Overview

• A new Environmental Research Letters study extends CMIP6 climate models to the 2300–2500 timeframe and finds that in all nine high-emission runs the deep overturning weakens into a shallow state and ultimately shuts down after 2100.
• Researchers identify a collapse of winter deep convection in the Labrador, Irminger and Nordic Seas as the trigger, with this threshold typically reached in the next few decades and the full wind-down taking 50 to 100 years thereafter.
• Recent observations over the past five to ten years show declining activity in North Atlantic deep-convection regions, which the authors say is consistent with model projections though it could reflect natural variability.
• The study notes standard models do not include added freshwater from Greenland ice loss, a gap that could understate the shutdown risk and strengthens calls for rapid greenhouse-gas reductions.
• Projected impacts of a shutdown include severe winter extremes and summer drying in northwestern Europe, shifts in tropical rainfall belts, higher sea levels along the U.S. East Coast, and potential changes to hurricane paths.