Climate and Carbon Cycle Responses to a 21st century AMOC collapse under a 2°C stabilization pathway

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the climate system, yet the consequences of a pronounced weakening under emission pathways consistent with the Paris Agreement remain poorly understood. Using the comprehensive GFDL ESM2M Earth System Model with the Adaptive Emissions Reduction Approach, we impose a freshwater-induced strong AMOC weakening to 20% of its preindustrial strength starting in year 2026. These simulations otherwise follow a pathway in which global warming stabilizes at 2°C and the AMOC weakens only modestly and partially recovers. Relative to the modest-weakening scenario, a strong AMOC weakening cools global mean surface air temperature by −0.8°C (5-member ensemble range: −0.7 to −0.9) by 2171-2200, with pronounced regional cooling in the North Atlantic, reaching up to −6.8 °C (−4.1 to −9.7) in winter over Iceland. The ocean stores an additional 385 ZJ (331–428) of heat, primarily south of 20°N, associated with reduced northward heat transport and enhanced heat uptake in the North Atlantic. The additional heat increases global thermosteric sea level rise by 10% (8–12). Atmospheric CO2 declines by 13 ppm due to anomalous land carbon uptake of 44 GtC (33–53), dominated by enhanced carbon storage in the Amazon under cooler and wetter conditions. In contrast, global ocean carbon storage decreases by 14 GtC, mainly north of 20°N, although carbon uptake increases in the northern North Atlantic. The AMOC-induced cooling breaks the near-linear relationship between cumulative CO2 emissions and warming, increasing the remaining carbon budget for limiting warming to 2°C by 63% (54–72). Compared to identical freshwater forcing under preindustrial conditions, the surface temperature, ocean heat content, and sea-level responses are substantially damped, indicating reduced climate sensitivity to AMOC collapse in a warmer world. These results demonstrate that a strong AMOC weakening would profoundly alter future climate–carbon cycle interactions and underscore the importance of explicitly accounting for AMOC risks in long-term climate assessments.