{"id":109182,"date":"2025-08-29T09:41:48","date_gmt":"2025-08-29T07:41:48","guid":{"rendered":"https:\/\/www.sonnenseite.com\/?p=109182"},"modified":"2025-08-29T09:42:03","modified_gmt":"2025-08-29T07:42:03","slug":"possible-north-atlantic-overturning-circulation-shutdown-after-2100-in-high-emission-future","status":"publish","type":"post","link":"https:\/\/www.sonnenseite.com\/en\/science\/possible-north-atlantic-overturning-circulation-shutdown-after-2100-in-high-emission-future\/","title":{"rendered":"Possible North Atlantic overturning circulation shutdown after 2100 in high-emission future"},"content":{"rendered":"\n

28.08.2025 – Under high-emission scenarios, the Atlantic Meridional Overturning Circulation (AMOC), a key system of ocean currents that also includes the Gulf Stream, could shut down after the year 2100. This is the conclusion of a new study, with contributions by the Potsdam Institute for Climate Impact Research (PIK). The shutdown would cut the ocean\u2019s northward heat supply, causing summer drying and severe winter extremes in northwestern Europe and shifts in tropical rainfall belts.<\/p>\n\n\n

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\"Possible<\/a>
Time-evolution of the AMOC strength at 26\u00b0N (where it is observed) in the model simulations in which the AMOC shuts down. The short cyan line shows the observed trend of the observations for 2005-2023, the colour of the lines indicates the emission scenario that was used for the simulations. Graphic: Drijfhout et al.<\/figcaption><\/figure>\n<\/div>\n\n\n

\u201cMost climate projections stop at 2100. But some of the standard models of the IPCC \u2013 the Intergovernmental Panel on Climate Change \u2013 have now run centuries into the future and show very worrying results,\u201d says Sybren Drijfhout from the Royal Netherlands Meteorological Institute, the lead author of the study published in Environmental Research Letters<\/em>. \u201cThe deep overturning in the northern Atlantic slows drastically by 2100 and completely shuts off thereafter in all high-emission scenarios, and even in some intermediate and low-emission scenarios. That shows the shutdown risk is more serious than many people realise.\u201d<\/p>\n\n\n\n

Collapse of deep convection in winter as the tipping point\u00a0<\/h4>\n\n\n\n

The AMOC carries sun-warmed tropical water northward near the surface and sends colder, denser water back south at depth. This ocean \u201cconveyor belt\u201d helps keep Europe relatively mild and influences weather patterns worldwide. In the simulations, the tipping point that triggers the AMOC shutdown is a collapse of deep convection in winter in the Labrador, Irminger and Nordic Seas. Global heating reduces winter heat loss from the ocean, because the atmosphere is not cool enough. This starts to weaken the vertical mixing of ocean waters: The sea surface stays warmer and lighter, making it less prone to sinking and mixing with deeper waters. This weakens the AMOC, resulting in less warm, salty water flowing northward. <\/p>\n\n\n\n

In northern regions, then, surface waters become cooler and less saline, and this reduced salinity makes the surface water even lighter and less likely to sink. This creates a self-reinforcing feedback loop, triggered by atmospheric warming but perpetuated by weakened currents and water desalination.<\/p>\n\n\n\n

\u201cIn the simulations, the tipping point in key North Atlantic seas typically occurs in the next few decades, which is very concerning,\u201d says Stefan Rahmstorf, Head of PIK\u2019s Earth System Analysis research department and co-author of the study. After the tipping point the shutdown of the AMOC becomes inevitable due to a self-amplifying feedback. The heat released by the far North Atlantic then drops to less than 20 percent of the present amount, in some models almost to zero, according to the study. <\/p>\n\n\n\n

Lead author Drijfhout adds that \u201crecent observations in these deep convection regions already show a downward trend over the past five to ten years. It could be variability, but it is consistent with the models\u2019 projections.\u201d<\/p>\n\n\n\n

It is crucial to cut emissions fast<\/h4>\n\n\n\n

To arrive at these results, the research team analysed CMIP6 (Coupled Model Intercomparison Project) simulations, which were used in the latest IPCC Assessment Report, with extended time horizons to years from 2300 to 2500. In all nine high-emission simulations, the models evolve into a weak, shallow circulation state with the deep overturning shutting down; this result is produced in some intermediate and low-emission simulations as well. In every case, this change follows a mid-century collapse of the deep convection in North Atlantic seas.<\/p>\n\n\n\n

\u201cA drastic weakening and shutdown of this ocean current system would have severe consequences worldwide,\u201d PIK researcher Rahmstorf points out. \u201cIn the models, the currents fully wind down 50 to 100 years after the tipping point is breached. But this may well underestimate the risk: these standard models do not include the extra fresh water from ice loss in Greenland, which would likely push the system even further. This is why it is crucial to cut emissions fast. It would greatly reduce the risk of an AMOC shutdown, even though it is too late to eliminate it completely.\u201d<\/p>\n\n\n\n