Vast ice blocks are slowly collapsing into the sea off Antarctica, increasing the threat from the rising level of the world's oceans, British scientists said. Their discovery that the West Antarctic ice sheet is unstable overturns the previous international consensus that it would take 1,000 years for the floating ice to respond to rising temperatures. It is also likely to cause increased concern about global fossil fuel emissions. Scientists from the British Antarctic Survey said that far from gaining in mass, as expected, because of increased snowfall in the polar regions, the West Antarctic ice sheet was losing 250 cubic kilometres of ice a year. This means Antarctica is contributing at least 15 per cent of the current 2mm annual rise in sea levels.