Asymmetry of AMOC Hysteresis in a State‐Of‐The‐Art Global Climate Model

Abstract

Abstract We study hysteresis properties of the Atlantic Meridional Overturning Circulation (AMOC) under a slowly‐varying North Atlantic (20°N–50°N) freshwater flux forcing in state‐of‐the‐art global climate model (GCM), the Community Earth System Model. Results are presented of a full hysteresis simulation (4,400 model years) and show that there is a hysteresis width of about 0.4 Sv. This demonstrates that an AMOC collapse and recovery do not only occur in conceptual and idealized climate models, but also in a state‐of‐the‐art GCM. The AMOC recovery is about a factor six faster than the AMOC collapse and this asymmetry is due to the major effect of the North Atlantic sea‐ice distribution on the AMOC recovery. The results have implications for projections of possible future AMOC behavior and for explaining relatively rapid climate transitions in the geological past.

Keywords

• ocean circulation
• tipping
• CESM
• hysteresis
• sea‐ice