A Thermodynamic Analysis of Earth's Energy Imbalance

Earth’s energy imbalance (EEI) is defined as the difference between the globally averaged incoming solar radiation absorbed by the climate system and the outgoing longwave and reflected shortwave radiation at the top of the atmosphere (TOA). Thermodynamically, EEI is a measure of the rate at which free energy is being stored in the Earth system and converted into increased internal energy, predominantly ocean heat content, as the system adjusts toward a new radiative equilibrium under anthropogenic forcing. Using recent observational estimates from satellite radiation measurements and global energy inventory data, this paper analyzes EEI over recent decades, interprets the imbalance within a thermodynamic framework, and assesses its implications for climate sensitivity and future warming. Results indicate that the global mean EEI has increased from about 0.5 ± 0.2 W m in the early 2000s to about 1.0 ± 0.2 W m over the last decade, implying a more than doubling of the rate of heat uptake by the Earth system (Loeb, N. G. et al. 2024, von Schuckmann, K. et al. 2023).Over 2005–2019, the average EEI is estimated to be about 0.90 ± 0.15 W m, consistent with independent constraints from ocean heat content observations and energy budget analyses (von Schuckmann, K. et al. 2023). Thermodynamic relations connecting radiative forcing, climate feedbacks, temperature change and entropy production clarify how this imbalance drives both persistent warming and an intensification of the climate system’s irreversible processes (Kleidon A., 2024., Swedan NH. 2023). The analysis underscores that EEI is a fundamental metric for diagnosing the state of global climate and constraining remaining warming “in the pipeline.”