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March 2, 2021

Is the AMOC really slowing down?

Risk-averse planners and investors should consider the scenario that the AMOC weakening is a product of climate change and continuing trend.

by Alan Blumberg
Jupiter Intelligence

It has been widely reported in the science and popular media that the Atlantic meridional overturning circulation (AMOC) is slowing down. Dramatic examples of the potential impact of AMOC slowing down are regularly included in much of this media reporting.

The AMOC is a system of currents that includes the Gulf Stream. Experts are confident the AMOC is now “in its weakest state in over a millennium.” This has implications for everything from the climate of Europe to the rates of flooding along the U.S. East Coast.

While evidence of the system’s weakening has been published before, the latest research cites 11 sources of “proxy” evidence of the circulation’s strength including clues hidden in seafloor mud as well as patterns of ocean temperatures. The proxy evidence suggests that slowing of the Gulf Stream may have started already, and the accelerated sea level rise that has been measured in the area over the last few years is related to the changing Gulf Stream.

But is it an oscillation or a real trend? Some credible climate models suggest that we may just now be seeing the greenhouse gas signal emerge from the noise (natural oscillations), other equally credible models indicate that we are still a couple decades away. The proxy data for this question currently show a slight decline, but not yet outside the historical noise.

AMOC will certainly decline due to greenhouse gas emissions. However, neither evidence from observations nor models allow us to attribute the current downturn primarily to global warming right now. It is not yet consensus science that AMOC weakening is a product of climate change.

Risk-averse planners and investors should consider the scenario that the AMOC weakening is a product of climate change. Stefan Rahmstorf, an author of the recent research and an oceanographer with the Potsdam Institute for Climate Impact Research in Germany says that the key to the conclusions is that all these pieces of the AMOC puzzle seem to fit together so nicely in the proxy data. Our view is consistent with comments from Marilena Oltmanns, an oceanographer at the National Oceanography Center in Britain: ”the current study’s conclusions “are, by necessity, only as good as the proxies are. And the complexity of different currents in the Atlantic, as well as different definitions of the AMOC, can call into question what the proxies are actually measuring”.

More observations and ongoing improvements in the modeling are essential to understanding the likely timing of climate impacts on the AMOC and the dramatic consequence of these changes.

Alan Blumberg is a Jupiter Co-founder and Advisor.

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