Strong but Intermittent Spatial Covariations in Tropical Land Temperature

Surface temperature variations across the tropics exhibit different levels of spatial coherence, yet this is poorly characterized. Years of high temperature anomalies occurring simultaneously across large geographical regions have the potential to adversely impact food production and societal well-being. Using cluster analysis of correlations between extensive temperature measurements from the last six decades, we find a major change occurs in the late 1970s. Two spatial clusters merge to a single dominant one, and therefore, warmer years are experienced at the same time across most tropical land regions. Noting this change occurs at the same time as the Pacific Decadal Oscillation shifts a warm phase, we investigate this potential driver by a range of coupled ocean-atmosphere-land climate models. These simulations verify that stronger spatial tropical land temperature coherence tends to occur in Pacific Decadal Oscillation warm phases, although model differences exist in projections of how climate change may modulate this dependence.