The 2004 disaster movie The Day After Tomorrow, showcased a sudden ice age in New York City brought about by a major climate change disruption of ocean currents in the North Atlantic.
The plot was preposterous and mostly tense. But still, the fundamental impression that global warming could modify some key ocean motion systems isn’t actually that implausible. Such an event wouldn’t cover Manhattan in ice, but it could inflict mayhem on fisheries or speed up sea-level rise in cities like Boston and New York.
Over the last few decades, scientists have been closely monitoring the Atlantic Meridional Overturning Circulation (AMOC), an ocean pattern that transports warm water from the tropics up to the North Atlantic and Nordic seas. (Sometimes called Gulf Stream system.)
This conveyor belt of heat is the main reason Europe has a moderately warm climate despite being so far north. It also takes nutrients to key fisheries. But the AMOC is also a potential source of concern. Paleoclimate evidence is suggesting that the circulation has abruptly slowed or stopped in the distant past. If that to happen again, it could prove quite nasty for both Europe and the United States.
A new study in Nature Climate Change claims the Atlantic overturning seems to be weakening dramatically. Led by Stefan Rahmstorf of the Potsdam Institute for Climate Research, the researchers created a reconstruction of the AMOC’s behavior from previous centuries. They concluded that in 1100 years the system hasn’t been this weak, perhaps due to an inflow of freshwater from Greenland’s melting ice sheet. This contradicts previous research signifying the AMOC was still fluctuating in natural cycles.
How worrisome could this be? Most scientists remain confident we won’t see a sudden shutdown anytime soon, for now. Mainstream climate models have long predicted that the AMOC would eventually weaken as the Earth warms, but those models don’t forecast huge, abrupt changes this century.
However, what this study is suggesting is that a slowdown may be imminent sooner than expected, and the AMOC could weaken further in the next few decades. That could result to important consequences, from speeding up sea-level rise along the Northeast US to potentially weather distortion in Europe.
The slowdown we see in the data is not what you see in the climate models,” Rahmstorf said. “And if climate models have underestimated the decline, we might be closer to that threshold [where abrupt changes happen] than we thought. If this study holds up, and melting ice in Greenland really is driving an unprecedented slowdown, it would suggest there’s a lot that scientists don’t understand about how the AMOC works. ”