The flood had been caused by a cluster of violent volcanic eruptions under the west Antarctic ice sheet. The land underneath the ice sheet, resembling North America’s basin and range country, had been depressed by the weight of the ice until it lay below sea level. So when the eruptions began the lava and gases had melted the ice over the volcanoes, causing vast slippages overhead; at the same time, ocean water had started to pour in under the ice, at various points around the swiftly eroding grounding line. Destabilized and shattering, enormous islands of ice had broken off all around the edges of the Ross Sea and the Ronne Sea. As these islands of ice floated away on the ocean currents, the breakup continued to move inland, and the turbulence caused the process to accelerate. In the months following the first big breaks, the Antarctic Sea filled with immense tabular icebergs, which displaced so much water that sea level all over the world rose. Water continued to rush into the depressed basin in west Antarctica that the ice had once filled, floating out the rest of it berg by berg, until the ice sheet was entirely gone, replaced by a shallow new sea roiled by the continuing underwater eruptions, which were being compared in their severity to the Deccan Traps eruptions of the late Cretaceous.

And so, a year after the eruptions began, Antarctica was only a bit over half as big as it had been— east Antarctic like a half-moon, the Antarctic peninsula like an iced-over New Zealand— in between them, a berg-clotted bubbling shallow sea. And around the rest of the world, sea level was seven meters higher than it had been before.

Not since the last ice age, ten thousand years before, had humanity experienced a natural catastrophe of such magnitude. And this time it affected not just a few million hunter-gatherers in nomadic tribes, but fifteen billion civilized citizens, living atop a precarious sociotechnological edifice which had already been in great danger of collapse. All the big coastal cities were inundated, whole countries like Bangladesh and Holland and Belize were awash. Most of the unfortunates who lived in such low-lying regions had time to move to higher ground, for the surge was more like a tide than a tidal wave; and then there they all were, somewhere between a tenth and a fifth of the world’s population— refugees.

It goes without saying that human society was not equipped to handle such a situation. Even in the best of times it would not have been easy, and the early twenty-second century had not been the best of times. Populations were still rising, resources were more and more depleted, conflicts between rich and poor, governments and metanats, had been sharpening everywhere: the catastrophe had struck in the midst of a crisis.