You probably know at least a little bit about ocean circulation around the world, also known as currents. In fact, you may have felt smaller currents yourself on a day at the beach. But have you heard bout the “great global ocean conveyor belt,” which is a vast network of currents that constantly moves water around the entire planet? This massive system helps distribute heat around the world, influencing everything from temperatures to rainfall. Unfortunately, it’s slowing down and on the verge of total collapse. Scientists have been studying this phenomenon, and according to recent research published in Nature Geoscience, it’s a bigger deal than we thought.

Why should we care ocean water circulation? “Our results show the Atlantic overturning circulation is likely to become a third weaker than it was 70 years ago at 2°C of global warming,” says the research team. “This would bring big changes to the climate and ecosystems, including faster warming in the southern hemisphere, harsher winters in Europe, and weakening of the northern hemisphere’s tropical monsoons.” Think about that for a second. A weaker ocean current could mean colder winters in Europe and shifts in rainfall patterns that affect millions of people. It’s not just about the ocean; it’s about our daily lives.

Meltwater and ocean circulation The Earth has already warmed 1.5ºC since the industrial revolution, and the Arctic has been heating up nearly four times faster than the rest of the planet. All that heat is melting Arctic sea ice, glaciers, and the Greenland ice sheet. “Since 2002, Greenland lost 5,900 billion tons (gigatons) of ice,” notes the research team. “To put that into perspective, imagine if the entire state of Texas was covered in ice 26 feet thick.” All this fresh meltwater flowing into the subarctic ocean is lighter than salty seawater, so it doesn’t sink as much. That messes with the southward flow of deep, cold waters from the Atlantic and weakens the Gulf Stream — the same current that gives Britain its mild winters.

Time is not on our side “Our simulations show changes in the far North Atlantic are felt in the South Atlantic Ocean in less than two decades,” the researchers reveal. This means the effects of the slowdown are spreading faster than we thought. Climate projections have suggested the Atlantic overturning circulation will weaken by about 30% by 2060. But hold on — that’s without considering all that extra meltwater. “The Greenland ice sheet will continue melting over the coming century, possibly raising global sea level by about 4 inches,” the study notes. “If this additional meltwater is included in climate projections, the overturning circulation will weaken faster. It could be 30% weaker by 2040. That’s 20 years earlier than initially projected.”