Glaciers Holding Back Sea-Level Rise Are Showing Signs of Collapse
There’s a new hot spot for ice loss in Antarctica, say scientists, which may add to the problems sea-level rise is causing around the world.
The Southern Antarctic Peninsula has long been stable, even as dramatic global warming–driven changes, such as the abrupt collapse of the enormous Larsen B ice shelf on the Northern Antarctic Peninsula in 2002, have hit other parts of the continent.
But starting around 2009, many of the Southern Antarctic Peninsula’s glaciers began to shed enormous amounts of ice into the ocean, according to a new analysis published Thursday in the journal Science.
Since then, about 300 billion tons of Southern Antarctic Peninsula ice have dropped into the ocean, where it melts. It’s the equivalent of as much water as “the volume of nearly 350,000 Empire State Buildings,” according to Bert Wouters, a geologist at the University of Bristol in the United Kingdom and the lead author of the study.
"Global warming has caused the wind patterns in the area to change, and these winds are pushing warmer water towards Antarctica, from further north in the Southern Ocean," said Wouters. The warmer waters are destabilizing coastal ice formations.
This melt has accounted for roughly 0.006 inches of sea rise per year since 2009, and it shows no signs of stopping.
A few thousandths of an inch may not seem like much. But as warming ocean waters cause ice shelves and glaciers to break off from land and melt, less ice is left at the water's edge to block the glacier's flow from inland to the sea. It begins to move faster, putting more ice into the ocean.
This positive feedback loop is happening in both the Antarctic and the Arctic, along with warming seawater expanding to take up more space in the world's ocean basins. Taken together, these changes are accelerating the rise of sea levels globally.
The study “shows that the Antarctic ice sheet can react very quickly to changes in the environment, at a very high rate,” Wouters said, adding that within a matter of just a few years, the previously unchanged area transformed from being “in balance” to “being the highest contributor to sea-level rise in Antarctica.”
“It also implies that this southern ice loss could start in other regions as well, where we don’t expect it,” he said. In March, scientists reported that the ice sheets of Western Antarctica were thinning at an unexpectedly high rate.
If the melt-off were to remain steady, that would add up to about half an inch of additional water in the ocean by 2100. But a recent study showed that global sea-level rise is accelerating.
“We know that ocean temperatures in the area have risen in the past several years and have warmed the waters around the ice shelves,” he said. “It’s still cold but above the freezing point, so it carries enough heat to melt the ice shelves.”
Wouters and his colleagues discovered the abrupt changes by mapping recent satellite data about the ice sheet’s elevation, including readings from the European Space Agency’s CryoSat-2, the “first radar altimeter dedicated to ice,” said Wouters.
“Most of the glaciers in this area end up as floating ice shelves,” which, when stable, hold back the flow of ice from land into the ocean, Wouters said. Changes in the area’s air temperatures and snowfall levels were too small to explain why the glaciers began flowing faster into the sea, he said, which left the ocean as the only reasonable explanation.
Why You Should Care: With nearly half of the world's population living near coastlines, rising and warming seas threaten ever more lives, homes, and costly infrastructure, as with Cyclone Pam in Vanuatu in March, Typhoon Haiyan in the Philippines in 2013, and Hurricane Sandy—which had a record-setting 14-foot storm surge—in 2012. If the burning of fossil fuels is not sharply cut back before 2050, according to the United Nations, sea levels are likely to rise 1.7 to 3.2 feet by the turn of the century.
This post has been revised to reflect the following correction:
Correction May 26, 2015: An earlier version of this article misidentified the journal in which this research was published. The paper appeared in the May 22, 2015, issue of Science.