Our relatively stable global climate is governed by an incredibly complex set of factors, all interacting with each other in dynamic and changing ways, but there are a couple of really big key players in that system. The Atlantic Meridional Overturning Circulation (AMOC) is one of them. This system of ocean currents redistributes heat from tropical regions to colder places and also cools warmer waters (important for sensitive marine life like corals). The nutrients that ocean species depend on are also pushed along this giant, mostly invisible conveyor belt beneath the waves. Right now, the AMOC is weakening due to human-caused climate change, which could have huge repercussions, changes in temperature and rainfall patterns that humans depend on to grow food. It therefore makes sense that researchers would want to understand when and how, as lead author Christo Buizert writes in a research report, “a critical threshold beyond which AMOC weakening becomes self-reinforcing and irreversible.” That was the focus of a study by a truly international team for Nature Geoscience that included Buizert. (A fun note: Buizert was encouraged to submit this work to the magazine after a talk about cheese fondue at a meeting in Switzerland. Proving once again that giving scientists free, delicious food is always a smart investment.) These changes corresponded with abrupt climatic phenomena known as Dansgaard-Oeschger events, or DO, recorded especially clearly in Greenland ice cores. frameborder=”0″ enable=”accelerometer; autoplay; writing on clipboard; encrypted media; gyroscope; picture in picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” enablefullscreen> The conventional explanation for these DO events was what the researchers call a “bipolar thermal seesaw.” This climate seesaw was a model that appeared to explain how AMOC-driven heat transport caused warming at one pole and cooling at the other pole. Taking a new perspective, the researchers devised another explanation that included “synthesizing two decades of observational and theoretical advances in understanding the factors “Ocean heat content (OHC), sea ice, and planetary radiation budget (the difference between incoming solar radiation and outgoing radiation emitted by the Earth) play an important role,” according to Buizert’s statement. Instead of thinking of the AMOC primarily as a conveyor belt that transports heat from one hemisphere to the other, the researchers propose thinking of it more as an “ocean heat valve.” He found that when the AMOC was strong, vigorous deep convection in the North Atlantic It allowed the ocean to lose large amounts of heat to the atmosphere, he says (Buizert, et al. Nature Geoscience, 2026.) In other words, the AMOC acted less as a simple heat transporter that moved heat from one place to another, and more like a valve that controlled whether heat was allowed to escape from the ocean. of ice cores, which showed rapid changes in Greenland and slower changes in Antarctica over Antarctica. This new heat valve model shows that this is due to rapid changes in heat loss from the North Atlantic and slower changes in the amount of heat stored throughout the ocean, as reflected by Antarctic records. Instead of the two poles simply playing on opposite ends of a heat transfer seesaw, the researchers argue that both were responding to. different aspects of a globally connected ocean heat cycle. “The AMOC acts as an ocean heat valve that regulates planetary temperature through Earth’s radiative balance,” wrote David Bonan, a climate scientist. So what happens in this valve model when applied to the warming world today? As human-caused climate change alters the ocean, weaker circulation could reduce deep convection and increase the amount of heat stored in the ocean. that the future weakening of AMOC could actually amplify planetary warming by “throttling” the ocean heat valve. The researchers note that their model has an important asterisk: The ice age climate system was very different from today’s DO cycles occurred under glacial conditions, when enormous amounts of sea ice helped create the feedbacks that allowed the AMOC to alternate between states. eliminating a mechanism that was central to those ancient oscillations. Related: A major ocean current is on the verge of collapse. But it offers something perhaps almost as useful: a natural experiment that shows that changes in this circulation can affect not only where the heat goes, but also how much heat the planet as a whole retains. transient weakening and irreversible collapse, with profound social implications.” verified by Fiona MacDonald and edited by Fiona MacDonald. While we take pride in our process, we are human. If you spot an error, please let us know.
