The Gulf Stream system may already be weakening. That's not good.In the 2004 disaster film The Day After Tomorrow, climate change causes a major disruption of ocean currents in the Atlantic Ocean, which in turn brings about a sudden ice age in New York City. That scenario was ridiculous and overwrought. Still, the underlying idea that global warming could mess with some important ocean circulation systems actually isn’t that far-fetched. Such an event wouldn’t blanket Manhattan in ice, but it could wreak havoc on fisheries or speed up sea-level rise in cities like Boston and New York. In particular, scientists have been paying close attention to the Atlantic Meridional Overturning Circulation (AMOC), an ocean pattern that transports warm water from the tropics to the North Atlantic. This Gulf Stream system is why Europe has a mild climate despite being so far north. But it’s also a source of concern: evidence suggests the circulation has slowed abruptly in the very distant past, leading to sharp climate shifts regionally. More recently, the AMOC has been seen weakening and strengthening, but scientists figured it was just fluctuating naturally. FULL REPORT