Antarctic summer ice melting 10 times faster

Summer ice in the Antarctic is melting 10 times quicker than it was 600 years ago, with the most rapid melt occurring in the last 50 years, a joint Australian-British study showed on April 15. A research team from the Australian National University and the British Antarctic Survey drilled a 364-metre (1,194 feet) long ice core from James Ross Island in the continent's north to measure past temperatures in the area.
Visible layers in the ice core indicated periods when summer snow on the ice cap thawed and then refroze. By measuring the thickness of these melt layers, the scientists were able to examine how the history of melting compared with changes in temperature at the ice core site over the last 1,000 years.
"We found that the coolest conditions on the Antarctic peninsula and the lowest amount of summer melt occurred around 600 years ago," said lead author Nerilie Abram of the ANU Research School of Earth Sciences. "At that time, temperatures were around 1.6 Celsius lower than those recorded in the late 20th century and the amount of annual snowfall that melted and refroze was about 0.5 percent. "Today, we see almost 10 times as much of the annual snowfall melting each year.
"Whilst temperatures at this site increased gradually in phases over many hundreds of years, most of the intensification of melting has happened since the mid-20th century," she added.
The research, published in the journal Nature Geoscience, is only the second reconstruction of past ice melt on the Antarctic continent.
Abram said it helped scientists gain more accurate projections about the direct and indirect contribution of Antarctica's ice shelves and glaciers to global sea level rise. "What it means is that the Antarctic peninsula has warmed to a level where even small increases in temperature can now lead to a big increase in summer ice melt," she said.
"This has important implications for ice instability and sea level rise in a warming climate." Robert Mulvaney, from the British Antarctic Survey, led the ice core drilling expedition and co-authored the paper.
"Having a record of previous melt intensity for the peninsula is particularly important because of the glacier retreat and ice shelf loss we are now seeing in the area," he said.
"Summer ice melt is a key process that is thought to have weakened ice shelves along the Antarctic peninsula leading to a succession of dramatic collapses, as well as speeding up glacier ice loss across the region over the last 50 years."