Using new and published satellite altimeter observations of the Antarctic ice shelf and Arctic sea ice researchers at the University of Leeds have provided the first estimate of changes in the quantity of ice floating in the world’s oceans and the consequent change in sea level.
Overall the researchers find that increases in sea level due to the loss of Arctic sea ice and the collapse of several Antarctic ice shelves have been mitigated by gains in the extent of Antarctic sea ice and an overall thickening of the remaining Antarctic ice shelves. Specifically, although the rate of ice loss at the Antarctic Peninsula and in the Amundsen Sea is high (481 ± 38 cubic km per year), this trend is offset by small increases in the thickness of the vast Filchner-Ronne, Ross, and Amery ice shelves. Altogether, 746 ± 127 cubic km per year of floating ice was lost between 1994 and 2004, a value that exceeds considerably the reduction in grounded ice over the same period. This is equivalent to the volume of Lake Titicaca in Bolivia or about 1.5 million Titanic-sized icebergs each year melting into the sea in the Arctic and Antarctic.
It is commonly believed that the melting of floating ice 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. However, because sea water is warmer and more salty than ice this is not quite correct. Melting sea ice does raise sea level by about 2.6 % of its volume – equivalent to the difference in density between fresh- and sea-water.
The contribution to sea-level change of this melting is miniscule, just 49 micrometres per year – around a hair’s breadth. At this rate it would take 200 years for the oceans to rise by 1 cm as a result of melting sea ice. If all the floating ice in the world melted it would cause sea levels to rise by just 4 cm. By comparison, if all the ice situated on land melted it would cause a rise of 70 m.
Despite its small value Professor Andrew Shepherd, one of the authors of the study published in Geophysical Research Letters, said it was still significant suggesting that it will be important to include the small changes when assessing sea level rise in the future, especially if global warming accelerates.
The research is to be published in Geophysical Research Letters.