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) 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).

GENESIS: co-location of geodetic techniques in space

“…In the case of the EEI derived from the geodetic approach the limiting factors at decadal time scales come from the uncertainty in the GIA correction and in the ITRF realization (see Blazquez et al 2018;Meyssignac et al 2019). In particular, the uncertainty on the Z motion of the geocenter of the ITRF which affects both the satellite altimetry estimate of the sea level changes at mid to high latitudes and the gravimetry estimate of the ocean mass changes is a primary source of uncertainty on the EEI at decadal and longer time scales (see Marti et al 2022;Blazquez et al 2018) (see also Guérou et al in preparation).…”

Unabated Global Ocean Warming Revealed by Ocean Heat Content from Remote Sensing Reconstruction

“…In recent decades, greenhouse gas emissions from human activities (such as burning fossil fuels and deforestation) have contributed to the greenhouse effect, causing heat to be trapped in the Earth's climate system and leading to global warming [1][2][3][4]. As a result, this leads to an imbalance of radiation at the top of the atmosphere (referred to as Earth's Energy Imbalance, EEI) [5][6][7][8]. In addition, anthropogenic climate change has already affected every region, with an increase in the frequency and intensity of extreme heat, ocean heat waves, intense precipitation and ecological droughts, and reductions in Arctic sea ice, snowpack, and perennial permafrost [9][10][11].…”

“…At the same time, the ocean, as the vital regulator of the global climate system [14,15], covers a large area and holds nearly 97% of the worldwide water. Approximately 93% of the EEI is stored in the oceans [4,7,8]. Therefore, the heat change in the ocean system drives and reflects global climate change [16].…”

A new bootstrap technique to quantify uncertainty in estimates of ground surface temperature and ground heat flux histories from geothermal data

“…Anthropogenic activities have contributed to a sustained increase in the Earth's energy imbalance at the top of the atmosphere (Hansen et al, 2011;Stephens et al, 2012;Johnson et al, 2016;Marti et al, 2022), inducing a radiative response from the climate system (Donohoe et al, 2014). As part of this response, energy exchanges among the ocean, the cryosphere, the continental land masses, and the atmosphere have been altered, leading to an increase in the heat stored in these components of the Earth System (Hansen et al, 2011;von Schuckmann et al, 2020).…”