Thwaites: Inside the 'Doomsday Glacier'

On the edge of West Antarctica sits a river of ice roughly the size of Florida. It is called Thwaites Glacier, and scientists have given it a scarier nickname: the Doomsday Glacier. That name is not for drama. Thwaites alone holds enough ice to raise global sea levels by about 65 centimeters, more than two feet, and it acts like a cork holding back neighboring ice that could add several meters more. Since the 1990s, Thwaites has been losing ice faster and faster. In 2019, researchers drilling through the ice found warm ocean water melting it from underneath, in a place no one could see before. Understanding this one glacier may be one of the most important science projects on Earth.

- Where Thwaites is and why its size and location make it so important - How warm ocean water melts a glacier from below at the grounding line - Why a marine ice sheet can retreat in a runaway feedback loop - How scientists measure a glacier they cannot easily reach

A glacier is a slow-moving river of ice. Where Thwaites slides off the land and begins to float on the ocean, there is a boundary called the grounding line. This line is the key to everything. At Thwaites, the land under the ice slopes downward as you go inland, sitting below sea level. This is called a marine ice sheet. Warm, deep ocean water, around 2 degrees Celsius, flows in beneath the floating ice and melts it right at the grounding line. As that point melts back, the ice above it thins, speeds up, and dumps more ice into the sea.

A feedback loop is when the result of a process makes that same process happen even faster. At Thwaites, melting causes thinning, thinning causes faster flow, faster flow causes more ice to reach the warm water and melt, which causes more thinning. Each turn of the loop speeds up the next. Data shows Thwaites' ice loss roughly doubled between the 1990s and the 2010s. In 2021, scientists warned that the floating ice shelf bracing the eastern side could shatter within a decade, like a cracked windshield giving way.

Thwaites is remote, freezing, and riddled with crevasses, so scientists get creative. Satellites like NASA's ICESat-2 bounce lasers off the surface to measure how the ice height changes, down to centimeters. A robotic submarine named Icefin was sent under the ice shelf in 2019 to film and measure the melting at the grounding line directly. Teams also drill boreholes with hot water to lower instruments thousands of meters down.