Nature Climate Change | Climate Feedback

Melting icebergs raise the sea level

Cross-posted from Quirin Schiermeier on The Great Beyond

Since 1994, around 750 cubic kilometers of floating ice – equivalent to the volume of Lake Titicaca in Bolivia – have been melting each year around the Arctic Ocean and off Antarctica, an analysis of satellite observation has revealed. The massive loss of sea ice actually adds a wee bit to global sea level rise, scientists report in a paper in Geophysical Research Letters.

Popular belief has it that the melting of drifting icebergs and floating ice shelves has no effect on the height of the surrounding sea level just like melting ice cubes in a drink don’t make your glass overflow.

But because sea water is warmer and more salty than ice this is not quite correct. In fact, melting sea ice does raise seal level by about 2.6 % of its volume – equivalent to the difference in density between fresh- and sea-water, the team reports.

Globally, the effect is almost negligible: Retreating Arctic sea ice and thinning ice shelves around Antarctica contribute about 50 micrometers, or half a hairbreadth, to the 3 millimeter or so annual rise in global sea level from melting glaciers and thermal expansion of ocean water.

Even so, the effect deserves monitoring, says Andrew Shepherd of the University of Leeds in Britain, who led the study.

Sea level contribution from floating ice might strongly increase in a warming climate, he says. If all present-day floating ice were lost, global sea level would rise by up to 6 centimetres.