Response of the meridional overturning circulation during differing pathways toward greenhouse gas stabilization

A series of experiments conducted with the Community Climate System Model version 3 is analyzed to investigate the response of the meridional overturning circulation in the Atlantic Ocean following greenhouse gas stabilization in the 22nd through mid-25th centuries. In addition, several “overshoot” experiments that approach the same stabilization level by temporarily exceeding their ultimate greenhouse gas concentrations are considered. In all cases, the index of maximum North Atlantic overturning declines during the 21st century then begins to recover once greenhouse gas stabilization is achieved. However, the vertical structure of the overturning continues to evolve, becoming shallower through the end of the integrations in the mid-25th century. In the overshoot experiments, the overturning circulation recovers a strength slightly higher than, and vertical structure similar to, that in an experiment where the same stabilization level is approached monotonically. The relationship between changes in the overturning strength and changes in the pressure distribution over the upper 1000m is explored.