Tropical modulations of global mean temperature

The tropical Pacific decadal variability (tPDV) emerged from recent studies as the major cause of the recent global warming hiatus. This connection is corroborated by the well-documented delayed global warming following El Nino on the interannual timescale. Multi-centennial control simulations in CMIP5 under constant radiative forcing are analyzed to characterize the three-dimensional structure of tPDV and its effect on the global mean temperature (GMT). While GMT is correlated with tPDV in all models, the correlation varies among models in magnitude because of the differences in extratropical response to tPDV. In models of high tPDV-GMT correlation, the air temperature response shows a pronounced seasonality in high latitudes, large in boreal winter and weak in summer. This seasonality is consistent with observations for the current hiatus. In the vertical, the tPDV-induced tropospheric temperature variations are of a deep structure due to convection in the tropics and eddies in the extratropics. In the horizontal, tPDV-induced surface temperature is highly variable, with warming in the tropics and cooling in many extratropical regions. This horizontal distribution is distinct from radiative-forced response and from the observed centennial warming pattern.

Our results show a strong diversity in tPDV's influence on the extratropical mean surface temperature variability, hinting that models of low correlation between the two would have difficulty reproducing the ongoing hiatus in the Pacific Ocean-Global Atmosphere (POGA) configuration. The distinct three-dimensional patterns between tPDV and radiative-forced response are useful for attribution studies.