Climate Change's Next Victim? The Stability of the Atlantic Meridional Overturning Circulation (AMOC)
Headlines of a Warming World no13: Scientists Warn of Potential Collapse of the Atlantic Meridional overturning Circulation
A new paper published in Science Advances shows that the Atlantic Meridional Overturning Circulation (AMOC), a vital circulatory system of ocean currents, is on a tipping course and could collapse due to freshwater input from melting ice and increased precipitation.
This new study adds significantly to the rising concern about an AMOC collapse in the not-too-distant future. It thus adds even more weight to recent reports sounding strong warnings, such as the OECD Climate Tipping Points report of December 2022 and the Global Tipping Points report published in December 2023.
The AMOC is a large system of ocean currents that circulates warm water from the tropics northward into the North Atlantic. Its collapse or significant weakening would have profound effects on global climate, such as a drastic cooling of northern Europe, shifts in tropical rainfall belts, and changes in ocean ecosystems and biogeochemistry. Due to the shifts in rainfall patterns and heat distribution, some regions, particularly in the southern hemisphere, could experience more severe droughts and heatwaves.
The ripple effects extend far beyond environmental concerns; agricultural productivity could plummet, coastal infrastructure might be jeopardized, and escalating migration could strain international relations.
The paper proposes a new, physics-based, and observable type of early warning signal for approaching the AMOC tipping point, based on a large-scale climate model simulation and the freshwater transport by the AMOC at the entrance of the South Atlantic.
We're already in a mess, but I don't even want to think about what the AMOC collapse would mean for global climate, economies, and political systems. We will continue to ignore this risk at our peril.
In the days following the publication of the study, there were some articles in the media, such as the one below on The Daily Mail, insisting that the Gulf Stream would collapse. It would not. The Gulf Stream plays a role in the AMOC but it's not the same.
The confusion often arises from mixing up the Gulf Stream with the Atlantic Meridional Overturning Circulation (AMOC), two distinct yet interconnected entities within our planet's complex climate system. While it's common for the public to confuse the two, journalists should be better informed. To address this, I started a discussion on Mastodon to clear up these misconceptions. This conversation resulted in a detailed thread outlining the differences between the Gulf Stream and the AMOC. Here's a summary of that thread.
The Atlantic Meridional Overturning Circulation (AMOC) is a large and complex system of ocean currents that circulates warm, salty water from the tropics northward into the North Atlantic. AMOC is sensitive to freshwater influx; it can dilute surface waters, reducing their density and hampering the sinking process essential for its continuation. Climate change poses a significant threat to the stability of the AMOC, with potential impacts on global climate, sea levels, and weather patterns.
The Gulf Stream is a warm Atlantic Ocean current that originates in the Gulf of Mexico, flows through the Straits of Florida into the North Atlantic, and affects the climate of the east coast of North America and western Europe. The Gulf Stream plays a role in the AMOC and it's a component of the global ocean conveyor belt, a system of ocean currents that circulate water around the globe. It also plays a significant role in moderating the climate of the regions it flows past, (the east coast of North America and parts of Europe, particularly the British Isles and Scandinavia), making them warmer in winter and cooler in summer than they otherwise would be given their latitudinal position.
If climate change disrupts AMOC, the Gulf Stream would be affected but it won’t necessarily shut down; it would shift South, leaving the Northern parts colder.
Sources and further reading:
Physics-based early warning signal shows that AMOC is on tipping course, https://www.science.org/doi/10.1126/sciadv.adk1189
Boers, N. (2021), “Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation”, Nature Climate Change, Vol. 11/8, pp. 680-688, https://doi.org/10.1038/s41558-021-01097-4.
Caesar, L. et al. (2021), “Current Atlantic Meridional Overturning Circulation weakest in last millennium”, Nature Geoscience, Vol. 14/3, pp. 118-120, https://doi.org/10.1038/s41561-021-00699-z.
Climate Tipping Points: Insights for Effective Policy Action https://doi.org/10.1787/abc5a69e-en