Antarctica faces the growing threat of sudden and possibly irreversible transformations to its ice, oceans, and ecosystems. The sweeping changes already underway there are “interlinked,” creating added stress on Earth’s climate systems, rising sea levels, and fragile ecosystems. If the West Antarctic Ice Sheet were to collapse, global sea levels could rise by more than three meters (almost ten feet), endangering millions living in coastal cities and low-lying regions around the world.