Antarctic melt rate tripled in last decade

Ice sheet pouring water into the ocean, raising sea levels every year

Antarctica’s ice sheet is melting at a rapidly increasing rate, now pouring more than 180 billion tonnes of ice into the ocean annually and raising sea levels a half-millimetre every year, a team of 80 scientists reported Wednesday.

The melt rate has tripled in the past decade, the study concluded. If the acceleration continues, some of scientists’ worst fears about rising oceans could be realized, leaving low-lying cities and communities with less time to prepare than they had hoped.

The result also reinforces that nations have a short window — perhaps no more than a decade — to cut greenhouse-gas emissions if they hope to avert some of the worst consequences of climate change.

Antarctica, the planet’s largest ice sheet, lost 199-billion tonnes of ice annually from 2012 through 2017 — approximately triple the 66-billion-tonne melt rate of a decade ago, the scientists concluded. From 1992 through 1997, Antarctica lost 44-billion tonnes of ice annually.

The study is the product of a large group of Antarctic experts who collectively reviewed 24 recent measurements of Antarctic ice loss, reconciling their differences to produce the most definitive figures yet on changes in Antarctica. Their results — known formally as the Ice Sheet Mass Balance Inter-Comparison Exercise (IMBIE) — were published Wednesday in the journal Nature.

“We took all the estimates across all the different techniques, and we got this consensus,” said Isabella Velicogna, an Antarctic expert at the University of California at Irvine and one of the many authors from institutions in 14 countries.

“The detailed record shows an acceleration, starting around 2002,” Beata Csatho, one of the study authors and a glaciologist at the University at Buffalo, said in an email.

Csatho noted that comparing the first and last five-year periods in the record reveals an even steeper acceleration. “Actually, if you compare 19972002 to 2012-2017, the increase is even larger, a factor of more than 5!!” she wrote.

For the total period from 1992 through the present, the ice sheet has lost nearly three trillion tonnes of ice, equating to just less than 8 millimetres of sea-level rise. Forty per cent of that loss has occurred in the past five years.

The rapid, recent changes are almost entirely driven by the West Antarctic ice sheet, which scientists have long viewed as an Achilles heel. It is known to be losing ice rapidly because it is being melted from below by warm ocean waters, a process that is rendering its largest glaciers unstable.

“The increasing mass loss that they’re finding is really worrying, particularly looking at the West Antarctic, the area that’s changing most rapidly,” said Christine Dow, a glaciologist at the University of Waterloo in Ontario who was not involved in the research. “And it’s the area that we’re most worried about, because it’s below sea level.”