Antarctic sea ice all-time low, How does this affect the planet?

The extent of Antarctic sea ice has registered a new historical minimum after it was reduced to 1.91 million square kilometres on February 13, according to data from the National Ice Data Center and Snow Protection Agency (NSIDC).

On that date, the levels fell below the previous record of 1.92 million square kilometres, set on February 25, 2022. Since mid-December, the ice extent has been well below last year's melt season levels.

This year is the second in which the Antarctic extension falls below 2 million square kilometres, according to the figures.

In recent years, the annual minimum has been between February 18 and March 3, so ice levels are likely to continue to fall.

Lowest extent since records began in 1979

The impact of the climate crisis on the melting of Arctic sea ice is clear from records going back to 1979. Antarctic sea ice varies much more from year to year, making it harder to see the effect of global warming.

However, "remarkable" losses of Antarctic sea ice over the past six years indicate that record levels of heat now in the ocean and related changes in weather patterns may mean that the climate crisis is finally showing up in observations.

Scientists were already very concerned about Antarctic ice. Climate models suggested as early as 2014 that the giant West Antarctic Ice Sheet (WAIS), which lies on the continent, was doomed to collapse due to the levels of global warming already seen at the time.

The increasing loss of sea ice exposes the ice sheets and their glaciers to waves that accelerate their disintegration and melting, the researchers warned.

A recent study estimated that the WAIS would tip towards a gradual collapse, and a sea level rise of four metres, with a global temperature rise as low as 1C, a point that has already passed.

"I have never seen such an extreme ice-free situation here before," said Professor Karsten Gohl, of the Helmholtz Center for Polar and Marine Research at the Alfred Wegener Institute, Germany, who first visited the region in 1994.

Antarctic coastline is ice-free

It is worrisome to consider how quickly this change has occurred, Professor Christian Haas, also from the Helmholtz Centre, said: "The rapid decline in sea ice in the last six years is quite remarkable, as the ice cover hardly changed in the previous 35 years." Scientists at the US National Snow and Ice Data Center have also said a new all-time low has been set.

Sea ice melts in the Antarctic summer before starting to grow again come fall. "In recent years, the annual low has occurred between February 18 and March 3, so a further decline is expected," the NSIDC researchers said. “Much of the Antarctic coastline is ice-free.

Previous studies have linked low sea ice cover to wave-induced stresses on the floating ice shelves that rim the continent, leading to the breakup of the weakest areas."

The German scientists said the "intense melting" could be due to unusually high air temperatures in the west and east of the Antarctic Peninsula, which were around 1.5°C above the long-term average. In addition, there have been strong westerly winds, increasing the retreat of sea ice.

Impact on sea level

While it is true that melting sea ice does not have a discernible impact on sea levels, since the ice is found in ocean water, it is important to note that sea ice surrounds the huge Antarctic ice shelves. If damaged or lost, the glaciers will flow faster and the sea level will rise more quickly.

These shelves are extensions of freshwater glaciers, and if they continue to melt as global temperatures rise, they will pose a catastrophic threat to sea level rise for centuries.

For example, one of the Nature studies claims that the Thwaites Glacier may have reached a tipping point of accelerated and irreversible ice loss. If it collapses completely in a few hundred years, this could contribute to a 25-inch rise in sea level. 

The result is "intensified melting of the ice shelves, an essential aspect of future global sea level rise," the researchers said.

Historical records also show dramatic changes in Antarctica, they said. The Belgian research vessel Belgica was trapped in a huge pack ice for more than a year in the Antarctic summer 125 years ago, in exactly the same region where the Polarstern now sails in completely ice-free waters.

Professor Carlos Moffat, from the University of Delaware, USA, who recently returned from a research cruise in the Southern Ocean, told Inside Climate News: “The extraordinary change we have seen this year is dramatic. Even as someone who has been watching these changing systems for a few decades, what I saw surprised me."

New observation techniques

Dr Peter Davis of the British Antarctic Survey (BAS) took oceanic measurements through a 600m deep well about two kilometres from the ground line, created by a hot water drill in late 2019.

These measurements were compared to melt rate observations taken at five other sites under the ice shelf. Over a nine-month period, the ocean near the grounding line became warmer and saltier, but the rate of melting at the base of the ice averaged between 2 and 5 m per year: less than had been previously modelled.

According to Britney Schmidt, an associate professor at Cornell University and lead author of the second study published in Nature, new glacier-observing techniques have allowed for a better understanding of how and where melting is taking place, which is especially important in glaciers in warm areas of Antarctica. 

What these investigations conducted on the white continent show is that it is not only important to know the amount of melting, but also the way in which it is happening to fully understand the implications of climate change in Antarctica.

Melting sea ice is problematic not only because it contributes to rising sea levels, but also because it accelerates global warming. When the white sea ice melts, which normally reflects up to 90% of the sun's energy back into space, it is replaced by a dark, unfrozen sea. 

Consequently, the water absorbs a large amount of the Sun's heat, which may further contribute to global warming, producing a feedback loop.

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