One of the main ways Earth channels heat away from the tropics towards the North Atlantic is weakening and could fail, causing a climate catastrophe as early as 2025, a new study predicts.
Measurements over the last fifteen years show the Atlantic Meridional Overturning Circulation (AMOC) has been getting notably weaker, while ocean temperatures have been warming. Nonetheless, the international climate community had not raised yet any immediate red flags and a recent announcement from the the Intergovermental Panel on Climate Change suggested AMOC would last out the 21st century at least.
That has now changed. A new University of Copenhagen study, led by Peter Ditlevsen from the Niels Bohr Institute, used statistical modelling to analyse ocean temperatures over the last 150 years, not just 15.
The results, published on July 25, 2023 in the journal Nature Communications, are shocking: the study predicts with 95% certainty that AMOC will cease working between 2025 and 2095. It even gives a specific year as most likely – 2057.
1. What is the Atlantic Meridional Overturning Circulation?
Often confused with the Gulf Stream (which is driven by winds), AMOC is a stream of water flowing from the tropical south Atlantic to the north. According to The Economist, AMOC is capable of transferring heat towards the pole at a rate about 60 times that at which humans produce energy by burning fossil fuels and “accounts for about a quarter of all the northward flow of heat from the tropics.”
You might think we want to avoid warm water moving towards the north pole, but as the water travels northward the warm water cools and ‘sinks’ like a conveyor belt, drawing along the water behind it. Sinking to depths of 3km, before rising again, it creates ‘overturn’ of the water and cuts the amount of heat moving north by 50%.
2. Why is it important?
The AMOC system is believed to be ‘bistable’, meaning, when pushed, it can suddenly simply switch from ‘on’ to ‘off’. If it fails, less heat will be transferred north. In northern and western Europe, growing seasons for crops will become far drier and shorter, impacting poorer nations. Populations there would experience more powerful inland storms and winters would be more severe.
Some readers may recall the 2004 climate catastrophe film The Day After Tomorrow, which depicted AMOC failure and a new Ice Age. Though scientists agree that portrayal is exaggerated, sea levels will rise on the USA’s already flood-vulnerable eastern seaboard. Meanwhile many parts of the world will dry out, including Central and South America and the southern Sahara.
In addition, “this shutdown will contribute to an increased warming of the tropics,” Ditlevsen said, “where rising temperatures have already given rise to challenging living conditions.”
“Our result underscores the importance of reducing global greenhouse gas emissions as soon as possible,” he urged.