Historical records give the surface temperatures of the seas
Experts have meanwhile found various solutions to the methodological problem. For example, by analyzing sediment samples from the sea floor, whose chemical composition provides clues to the conditions in the oceans hundreds of years ago. For the new study, the researchers working with Latif used historical records that document surface temperatures across the Atlantic and date back to 1900. Since changes in the AMOC can affect the water temperatures differently, the status of the current could be assessed with the aid of the recordings. In addition, Latif and co have combined their historical analyzes with climate model simulations to determine the causes of the weakened AMOC.
Their result: man-made global warming is in fact influencing the flow system. It is “a kind of fingerprint” of climate change, as Latif puts it. The natural variability still dominates what is happening at the moment. However, the influence of climate change is increasing in the background. “As greenhouse gases continue to accumulate in the atmosphere, all models predict a sharp slowdown in the circulation,” explains Latif. The question is when this signal becomes the dominant force acting on the flow. If not now, then certainly sometime in the future should the planet continue to warm.
The results of the study are fully consistent with other current research on slowing down the AMOC, writes Stefan Rahmstorf, ocean expert at the Potsdam Institute for Climate Impact Research, in an email to »E&E News«. Rahmstorf was not involved in the new study, but has published several important papers on AMOC attenuation over the past several years.
In his view, there is ample evidence of at least some influence from man-made global warming. These include the “fingerprint” of climate change that the new study cites, then the fact that climate models predict there will be a slowdown due to greenhouse gas emissions, and the trend that the recent slowdown appears to be the most extreme of the past millennium .