Antarctica is melting at record rates. But, unlike the rest of the warming world, this change began just a few years ago instead of decades, and scientists don’t know why.
Sea ice in Antarctica grows and diminishes every year in line with the seasons. But this year’s winter growth is significantly lower than expected.
“What’s going on is extraordinary in my mind,” says Professor Nathan Bindoff, a glaciologist at the University of Tasmania.
“This year there’s a much lower rate of actual ice expansion … We’re more than four standard deviations from where we ought to be in an average year.”
Antarctica’s sea ice had puzzled scientists for years. Instead of decreasing like the Arctic and the Greenland ice sheet, Antarctica stubbornly refused, instead growing slightly year on year since records began in the 70s.
This trend finally changed in 2016 with less sea ice than expected, followed by 2022 and now 2023 showing a significant drop in sea ice extent. Sea ice this year was at a record low in February, and is still at a record low for this time of year now.
This has led to worrying graphs showing the extent of the change.
But scientists are scratching their heads as to why this is happening so late. Most climate effects get slowly worse over a long period of time, they don’t suddenly switch over a few years.
“The climate change projections are that Antarctic sea ice should actually reduce progressively in time. So maybe the bigger question is actually why hasn’t it reduced?” said Bindoff.
“The challenge is to disentangle the contribution that’s from climate change, versus the actual internal variations that we understand in the climate system.”
That’s not to say the climate hasn’t affected it – it likely has. But more research will need to be done to understand why Antarctica’s sea ice has eschewed climate models for so long.
One theory is that as freshwater ice melts it spreads across the sea ice and provides a slight increase in sea ice area when it refroze. However, this has not been confirmed.
“Sea ice remains an outlier in our understanding,” says Bindoff.
“It’s very clear that the sea ice extent has shrunk everywhere – that’s not simply an El Niño/La Niña signal.”
“It’s really an area of active research.”
The Arctic and Greenland has not enjoyed such gains. Instead, both have been losing more and more ice each year. The World Meteorological Organisation recently noted that the past 16 years marked the lowest 16 year period on record for Arctic ice.
Of course, the next question is whether this trend will continue, or whether Antarctica will go back to the small increases it experienced since record keeping began in the 70s.
But when asked, Bindoff responded, “that’s a question for betting man, not a scientist.”
Originally published by Cosmos as Antarctica’s sea ice growth is at record lows. But it’s more complicated than just climate change
Jacinta Bowler
Jacinta Bowler is a science journalist at Cosmos.
They were published in the Best Australian Science Writing 2023.
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