evidence: An unexpected ice shelf collapse in East Antarctica, after temperatures spiked 70°F above normal, highlights bigger problems in the West, where one glacier could singlehandedly raise global sea levels several feet. [...] In March, East Antarctica—the other, colder side of the continent—saw its first-ever ice-shelf collapse. As a late Austral summer heat wave brought extraordinary temperatures and high winds to the region, the Conger ice shelf disintegrated within days. The unexpected collapse highlighted the importance of—and uncertainty about—the continent’s ice shelves, which act like bottle stoppers controlling the flow of ice from land to sea. Their incipient demise, scientists fear, could be the beginning of more ice loss—and much more sea level rise that would affect countries all over the world. [...] The instability of the West Antarctic Ice Sheet is, in essence, a tipping point: Cross it and there’s little hope of return. Sustained warming of more than 3ºC, for example, could lock Earth into an eventual sea level rise of 20 to 40 feet over the next several hundred or 1000 years. Even if in the future it became possible to remove enough carbon dioxide from the atmosphere to bring temperatures back down, the ice sheets would probably be unrecoverable: They are much harder to grow than to break.