The Thwaites Glacier
West Antarctica’s Thwaites Glacier is a remote and otherworldly river of compressed snow and ice that flows through a vast ice sheet two miles thick to the Amundsen Sea. The ice of Thwaites, like the ice of most cold-region glaciers, doesn’t break off immediately upon entering the sea, but forms a floating ice shelf that remains attached to the coastline and slows the flow of additional glacier ice to the sea.
But in recent years, scientists have watched a new dynamic at work that, in the worst case, could drown coastal communities the world over. Warmer ocean waters are causing the Thwaites ice shelf to thin. Large parts have broken off. This warming is being driven by some combination of climate change, shifts in winds and currents caused by the ozone hole above the Antarctic, and the variability of other natural processes.
What will this mean? Like highway traffic merging from many lanes on multiple levels into a tunnel or bridge, thick inland ice squeezes both horizontally and vertically into the Thwaites glacier. Too much thinning and retreat along its 75-mile-wide front, where it meets the warming sea, would remove the merge, speeding up this traffic of ice and dumping more of it into the sea, where it will melt. Of all the glaciers in the world’s polar regions, Thwaites may be the most vulnerable to this runaway acceleration.
The world’s coastal planners are preparing for as much as three feet or so of sea-level rise over the next century in response to continuing, rapid planetary warming, but Thwaites could drain enough ice in West Antarctica to raise sea level by an additional 11 feet or so.
We may have already crossed the threshold for an irreversible collapse of this ice sheet, though the data is not conclusive, and there may be processes at work that we don’t fully understand. Given these considerable uncertainties, it is possible that the Thwaites ice sheet will remain nearly stable, or melt slowly enough to have relatively small or long-delayed impacts on coastal regions. But we don’t really know the worst-case for how fast Thwaites could go, and to add to the worries, some parts of East Antarctica and Greenland may behave similarly as the climate continues to warm.
A melting ice shelf could drain enough ice in west Antarctica to drown coastal communities the world over
Solid scholarship shows almost no chance that rapidly rising carbon dioxide concentrations in the atmosphere will create a new Garden of Eden, but some chance of rapidly breaking many things we care about. The impacts of warming may be slightly better or worse than we expect. Or much worse. In response to this warming, sea-level rise from melting ice and expanding ocean water is almost unavoidable. How high will depend, to a substantial degree, on what happens over the next few decades in the West Antarctic. Richard Alley is a glaciologist and professor of geosciences at Penn State.