- Large patches of ice-free water could especially be found in Canada’s Arctic coastal waters, and in the Barents and Kara Seas. In the Antarctic, the amount of pack ice was chiefly far below the long-term mean in the influence sectors of the Indian and Pacific Oceans.
- New challenge for polar bears: a wet ice-and-snow mix clumps up on their paws, slowing the massive creatures down.
- New study: Earth’s albedo is in decline, contributing to global warming. This is due in part to the shrinking areas covered by ice and snow in the polar regions, but even more so to a decline in clouds.
The sea-ice extent is one of the most important parameters in sea-ice monitoring. Accordingly, the SEA ICE PORTAL displays the latest sea-ice extent (updated daily) in the Arctic and Antarctic, also as the annual cycle, on its landing page. In our team, we refer to the diagram as the “fever curve” – since it shows at a glance how the current sea-ice extent compares to the bright-green minimum and maximum values from the years 1981 to 2010, and to last year and the respective record-low year. In November, the line for the year hovered at the lower limit of the minima-and-maxima range in both polar regions. In the Antarctic; it was even below this range, marked in green. In other words, this November the area of ocean covered with sea ice was markedly low compared to the long-term mean for 1981–2010 in the Arctic and Antarctic alike.
Arctic Ocean: Formation of new ice in large regions
In the Arctic, the warm ocean still appears to be slowing the winter formation of new sea ice in many regions. Both in the island world of the Canadian Arctic Archipelago and in the northern regions of Hudson Bay, Baffin Bay, and the Barents and Kara Seas, there was substantially less sea ice this November than in the previous year and in comparison to the long-term mean and the record-low year 2012; satellites only detected increased pack ice (in comparison to the long-term mean) in the northern Chukchi Sea. At the end of the month, the Arctic sea ice covered just 10.45 million square kilometres. The monthly mean value for the sea-ice extent was 9.4 million square kilometres – the third-lowest mean value for November since the beginning of satellite observations (Figures 1, 2 & 3).
This delayed freezing has especially produced effects in the coastal regions of Canada, the waters of which are normally frozen over by this time of year. “Many people living in these areas, not to mention animals like polar bears, need the sea ice to hunt seals. The patches of open water are a real challenge for them. At the same time, these ice-free zones show how variable sea-ice development has now become in these marginal zones of the Arctic Ocean. In this regard, air and water temperatures are key, along with local winds,” says Dr Gunnar Spreen, an expert on remote sensing of sea ice at the University of Bremen.
It’s still too early in the Arctic winter to make predictions on the remainder of the freezing season. That being said, the unusually high sea-surface temperatures in the Barents and Kara Seas, and in Hudson Bay and adjacent waters, are an indicator that these areas will freeze over later than in past years (Figure 3).
Clumps of ice on their paws: Polar bears are suffering from changed ice and snow conditions
The changing sea-ice and snow conditions in the Arctic pose a new challenge for the polar bears living there, as two biologists from the US-based University of Washington report in a new study. While observing two polar bear populations in eastern and western Greenland, Kristin Laidre and her colleague Stephen Atkinson had seen several bears with clumps of ice up to 30 centimetres thick on their paws, or which were effectively lamed because they had deep, bleeding wounds on the balls of their feet (Figure 4). Other specimens had wounds on the tops of their paws or patches of missing fur on other parts of their bodies – types of injury that the two polar bear specialists had never seen before. Nor did they find any corresponding reports in the extant literature.
The two scientists got in touch with indigenous communities from both regions. Their experience helped the researchers identify three possible explanations for the new phenomena:
- First, due to climate change, the sea ice is more frequently exposed to rain. The snow cover becomes warmer and wetter, later freezing into ice. In turn, this new ice is clumpy and sticks to the polar bears’ particularly thick coats. Although the dense, specially developed hairs normally help the animals safely walk and run on the sea ice, in connection with wet snow they are conducive to clumping.
- Second, due to the increasing warming of the Arctic, the sea ice’s snow cover more frequently melts, only to refreeze when the frost comes. This can form a hard sheet of ice on the snow’s surface. When polar bears run through the snow, they repeatedly break through this comparatively hard ice layer, cutting themselves in the process. Some members of the indigenous communities had seen the same wounds on their sledge dogs.
- Third, the sea ice itself could be a factor. The bears examined lived on the ice near some of Greenland’s larger glaciers. When there is heavy snow cover, it’s an indication that the ice below is thin; as a result, during the brief warm phases, seawater can penetrate the ice from below. The result is the same: the snow becomes wet and later freezes to ice, sticking tenaciously to the polar bears’ large paws.
