Monitoring the ocean heat content change and the Earth energy imbalance from space altimetry and space gravimetry

Abstract

Abstract. The Earth energy imbalance (EEI) at the top of the atmosphere is responsible for the accumulation of heat in the climate system. Monitoring the EEI is therefore necessary to better understand the Earth’s warming climate. Measuring the EEI is challenging as it is a globally integrated variable whose variations are small (0.5–1 W m−2) compared to the amount of energy entering and leaving the climate system (~ 340 W m−2). Since the ocean absorbs more than 90 % of the excess energy stored by the Earth system, estimating the ocean heat content (OHC) provides an accurate proxy of the EEI. This study provides a space geodetic estimation of the OHC changes at global and regional scales based on the combination of space altimetry and space gravimetry measurements. From this estimate, the global variations in the EEI are derived with realistic estimates of its uncertainty. The mean EEI value is estimated at +0.74 ± 0.22 W m−2 (90 % confidence level) between August 2002 and August 2016. Comparisons against independent estimates based on Argo data and on CERES measurements show good agreement within the error bars of the global mean and the time variations in EEI. Further improvements are needed to reduce uncertainties and to improve the time series especially at interannual and smaller time scales. The space geodetic OHC-EEI product is freely available at https://doi.org/10.24400/527896/a01-2020.003.

Past and future ocean warming

“…Indirect methods can be used to infer OHC change from physical relationships between OHC and other variables 33,64,65 . For instance, altimetry and space gravimetry have been used since the early 2000s to estimate OHC based on a sea level budget constraint 64,[66][67][68] , and SST used based on an assumption that temperature Representative concentration pathway rCP. The rCPs are scenarios of concentrations, and thereby emissions, of the full suite of greenhouse gases, aerosols and chemically active gases, as well as land use/land cover.…”

“…c | As in a but for 0-2,000 m (rEFs 37,52,56,59,60,62,63,65,67,69,269 ). d | As in b but for 0-2,000 m, and also including rates of change from CMIP5 (dashed lines).…”

Revisiting the global mean ocean mass budget over 2005–2020

“…Vishwakarma et al, 2021), ice sheet melting (e.g. Velicogna et al, 2020;Shepherd et al, 2021), interannual variability of water mass transport (Pfeffer et al, 2022), variations of Earth's energy imbalance (Hakuba et al, 2021;Marti et al, 2022). Ensuring the stability of GRACE and GRACE-FO data is therefore very important for climate and hydrological applications.…”