The Atlantic Current circulation is getting closer and closer to collapse, and this could have devastating climate impacts. This is according to a study published in Science Advances that shows how global warming is undermining heat interchange between ocean currents. If the Atlantic Meridional Overturning Circulation (AMOC) were to come to a halt, temperatures in Europe would drop dramatically, wet seasons in the Amazon rainforest would be reversed to dry seasons, and in coastal cities the sea would rise even faster by tens of centimeters.

There is not enough data to know when all this will happen, but scientific evidence has concluded that exists a "point of no return" toward which we are rapidly heading. "Bad news for the climate system and for humanity," the researchers wrote.

How the AMOC works and why it could be stopped

The AMOC is a sort of "conveyor belt" that moves ocean currents by differences in water density. "This circulation, of which the Gulf Stream is a part, plays the fundamental role of a climate equalizer and is essentially triggered by the weight of water, its density," Sandro Carniel, a climatologist and oceanographer at the National Research Center, explains. "The colder and saltier the water is, the greater its density, and the easier it is for its mass to sink. Whereas if the water is warm and fresh (i.e., not salty), it is lighter and therefore stays at the surface more." 

It is this difference in density that allows warm currents to move from the Equator toward the Arctic Circle, bringing warmth to regions of northern Europe. Once they reach their destination, the water masses cool, become dense and then sink, making way again for warm currents from the Equator. This is the process that over the past 10,000 years has allowed the temperate and essentially stable Northern European climate to be maintained.

Today, however, warming seas and melting ice are hindering the sinking of water masses. "The huge amounts of melting ice are pouring an incredible amount of fresh water into the North Atlantic," Carniel adds. "Less and less salty and warmer waters are helping to lag the general circulation of currents."




From AMOC collapse, a new ice age?

Global warming and AMOC slowdown are two related phenomena, but their effects run at different speeds. Under the effects of an increasing concentration of carbon dioxide, the temperature of the atmosphere is warming at the already extremely alarming rate of a few tenths of a degree every decade. An irreversible slowdown in the circulation of Atlantic currents, on the other hand, would cause much more rapid climatic effects, on the order of a few degrees per decade.

The well-known apocalyptic film The Day After Tomorrow, in which within hours the planet's north is in the grip of a terrifying glaciation, is inspired precisely by the slowing of Atlantic currents and the melting of polar ice. Should the AMOC collapse, researchers predict that some European cities could experience a 5 to 15°C drop in temperatures in a few decades. In some areas the effects would be even worse: February months in Bergen, Norway, could become 3.5°C colder every decade.

However, Europe would not be the only region to be affected. The level of the Atlantic Ocean would rise by 70 cm, submerging many coastal cities. Rainfall in the Amazon rainforest would undergo a drastic change, and the southern hemisphere would become increasingly warmer. These predictions were obtained through state-of-the-art computational models that simulated the effects on climate over 2,000 years.

To get an idea of what would happen in the face of an AMOC disruption, one has to go back thousands of years. The last Atlantic Current halt occurred about 12,900 years ago, when in North America the melting of the giant frozen Lake Agassiz caused large amounts of fresh water to spill into the sea. The event, probably caused by a comet impact, was followed by 1,300 years of freezing.

The solution: reduce emissions

People have been trying to understand more about the Atlantic currents for years. According to a study published in Nature in 2018, the buoyancy of the Atlantic Current has decreased by 15 percent over the past 70 years. Another more recent research estimated that the point of no return could occur before 2095. This is a thesis, however, debunked by the Met Office, the British weather service, which has deemed a halt in this century "very unlikely." 

Extinction of some animal species, lack of fresh water or stifling heat are some of the tipping points (points of no return) that threaten the survival of the human species. The possible collapse of the AMOC adds to the list. Climate models speak for themselves: due to increasing concentrations of greenhouse gases in the atmosphere, Atlantic currents are weakening rapidly. We have no choice but to reduce greenhouse gas emissions.