According to new evidence, the Atlantic Ocean overturning, which is largely responsible for Europe’s relatively mild climate, is slowing down. The overturning brings warmer tropical water north and, as that water cools and sinks lower, it in turn heads south. Ocean currents have a remarkable effect on temperatures in the North Atlantic, and it is because of this warm weather heading north that temperatures aren’t colder.

The problem seems to be the Greenland ice sheet, namely that it’s melting, thanks to human interference, more than it should be. Freshwater is not as dense as salt water, and so does not sink as much or as quickly, resulting a slower overturn.

Researchers from the Potsdam Institute for Climate Impact Research discovered this by studying a variety of factors. Although scientists have been able to trace the current’s speed in recent years, that data doesn’t predate satellites. Instead, scientists have to turn to things like tree rings, ice cores, and sediment, to determine relative temperatures at different times. They found that the current’s speed has changed since about 900 CE, with the most dramatic changes happening since 1970, which coincides with human -made global warming.

It is unlikely that this slowing will cause anything approaching a new ice age, but it will have an impact on the world. Such changes will have a huge impact on life in these regions,and would likely impact ocean ecosystems and lead to weather fluctuations through Europe and North America. Fisheries and coastal livelihoods would be at-risk, and a slowdown would lead to a rise in sea levels as well.

AA permanent slow-down would be nearly impossible to reverse, and the International Panel on Climate Change has suggested there is around a one-in-ten chance of such a change happening within this century. Other scientists suggest a higher risk, meaning that there’s a good chance the Atlantic overturn will be permanently damaged in the near future without more research into preventative measures.