Climate change is turning Antarctica green. It may conjure up an image of a pristine white landscape, but researchers say climate change is turning the continent green.

Antarctica’s ice may melt faster than previously thought as result of a newly discovered network of lakes and streams that destabilize the continent’s ice shelves, according to new research — making them more vulnerable to collapse.

Because the collapse of vulnerable parts of the ice sheet could rise the sea level dramatically, the continued existence of the world’s great coastal cities — Miami, New York, Shanghai and many more — is tied to Antarctica’s fate.

Antarctica holds 90% of the world’s ice and rapid ice melt and the associated collapse of ice sheets could have profound effects across the globe, including a steep rise in sea levels, but much remains unknown about the speed at which Antarctic ice is melting. An accompanying study also published in Nature this week evaluates a specific region in Antarctica — the Nansen Ice Shelf — and finds that the worst destabilizing effects are avoided as the melted water drains into the ocean. It remains unclear which ice sheets will respond like Nansen and which will have the destabilizing effect seen elsewhere.

Ice sheets flow downhill, seemingly in slow motion. Mountains funnel the ice into glaciers. And ice flowing from the land into the sea can form a floating ice shelf.

A rapid disintegration of Antarctica might, in the worst case, cause the sea to rise so fast that tens of millions of coastal refugees would have to flee inland, potentially straining societies to the breaking point. Climate scientists used to regard that scenario as fit only for Hollywood disaster scripts. But these days, they cannot rule it out with any great confidence.

Countries around the globe committed in the 2015 Paris Agreement to work to keep temperatures from rising more than 2°C (3.6°F) by 2100, though it remains unclear whether they will be able to meet that target. Even if that target is met, sea level rise will average 0.2 meters (0.67 feet) by 2100, though many places like the East coast of the U.S. will face a far greater rise, according to recent research.