The global ocean circulation doesn’t only move water. It also determines the global climate. Without the Gulf Stream, for example, Europe’s climate wouldn’t be as mild. Besides, ocean currents redistribute oxygen and nutrients and other compounds. This doesn’t only happen horizontally but also vertically through upwelling and downwelling. Thus the thermohaline circulation ensures homogenous oxygenation and forms the physical basis for much of ocean primary production.

It is not surprising then that a weakening or even loss of some ocean currents would have catastrophic consequences. But this is precisely what some scientists are predicting as a consequence of anthropogenic climate change. Melting ice at the poles combined with rising temperatures could lead to a reduction in seawater density at the poles, which drives the thermohaline circulation. In particular, the focus has been the Atlantic Meridional Overturning Circulation, which is predicted by some to collapse by the end of the century. It is one of the main tipping points considered by the Intergovernmental Panel on Climate Change and was dramatically thematized in Roland Emmerich’s blockbuster The Day After Tomorrow.

Next Section »