The Role of the AMOC in Shaping Internal Climate Variability

The Atlantic Meridional Overturning Circulation (AMOC) regulates large-scale heat and freshwater transport, and strongly influencing global climate patterns. Beyond its role in shaping mean climate conditions, the AMOC background state also modulates climate variability. The AMOC is a tipping element of the climate system and a collapse of the AMOC alters atmospheric circulation patterns such as the Hadley circulation, polar jet stream, and tropical trade winds, with consequences that extend far beyond the Atlantic basin. These changes affect atmospheric and oceanic variability, thereby reshaping global teleconnection patterns. Using the results of a full hysteresis simulation of the AMOC in the CMIP5 version of the Community Earth System Model (CESM), we study the importance of the present-day AMOC mean state in shaping the large-scale atmospheric circulation, the global oceanic circulation, and internal climate variability. By comparing equilibrium climate states under AMOC on- and off conditions, we investigate the role of the AMOC in climate variability phenomena, such as the El Niño-Southern Oscillation and the midlatitude patterns of sea surface temperature variability. Our results highlight the AMOC as a critical regulator of global climate variability, emphasising the importance of understanding its stability in a warming climate.