Weakening Atlantic Ocean Current Could Add More Heat to the Planet, Study Finds

The Atlantic Meridional Overturning Circulation, or AMOC, is a system of ocean currents that shapes regional climates and distributes ocean nutrients. A new study, led by Oregon State University paleoclimatologist Christo Buizert and published in Nature Geoscience, finds it also acts as a control knob for the planet's overall temperature: during past periods when the AMOC was strong, the global ocean and planet lost heat; when it was weak, they gained additional heat. "The AMOC works like a heat valve that controls the energy budget of the planet," Buizert said.

The AMOC has remained strong over the roughly 11,700 years since the end of the last Ice Age, but many climate models project it will weaken as human-driven climate change continues. The most direct effect of a weaker AMOC is cooling in the North Atlantic and surrounding regions, including Greenland. But when the researchers looked at the whole planet, they found the total heat stored by the global ocean actually increases. During each of Earth's ice ages, from 2.7 million to 11,700 years ago, the AMOC underwent abrupt changes known as Dansgaard-Oeschger events, considered among the clearest examples of climate "tipping points."

Using simulations of abrupt AMOC change from three different climate models, the researchers tracked how heat moved through the oceans. They found that when the AMOC weakens, heat that would normally be carried to the North Atlantic and lost to the atmosphere instead builds up in the ocean interior; only a thin surface layer of the North Atlantic cools, while the rest of the ocean warms. Buizert said events of AMOC weakening during the last Ice Age caused as much warming as 25 parts per million of carbon dioxide would today - roughly equivalent to a decade of current human emissions.

The study also found that in a warmer world, the AMOC tends to be more stable, suggesting future tipping-point events may be less likely, though the current could still weaken with climate change and potentially recover rather than collapse irreversibly. Buizert said more research is needed to understand the AMOC's future stability. Co-authors on the study came from the University of Tokyo, the University of Copenhagen, the British Antarctic Survey, Xi'an Jiaotong University, Woods Hole Oceanographic Institution, the Australian Antarctic Division, the University of Tasmania, McGill University and the University of Bern.