Reconciling disparate twentieth-century Indo-Pacific ocean temperature trends in the instrumental record

Large discrepancies exist between twentieth-century tropical Indo-Pacific sea surface temperature trends determined from present reconstructions. These discrepancies prevent an unambiguous verification and validation of climate models used for projections of future climate change. Here we demonstrate that a more consistent and robust trend among all the reconstructions is found by filtering each data set to remove El Nino/Southern Oscillation (ENSO), which is represented not by a single-index time series but rather by an evolving dynamical process. That is, the discrepancies seem to be largely the result of different estimates of ENSO variability in each reconstruction. The robust ENSO-residual trend pattern represents a strengthening of the equatorial Pacific temperature gradient since 1900, owing to a systematic warming trend in the warm pool and weak cooling in the cold tongue. Similarly, the ENSO-residual trend in sea-level pressure represents no weakening of the equatorial Walker circulation over the same period. Additionally, none of the disparate estimates of post-1900 total eastern equatorial Pacific sea surface temperature trends are larger than can be generated by statistically stationary, stochastically forced empirical models that reproduce ENSO evolution in each reconstruction.