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) change 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 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 timescales. The space geodetic OHC-EEI product (version 2.1) is freely available at https://doi.org/10.24400/527896/a01-2020.003 (Magellium/LEGOS, 2020).
Highlights
Over the last decades, greenhouse gases and aerosol concentrations have been increasing in the atmosphere, disrupting the balance in the Earth system between incoming and outgoing radiation fluxes
In the space geodetic approach, ocean heat content (OHC) changes are estimated from steric sea level changes, which are due to the thermal expansion and the haline contraction of the ocean column of water
This study provides the first space geodetic estimate with a rigorous uncertainty propagation algorithm of the Earth energy imbalance and changes in ocean heat content at the global scale
Summary
Greenhouse gases and aerosol concentrations have been increasing in the atmosphere, disrupting the balance in the Earth system between incoming and outgoing radiation fluxes. OHC change time series may be inferred by different approaches: (1) direct measurement of temperature–salinity profiles mainly derived from the Argo float network (von Schuckmann et al, 2020b), (2) re-analysis which combines in situ measurements of temperature–salinity and space measurements of sea level with ocean modelling (Stammer et al, 2016), (3) the ocean surface net flux from satellite observations (Kato et al, 2018; L’Ecuyer et al, 2015), and (4) the space geodetic approach (introduced in Meyssignac et al, 2019, and this study; see Hakuba et al, 2021). All uncertainties are reported with a 5 %– 95 % confidence level interval ( noted 90 % CL)
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