Shaping our climate: The Atlantic Meridional Overturning Circulation
The Atlantic Meridional Overturning Circulation (AMOC) is the Atlantic branch of a global system of overturning ocean currents. The more famous Gulf Stream is part of this system. “Globally, the AMOC is a slow, steady circulation that takes about a thousand years to complete a circle. However, even small changes in the strength of this circulation can have widespread impacts on winds, temperature, and precipitation, including extreme events,” explains Katinka Bellomo, principal investigator of the CliMOC project. As reported in the Synthesis Report: Climate Change 2023, finalised by the Intergovernmental Panel on Climate Change, all projections of future climate change agree that the AMOC strength will decline as a consequence of increasing greenhouse gas concentrations in the atmosphere. Investigating this further is the EU-funded CliMOC project, with the support of the Marie Skłodowska-Curie Actions programme. The project aimed at building a modelling framework to specifically investigate the impacts of changing AMOC strength on the European climate using a state-of-the-art global climate model called EC-Earth3. “In CliMOC, we wanted to modify parts of the numerical code in EC-Earth3 to specifically control the strength of the AMOC circulation and conduct ad-hoc model experiments to assess the climate impacts associated with an AMOC weakening in a warming climate,” explains Bellomo.
The impact of AMOC in a warming climate
“In CliMOC, we conducted crucial and targeted model experiments that allowed us to assess the impact of AMOC in a warming climate. In particular, we uncovered the climate-weather nexus between the AMOC decline and changes in atmospheric weather regimes in the Euro-Atlantic sector,” highlights Bellomo. Weather regimes are preferential modes of atmospheric circulation that affect day-to-day weather. Project results showed that a weakened AMOC leads to more frequent wintertime positive North Atlantic Oscillation (NAO) days, which corresponds to a warmer and wetter northwestern Europe, and to a colder and drier southern Europe. “We also showed that the persistence of the positive NAO days increased, leading to more extreme precipitation events,” adds Bellomo.
Shaping climate change
The principal investigator’s research, including CliMOC, demonstrated that the AMOC plays a key role in shaping the current climate. It plays a strong role in future climate change impacts as well. Research has also revealed that it is a major source of inter-model uncertainty – one that does require continued observation in order to constrain the AMOC response in the future climate change. Discussing next steps, Bellomo concludes: “There are two open questions that I hope to tackle in the near future. Firstly, I would like to further investigate the climate-weather nexus associated with the interplay of ocean and ocean circulations. Furthermore, I would like to be able to better estimate how much the AMOC will decline by the end of the 21st century.”
Keywords
CliMOC, Atlantic Meridional Overturning Circulation (AMOC), climate, Europe, EC-Earth3