The towering glaciers of West Antarctica hold the fate of the world’s coasts in their flanks. Their collapse could send sea levels up by at least a foot by 2100—and potentially much more.
For years, scientists have watched and learned that those glaciers are crumbling and melting, the rate speeding up over the decades and imperiling the stability of the entire ice sheet. But while the science was clear that human influences on climate would affect the ice down the line, it has been hard to tell whether human-driven global warming has affected the melting already underway.
Now, a team has unraveled evidence of that human influence. In a study published Monday in Nature Geoscience, a team of scientists showed that over the past century, human-driven global warming has changed the character of the winds that blow over the ocean near some of the most fragile glaciers in West Antarctica. Sometimes, those winds have weakened or reversed, which in turn causes changes in the ocean water that laps up against the ice in a way that caused the glaciers to melt.
“We now have evidence to support that human activities have influenced the sea level rise we’ve seen from West Antarctica,” says lead author Paul Holland, a polar scientist at the British Antarctic Survey.
The ocean eats the ice
The massive West Antarctic ice sheet holds something like 6 percent of the world’s fresh water frozen in its guts. If it all melted away, global sea levels would rise by about 10 feet or more. That’s not likely to happen anytime particularly soon, scientists think, but some parts of the ice sheet are particularly vulnerable, in danger of crossing a crucial “tipping point” if they retreat too far. (Read about the “tipping point” here).
In the past decades, some glaciers in the region have been retreating shockingly quickly. Pine Island Glacier and Thwaites Glaciers, for example, are losing about 100 billion tons of ice each year, and more in bad years. (See what a 10 billion ton chunk of ice looks like in this video).
The glaciers have been receding because their snouts spill over the edge of the continent into the surrounding ocean, which is warmer than the ice. The warm water melts away the ice.
Just how warm the ocean is, though, matters a lot. Over decades, the temperature of the water has waxed and waned, driven in part by natural climate cycles that send different water masses close to the edge of the ice sheet at different times, cycling through from cold to a little less cold every five years or so.