Tropical Pacific decadal climate variability (TPDV) affects billions of people and ecosystems worldwide. While major international efforts are underway to provide decadal climate predictions, there is still a great deal of uncertainty about the characteristics and causes of TPDV, and the accuracy to which it can be simulated and predicted.
We critically synthesize what is currently known and what is not known about TPDV, and provide recommendations to improve our understanding of TPDV and ability to predict it. While several mechanisms have been proposed to explain TPDV, their relative importance as sources of decadal prediction remains unclear.
Issues in need of greater understanding include the role played by the upper ocean overturning circulation in controlling tropical Pacific sea surface temperatures at decadal timescales, as well as the impact of external forcing on the Walker circulation and characteristics of internally-generated TPDV. Model improvements will benefit from an in-depth understanding of processes and mechanisms in the tropical Pacific that produce TPDV, their sources of error, and advances in computing technology.