Antarctic ice loss surging

Antarctic glaciers have been melting at an accelerating pace over the past four decades due to an influx of warm ocean water – a startling new finding that researchers say could mean sea levels are poised to rise more quickly than predicted in coming decades.

The Antarctic lost 36 billion tonnes of melting ice to the ocean each year from 1979 to 1989. That figure rose to 228 billion tonnes lost per year beginning in 2009, according to a study published Monday in the Proceedings of the National Academy of Sciences. That means the region is losing six times as much ice as it was four decades ago, an unprecedented pace in the era of modern measurements. (It takes about 326 billion tonnes of ice to produce one millimetre of global sea-level rise.)

‘‘I don’t want to be alarmist,’’ said Eric Rignot, an Earthsystems scientist for the University of California at Irvine and Nasa who led the work. But he said the weaknesses that researchers have detected in East Antarctica – home to the largest ice sheet on the planet – deserve deeper study.

‘‘The places undergoing changes in Antarctica are not limited to just a couple places,’’ Rignot said. ‘‘They seem to be more extensive than what we thought. That, to me, seems to be reason for concern.’’

The findings are the latest sign that the world could face catastrophic consequences if climate change continues unabated. In addition to more frequent droughts, heat waves, severe storms and other extreme weather that could come with a continually warming Earth, scientists already have predicted that seas could rise nearly 1m globally by 2100 if the world does not sharply decrease its carbon output. But in recent years, there has been growing concern that the Antarctic could push that even higher.

That kind of sea level rise would result in the inundation of island communities around the globe, devastating wildlife habitats and threatening drinking water supplies. Global sea levels have already risen 18cm since 1900.

The ice of Antarctica contains 57.2m of potential sea level rise. This massive body of ice flows out into the ocean through a complex array of partially submerged glaciers and thick floating expanses of ice called ice shelves. Both the glaciers themselves, as well as the ice shelves, can be as large as entire countries.

The outward ice flow is normal and natural, and it is typically offset by some 1.8 trillion tonnes of snowfall atop Antarctica each year, a process that on its own would leave the Earth’s sea level relatively unchanged. However, if the ice flow speeds up, the ice sheet’s losses can outpace snowfall volume. When that happens, seas rise.

That’s what the new research says is happening. Scientists came to that conclusion after systematically computing gains and losses across 65 separate sectors of Antarctica where large glaciers – or glaciers flowing into an ice shelf – reach the sea.

West Antarctica is the continent’s major ice loser.

– Washington Post