Reconciling Earth’s growing energy imbalance with ocean warming

Rising greenhouse gas concentrations and declining global aerosol emissions are causing energy to accumulate in Earth’s climate system at an increasing rate. Incomplete understanding of increases in Earth’s energy imbalance and ocean warming reduces the capability to accurately prepare for near term climate change and associated impacts. Here, satellite-based observations of Earth’s energy budget and ocean surface temperature are combined with the ERA5 atmospheric reanalysis over 1985–2024 to improve physical understanding of changes in Earth’s net energy imbalance and resulting ocean surface warming. A doubling of Earth’s energy imbalance from 0.6±0.2 Wm ^−2 in 2001–2014 to 1.2±0.2 Wm ^−2 in 2015–2023 is primarily explained by increases in absorbed sunlight related to cloud-radiative effects over the oceans. Observed increases in absorbed sunlight are not fully captured by ERA5 and determined by widespread decreases in reflected sunlight by cloud over the global ocean. Strongly contributing to reduced reflection of sunlight are the Californian and Namibian stratocumulus cloud regimes, but also recent Antarctic sea ice decline in the Weddell Sea and Ross Sea. An observed increase in near-global ocean annual warming by 0.1 $^\circ\mathrm{C}\,\mathrm{yr}^{-1}$ for each 1 Wm ^−2 increase in Earth’s energy imbalance is identified over an interannual time-scale (2000–2023). This is understood in terms of a simple ocean mixed layer energy budget only when assuming no concurrent response in heat flux below the mixed layer. Based on this simple energy balance approach and observational evidence, the large observed near-global ocean surface warming of 0.27  ${\,}^\circ\mathrm{C}$ from 2022 to 2023 is found to be physically consistent with the large energy imbalance of 1.85±0.2 Wm ^−2 from August 2022 to July 2023 but only if (1) a reduced depth of the mixed layer is experiencing the heating or (2) there is a reversal in the direction of heat flux beneath the mixed layer associated with the transition from La Niña to El Niño conditions. This new interpretation of the drivers of Earth’s energy budget changes and their links to ocean warming can improve confidence in near term warming and climate projections.