Title: The evolution of the equatorial Pacific zonal SST gradient during the twentieth century 1 2 Authors: 3 (original) (raw)

Two popular reconstructions of observed sea surface temperature, HadISST1 and NOAA ERSST (recently released version 3), are analyzed to clarify the evolution of the equatorial Pacific zonal SST gradient over the period. A brief survey of recently published analyses illustrates the widespread disagreement over the observed change in the SST gradient, which has implications for its projected response to global warming. Differences exist between the two reconstructions, but straightforward analyses show that the observations allow us to be confident of three things: (1) the western equatorial Pacific has been warming, (2) the eastern equatorial Pacific has not been warming as much as the west, and (3) the equatorial Pacific zonal SST gradient has not been weakening. Observational results are compared with and discussed in the context of IPCC AR4 model simulations of the twentieth century climate and beyond.