The rate of ice loss in Greenland has sped up massively, from 51 billion tons in the 1980s to 286 billion tons between 2010 and 2018, according to a study based on nearly a half-century of data published last week in the Proceedings of the National Academy of Sciences.
Greenland holds the world’s second-largest ice sheet, and the result of the accelerated loss “is that out of nearly 14 millimetres of sea level rise in total caused by Greenland since 1972, half of it has occurred in the past eight years,” the Washington Post reports.
“And the ice losses are likely to get worse. The regions with the biggest potential ice loss—the frigid far northwest and northeast of the island, which sit up against the Arctic Ocean—have not changed as quickly as other parts of Greenland. Should they begin to melt more rapidly, then Greenland’s overall ice loss—and contribution to sea level rise—could grow even more.”
“The 1980s marked the transition time when the Earth’s climate started to drift significantly from its natural variability as a result of man-made emissions of greenhouse gases,” wrote study co-author and NASA Earth scientist Eric Rignot. As a result, “the entire periphery of Greenland is affected. I am particularly concerned about the northern regions, which host the largest amount of potential sea level rise and are already changing fast.”
In an email to the Post, Rignot also expressed concern about Antarctic ice loss, based on research he led last year that showed the continent losing six times as much ice today as it was four decades ago. “In Antarctica, some big sleeping giants in East Antarctica are waking up, in addition to a large part of West Antarctica being significantly affected. None of this is good news,” he wrote. “We ought to prepare ourselves for what is coming up and take action as soon as possible to avoid the most drastic scenarios.”
A separate study in the journal Nature Geoscience shows the Ross Ice Shelf in Antarctica, the world’s largest, melting 10 times faster than the rest. “The findings have implications for future sea level rise,” the BBC reports, since the structure “plays an important role in stabilizing this wider region of Antarctica.”
The BBC describes the Ross as a huge, floating block of ice, roughly the size of France and up to 750 metres thick in some places. “Ice shelves like this one are formed continuously by glaciers which feed them,” the news agency explains. “In turn, the shelves act as a ‘brake’ on the glaciers and also moderate the amount of melting that occurs on the glaciers’ surfaces.”
While the Ross Ice Shelf, unlike others in Antarctica, has seemed stable in recent years, scientists have been building up a record of how its northwest sector interacts with the ocean waters below. “They found that the sun heats ocean surface water which then flows into a cavity under the shelf causing melt rates to rise—particularly during the summer months,” the BBC writes. “The findings are important because the Ross Ice Shelf stabilizes the West Antarctic Ice Sheet by blocking the ice which flows into it from some of the world’s largest glaciers. This in turn has implications for sea level rise in future.”
“Previous studies have shown that when ice shelves collapse, the feeding glaciers can speed up by a factor of two or three,” said study co-author Dr. Poul Christoffersen of the Scott Polar Research Institute in Cambridge, UK. “The difference here is the sheer size of Ross Ice Shelf, which is over 100 times larger than the ice shelves we’ve already seen disappear.”
The Post coverage includes details on Greenland’s ice cover, the 2.0 to 4.0°C warming it has already undergone, and the ice loss it has undergone—noting that the precise volume lost is tough to tie down, but “it matters a great deal, as every 360 billion tons equates to a millimetre of sea-level rise.” Marco Tedesco, a Greenland specialist at Columbia University’s Lamont-Doherty Earth Observatory, told the paper the “current melting and runoff is unprecedented over the past 150 years,” adding in an email that the PNAS study “highlights the importance of understanding and quantifying how the glaciers respond to warming and enhanced surface melting.”
Rignot said the findings are “consistent with our understanding of how climate change affects ice, only that it is happening sooner and faster than anticipated by models”—meaning that some degree of ice loss and sea level rise is inevitable, but today’s decisions on human-generated emissions will have a massive future impact.
“If we do something now, it will take 30 years to affect the climate and another few decades to turn the melt down of glaciers, so probably half of that signal is already written in stone,” he told the Post. “But the impact sea level will have on humanity increases with every 10 [centimetres] of sea level rise, and right now we are about to commit to multi-metre sea-level rise in the coming century if we don’t do something drastic.”