Scientists have found that a major ocean current system, the Atlantic Meridional Overturning Circulation, may weaken more than previously expected and sooner, with serious consequences for global climate.

Climate models are used to predict future conditions, helping governments plan for climate change. But these models don’t always agree. Predictions can vary depending on how the models are built, the emissions scenarios used, and natural climate variability.

For most climate projections, differences in future emissions are the biggest source of uncertainty. However, this new research shows that for the AMOC – the system of ocean currents regarded as one of the main temperature regulators on the planet – the main uncertainty comes from differences between the models themselves.

The AMOC is a system of ocean currents that moves warm water northwards in the Atlantic, where it cools, sinks, and flows back south at depth. This process helps regulate temperatures and weather patterns around the world. If the AMOC slows down, it can disrupt rainfall patterns, shift weather systems, and contribute to drying in vulnerable regions such as the Sahel in Africa.

Scientists already agree that the AMOC is likely to weaken this century. But how much it will weaken has remained unclear.

To improve predictions, researchers tested new methods that combine climate models with real-world observations, such as sea surface temperature and salinity. These factors influence how ocean water sinks and circulates.

Unlike earlier studies that used just one variable, this research included multiple ocean measurements from different regions around the world. The team also compared several statistical approaches to see which gave the most reliable results.

They found that using more observational data significantly improves predictions – and suggests the AMOC could weaken about 60% more than standard estimates under a moderate emissions scenario.

This stronger slowdown could have wide-reaching impacts on climate, affecting weather, ecosystems, and food security.

The findings also raise concerns that the AMOC may be closer to a tipping point than previously thought, highlighting the need for more accurate models and better use of ocean data in future climate predictions.

Talking to the Guardian, Dr Valentin Portmann, at the Inria Centre de recherche Bordeaux Sud-Ouest in France and who led the new research, said: “We found that the AMOC is going to decline more than expected compared to the average of all climate models. This means we have an AMOC that is closer to a tipping point.”

Prof Stefan Rahmstorf, at the Potsdam Institute for Climate Impact Research in Germany, said: “This is an important and very concerning result. It shows that the ‘pessimistic’ models, which show a strong weakening of the AMOC by 2100, are, unfortunately, the realistic ones, in that they agree better with observational data.”

He added: “I now am increasingly worried that we may well pass that AMOC shutdown tipping point, where it becomes inevitable, in the middle of this century, which is quite close.”

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