Unlike what one imagines about the effect of climate change in Europe, a colder future may be coming. In recent research, scientists from the University of Copenhagen’s Niels Bohr Institute and Department of Mathematical Sciences forecast that the system of ocean currents that currently distribute heat and cold between the North Atlantic region and tropics will entirely stop if people keep emitting the same levels of greenhouse gases as they do right now.
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With the use of sophisticated statistical tools and ocean temperature information from the past 150 years, the scientists calculated that the ocean current, called the Atlantic Meridional Overturning Circulation (AMOC) or Thermohaline Circulation, will collapse—with 95% certainty—from 2025 to 2095. This will probably happen in 34 years, in 2057, and could lead to significant challenges, especially warming in the tropics and elevated storminess in the North Atlantic region.
Shutting down the AMOC can have very serious consequences for Earth's climate, for example, by changing how heat and precipitation are distributed globally. While a cooling of Europe may seem less severe as the globe as a whole becomes warmer and heat waves occur more frequently, this shutdown will contribute to an increased warming of the tropics, 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.
Professor Peter Ditlevsen, Niels Bohr Institute
The calculations were recently published in Nature Communications. They contradict the message of the recent IPCC report, which, depending on climate model simulations, takes into account a sudden change in the thermohaline circulation very improbable in this century.
Early Warning Signals Present
Predictions will depend on observations of early warning signs that ocean currents show as they get unstable. Such Early Warning Signals for Thermohaline Circulation have been reported earlier, but only now has the development of sophisticated statistical methods made it feasible to anticipate just when a collapse will happen.
The scientists examined sea surface temperatures in a particular region of the North Atlantic between 1870 and the present days. Such sea surface temperatures are “fingerprints” attesting to the AMOC strength, which has been only quantified directly for the last 15 years.
Using new and improved statistical tools, we’ve made calculations that provide a more robust estimate of when a collapse of the Thermohaline Circulation is most likely to occur, something we had not been able to do before.
Professor Susanne Ditlevsen, Department of Mathematical Sciences, University of Copenhagen
The thermohaline circulation has functioned in its current mode since the previous ice age when the circulation collapsed. Sudden climate jumps from the current state of the AMOC to the collapsed state have been noted to occur 25 times in association with ice age climate. These are the famed Dansgaard-Oeschger events first noted from the Greenlandic ice sheet in ice cores. At such events, climate changes were adverse with 10-15 degrees changes over ten years, whereas the current days’ climate change is 1.5 degrees warming in a 100-year period.
Ditlevsen, P., & Ditlevsen, S. (2023). Warning of a forthcoming collapse of the Atlantic meridional overturning circulation. Nature Communications. doi.org/10.1038/s41467-023-39810-w.