This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A current system in the Atlantic Ocean that shapes regional climates and distributes ocean nutrients also serves as a control knob to help regulate temperatures across the planet, new research has found. An analysis of past natural oscillations in the strength of the Atlantic Meridional Overturning Circulation, or AMOC, shows that during periods with a strong AMOC, the global ocean and planet lost heat.
When the AMOC was weak, the global ocean and planet gained additional heat. "The AMOC works like a heat valve that controls the energy budget of the planet," said Christo Buizert, a paleoclimatologist at Oregon State University and lead author of the study, which was just published in Nature Geoscience. Researchers have long known that the AMOC plays an important role in the circulation of heat by global ocean currents.
While the AMOC has been strong over the past 11,700 years, since the end of the last Ice Age, many climate models project future weakening of the AMOC due to human-driven climate change. Such AMOC weakening would exacerbate warming across the planet, said Buizert, an associate professor in OSU's College of Earth, Ocean, and Atmospheric Sciences. The most direct impact of AMOC weakening is cooling in the North Atlantic and surrounding regions, including Greenland.
"However, when we zoom out and look at the entire planet, the total amount of heat actually increases," Buizert said. Previous research has shown that during each of Earth's ice ages, which occurred repeatedly from 2.7 million years ago to 11,700 years ago, the AMOC underwent a series of abrupt changes, known as Dansgaard-Oeschger events. These abrupt changes are probably the best example of climate "tipping points"—the critical thresholds that, when crossed, lead to sudden and potentially irreversible climate change.
During weak AMOC periods, abrupt cooling in the North Atlantic plunged areas such as present-day Europe, Greenland and New York into much colder temperatures. The prevailing scientific theory suggested that heat was transferred to the Southern Hemisphere in a process known as the "thermal bipolar seesaw." The new research shows that instead of a simple redistribution of heat, there is actually a net increase in the heat stored by the global ocean. "To put this into perspective, events of AMOC weakening during the last Ice Age caused the same amount of warming as 25 ppm of carbon dioxide would today.
That is the equivalent of about 10 years of human emissions." To reach these conclusions, the researchers created a new framework using simulations of abrupt AMOC change from three different climate models. In these three models, they tracked how heat moves around in the oceans and how much was lost or gained by the planet as a whole. The ocean is continually taking up heat from sunlight, mostly in the tropics.
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