Antarctic glaciers have melted at an accelerated rate over the past four decades due to an influx of hot ocean water – a surprising new finding that researchers say may mean that sea levels must rise faster than expected in the coming decades .
Antarctica lost 40 billion tonnes of ice melted into the ocean each year from 1979 to 1989. That number rose to 252 billion tonnes lost per year from 2009, according to a study published in the Proceedings of the National Academy of Sciences. This means that the region is losing six times more ice than it did four decades ago, a pace unprecedented in the age of modern measurements. (It takes about 360 billion tons of ice to produce one millimeter of global sea-level rise.)
"I do not want to be an alarmist," said Eric Rignot, a scientist at the University of California at Irvine and NASA who led the work. But he said the weaknesses researchers have spotted in eastern Antarctica – home to the world's largest ice sheet – deserve further study.
"Places that go through changes in Antarctica are not limited to just a few places," Rignot said. "They seem to be more extensive than we thought, which to me seems to be cause for concern."
The findings are the latest sign that the world could face catastrophic consequences if climate change persists. In addition to more frequent droughts, hot flashes, severe storms and other extreme weather conditions that could continually heat up the Earth, scientists had already predicted that the seas could rise by about one meter globally by 2100 if the world did not drastically reduce its production of carbon. But in recent years there has been a growing concern that Antarctica could push this further.
Such a rise in sea level would result in flooding of island communities around the world, devastating wildlife habitats and threatening the supply of drinking water. Global sea levels have already risen 7 to 8 inches since 1900.
The Antarctic ice contains 57.2 meters, or 187.66 feet, of potential sea level rise. This massive body of ice flows into the ocean through a complex set of partially submerged glaciers and thick floating ice expanses called ice shelves. Both the glaciers themselves and the ice shelves can be as large as the major states of the United States or entire countries.
The external ice flow is normal and natural, and is usually offset by about two trillion tons of snow at the top of Antarctica each year, a process that by itself would leave the sea level of the Earth relatively unchanged. However, if the ice flow accelerates, the losses of the ice sheet may exceed the volume of snow. When that happens, the seas rise.
That's what the new research says is happening. Scientists have come to this conclusion after systematically computing the gains and losses in 65 separate sectors of Antarctica, where large glaciers – or glaciers flowing on an ice shelf – reach the sea.
Western Antarctica is the continent's biggest ice loser. Monday's survey confirms these findings, detailing how a single glacier, Pine Island, has lost more than a trillion tons of ice since 1979. Thwaites, the largest and potentially most vulnerable glacier in the region, lost another 634 billion. The entire West Antarctic ice sheet is capable of raising sea level by 5.28 meters and is now losing 159 billion tons per year.
The most notable finding in Monday's study is the claim that East Antarctica, which contains by far the continent's largest ice – a large sheet capable of reaching nearly 70 meters of sea level rise potential – is also experimenting serious melting.
The new research highlights how some gigantic glaciers, which until now have been little studied, are actually losing significant amounts of ice. This includes Cook and Ninnis, who are the gateway to the huge Wilkes Subglacial Basin and other glaciers known as Dibble, Frost, Holmes, and Denman.
Denman, for example, contains nearly 1.5 meters of sea-level rise potential and lost almost 200 billion tonnes of ice, the study said. And it remains alarmingly vulnerable. The study notes that the glacier is "grounded in a mountain range with a steep retrograde slope immediately upstream," meaning that additional losses could cause the glacier to retreat rapidly.
"It has been known for some time that the West and Antarctic Antarctic Peninsula has lost mass, but finding that significant mass loss is also occurring in eastern Antarctica is really important because there is such a large volume of sea-level equivalent contained in these basins, "said Christine Dow, a glacier specialist at the University of Waterloo in Canada. "This shows that we can not ignore Eastern Antarctica and we need to focus on areas that are losing mass faster, particularly those with reverse bed slopes that can result in rapid ice disintegration and sea level rise."
The new research is consistent in some ways with a large study published last year by a team of 80 scientists, finding that ice losses in the Antarctic tripled in a decade and now total 219 billion tonnes per year. This research did not find similar major losses from Eastern Antarctica, although it has noticed that there is great uncertainty about what is going on there.
"More work is needed to reconcile these new estimates," said Beata Csatho, an Antarctic expert at the University of Buffalo, who authored the earlier study.
The result is that Antarctica is losing a lot of ice and that vulnerable areas exist in eastern and western Antarctica with few signs of slowing as the oceans only get warmer. In particular, says Rignot, key parts of Eastern Antarctica, which has been the focus of lesser focus of researchers in the past, need a more detailed and fast look.
"The traditional view of many decades ago is that nothing is happening in Eastern Antarctica," Rignot said, adding, "It's a bit like a positive thought."
The Washington Post