Earth’s energy imbalance and the global warming ‘hiatus’: insights from climate models and ocean reanalyses

Earth’s energy imbalance is the most fundamental metric defining the rate of global climate change. Using CMIP5 climate model simulations, we show that trends in surface temperature are only weakly indicative of the net energy imbalance on decadal timescales, due to the ocean’s ability to re-arrange large quantities of heat on these timescales. Therefore, the apparent ‘hiatus’ in global surface temperature rise may tell us nothing about the rate of global climate change over the recent past. CMIP5 models suggest that the ocean becomes dominant term in Earth’s energy budget at timescales longer than about 1 year, illustrating the need to improve estimates of the rate-of-change of ocean heat content (OHC) in order to better monitor ongoing anthropogenic climate change. An intercomparison of OHC changes in an ensemble of ocean reanalyses shows some robust signals in the upper few hundred metres but little agreement for deeper layers. This work highlights the need to maintain the Argo observations of the upper 2000m and extend the ocean observing array into the deep and abyssal ocean in order to better monitor and understand variability and long-term changes in Earth’s energy imbalance.