By Geomar

New studies on the Atlantic flow system sound out the threshold between natural fluctuations and climate change-driven development

25.04.2022/Kiel.

With a publication in the journal Nature Climate Change, Kiel researchers are once again contributing to the understanding of the changes in the Atlantic Meridional Overturning Circulation – known to the public as the “Gulf Stream System”. It is just as important for the global climate as it is for climate events in Europe. The investigations focus on the question of whether man-made climate change is already slowing down the oceanic upheaval. According to the new study, natural fluctuations still dominate. Improved observation systems could help to detect the human influence on the flow system at an early stage.

Is the Atlantic Meridional Overturning Circulation (AMOC) slowing down? Will this system of ocean currents, which is so important for our climate, possibly come to a standstill in the future? Are the observed fluctuations of natural origin or already a consequence of man-made climate change? Using a variety of methods, researchers from different scientific disciplines are trying to better understand the gigantic oceanic overturning motion.

“The AMOC ensures a mild climate in Europe and determines seasonal rain patterns in many countries around the Atlantic. If it weakens in the long term, it also affects our weather and climate. In addition, sea levels on some coasts could rise faster and the ocean’s ability to absorb carbon dioxide and mitigate climate change could decrease,” explains Professor Dr. Mojib Latif, Head of the Maritime Meteorology Research Unit at GEOMAR Helmholtz Centre for Ocean Research Kiel. “We depend on the AMOC in many ways – and yet so far we can only guess how it will develop, and whether and how strongly we humans ourselves are driving it towards a tipping point where an unstoppable collapse takes its course.”

By means of evaluations of observational data, statistical analyses and model calculations, a team led by Professor Latif has therefore investigated changes in the flow system over the past one hundred years in more detail. The researchers have now published their results in the journal Nature Climate Change. Accordingly, part of the North Atlantic is cooling down – a striking contrast to the vast majority of marine regions. The evaluations indicate that since the beginning of the 20th century, natural fluctuations have been primarily responsible for this cooling. Nevertheless, the studies point to an incipient slowdown of the AMOC in recent decades.

Climate models unanimously predict a significant slowdown in the current system in the future as our carbon dioxide emissions continue to rise, the ocean continues to warm and the melting of Greenland ice accelerates. “However, our study provides additional evidence that internal climate variability has played a significant role in climate change since 1900, and also reveals a wide range of plausible future climate trends,” says Hadi Bordbar, co-author of the publication and physical oceanographer at the Leibniz Institute for Baltic Sea Research Warnemünde (IOW). “Our results confirm previous scientific findings. But the question remains as to how long we will be in the realm of natural fluctuations and when climate change will take control of the AMOC. Then the development would only proceed in the direction of weakening and risks could increase significantly,” emphasizes Dr. Jing Sun, meteorologist at GEOMAR and co-author of the study.

In order to determine the critical limit, better observational data are needed, the authors conclude. “If we systematically and permanently measure the changes already taking place in all regions of the Atlantic, we will also be able to say with greater certainty what influence climate change has on the AMOC flow system today and in the future,” says Professor Dr. Martin Visbeck. The head of the Research Unit Physical Oceanography at GEOMAR is also co-author of the publication. “We don’t see any definite signs at the moment that the system is slowing down dramatically – it’s fluctuating. But with the latest climate models agreeing that a significant reduction will occur, we should know how long we will be on the relatively safe side of natural change.”

Publication:

Latif, M., Sun, J., Visbeck, M., Bordbar M.H. (2022): Natural variability dominates Atlantic Meridional Overturning since 1900.

Nature Climate Change, doi: 10.1038/s41558-022-01342-4.