The effect of forced Atlantic Meridional Overturning Circulation weakening on atmospheric pCO2

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is thought to be a tipping element in the Earth System with two stable states. Currently, the AMOC is in a state of strong overturning, but studies have shown that climate change might tip the AMOC to a state of weak overturning. Changing the state of the AMOC changes the global climate, but especially the climate in the North Atlantic. Due to disrupted heat transport the Northern Hemisphere is expected to cool, while the Southern Hemisphere is expected to warm. Besides effects on the climate, the AMOC also influences the carbon cycle by transporting nutrients and Dissolved Inorganic Carbon. Deep water formation in the North Atlantic is for example an important pathway of carbon from the surface to the deep ocean. It can therefore be expected that a weakening of the AMOC affects the marine carbon cycle and therefore also atmospheric pCO2. Here, we investigate the effect of a forced AMOC weakening on atmospheric pCO2 using simulations performed with the Community Earth System Model v2 (CESM2). We force the simulations with the emission driven SSP5-8.5 scenario and additionally, force the simulations with freshwater forcing in the North Atlantic Ocean. This so-called hosing weakens the AMOC on top of a weakening caused by the greenhouse gas emissions. We use these simulations to determine how much and through what mechanisms, an AMOC weakening influences atmospheric pCO2.