Consolidating Global Estimates of Ocean Heat Content: Toward a Consistent Earth Heat Inventory

Abstract. The Earth’s Energy Imbalance (EEI), defined as the difference between the incoming solar radiation and the outgoing terrestrial radiation at the top of the atmosphere, provides a fundamental measure of anthropogenic climate change. Today, this imbalance is positive, indicating that the Earth system is accumulating heat, of which more than 90 % is stored in the ocean. The evolution of Global Ocean Heat Content (GOHC) thus constitutes a critical indicator of planetary warming and underpins the Earth Heat Inventory, currently the only approach capable of quantifying the observed absolute value of the EEI. Yet, the lack of standardized calculation protocols and the diversity of methodological choices across studies hinder the comparability of GOHC estimates and obscure the traceability of associated uncertainties. Here, we present a comprehensive, transparent assessment of GOHC trends and uncertainties based on an ensemble of 13 gridded in situ ocean temperature products spanning 1960–2024. Building on prior community efforts, we systematically evaluate the sensitivity of GOHC trends to key methodological choices, including (i) the temperature product, (ii) the definition of the temperature variable, (iii) the treatment of seawater density and heat capacity, (iv) the ocean domain used for integration, and (v) the method used for trend estimation. Our results demonstrate that GOHC trends are remarkably robust across methodological configurations. Variations associated with the temperature variable definition, thermodynamic parameters, ocean domain, or trend estimation method remain below 0.1 W m⁻², well within the ensemble-mean uncertainty range of 0.21 W m⁻², across both recent decades and multi-decadal timescales. We further show that the substantial spread among published EEI estimates reflects pronounced temporal variability in ocean heat uptake rates. This variability renders EEI estimates highly sensitive to the selected averaging period, underscoring that present-day absolute EEI values can only be meaningfully interpreted in a long-term context. We demonstrate that the ensemble spread provides a practical and comprehensive proxy for GOHC uncertainty, consistent with product-specific uncertainty estimates. By consolidating international assessment practices, this study delivers a transparent characterization of the state of ocean warming and provides a fully documented, openly available framework for constructing a GOHC indicator. Together, these advances strengthen the Earth Heat Inventory estimate, establish a reliable benchmark for monitoring ocean warming and EEI, facilitate intercomparison across studies, and reinforce international climate assessments at the science and policy interface.