Arctic sea ice has reached its minimum extent on September 16th. But it was far from lowest on record and was actually just 12th lowest in the past decades. 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 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 what is up with the age of the ice, as the arctic sea ice is getting younger, and weaker.
2021 ARCTIC SEA ICE MELT SEASON
The Arctic region is in fact a 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 surface area (Russia).
In the image below, you see 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 Sun’s influence over the Northern regions gets strong enough, the temperatures rise and the melting process slowly starts on the outer edges of the ice sheet.
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 other graphics.
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.
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 minimum sea ice extent for the 2021 season was around 4.724 million square kilometers in area, which is roughly 1.6 million square kilometers below the long-term average. It is currently running almost a full million square kilometers larger than this time last year. The biggest difference occurred in early 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. This kept the western Arctic cooler, greatly reducing the melt rates.
looking at sea level pressure anomalies below for the first half of September. We can see a strong low-pressure zone over the western half of the Arctic and Alaska. This has counter-clockwise circulation, transporting air from north Canada over the western Arctic. Air temperature in northern Canada is much lower than if the air would be transported from the warm North Pacific ocean. This helped to limit any strong melting, creating a much larger minimum extent than in the past years.
The surface temperature anomaly analysis for September 2021 shows colder than normal surface temperatures in the western Arctic. Warmer than normal temperatures were dominating most of the Siberian Arctic. If the air would be transported from there, it would not help to limit the melting process.
The global temperature anomaly for September 2021 shows colder than normal temperatures in the western and central Arctic sectors. We can also see colder temperatures over eastern Europe and warmer than normal conditions over the central and northern 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 own 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 and in the eastern zone. It is reducing towards the west which has the thinnest and most fragile ice currently, after battling the elements to stay alive.
We can compare it to the start of the month below. It is clear right away that the central and eastern regions were much less concentrated, and have since gained a fair bit of volume. Some of the western fragile ice has melted away since the early month, but the situation could end much worse under different weather conditions.
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 than usual.
Looking at the monthly sea ice thickness for last month, we see the entire Arctic icecap was thinner than normal, with more than 1m of ice below the long-term average.
Looking ahead into early October, we can see a strong high-pressure area building over the United States and into eastern Canada. 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 help the sea ice recovery process, as the temperatures are dropping fast, and there is less sunlight, so the ice will start to recover. We can also see a cold air intrusion into central Aisa, and some cooler weather into the northeastern United States.
Looking at the surface temperature anomaly forecast, 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 regions of the ocean and over much of central-north Canada, under the high-pressure buildup.
Knowing the weather forecast and the state of the ocean, we can look at the forecasted changes of the Arctic icecap in the first week of October 2021.
The Arctic sea ice concentration change forecast does show the reduction in concentrations around the central regions of the icecap (yellow-red colors). But low pressure and colder air in the western Arctic will help to quickly increase the sea ice concentrations over the western regions (blue/violet)
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.
ARCITC SEA ICE CONDITIONS IN CONTEXT
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. This was a very good forecast actually and has nicely hit close the final 4.7 million square kilometer sea ice minimum.
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 7th highest in the past 15 years. It is also the highest sea ice extent in the past 7 years. The data shown is for September 24th. At this point, the 2012 extent was already at record low values for this time of year.
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.
The one exception is of course the Laptev Sea (Siberian side), which was melting at a record pace this season. Last year it melted entirely for only the second time in known records. This year (black line) 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.
Looking at the long-term trends for the Laptev Sea, it had the lowest August sea ice extent since satellite records began. Since 2004 the seasonal melting of the Laptev sea has increased, with recent years being ice-free for the first time.
An unusual situation is also found in the Greenland sea, where we see unusually strong melting this year. It is currently at the lowest extent since the satellite observations began. The reason behind it is an unfavorable weather pattern and warmer ocean temperatures.
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. The latest days show sea ice growth, indicating the end of the Arctic sea ice melt season.
Looking closely at September, we can see the growing trend of sea ice in the second half of the month. September 2021 is ending with a normal growth rate and will end with more sea ice than at the beginning of the month.
In the last 5 days, most Arctic regions experienced sea ice growth. The fastest re-melt was observed in the East Siberian Sea, while some melt was still detected in the Canadian Archipelago.
ARCTIC SEA ICE VOLUME AND AGE
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 in the end of September.
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 in the past 10 years, we might notice 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 extends to the Siberian side.
Another important factor is also the age of sea ice. Older ice is much more robust than younger ice. Over the years, we are observing the reduction of the “multiyear” ice, especially after the mid-2000s. You can see the yearly data for the end of melt season each year on the graph below. 2021 has ended with nearly the lowest amount of robust multi-year ice.
Below we have a very special graphic, which shows the age of the sea ice over the area. Not all ice is of the same age, as some are the newly formed “one year ice”, while some sea ice can be over 4 years old.
Over the years, a lot of the older sea ice was lost, replaced with much weaker one-year ice. The graphic below shows the age of the sea ice, comparing 1985 and 2019. You can see how much of the old sea ice (red) was lost in the last 35 years.
The bottom half of the graphic above shows the percentage of sea ice by age. It is obvious how much the old sea ice has reduced, especially in the past 15 years.
Looking at the sea ice age in late June 2021, we can see very little old ice has remained. Some of it was actually spread out into the Beaufort Sea during winter. That is bad, as the older sea ice is more vulnerable to melting when it is spread out and not as compact.
The satellite image below taken in June by the NASA-Terra satellite shows this old ice in the Beaufort sea. It is seen more white-bluish in color towards the right of the image, while the newer/younger sea ice is darker/grayish in color towards the coast.
RECORD ARCTIC SEA ICE 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, quite higher than many of the recent years.
Below we have a map that shows the lowest sea ice extent in the modern records, which was reached in mid-September 2012. Arctic sea ice cover has been shrinking since the 1970s when it averaged around 8 million square km a year. But such a dramatic collapse in ice cover in one year was highly unusual.
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