Last week, British scientists announced a disturbing finding - a crack in the Larsen C ice shelf in the Antarctic Peninsula had dramatically accelerated its spread, increasing 18km in length in the space of a month.

This means the floating ice shelf, which is nearly as big as Scotland and the fourth largest of its kind in Antarctica, is poised to break off a piece nearly 5180sq km in size, or over 10 per cent of its total area. An ice island the size of a small US state would then be afloat in the Southern Ocean.

That's dramatic enough, but there is uncertainty in the science world about what would happen next.
On the one hand, the researchers with Project Midas, who announced the growth of the rift, have published research suggesting that, in their words, it "presents a considerable risk to the stability of the Larsen C Ice Shelf".

If they're right, it's hard to understate how big a deal it is - Antarctica has lost ice shelves before, but not one so enormous. Not only would a loss of Larsen C change the map of the Earth itself; the shelf holds back glaciers capable of contributing about 10cm of global sea level rise over time.

The rift is now largely following the second, and worse scenario from their research, said glaciologist Daniela Jansen of the Alfred Wegner Institute in Germany - if it is correct. "This calving will be a test for our calving front stability criterion," she said by email.

However, other analyses have suggested that most of the ice that would be lost is so-called "passive ice" that does not play a key role in holding the glaciers behind the shelf in place. And some scientists have expressed scepticism about whether what's happening at Larsen C is "cause for alarm".

Time, ultimately, will show who is right. But in the meantime we can sketch, a little, the kinds of things that scientists are thinking about as they watch all of this unfold.