Whichever of the three possible explanations is the right one: the fact is, the ice clumps and wounds on their paws make it harder for the animals to move freely and successfully hunt. At the same time, the trend indicates that the conditions will more often be conducive to wet snow cover on Arctic sea ice in future.
The Antarctic: Bound for a new record low?
In the Antarctic, the melting season for the sea ice gathered momentum in November. Given that the sea-ice formation the previous winter was below the long-term mean, it’s hardly surprising that the “fever curve” for the sea-ice extent lies below the minima-and-maxima range. At the beginning of the month, the curve was even below the record-low year 2023 (Figure 5), though the trend did not continue in the second half of the month. On the last day of November, the sea-ice extent, at 12.14 million square kilometres, was slightly above the figure from last November.
In comparison to November 2023 (Figure 6), the sea-ice extent was higher this November in the Weddell Sea, the Dumont-d’Urville Sea, and the area from 120 to 150 degrees East in the Ross Sea. In contrast, satellites observed substantially less pack ice in the Cosmonauts Sea (south of the Indian Ocean) and in the area from 155 degrees East to 155 degrees West in the Ross Sea. If we look at the sea-ice distribution in the previous months compared to the long-term mean (Figure 7), the sea-ice cover in November 2024, especially between 30 and 60 degrees East, was significantly below the long-term mean.
Right now, the real question is whether the Antarctic is headed for another record-breaking low summer sea-ice extent. In December, the overwintering team at the German Antarctic research station Neumayer III will conclude their sea-ice observations for this year on the eastern margin of the Weddell Sea. Their local data, together with satellite observations from the month of December, will offer us more conclusive indicators of how the 2024/2025 summer sea-ice melting in the Antarctic is likely to progress.
Global warming: Earth’s albedo is declining, but not due to sea-ice loss alone
2023 was an exceptionally warm year. Though there were record-breaking highs in many regions, climate researchers were unable to fully determine which type of change in Earth’s climate system was responsible. Experts from the Alfred Wegener Institute (AWI) and the European Centre for Medium-Range Weather Forecasts (ECMWF) have now identified a key influencing factor. According to their analysis, our planet’s reflectivity (albedo) has declined. In other words, less and less incoming solar radiation is reflected by Earth’s surface or by the atmosphere and bounces back into space. Instead, this solar energy remains in the climate system, intensifying global warming – which also helps to explain the “extra” 0.2-degree Celsius rise in global mean temperature in 2023. A team of researchers led by AWI climate modeller Dr Helge Gößling report on their findings in a study released today in the journal Science.
For those readers with a scientific background, this likely comes as no surprise – as researchers have observed a decline in planetary albedo since the 1970s, chiefly due to the loss of snow, sea ice and glaciers around the globe. However, the new study shows that this aspect accounts for a comparatively small percentage of the recent decline in albedo. “The analysis of our datasets collected since December 2020 shows that the decreased surface albedo in the polar regions only contributed roughly 15 percent of the recent decrease in planetary albedo,” explains AWI climate modeller Helge Gößling.
Instead, the experts have identified as a major factor the decline in low-altitude clouds in the tropics and the northern temperate latitudes – including the eastern North Atlantic. The warming of this region was a main driver of the most recent increase in global mean temperature. “Clouds at all altitudes reflect sunlight, producing a cooling effect,” Helge Gößling explains. “But our new study shows that the eastern North Atlantic was characterised by a substantial decline in low-altitude clouds not just in 2023, but also – like almost all of the Atlantic – in the past ten years.”
Do these new findings mean the importance of the albedo of snow and ice-covered areas in the polar regions has been overestimated? “No, absolutely not,” says Helge Gößling. “At the local and regional levels, it makes a massive difference whether or not the ocean is covered with sea ice and whether or not the air above the ice can drop to minus 40 degrees Celsius in winter; over an ice-free ocean, such temperatures would hardly be possible.” But the new study also shows that those regions in which the snow and ice cover has retreated in the past ten years were, all told, too small to have had a greater effect on the latest rise in global mean temperature.
Original publication:
H. F. Goessling, T. Rackow, T. Jung, Recent global temperature surge intensified by record-low planetary albedo, Science (2024). doi: 10.1126/science.adq7280
Contact
Dr Gunnar Spreen (IUP/University of Bremen)
Author
Sina Löschke (Science Writer); www.schneehohl.net
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