looking closely at the last 10 years, there is perhaps a slower decline than in the early 2000s. But the long-term trend is perhaps more important, and It is on a stable decline, corresponding to the rise in global temperatures.
Sea ice volume reduction is not just a result of the reduced sea ice extent, but also its thickness. Below we have an image, which shows the average sea ice thickness in September. September is the peak of the melt season, and we can see a very obvious reduction in sea ice thickness, especially in the last decade, where the icecap no longer touches the Siberian side.
ARCTIC SEA ICE MINIMUM FORECAST
Looking ahead over the month of September, we have the pressure anomaly forecast below from the CFS model of NOAA-NCEP. It shows a high-pressure region over northeastern Canada and Siberia. over the Arctic Ocean, we actually have hints of a normal to the below-normal pressure area. Based on the location of the high-pressure systems, that is a likely solution.
The temperature anomaly forecast below actually shows the colder than normal temperatures over much of the Arctic Ocean. Especially over the Canadian and Alaskan regions. This should help to keep the sea ice minimum extent this year far above the 2020 minimum.
The record low sea ice extent was reached in September 2012, at just 3.4 million square kilometers. The second-lowest Arctic sea ice extent was reached last year, at around 3.8 million square kilometers. You can just see the 2021 season on the graph, still dropping down, but at a much slower rate than last year or the record 2012 year.
Below we have a map which shows the lowest sea ice extent in the modern records, reached in mid-September 2012. This year we have much more sea ice in the Canadian and Alaskan regions, compared to 2012.
The minimum sea ice projections from early August were forecasting a modest minimum. Still below the long term average, but above the record low values, finishing around 4.5 million square kilometers.
The different methods forecast also shows the minimum to be reached around 4.3-4.6 million square kilometers. That is above last year’s minimum, and in the higher end of the past 10 years at least.
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