An iceberg the size of a quarter of Wales is very close to splitting off from one of the largest ice shelves in Antarctica, scientists say, after a fast-growing crack stretched to within 13 kilometres of the open ocean this week.
Last month, aerial observations showed that the crack had shifted toward the edge of the ice sheet and the open ocean, leading scientists to estimate that an iceberg more than 300,000 times the size of the one that sunk the Titanic could calve off as soon as summer.
The formation of the iceberg fits within a broader trend of shrinking ice shelves in the region, which scientists believe is linked to global warming.
The crack has grown an additional 17 kilometres in just the last week, according to observations released on Wednesday by Project MIDAS, a European research group that has been monitoring the region, making the iceberg's separation imminent.
The loss of such a large mass of ice would create a "significant risk" of the shelf as a whole becoming unstable
“I would expect it to occur quite rapidly, within days or weeks," Dan McGrath, a scientist with the US Geological Survey who has studied the ice sheet extensively, said in a phone interview.
The 5,000-square-kilometre chunk of ice has nearly completely broken off the Larsen C ice shelf, the fourth largest in Antarctica. When it does, it will shrink Larsen C by about 10 per cent and leave it with the smallest area ever recorded.
Scientists from Project MIDAS warned in 2015 that the loss of such a large mass of ice would create a "significant risk" of the shelf as a whole becoming unstable and breaking up, although McGrath cautioned that the larger outcome is not guaranteed.
While the generation of such a large iceberg was striking, McGrath said, it was less worrisome than other processes scientists have recently observed in the Antarctic, most of which are thought to be tied to climate change.
Chief among those is the destabilisation of major glaciers in Western Antarctica connected to the interior portion of the larger Antarctic ice sheet.
“If Larsen C were to collapse, it would be concerning for its own reasons, but the contribution to global sea level rise would be very small, something in the centimetres," McGrath said.
Continued destablisation and eventual breakup of the larger masses of ice in Western Antarctica, by comparison, would likely raise sea levels by 1 metre or more, McGrath added.
"It's dramatic," McGrath said of the potential split of the Larsen C iceberg. "But ... it's not the most concerning (part) of what we’re seeing down there.”