While summer ice cover in the Arctic has been steadily decreasing in recent decades, this has not been the case in the Antarctic. On the contrary, the ice area even tended to increase slightly over the years. However, the ice mass tended to decrease and the ice became thinner. Since 2016, this trend has come to an end, and the ice area has also been decreasing since then - and apparently at an ever faster rate.
Increasingly large anomaly in the middle of the southern winter
In February of this year, sea ice cover in Antarctica dropped to a new record minimum. Meanwhile, we are in the middle of the austral winter and polar night, during which the ice area usually increases rapidly. Currently, the ice area is also increasing, but to a much lesser extent. Never since satellite observations began has there been so little sea ice at this time of year.
Fig. 1: Sea ice extent in Antarctica. Current curve still clearly below that of the old record year 2022; Source: meereisportal.de
This fact becomes even more striking when one looks at the degree of the anomaly. Since 1979, the ice shelf area in the southern winter has never been so small – and by a huge margin! In most subregions around the Antarctic continental shelf there is less ice than normal, only in the northern Amundsen Sea is the area above average. The second striking anomaly in the figure below comes from the late austral spring and austral summer of 2016, a year of strong El Niño. This phenomenon is also currently picking up steam in the Pacific and is very likely to intensify in the coming months. So it will be exciting, but also troubling, to watch how this extraordinary anomaly continues to develop in the second half of 2023 and then again in 2024.
Fig. 2: Anomaly in Antarctic sea ice extent since 1979; Source: zacklabe.com
On the way to a new record minimum
Antarctic sea ice normally reaches its maximum in September or October and its minimum in February. The record holder for the smallest ice extent in Antarctica was for a long time the year 1997; this minimum was 2.48 million square kilometers. This value was significantly undercut in 2017 with 2.24 million square kilometers. In 2022, this mark was broken downward again with 2.17 million square kilometers. Two minus records within five years are not yet a real trend, but they do make us sit up and take notice.
Fig. 1: Anomaly of Antarctic sea ice extent since 1979, (image source: zacklabe.com).; Source: zacklabe.com
At the end of last year, the ice area reached an absolute minimum in December, and the current ice area is also significantly below that of 2017 and 2022. 6 to 8 weeks will pass before the absolute annual minimum is reached; if the current trend continues in this form, we will be heading for another new minus record. Comparing the degree of anomaly at this point with 2017 and 2022, it is noticeable that 2023 is in a league of its own in this respect.
Fig. 2: Sea ice extent in Antarctica. Current curve clearly below that of the last years (Source: meereisportal.de) ; Source: meereisportal.de
The decline is particularly strong in West Antarctica, but also in East Antarctica, which has been comparatively stable until then, the ice shelf area is clearly below average (as it was last year).
Fig. 3: Sea ice extent on January 8, comparison with mean extent from 1981 to 2010 (source: nsidc.org).; Source: nsidc.org
There are no simple answers to the question of the causes! Directly responsible are probably changed wind flow patterns and current conditions in the sea. Their origin, in turn, can be traced back to climate change. These developments are still relatively new in climatic time scales and are the subject of intensive research, but the degree of change is worrying. The coming years will show whether this fresh trend will continue and accelerate, or level off again. Sometimes we are already crossing tipping points. Because the smaller (white) ice surface also reduces the back radiation into space (albedo), the heat input into the system increases. The melting ice shelf has no influence on the sea level, because it floats itself, but it supports the ice masses of the glaciers flowing in from the interior of the high continent and slows them down. Less ice shelf means less braking effect, the flow velocity increases. This melting continental ice is causing sea level to rise, and the current rate of 3.4 mm per year could increase further as a result. Thwaites Glacier is of particular concern in this regard. It is located in West Antarctica's Marie Byrd Land and is about the size of Florida. It in turn supports the West Antarctic Ice Sheet inland. In the last 2 to 3 years, Thwaites Glacier has shown increasing signs of erosion. The flow rate is increasing, larger and larger parts of its tongue are floating up and subsequently breaking off. This glacier is already responsible for 4% of the annual sea level rise.
New negative record for Antarctic sea ice
What was already apparent a month ago has now become reality – the negative record from last year was undercut about a week ago. Never since satellite observations began has sea ice coverage in Antarctica been so low. On February 8, the area dropped to 2.20 million square kilometers, and yesterday it was only 2.06 million square kilometers. The absolute minimum is typically reached at the end of February, so this number may decline even further in the next week or two. Possibly even the "sound barrier" of 2 million square kilometers will be broken downwards. Further updates will follow at this point.
Fig. 1: Sea ice extent in Antarctica. Current curve clearly below that of the last years.; Source: meereisportal.de
Fig. 2: Sea ice concentration on February 14, 2023.; Source: meereisportal.de
