Assessing Spatial and Temporal Variations in the Ocean Heat Content and Earth Energy Imbalance from Space Geodetic Data

The GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (Gravity Recovery and Climate Experiment - Follow On) satellite missions have enabled global monitoring of mass transport within the Earth's system, leading to unprecedented advances in understanding the global water cycle in the context of a changing climate. Over the past two decades (2002–2022), the combination of satellite gravimetry with altimetry data has allowed us to monitor the change in the ocean heat content (OHC) which is the main reservoir to store the excess of energy accumulated in the Earth system due to human activities. From the global OHC estimate, the Earth's energy imbalance (EEI: +0.8 W/m²) was derived with high accuracy (±0.16 W/m² within a 90% confidence interval). The primary source of uncertainty in our geodetic EEI estimate arises from the post-processing of satellite gravity measurements, which has been rigorously evaluated using an ensemble approach. Independent comparisons with the Clouds and the Earth's Radiant Energy System (CERES) mission further highlighted the critical importance of post-processing corrections for the detection of realistic changes in EEI at interannual and decadal time scales. These findings underscore the need to enhance consistency between satellite altimetry and gravimetry measurements, particularly concerning geocenter corrections. Additionally, investigations into the spatial and temporal variations in OHC have shown that post-processing corrections applied to satellite gravimetry data, such as leakage correction, are crucial for accurately capturing temporal variations in EEI. Better-informed decisions regarding the selection of post-processing corrections can be made by leveraging the redundancy of the ocean and climate monitoring system to ensure the closure of the energy and sea level budgets at the global and regional scales.