Top-to-Bottom Ocean Heat Content Reveals Multi-Decadal Acceleration in Earth’s Energy Imbalance

The ocean is the dominant energy sink in the Earth system, and variations in Earth’s energy imbalance are recorded by changes in ocean heat content. Here, we use in-situ temperature data and an ensemble of autoregressive artificial neural networks to reconstruct historical changes in top-to-bottom ocean heat content. We find that the global oceans accumulated 200±80 ZJ of heat from 1946-2018, nearly all of which has occurred since 1990. While internal climate variability dominated changes in Earth’s energy imbalance over most of the 20th century, with cooling of the deep ocean counteracting a small warming in the upper ocean, the past three decades have seen a rapid acceleration in warming due to a positive planetary energy imbalance of roughly 0.5±0.1 W m^-2.