Influence of Anthropogenic Warming on the Atlantic Multidecadal Variability and Its Impact on Global Climate in the Twenty-First Century in the MPI-GE Simulations

The Atlantic multidecadal variability (AMV), a dominant mode of multidecadal variations in North Atlantic sea surface temperatures (NASST), has major impacts on global climate. Given that both internal variability and external forcing have contributed to the historical AMV, how future anthropogenic forcing may regulate the AMV is of concern but remains unclear. By analyzing observations and a large ensemble of model simulations [i.e., the Max Planck Institute Grand Ensemble (MPI-GE)], the internally generated (AMVIV) and externally forced (AMVEX) components of the AMV and their climatic impacts during the twenty-first century are examined. Consistent with previous findings, the AMVIV would weaken with future warming by 11%-17% in its amplitude by the end of the twenty-first century, along with reduced warming anomaly over the midlatitude North Atlantic under future warming during the positive AMVIV phases. In contrast, the AMVEX is projected to strengthen with reduced frequency under future warming. Furthermore, future AMVIV-related temperature variations would weaken over Eurasia and North Africa but strengthen over the United States, whereas AMVIV-related precipitation over parts of North America and Eurasia would weaken in a warmer climate. The AMVEX's impact on global precipitation would also weaken. The results provide new evidence that future anthropogenic forcing (i.e., nonlinear changes in GHGs and aerosols) under different scenarios can generate distinct multidecadal variations and influence the internally generated AMV, and that multidecadal changes in anthropogenic forcing are important for future AMV.