The edges of Antarctica's ice sheets have been thinning at a rapid rate over the past decade—up to 70 percent faster than average in some spots—due to warming oceans and air.
Known technically as ice shelves, these edges float just offshore in bays or fjords and act as barriers that keep larger, land-based ice sheets from slipping into the ocean. Once they are gone, there will be nothing to hold back the continent-sized ice masses from sliding into the warmer oceans and melting, raising sea levels precipitously.
According to a new study published in the journal Science this week, this could happen by the end of the century.
"Within a lifetime of people who read this story, many of these shelves will be gone," said Andrew Shepherd, a polar scientist at the University of Leeds who reviewed the study before publication. "This is real, rapid environmental change. These shelves have been around for 10,000 years. It is a classic example of how drastically you can disturb the planet with small changes."
Researchers have historically focused their attention on land-based ice sheets in Greenland and Antarctica because they are massive contributors to sea level rise, said Fernando Paolo, a graduate student at the Scripps Institution of Oceanography at the University of California-San Diego and the lead author of the new paper.
When ice shelves melt, however, they don't raise sea levels directly because they are already in the ocean. But Paolo calls them an "overlooked, yet fundamental piece in the whole sea level rise process." Monitoring them could yield clues as to when this climate impact will go from bad to worse.
The paper comes two weeks after it was revealed that a glacier the size of California in East Antarctica has experienced rapid melting in recent years. If this particular glacier, the Totten Glacier, reaches the ocean, it could cause sea level to rise more than 11 feet.
Researchers from the University of California-San Diego and Earth and Space Research, a non-profit oceanographic research institute in Oregon, analyzed 18 years of satellite data, broken into three-month intervals, for the study published this week.
They found the ice shelves had been gradually thinning for a few decades, but melting accelerated around the start of the century, increasing from approximately 15 cubic miles of ice loss per year between 1994-2003 to 192 cubic miles per year between 2003-2012.
Two ice shelves—the Crosson and Venable—in western Antarctica, across from the southern tip of South America, have lost 18 percent of their mass in the last two decades. Another shelf, the Getz, thinned six percent in the same time period.
Ice loss was worse in the western portion of the continent where the ocean is warmer than in the east. The exact reason for this, however, isn't known. One theory is that a warm water current that once flowed 2.5 miles below the ocean surface has shifted toward Antarctica and moved closer to the surface, coming in contact with the ice shelves. The higher water temperatures erode and calve the western shelves from underneath at a much faster rate than in the east, where warming air temperatures are the main driver of melting.
The new work "is solid science by great scientists," said Richard Alley, a climate researcher at Pennsylvania State University. The paper "does not give us the story of how much [sea level rise there will be] and how fast, but it points in important directions for more research."
Ice Shelves Thinning, via Scripps Oceanography: