The Uninhabitable Earth: Life After Warming

by David Wallace-Wells

And then there is the possible slowdown of the “ocean conveyor belt,” the great circulatory system made up of the Gulf Stream and other currents that is the primary way the planet regulates regional temperatures. How does this work? The water of the Gulf Stream cools off in the atmosphere of the Norwegian Sea, making the water itself denser, which sends it down into the bottom of the ocean, where it is then pushed southward by more Gulf Stream water—itself cooling in the north and falling to the ocean floor—eventually all the way to Antarctica, where the cold water returns to the surface and begins to heat up and travel north. The trip can take a thousand years. As soon as the conveyor belt became the subject of real study, in the 1980s, there were those oceanographers who worried it might shut down, which would lead to a dramatic disequilibration of the planet’s climate—the hotter parts getting much hotter and the colder parts much colder. A total shutdown would be inconceivably catastrophic, though the impacts look deceptively innocuous on first scan—a colder Europe, more intense weather, additional sea-level rise. Invariably, this is described as the Day After Tomorrow scenario, and it is a strange twist of fate that so forgettable a movie has become the memorable shorthand for this particular worst-case nightmare.