The currents that circulate in the Atlantic are approaching a “tipping point” that will change the way water flows around the oceans of the world and could cause a return to ice age conditions in Europe, according to a new study released last week.

The currents of water, known as the AMOC, or Atlantic Meridional Overturning Circulation, determine the world’s weather patterns by moving huge volumes of warm or cold water around the globe that in turn drives the wind and rainfall.

If these currents change course, then monsoons could be permanently displaced, turning previously lush regions like the Amazon arid and bringing Russian-like winters to Europe. Changing the AMOC patterns will have far-reaching consequences and would probably cause a cascade of other environmental disasters, says the experts.

The AMOC has remained stable for thousands of years, but now the tell-tale appearance of a very warm concentration of water off the east coast of the US together with a “cold blob” in the sea to the south of Greenland, visible in the image, are ringing alarm bells.

The currents of the AMOC determine the whole world's weather

The way it works is warm salty sea water flows north where it meets fresh snow and ice-melt water. The heavier salt water sinks to the ocean floor creating a seabed current of cold water that flows south again.

“The AMOC has a tipping point beyond which it breaks down if the northern Atlantic Ocean is diluted with freshwater (by increasing rainfall, river runoff and meltwater), thus reducing its salinity and density. This has been suggested by simple conceptual models since Stommel in 1961,” Professor Stefan Rahmstorf at the Potsdam-Institute for Climate Science said in a blog.

With last year’s sea temperatures at highs not seen for thousands of years, this pattern is approaching a tipping point where the directions of the currents may change and once they have passed this tipping point the changes can’t be undone, even if the sea cools to its long-term average temperatures again.

The last AMOC breakdown occurred about 12,000 years ago and triggered the Younger Dryas cold event around the northern Atlantic, a rapid return to ice age conditions in parts of the Northern Hemisphere.

The new study provides much more detailed and higher resolution simulations of the impacts of an AMOC collapse on climate than in the past, albeit considered in isolation and not combined with the effects of CO2-induced global warming.

They show how particularly northern Europe from Britain to Scandinavia would suffer devastating impacts, such as a cooling of winter temperatures by between 10 °C and 30 °C occurring within a century, leading to a completely different climate within a decade or two. London’s climate could become that of Stockholm and Stockholm that of Siberia. In addition, they show major shifts in tropical rainfall belts that will radically change the biosphere of large swathes of major land masses in Africa, Asia and Latin America.

“These (and many more) impacts of an AMOC collapse have been known for a long time but thus far have not been shown in a climate model of such high quality," Rahmstorf said.

The idea of an AMOC tipping point has been around for a long time, but the research demonstrated for the first time in a state-of-the-art global coupled climate model that not only is it possible, but it has a 95% certainty of happening before the end of the century, according to another study by Peter Ditlevsen published in Nature last year.

“A forthcoming collapse of the Atlantic meridional overturning circulation (AMOC) is a major concern as it is one of the most important tipping elements in Earth’s climate system,” Ditlevsen said.

Van Western would not be drawn on predicting a more precise date for the tipping point as there are still too many variables and unknowns, but he and his colleagues were sufficiently alarmed to conclude their paper with strident calls for the global Climate Crisis to be addressed and the Paris Accord targets met.

The AMOC flows themselves have only been recorded in detail since 2004, but in that time noticeable changes in the flow of the currents is already very clear in what scientists say is a very worrying sign.

“The billion-dollar question is: how far away is this tipping point? Three recent studies, using different data and methods, have argued that we are approaching the tipping point and that it might be too close for comfort, even posing a risk of crossing it in the next decades,” said Rahmstorf.