The Atlantic Meridional Overturning Circulation (AMOC) is a major Atlantic ocean current, to which the Gulf Stream belongs, and at the top of the ocean it transports warm water masses from the tropics northward, while cold water is transported south, at the ocean bottom. It influences weather systems worldwide, making the consequences of a potential collapse all the more dangerous.
The AMOC is currently at its weakest state in over 1,000 years, meaning the currents have slowed, and new evidence has indicated that it could already be nearing complete shutdown.
Such an event is considered one of the tipping points of climate change, which are defined as large, fast, and irreversible changes to the climate.
In the event of the AMOC collapse, rainfall would be disrupted in India, South America and West Africa, which would cause mass food shortages. Increasing storms and colder temperatures would be felt across Europe, and the sea level would rise off the eastern coast of North America. The Amazon rainforest and Antarctic ice sheets would be further endangered.
However, due to the complex nature of the AMOC, and the uncertainty of future global warming caused by tipping points, there is no way of knowing how close to total collapse the system is.
Scientists say it could happen within the next decade at soonest, but that several centuries could still pass before it does, and that there is no way to accurately estimate the time-frame.
"We urgently need to reconcile our models with the presented observational evidence to assess how far from or how close to its critical threshold the AMOC really is," said author of the study, Niklas Boers from the Potsdam Institute for Climate Impact Research, Freie Universität Berlin and Exeter University.
Boers explained that the C02 level which would trigger an AMOC collapse is also unknown, which means that the only possible thing to do in order to prevent it from happening is to keep emissions as low as possible.
"The likelihood of this extremely high-impact event happening increases with every gram of C02 we put into the atmosphere," he stated.
A number of factors besides C02 emissions also factor into the breakdown of the AMOC system, including freshwater inflow, which is also directly linked to climate change.
As the Greenland ice sheet melts, it increases the amount of freshwater flowing into the sea. Freshwater is lighter than saltwater which means it prevents water from sinking to the bottom of the ocean, a process which is key to the continued movement of the AMOC.
While the timeframe and exact trigger for the event are unknown, scientists are certain about one thing - that the collapse of the AMOC must never be allowed to happen.