Antarctica’s ice sheet is melting at a rapidly increasing rate, now pouring more than 200 billion tons of ice into the ocean annually and raising sea levels a half-millimeter 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’d 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 219 billion tons of ice annually from 2012 through 2017 — approximately triple the 73 billion ton melt rate of a decade ago, the scientists concluded. From 1992 through 1997, Antarctica lost 49 billion tons 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 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, Irvine, and one of the many authors from institutions in 14 separate countries. The lead author was Andrew Shepherd of the University of Leeds in the UK.
‘‘The detailed record shows an acceleration, starting around 2002,’’ said Beata Csatho, one of the study authors and a glaciologist at the State University of New York at Buffalo, in an e-mail.
Csatho noted that comparing the first and last five-year periods in the record reveals an even steeper acceleration. ‘‘Actually, if you compare 1997-2002 to 2012-2017, the increase is even larger, a factor of more than 5!!’’
For the total period from 1992 through the present, the ice sheet has lost nearly 3 trillion tons of ice, equating to just under 8 millimeters of sea level rise. Forty percent of that loss has occurred in just the last 5 years, again underscoring the recent increase in losses.
Looking closer, 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.
West Antarctica lost 159 billion tons of ice a year from 2012 through 2017, compared with just 65 billion tons from 2002 through 2007.
The growth is largely attributable to just two huge glaciers — Pine Island and Thwaites. The latter is increasingly being viewed as posing a potential planetary emergency, because of its enormous size and its role as a gateway that could allow the ocean to someday access the entirety of West Antarctica, turning the marine-based ice sheet into a new sea.
Pine Island is now losing about 45 billion tons per year, and Thwaites is losing 50 billion. Both numbers are higher than the annual losses for any other glacier anywhere in the world.
‘‘The increasing mass loss that they’re finding is really worrying, particularly looking at the West Antarctic, the area that’s changing most rapidly, and it’s the area that we’re most worried about, because it’s below sea level,’’ said Christine Dow, a glaciologist at the University of Waterloo in Canada who was not involved in the research.
‘‘If you start removing mass from there, you can have a very large-scale evacuation of ice into the ocean and significant sea level rise,’’ she continued.
An additional increase in ice losses came from the smaller glaciers of the Antarctic Peninsula, which are also melting rapidly but contain less sea level rise potential.
The largest part of the continent, East Antarctica, has remained more stable and didn’t contribute much ice to the ocean during the period of study, the assessment says. However, in the last five years, it too has begun to lose ice, perhaps as much as 28 billion tons per year.
What’s happening in East Antarctica is extremely important because it has by far the most ice to give, being capable of raising sea levels by well over 100 feet.