Much of the Antarctic coast has been registering a notable decrease in sea ice in recent years, due to the warming of the water, the arrival of meltwater from glaciers and the alteration of marine currents.
One of the main victims of the loss of floating ice are penguin colonies that, under normal conditions, use these surfaces for nesting and breeding.
A study led by experts from the public scientific institution British Antarctic Survey (BAS) has confirmed these negative effects by analyzing what they consider a "catastrophic failure" in four large colonies of emperor penguins (Aptenodytes forsteri). Thus, a study published by these experts in this month's issue of the Communications Earth magazine
The discovery supports predictions that more than 90% of emperor penguin colonies will be nearly extinct by the end of the century, according to current world statistics. based on climate change models.
The scientists examined satellite images showing the loss of sea ice at breeding sites, long before the chicks developed waterproof feathers.
Emperor penguins rely on stable sea ice that is firmly attached to the shoreline ("mainland" ice) for most of the year, from April to January. Once they arrive at their chosen breeding site, the penguins lay eggs during the Antarctic winter, from May to June. The eggs hatch after 65 days, but the chicks do not fledge until the summer, between December and January.
By early December 2022, Antarctic sea ice extent had equaled the previous record low set in 2021. The most extreme loss was observed in the central and eastern Bellingshausen Sea, west of the Antarctic Peninsula, where there was a 100% Loss of sea ice by November 2022.
"We have never seen reproductive failure on this scale in emperor penguins before, the loss of ice has made it very unlikely that the displaced chicks will survive," said lead study author Peter Fretwell.
We know that emperor penguins are highly vulnerable in an increasingly warming climate, and current scientific evidence suggests that extreme sea ice loss events like this will become more frequent and widespread."
Since 2016, Antarctica has experienced the four lowest sea ice extent years (on record with satellite imagery) in 45 years, with the lowest two years in 2021/22 and 2022/23.
Between 2018 and 2022, 30% of the 62 known emperor penguin colonies in Antarctica were affected by partial or complete loss of sea ice. Although it is difficult to immediately link specific extreme seasons to climate change, a long-term decline in sea ice extent is expected from the current generation of climate models.
Emperor penguins have previously responded to incidents of sea ice loss by moving to more stable sites the following year. However, the scientists say this strategy will not work if the sea ice habitat in an entire region is affected.
Emperor penguin populations have never been subject to large-scale hunting, habitat loss, overfishing, or other local anthropogenic interactions in the modern era. Unusually for a vertebrate species, climate change is considered the only major factor influencing long-term population change.
Recent efforts to predict emperor penguin population trends from forecasts of sea ice loss have painted a bleak picture, showing that if current rates of warming persist, more than 90% of colonies will be nearly extinct by the end of the year. of this century.
The five penguin colonies studied were discovered in the last 14 years using satellite imagery: Rothschild Island, Verdi Inlet, Smyley Island, Bryan Peninsula and Pfrogner Point. All five colonies had been shown to return to the same location each year to breed, with only one previous case of breeding failure on the Bryan Peninsula in 2010.
Scientists now routinely use satellite imagery to discover and monitor emperor penguin colonies, as the brown patches of the birds' guano stand out clearly against the pure white of ice and snow. The team used images from the European Commission's Copernicus Sentinel-2 satellite mission, which has continuously monitored the Antarctic area since 2018.
In the last seven years, the sea ice around Antarctica has decreased significantly. As of late December 2022, sea ice extent was the lowest in 45-year satellite records. In the Bellingshausen Sea, home to the penguin colonies in this study, sea ice did not begin to rebuild until late April 2023.
Since then, the deviation from the norm has intensified: as of August 20, 2023, sea ice extent was 2.2 million km2 less than the 1981-2022 median (17.9 million km2), exceeding significantly the winter record minimum of 20 August 2022 of 17.1 million km2. . This missing area is larger than the size of Greenland, or about ten times the size of the United Kingdom.
Dr Caroline Holmes, Polar Climate Scientist at BAS, explains that “right now, in August 2023, the Antarctic sea ice extent is much less than other years around this time; We're looking at areas that are surprisingly still largely ice-free."
Annual changes in sea ice extent are related to natural weather patterns such as the El Niño-Southern Oscillation, the strength of the Southern Hemisphere jet stream, and regional low-pressure systems.
We will need years of observations and specific models to know precisely to what extent current conditions are being influenced by these phenomena and by the natural variability of the oceans. However, recent years of falling sea ice records and Southern Ocean subsurface warming strongly point to human-induced global warming exacerbating these extremes."
Climate models show a decrease in Antarctic sea ice both in comparison with human emissions of greenhouse gases and carbon dioxide, recalls the BAS. Jeremy Wilkinson, a physicist of sea ice at this scientific institution, points out that the new study "dramatically reveals the connection between the loss of sea ice and the annihilation of ecosystems." "Climate change is melting sea ice at an alarming rate. It is likely to disappear from the Arctic in the 2030s, and in Antarctica, the four lowest sea ice extents on record have been recorded since 2016.
"It is another warning sign for humanity that we cannot continue on this path, politicians must act to minimize the impact of climate change. There is no time left," says Jeremy Wilkinson.
