![]() ![]() “Observations are showing more statistically significant early-warning signals of a collapse of the AMOC, whereas most models are not showing that,” says Garuba. Compared to the studies indicating a slowdown and eventual collapse of the circulation, models indicate more stability, says Oluwayemi Garuba, a climate scientist who studies ocean-atmosphere interactions at the Pacific Northwest National Laboratory. Scientists also use models to simulate how the current system might change as the climate does. And people jumped on that, saying that it's declining, and we have observational evidence of it. “The first six years, there was a very strong decline. “We've been directly measuring AMOC since 2004, and we don't have any evidence of long-term decline,” says Foukal. ![]() Since RAPID started operating, scientists have seen a good amount of variability. “We haven't had an AMOC collapse in the past 20 years, so it’s like trying to predict a hurricane-having never seen a hurricane.” “It's just hard to tease apart, because we really don't know what the intrinsic timescales of AMOC are,” says Nicholas Foukal, an assistant scientist at Woods Hole Oceanographic Institution, who wasn’t involved in the new paper. When the RAPID array went online, the assumption was that it’d take 40 years to get an idea of whether the current system was in decline. “It is not ideal, but it’s the best we can do,” says Peter Ditlevsen, “since we need measurements to go back to the pre-industrial era to assess the natural state of the AMOC, before it began slowing down toward the collapse.” However, those early shipboard measurements were made by people hauling buckets of water aboard and sticking a thermometer in-not exactly the precision that modern science demands. The beauty of the SST dataset is that it stretches back 150 years, so scientists can see longer-term trends in temperatures. “Current climate models do not give a strong probability of the collapse of the AMOC this century.” “This SST fingerprint, although sensitive to the AMOC, is not solely driven by it, so these changes may be overestimated,” agrees Goes, the oceanographer from the University of Miami and NOAA. “And that's not at all related to ocean circulation.” “There's a lot of what we call air-sea interactions-the heat exchange between the atmosphere and the ocean,” Kilbourne says. Warm waters flowing north have an effect, but so does the atmosphere touching the water. The core of the issue is that sea surface temperatures are just one component of the AMOC system other factors also help determine Atlantic temperatures. “But the trouble is there aren't really adequate measurements.” “I really question whether is an adequate proxy for AMOC itself,” agrees Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research. I don't think we have a good alternative, which is why people are using it." “But there's certainly a school of thought of people who think it's the best thing going-and it may be the best thing going right now. “Fundamentally, I am deeply skeptical that SST is actually a proxy of AMOC,” says climate scientist Hali Kilbourne, who studies the current system at the University of Maryland Center for Environmental Science. Still, scientists don’t agree about whether sea surface temperature (SST) is a good indicator of the health of this massively consequential circulation. Of course, we might be wrong, and I hope we are.” But there’s vigorous debate in the scientific community over just how quickly the AMOC might decline, and how best to even figure that out. “We checked and checked and checked and checked, and I do believe that they're right. “We got scared by our own results,” says Susanne Ditlevsen, a statistician at the University of Copenhagen and coauthor of the new paper. That’s a tipping point that would come much sooner than anyone thought. By this team’s calculations, the circulation could shut down as early as 2025, and no later than 2095. ![]() A paper published yesterday in the journal Nature Communications warns that the collapse of the AMOC isn’t just possible, but imminent. In recent years, researchers have suggested that because of climate change, the AMOC current system could be slowing down and may eventually collapse. This system of currents, known as the Atlantic Meridional Overturning Circulation, or AMOC, moves 15 million cubic meters of water per second. That makes it denser, so it sinks and heads back south, finishing the loop. ![]() In the Atlantic Ocean, a conveyor belt of warm water heads north from the tropics, reaching the Arctic and chilling. So much on this planet depends on a simple matter of density. ![]()
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