Effect of remote sea surface temperature change in tropical cyclone potential intensity

We examine the relationship between changes in sea surface temperature (SST) and in tropical cyclone maximum potential intensity (MPI), using both observations and global climate model (GCM) projections. We show that local SST changes alone are inadequate for characterizing changes in tropical cyclone MPI, with the sign of MPI change not constrained by that of the SST change (warming can be associated with MPI decrease). However, long-term changes in MPI can be largely recovered by accounting for both local and remote SST changes. The remote effect of SST can be approximated by the tropical-mean SST change, such that regions that warm more (less) than the tropical mean are characterized by increased (reduced) MPI. We exploit this simple relationship to develop a simplified index for long-term changes in MPI, which we use to assess the implications of historical SST changes for long-term changes in MPI. We find that, even though tropical Atlantic sea surface temperatures are currently at a historical high, Atlantic potential intensity probably peaked in the 1930s and 1950s and recent values are near the historical average. Our results indicate that – per unit local sea surface temperature change - the response of tropical cyclone activity to natural climate variations, which tend to involve localised changes in sea surface temperature, may be larger than the response to the more uniform patterns of greenhouse-gas induced warming.