“Our paper says that the Atlantic overturning has not declined yet,” said Foukal, who conducted the research while at Woods Hole Oceanographic Institution (WHOI). “That doesn’t say anything about its future, but it doesn’t appear the anticipated changes have occurred yet.”
Their findings contrast with previous work, notably a paper from 2018 cited in their study, which reported that the AMOC has declined over the last 70 years. This past work relied on sea surface temperature measurements to understand how the AMOC has changed, but “we’ve learned that sea surface temperature doesn’t work as well as initially thought,” said Terhaar, who began leading this study at WHOI as a postdoctoral scientist and completed the work in Bern.
As with all proxy-based reconstructions, there are limitations and caveats. The authors point out that direct measurements of air-sea heat flux going back in time are sparse, and thus the reanalysis products contain significant uncertainty. However, despite these limitations, “a decline in AMOC over the last 60 years,” Terhaar concludes, “seems very unlikely.”
The paper states that air-sea heat flux anomalies in the North Atlantic are tightly linked to the AMOC and that “the decadal averaged AMOC has not weakened from 1963 to 2017.”
“It’s almost unanimous at this point that the Atlantic overturning will slow in the future, but whether or not it will collapse is still up for debate,” Foukal said. “This work indicates that there is still time to act before we reach this potential tipping point.”