A vital system of ocean currents could collapse within a few decades if the world continues to pump out planet-heating pollution, scientists are warning – an event that would be catastrophic for global weather and “affect every person on the planet.”
A new study published Tuesday in the journal Nature, found that the Atlantic Meridional Overturning Current – of which the Gulf Stream is a part – could collapse around the middle of the century, or even as early as 2025.
Scientists uninvolved with this study told CNN the exact tipping point for the critical system is uncertain, and that measurements of the currents have so far showed little trend or change. But they agreed these results are alarming and provide new evidence that the tipping point could occur sooner than previously thought.
The AMOC is a complex tangle of currents that works like a giant global conveyor belt. It transports warm water from the tropics toward the North Atlantic, where the water cools, becomes saltier and sinks deep into the ocean, before spreading southwards.
It plays a crucial role in the climate system, helping regulate global weather patterns. Its collapse would have enormous implications, including much more extreme winters and sea level rises affecting parts of Europe and the US, and a shifting of the monsoon in the tropics.
For years, scientists have been warning of its instability as the climate crisis accelerates, threatening to upset the balance of temperature and salinity on which the strength of these currents depend.
As the oceans heat up and ice melts, more freshwater flows into the ocean and reduces the water’s density, making it less able to sink. When waters become too fresh, too warm or both, the conveyor belt stops.
It has happened before. More than 12,000 years ago, rapid glacier melt caused the AMOC to shut down, leading to huge Northern Hemisphere temperature fluctuations of 10 to 15 degrees Celsius (18 to 27 Fahrenheit) within a decade.
A shutdown “would affect every person on the planet – it’s that big and important,” said Peter de Menocal, the president of the Woods Hole Oceanographic Institution, who was not involved in the study.
A 2019 report by the UN’s Intergovernmental Panel on Climate Change predicted that the AMOC would weaken over this century, but that its full collapse before 2100 was unlikely.
This new study comes to a much more alarming conclusion.
As the AMOC has only been continuously monitored since 2004, the study authors looked to a much larger dataset, and one which could show how the currents behaved in a period without human-caused climate change.
“We needed to go back in time,” said Peter Ditlevsen, a professor of climate physics at the University of Copenhagen and one of the authors of the report. The scientists analyzed sea surface temperatures in the North Atlantic in an area south of Greenland over a period of 150 years between 1870 and 2020.
This part of the ocean is warmed by the water transported north from the tropics by the AMOC, Ditlevsen said, “so if it cools, it’s because the AMOC is weakening.” The authors then subtracted the impacts of human-caused global warming on the water temperature to understand how the currents were changing.