Antarctic sea ice levels reached record low

By Gwyn Wright via SWNS

The volume of Antarctic sea ice is now at its lowest since records began, reversing a trend of expansion over the last five years, according to scientists.

Less than two million square kilometres (772,000 miles) of ice sheet remain at the South Pole for the first time since records began in 1978.

While the Arctic ice cap has been shrinking at an alarming rate for decades until recently the volume of Antarctic sea ice was in fact expanding at a rate of around one per cent a decade since the 1970s.

However in February this year, the extent of sea ice at the southern tip of the planet reached a new record low of 1.9 million square kilometres, breaking a previous record low of 2.3 million square kilometres set in 2017.

The new record low was set on 25 February this year, just days from the end of the Antarctic summer.

Data showed ice cover was significantly lower than usual in the Bellingshausen, Amundsen and Weddell seas off Western Antarctica and the western Indian Ocean.

Sea ice extent was 30 per cent lower than the average between 1981 and 2010.

Scientists have long been curious about why the extent of Antarctic sea ice varies so much, but so far there has been little research into the topic and no scientific consensus has yet been reached about its causes.

For the new study, researchers based in the US and China analysed data on the per cent of an area that is covered by sea ice on a given day (called daily sea ice concentration) and weekly sea ice drift between 1979 and 2022, using data from the National Snow and Ice Data Centre in the US.

They had to consider sea ice that was added and lost alongside dynamics, freezing and melting for their analysis.

Their “sea-ice budget analysis” was carried out to cover the melting seasons and then connect this to atmospheric circulation over the same periods.

During the summer, anomalies in the transport of heat dominate the processes that cause sea ice to melt.

Infrared radiation and visible light also increase during the summer.

During spring, the same processes take place but ice also gets pushed towards the tropics, which in turn causes melting.

The scientists found the record low was reached at a time when two unique weather events, La Niña and a positive Southern Annular Mode, were affecting the region.

La Niña is a set of powerful winds that blow warm ocean surface water from South America to Indonesia.

Meanwhile, the Southern Annular Mode is a belt of strong westerly winds or low pressure surrounding Antarctica.

Both these weather patterns deepen the Amundsen Sea low, a centre of low atmospheric pressure over the far south of the Pacific Ocean and off the coast of West Antarctica.

Atmospheric conditions in the region vary far more than they do anywhere else in the Southern Hemisphere.

The researchers found all the atmospheric impacts on the sea-ice extent anomalies start with the intensity and position of the Amundsen Sea low.

The study’s corresponding author Hao Luo said: “Contrary to the rapid decline of the Arctic sea ice extent in the context of global warming, Antarctic sea ice extent displays a modest increasing trend of around 1.0 per cent ± 0.5 per cent per decade since late 1978, masking significant interannual and regional variations.

“Annual mean Antarctic sea ice extent hit a record high in 2014 of 12.8 million square kilometres after a long-term increase since 1978 and then plunged to a record low in 2017 of 10.7 million square kilometres.

“Seasonal minimum sea ice extent also hit a record low of 2.3 million square kilometres on 1 March 2017.

“However, it has been broken after merely five years, as sea ice extent reached 1.9 million square kilometres on 25 February 2022.

“This is the first time sea ice extent has reached below 2 million square kilometres since satellite observation began.”

The findings were published in the journal Advances in Atmospheric Sciences.