CoAuthors

Marti Florence (Magellium, France); Rousseau Victor (Magellium, France); Fraudeau Robin (Magellium, France); Benoit Meyssignac (LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, France); Alejandro Blazquez (LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, France)

The ocean absorbs much of the excess energy stored by the Earth system that results from the greenhouse gas emission by human activities in the form of heat (~91%). As the ocean acts as a huge heat reservoir, global ocean heat content (GOHC) is therefore a key component in the Earth's energy budget. An accurate knowledge of the GOHC change allows us to assess the Earth energy imbalance (EEI), which refers to the difference between the amount of energy the Earth receives from the sun and the amount of energy it radiates back into space. Various methodologies exist to estimate EEI from the GOHC, including the use of temperature and salinity profiles, the measurement of the ocean thermal expansion from space geodesy, ocean reanalysis and net flux measurements. Among these approaches, the space geodetic approach, detailed in Marti et al. (2022), leverages the maturity of satellite altimetry and gravimetry measurements, enabling precise, extensive spatial and temporal coverage, and full-depth estimates of ocean thermal expansion. As the EEI magnitude is small (0.5-1.0 W/m²) compared to the amount of energy entering and leaving the climate system (~340 W/m²), a high level of precision and accuracy are required to estimate the EEI mean (< 0.3 W/m²) and its time variations at decadal scale (< 0.1 W/m²). In this regard, the space geodetic approach emerges as a promising candidate capable of meeting the stringent EEI precision and accuracy requirements.

In this study, we present updated GOHC and EEI estimates from space geodetic data, including several major evolutions in the input data, algorithms and a temporal extension into the past since 1993 until 2022. The geodetic estimate of the EEI shows a significant positive trend of 0.75 W/m² over the period 1993-2022, indicating accelerated warming of the ocean and increasing EEI, in line with CERES observations. Comparisons with in situ data GOHC changes shows good agreement over 2005-2019. This study also highlights the importance of rigorously estimating uncertainties based on space geodetic data to robustly assess EEI changes.

The space geodetic GOHC-EEI product based on space altimetry and space gravimetry is available on the AVISO website at https://doi.org/10.24400/527896/a01-2020.003.