Thwaites Glacier, sometimes referred to as the Doomsday Glacier, is an unusually broad and fast Antarctic glacier flowing into Pine Island Bay, part of the Amundsen Sea. For the first time now, scientists of the International Thwaites Glacier Collaboration have recorded unusually warm water beneath the Florida-sized glacier that is already melting and contributing to a rise in sea levels. The researchers, working on the Thwaites Glacier, recorded water temperatures at the base of the ice of more than 2 degrees Celsius above the normal freezing point. Critically, the measurements were taken at the glacier’s grounding line, the area where it transitions from resting wholly on bedrock to spreading out on the sea as ice shelves. That is significant because the Thwaites, along with the Pine Island Glacier and a number of smaller glaciers, acts as a brake on part of the much larger West Antarctic Ice Sheet. Together, the two bigger glaciers are currently holding back ice that, if melted, would raise the world’s oceans by more than a meter over centuries, an amount that would put many coastal cities underwater.