evidence: Over a third of the Antarctic's ice shelf area may be at risk of collapsing into the sea if global temperatures reach four degrees Celsius above pre-industrial levels, according to a study. The research, published in the Geophysical Research Letters journal, found that 34% of the area of all Antarctic ice shelves -- around half a million square kilometers -- including 67% of ice shelf area on the Antarctic Peninsula, would be at risk of destabilisation under such a warming scenario. [...] The researchers noted that limiting temperature rise to two degrees Celsius rather than four degrees Celsius would halve the area at risk, and potentially avoid significant sea level rise. They noted that when melted ice accumulates on the surface of ice shelves, it can make them fracture and collapse spectacularly. [...] Ice shelves are permanent floating platforms of ice attached to areas of the coastline and are formed where glaciers flowing off the land meet the sea, they said. The researchers identified the Larsen C, Shackleton, Pine Island and Wilkins ice shelves as most at-risk under four degrees Celsius of warming, due to their geography and the significant runoff predicted in those areas.