In July of last year, a 5,800-square-kilometer (2,239-square-mile) block of ice broke off of the Larsen Ice Shelf in Antarctica and fell into the Southern Ocean.
The newly created iceberg was massive, about the size of the US state of Delaware, but it did not contribute to rising sea levels, as it was already floating on the ocean’s surface before it became detached from the larger body of ice. But many of the glaciers on the continent are melting, as well, and because they’re on land, the runoff from that melting ice does cause Earth’s sea levels to rise — and we now have one of the most robust estimates ever of just how much that melting glacial ice in the Antarctic is contributing to sea level rise.
According to new research, ice-melt in Antarctica has caused global sea levels to rise by as much as 7.6 millimeters since 1992 — and about 40 percent of that, some 3 millimeters, came in just the past five years.
That’s the finding of a major climate assessment called the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE), the results of which were published in the journal Nature last week. Andrew Shepherd of the UK’s University of Leeds and Erik Ivins of NASA’s Jet Propulsion Laboratory in the US state of California led a team of 84 scientists from 44 international organizations that used 24 different satellite surveys to produce the assessment.
There’s enough frozen water stored in Antarctica to raise global sea levels by 58 metres, the researchers note, meaning that it’s imperative for us to understand how much ice the continent is losing in order to measure the impacts of Earth’s changing climate.
The findings of the IMBIE show that Antarctica is losing ice at a rate three times faster than it was just six years ago. Prior to 2012, Antarctica lost ice at a fairly steady rate of 76 billion metric tons annually, contributing about 0.2 millimeters to sea level rise. From 2012 to 2017, however, that rate of loss increased sharply to 219 billion metric tons of ice per year, contributing about 0.6 millimeters to rising sea levels.
“We have long suspected that changes in Earth’s climate will affect the polar ice sheets. Thanks to the satellites our space agencies have launched, we can now track their ice losses and global sea level contribution with confidence,” the University of Leeds’ Shepherd said in a statement.
“According to our analysis, there has been a steep increase in ice losses from Antarctica during the past decade, and the continent is causing sea levels to rise faster today than at any time in the past 25 years. This has to be a concern for the governments we trust to protect our coastal cities and communities.”
Shepherd and team found that the increase in ice loss since 2012 is largely due to glacier speedup in West Antarctica and on the Antarctic Peninsula combined with reduced growth of East Antarctica’s ice sheet.
West Antarctica has been the site of the biggest changes, as annual ice losses have grown from 53 billion metric tons in the 1990s to 159 billion metric tons in recent years due mostly to ocean melting driving the rapid retreat of the Pine Island and Thwaites Glaciers. Meanwhile, the collapse of ice shelves on the Antarctic Peninsula, like the Larsen Ice Shelf, has caused an increase in ice losses of 25 billion metric tons per year since the early 2000s, the researchers found.
The East Antarctic ice sheet, on the other hand, has hovered near a state of balance for the past 25 years, gaining an average of just 5 billion metric tons of ice per year.
“Satellites have given us an amazing, continent-wide picture of how Antarctica is changing. The length of the satellite record now makes it possible for us to identify regions that have been undergoing sustained ice loss for over a decade,” Pippa Whitehouse, a researcher at Durham University in the UK and a member of the IMBIE team, said in a statement.
“The next piece of the puzzle is to understand the processes driving this change. To do this, we need to keep watching the ice sheet closely, but we also need to look back in time and try to understand how the ice sheet responded to past climate change.”
Banner image: Leeds University scientists ice coring at George VI Ice Shelf, Antarctica. Photo Credit: Ian Potten.
Shepherd, A., Ivins, E., Rignot, E., Smith, B., van den Broeke, M., Velicogna, I., … & Nowicki, S. (2018). Mass balance of the Antarctic Ice Sheet from 1992 to 2017. Nature, 556, pages219-222. doi:10.1038/s41586-018-0179-y
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