Previously, scientists had suggested that sea levels could rise by five or six metres if the ice sheet melted, but a new study published in Science says the rise could actually be around 3.3 metres.

The WAIS is thought to be particularly vulnerable to rising temperatures because much of the bedrock on which it sits is below sea level. Scientists believe that if the sheet lost the ice fringes around its edges, the interior ice would flow into the sea and the sheet would rapidly disintegrate. However, using computer models based on the behaviour of glaciers, the authors of the new report calculated that only the parts of the ice sheet below sea level would melt, and that large amounts of ice would remain on the areas above sea level.

The downgrading of the rise in sea level is no reason for complacency, however. ‘Even if the WAIS contributed only a metre of sea level rise over many years, sea levels along North America’s shorelines would still increase by 25 per cent more than the global average,’ said Jonathan Bamber of Bristol University, the report’s lead author.

Sea levels would rise by different amounts around the world, Bamber said, because the movement of ice from the Antarctic continent to the oceans would weaken the Earth’s gravity field in the Southern Hemisphere and strengthen it in the north, causing water to pile up in the northern oceans.

July 2009