A hundred years from now, humans may remember 2014 as the year that we first learned that we may have irreversibly destabilized the great ice sheet of West Antarctica, and thus set in motion more than 10 feet of sea level rise.
Meanwhile, 2015 could be the year of the double whammy - when we learned the same about one gigantic glacier of East Antarctica, which could set in motion roughly the same amount all over again. Northern Hemisphere residents and Americans in particular should take note - when the bottom of the world loses vast amounts of ice, those of us living closer to its top get more sea level rise than the rest of the planet, thanks to the law of gravity.
The findings about East Antarctica emerge from a paper just out in Nature Geoscience by a team of scientists representing the United States, Britain, France, and Australia. They flew a number of research flights over the Totten Glacier of East Antarctica - the fastest-thinning sector of the world's largest ice sheet - and took a variety of measurements to try to figure out the reasons behind its retreat. And the news wasn't good: It appears that Totten, too, is losing ice because warm ocean water is getting underneath it.
"The idea of warm ocean water eroding the ice in West Antarctica, what we're finding is that may well be applicable in East Antarctica as well," says Martin Siegert, a coauthor of the study who is based at the Grantham Institute at Imperial College London.
The Totten Glacier covers an area 40 miles by 18 miles. It it is losing an amount of ice "equivalent to 100 times the volume of Sydney Harbour every year," notes the Australian Antarctic Division.
That's alarming, because the glacier holds back a more vast catchment of ice that, were its vulnerable parts to flow into the ocean, could produce a sea level rise of more than 11 feet, comparable to the impact from a loss of the West Antarctica ice sheet. And that's "a conservative lower limit," says lead study author Jamin Greenbaum, a Ph.D. candidate at the University of Texas at Austin.
In its alignment with the land and the sea, the Totten Glacier is similar to the West Antarctic glaciers, which also feature ice shelves that slope out from the vast sheet of ice on land and extend into the water. These ice shelves are a key source of instability, because if ocean waters beneath them warm, they can lose ice rapidly, allowing the ice sheet to flow more quickly into the sea.
The researchers used three types of measurements taken during their flights - gravitational measurements, radar, and laser altimetry - to get a glimpse of what might be happening beneath the massive glacier, whose ice shelves are more than 1,600 feet thick in places. Using radar, they could measure the ice's thickness. Meanwhile, by measuring the pull of Earth's gravity on the airplane in different places, the scientists were able to determine how far below that ice the seafloor was.
The result was the discovery of two undersea troughs or valleys beneath the ice shelf - regions where the seafloor slopes downward, allowing a greater depth of water beneath the floating ice. These cavities or subsea valleys, the researchers suggest, may explain the glacier's retreat - they could allow warmer deep waters to get underneath the ice shelf, accelerating its melting.
One limitation of the study is that the scientists were not able to directly measure the temperature of ocean water that is reaching the glacier itself. While this could be done with robotic underwater vehicles or other methods, that wasn't part of the study at this time.
For the U.S., the amount of sea level rise could be 25 percent or more than the global average. But just because a retreat has been observed does not mean that we'll see anything near that much sea level rise in our lifetimes.