Scientists say that the pressing need to reach net-zero carbon dioxide emissions has ramped up as a result of new predictions about the potential collapse of the Atlantic Meridional Overturning Circulation (AMOC).

A recent study, published in Environmental Research Letters, warns that the shutdown of the AMOC could occur sooner than previously thought and have far more severe consequences.

How soon could the AMOC collapse?

Under various emissions scenarios extending beyond the time limit of 2100, the results pointed to the event no longer being a ‘low likelihood’ risk. Instead, it seems likely even in a low-emission future aligned with the Paris Agreement’s targets. The authors challenged previous Intergovernmental Panel on Climate Change (IPCC) reports that concluded, “there is medium confidence that there will not be an abrupt collapse before 2100”, arguing that these models overlooked the impact of meltwater release from the Greenland Ice Sheet in their future projections.

This new report says, “Under a high-emission scenario (SSP585), the AMOC declines throughout the 21st century and reaches a shutdown of its deep northern overturning in all nine models that were run beyond 2100”.

The authors call for a review of previous assertions and conclusions and hope that these new findings will be incorporated into the new IPCC report.

The scientists suggest that with high emissions, around 70% of the models point to a collapse of the northern AMOC. In mid-range scenarios, the figure is around 30%, and even in low-emission pathways, around 20% of models still show shutdown:

“In the CMIP6 ensemble, a northern AMOC shutdown by 2300 occurs in 67% of all model-runs in an SSP585 scenario; 30% of all model-runs in an SSP245, and 21%, in an SSP126 scenario. Such numbers do no longer comply with the low-likelihood-high-impact event that is used to discuss an abrupt AMOC collapse in AR6 [1] and this assessment needs to be revised in AR7.”

(In other words, an AMOC collapse can no longer be considered just a remote possibility.)

What would AMOC collapse mean for the UK?

The AMOC is a system of ocean currents that carries warmer tropical waters northwards across the Atlantic to the UK and Europe, helping to moderate the region’s climate. In the North Atlantic, as the water cools, it becomes saltier, denser and sinks deeper before being carried southwards again. A weakening and collapse would have a significant global impact, leading to more intense and extreme winter weather in the UK, with temperatures dropping by several degrees within decades. At present, this system keeps Europe reasonably mild and stable, but this would change if the system were to collapse.

Is the AMOC doomed?

Professor Sybren Drijfhout, chair in Ocean & Earth at the University of Southampton and lead author of the report, explained to Yorkshire Bylines:

“We find in many models an abrupt collapse of deep mixing in the North Atlantic occurs before 2050. When that happens, the AMOC is doomed … When the feed stops, it takes another 50 before these dense water masses completely disappear and the northern branch of the AMOC stops, and in Europe we then receive the full climate impact of an AMOC collapse. “Our study demonstrates that the likelihood of this scenario is much greater than previously thought, ranging from 25% to more than 70%, depending on how much carbon dioxide will be released to the atmosphere, urging for a speed-up in realising substantial decrease in those emissions and preparing adaptation measures in case the AMOC does start to collapse. “While a full AMOC collapse and its impact is likely only realised after 2100, the first, almost half of the associated impacts, may already come around 2050.”

“There are no solutions in place”

Yorkshire Bylines asked Professor Drijfhout if there were any solutions in place to delay the stopping of the deep convection in the next decade or two. Drijfhout’s response was chilling:

“There are no solutions in place. It would involve adding every second, millions of kilograms of salt to the northern North Atlantic, which is unfeasible. We can’t geo-engineer this. We can only lower the chances that it happens by limiting the warming as fast as possible, implying speeding up the decrease in carbon dioxide emissions to net zero.”

Drijfhout acknowledged that there are some projects already in place, aimed at creating early warning systems.

“Apart from mitigation, we need to prepare adaptation measures, and for that, and before we start investigating millions of pounds, we need to improve our ability to forecast/forewarn of such an event. “In the UK, the [Advanced Research and Innovation Agency] has funded quite a few scientific consortia with projects targeting the set-up of an early warning system for climate tipping points associated with the Greenland Ice Sheet and deep mixing in the northern North Atlantic. That will be a research area where new insights on this topic can be expected.”

The potential collapse of the AMOC could change weather patterns drastically, particularly in the UK and Europe. With new modelling showing that this is likely to come sooner than previously thought, carbon emissions need to be reduced urgently. Scientists are calling for a re-evaluation of previous projections, stressing that we must prepare for the worst-case scenario, while at the same time reducing greenhouse gases significantly. We need to act now, before it is too late.