Antarctic sea ice reaches record low, but role of warming unclear

CLIMATEWIRE | Antarctic sea ice shrank to an all-time record in February – the smallest it has been since satellites began tracking more than 40 years ago.

It was the second year in a row that the remote southern continent saw its ice reach a record low, and the fourth time since 2017.

The series of records could be a fingerprint of climate change. But scientists can’t say for sure.

Warming is already affecting Antarctica in other ways, including accelerating ice loss from melting glaciers. But the region’s sea ice is more complex and doesn’t always behave in a predictable way.

“Antarctic’s response to climate change has been different than the Arctic’s,” Ted Scambos, an Antarctic ice expert at the University of Colorado, Boulder, said in a statement. “The downward trend in sea ice may be a signal that global warming is finally affecting the ice floes around Antarctica, but it will take several more years to know for sure.”

Until 10 years ago, Antarctic sea ice had actually been growing for decades. This is in stark contrast to Arctic sea ice, which has been steadily declining due to rising temperatures.

Then, around 2014, the Antarctic trend abruptly reversed and sea ice began to decline rapidly. It reached record lows in 2017 and 2018 and then recovered slightly before hitting new records in 2022 and 2023.

This may not be the first time Antarctic sea ice has fallen. A recent study attempted to reconstruct sea ice trends before the satellite record began, using other forms of data from the past century. He suggested that Antarctic sea ice may have been declining until the year 1960, when it began to increase.

The reasons are unclear.

In a 2019 study, NASA scientist Claire Parkinson noted that the cause of the decades-long increase in ice in the late 20th century “remains perplexed.” Not enough time has passed to be sure what is causing the falls.

Several factors may be at play, he noted, including natural fluctuations in the Earth’s climate cycle, which can cause ice-related conditions to shift over time. Some studies have also suggested that the gradual healing of Earth’s ozone hole, which has been in recovery for several decades, may be altering the atmosphere in ways that could affect Antarctic winds and their influence on sea ice.

At the same time, the effects of climate change are becoming stronger — and may be a factor in the recent declines.

Polar opposites

Factors other than human-induced warming are often more influential in the Antarctic than in the Arctic. This is partly because the two regions are so different physically.

The Arctic is extremely isolated and self-contained, closed in on all sides by land masses. Antarctica is essentially the opposite – it’s a large land mass surrounded by a vast, deep sea that merges with other oceans.

Because the Southern Ocean is so large and deep, it “takes longer to respond” to the influence of human-induced climate change than other ocean basins, said Liping Zhang, a NOAA scientist who has researched the Southern Ocean and marine Antarctic ice. .

This means that strong natural variations in climate can sometimes overwhelm the signal of human-caused warming. This may explain why trends in Antarctic sea ice so far have been so confused compared to the Arctic.

However, the impact of climate change is likely to catch up eventually, if it hasn’t already. It’s just unclear exactly how long that process might take, according to Zhang.

It’s possible that very strong natural climate fluctuations could continue to overwhelm the human-induced climate signal for a while longer, with another sea ice reversal on the way. Or it is possible that Antarctic sea ice will continue to decline indefinitely as the warming signal grows stronger.

In fact, the most recent declines “may be a result of climate change,” Zhang said. A combination of atmospheric and oceanic factors likely led to the record low this February, he added, including warming in the Southern Ocean.

“However, we do not have enough evidence for certainty at this point,” he added. “A wide variety of factors must be considered to better understand the observed changes and their implications for future behavior.”

If sea ice continues to decline, it could have far-reaching effects on Antarctica.

Sea ice can serve as a kind of buffer between the ocean and the Antarctic ice sheet. As it shrinks, it leaves coastal glaciers more susceptible to the effect of warming water, said Scambos of the University of Colorado, Boulder.

“Lower sea ice extent means ocean waves will hit the coast of the giant ice sheet, further reducing the ice shelves around Antarctica,” he said.

Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2023. E&E News provides essential news for energy and environmental professionals.

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