Development in the Arctic
The slight upward trend following the Arctic minimum continued in early 2024; although the sea-ice extent was below the mean value for the years 1981 – 2010 at the beginning of the year, it was in the lower range of the extrema (minima / maxima) for this international comparison period (Figure 1). If we consider 1991 – 2020, the new comparison period introduced by the World Meteorological Organization in 2021, January 2024 roughly matches the mean value for the period (see the interactive graphic). In January, the mean Arctic sea-ice extent was 13.99 million square kilometres, ca. 400,000 square kilometres more than the mean ice cover in January for the past 20 years (Figure 2). During the month, the extent increased by roughly 29,000 square kilometres per day, which represents slower growth than the mean value for 1981 to 2010.
In January, it was comparatively warm over the Central Arctic. The temperature anomalies at 925 hPa were up to six degrees Celsius above the long-term mean in the Central Arctic and the Canadian Arctic Archipelago. Atmospheric temperatures in the Bering Sea were two to three degrees Celsius above the mean. Over the East Siberian Sea, temperatures were slightly below the long-term mean (see Figure 3).
This year’s maximum sea-ice extent, at 14.94 million square kilometres, was most likely reached on 27 February. The monthly mean ice extent was 14.65 million square kilometres, putting February in 16th place on the list of lowest sea-ice extents since the beginning of satellite observation in 1979. In comparison to the long-term mean for the years 2003 – 2014, we can see that the sea-ice cover in the northern Barents Sea declined, while the Greenland Sea, the northern Baltic Sea (Gulf of Bothnia), and the coastal zones of the Barents Sea were characterised by extensive sea-ice cover, which is indicative of intensive and prolonged cold periods in these regions.
It remains to be seen whether this year’s sea-ice extent will continue to surpass the levels seen in previous years and how the ice cover will break up.
Development in the Antarctic
After the unusual sea-ice development in 2023, where we saw new record lows for the ice extent in eight of twelve months, the sea-ice concentration in the Antarctic was 5.85 million square kilometres on 1 January 2024. The monthly mean value was 3.98 million square kilometres, the sixth lowest since the beginning of continuous satellite observation. In direct comparison, that’s roughly 760,000 square kilometres more than in January 2023, which reported the lowest sea-ice extent between 1979 and 2024. The sea-ice extent was particularly low in the Ross, Bellingshausen and Amundsen Seas, whereas it was nearly average in the Weddell Sea and substantially higher than in the previous year (Figure 4). Generally speaking, very little sea ice remains in the east Antarctic sectors.
The minimum sea ice extent in the Antarctic, at 2.26 million square kilometres, was reached on 17 February – only ca. 258,000 square kilometres above last year’s record-breaking minimum and tying with 2022 for the second lowest February value. In terms of the monthly mean extent for February, the year 2024, at 2.40 million square kilometres, was the second lowest, continuing the trend of below-average values seen over the past eight years (Figure 5). This development could be due in part to the prolonged air temperature anomaly over West Antarctica and the expanses of open water in the Weddell, Ross and Amundsen Seas, where mean temperatures were 1.5 – 2 degrees Celsius above the long-term mean in January (Figure 6). In the area of Coats Land and Queen Maud Land, the air temperature is up to 6 °C above the long-term average. The heat contained in the ocean and the atmospheric circulation will now help determine the nature of new-ice formation and ice growth in the late summer and autumn.
The role of sea ice in the global climate system – background
The sea ice of the polar regions is an important indicator for climate change. It is also a central influencing factor on large-scale processes like ice-albedo feedback or oceanic and atmospheric circulation patterns. Sea ice reflects up to 90% of solar radiation. If the ice disappears, this radiation can warm the ocean, which in turn passes the heat on to the atmosphere. In terms of the atmosphere itself, ice in higher latitudes affects exchanges of heat and moisture at the lower edge of the atmosphere. For example, the lessening temperature contrast between the high and middle latitudes is affecting thermal transport between these regions, and with it, the tracks of low-pressure cells and therefore the weather in Germany and throughout Europe. Especially in winter, thermal flows can be significantly reduced by compact sea-ice cover, an important aspect that should not be underestimated given the current state of global warming. As the atmosphere and ocean grow progressively warmer, more and more ice melts in the polar regions. This leads to a chain reaction in which the ocean absorbs more heat than it can rapidly pass on. The subsequent decline in new-ice formation is due in part to polar amplification, which is why the Arctic regions have warmed 3 to 4 times as much as the rest of the world. In the Antarctic, so far, amplified warming has only been observed on the Antarctic Peninsula. There are likely similar amplification mechanisms to those in the Arctic; however, the Southern Ocean absorbs a great deal of the heat. As a result, there is a delay before air temperatures increasingly rise.
It can be assumed that climate change in the polar regions, through atmospheric and oceanic circulation cells, influences the weather and climate in Europe and around the globe, especially the frequency of extreme weather events. According to a study by Duffey et al. (2023), to date the warming of the Arctic has contributed roughly 10% of total global warming, even though the region only covers 4% of the Earth’s surface. Based on global warming of 2 degrees Celsius, temperatures in the Arctic would climb by an estimated 4 degrees (annual mean) and 7 degrees (in winter). These potential consequences are an important argument for efforts to improve climate prediction models, and for the continuing close observation of the region to improve our understanding of the processes and complex interactions therein. And of course, also for the intensification of climate protection measures, without which warming will continue to progress.
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Leonhard Günther (AWI)
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