The Conger Ice Shelf collapsed around March 15, probably as a result of Antarctica's recent heatwave. Although the shelf itself is relatively small – the size of a large city rather than a country – its sudden demise has shocked glaciologists. The Conger is a small part of East Antarctica, the one frozen region that had previously largely resisted the effects of Global Heating, and the part with the potential to do by far the most damage.

East Antarctica holds more ice than the rest of the world combined. If all the frozen water in Greenland or West Antarctica were to melt, the oceans would rise by 7 and 5 meters (23 and 16 feet), respectively – catastrophic for people in low-lying areas, but potentially survivable for civilization as a whole. East Antarctica, however, has the potential to raise sea levels by 53 meters (170 feet), putting most of the world's great cities underwater.

Consequently, while Greenland, West Antarctica, and Alpine glaciers have all been melting fast, many have taken comfort that changes in East Antarctica have been much slower if they've been observed at all. All that may have changed, however, with satellite images revealing the Conger has almost entirely disappeared.

^{Demise and collapse of Conger ice shelf from Stef Lhermitte on Vimeo.}

The event has happened too recently for peer-reviewed studies, but on Twitter scientists are debating its causes. Ice bodies can break up for different reasons, for example through ponds forming on the surface that find a break that allows them to rush to the bottom, lubricating movement from below. However, no signs of this process have been seen in the satellite images and Durham University PhD student Jenny Arthur tweeted:

Although a variety of short and long-term forces probably contributed, the astonishing heatwave experienced by Antarctica recently is certainly a prime suspect.

Ice shelves are permanent (or at least usually so) sheets of floating ice connected to land. They are far more common and extensive around Antarctica than in the Northern Hemisphere. The Conger is amongst the smallest, not even making Wikipedia's list of Antarctic ice shelves. Facing the Indian Ocean it's also more poorly explored than places closer to southern continents.

Since they float, ice shelves already contribute to ocean volume, so their melting has no direct effect on sea levels. However, they can have powerful indirect effects, because when blocked by islands or anchored to shallow sea beds they obstruct the flow of glaciers behind them. On melting, the pressure previously applied to the glacier is released, causing it to flow up to five times faster, dumping ice from the land into the oceans.

The Conger had been wedged against Bowman island, and its release is likely to cause increased flow from the glacier behind, further accelerating the rise in sea levels, albeit only slightly. The much more important issue is whether this collapse is a forerunner of the break up of sheets holding back larger glaciers.

Scientists first noticed something was wrong with the Conger on March 17, when an iceberg named C-38 was reported to have broken off the ice shelf. Although it is normal for icebergs to break away from shelves, C-38 was so large relative to the shelf and came so soon after the calving of C-37, that it indicated the Conger's near-complete collapse.

Antarctic sea ice hit a record low last month, ten percent below the previous record. The Conger aside, most of that has been off West Antarctica. Colder seas around the east provide a buffer against warming caused by rising greenhouse gasses. How long that lasts is among the most crucial questions facing humanity.