Heat stored in the Earth system: where does the energy go?
Authors: von Schuckmann Karina , Cheng Lijing , Palmer Matthew D. , Hansen James , Tassone Caterina , Aich Valentin , Adusumilli Susheel , Beltrami Hugo , Boyer Tim , Cuesta-Valero Francisco José , Desbruyères Damien , Domingues Catia , García-García Almudena , Gentine Pierre , Gilson John , Gorfer Maximilian , Haimberger Leopold , Ishii Masayoshi , Johnson Gregory C. , Killick Rachel , King Brian A. , Kirchengast Gottfried , Kolodziejczyk Nicolas , Lyman John , Marzeion Ben , Mayer Michael , Monier Maeva , Monselesan Didier Paolo , Purkey Sarah , Roemmich Dean , Schweiger Axel , Seneviratne Sonia I. , Shepherd Andrew , Slater Donald A. , Steiner Andrea K. , Straneo Fiammetta , Timmermans Mary-Louise , Wijffels Susan E. 
Published: September 2020

Abstract. Human-induced atmospheric composition changes cause a radiative imbalance at
the top of the atmosphere which is driving global warming. This Earth energy imbalance (EEI) is the most critical number defining the prospects for continued global warming and climate change. Understanding the heat gain of
the Earth system – and particularly how much and where the heat is
distributed – is fundamental to understanding how this affects warming
ocean, atmosphere and land; rising surface temperature; sea level; and loss
of grounded and floating ice, which are fundamental concerns for society.
This study is a Global Climate Observing System (GCOS) concerted
international effort to update the Earth heat inventory and presents an
updated assessment of ocean warming estimates as well as new and updated estimates
of heat gain in the atmosphere, cryosphere and land over the period
1960–2018. The study obtains a consistent long-term Earth system heat gain
over the period 1971–2018, with a total heat gain of 358±37 ZJ,
which is equivalent to a global heating rate of 0.47±0.1 W m−2.
Over the period 1971–2018 (2010–2018), the majority of heat gain is reported
for the global ocean with 89 % (90 %), with 52 % for both periods in
the upper 700 m depth, 28 % (30 %) for the 700–2000 m depth layer and 9 % (8 %) below 2000 m depth. Heat gain over land amounts to 6 %
(5 %) over these periods, 4 % (3 %) is available for the melting of
grounded and floating ice, and 1 % (2 %) is available for atmospheric warming. Our
results also show that EEI is not only continuing, but also increasing: the EEI
amounts to 0.87±0.12 W m−2 during 2010–2018. Stabilization of
climate, the goal of the universally agreed United Nations Framework Convention on Climate
Change (UNFCCC) in 1992 and the Paris
Agreement in 2015, requires that EEI be reduced to approximately zero to
achieve Earth's system quasi-equilibrium. The amount of CO2 in the
atmosphere would need to be reduced from 410 to 353 ppm to increase heat
radiation to space by 0.87 W m−2, bringing Earth back towards energy
balance. This simple number, EEI, is the most fundamental metric that the
scientific community and public must be aware of as the measure of how well
the world is doing in the task of bringing climate change under control, and
we call for an implementation of the EEI into the global stocktake based on
best available science. Continued quantification and reduced uncertainties
in the Earth heat inventory can be best achieved through the maintenance of
the current global climate observing system, its extension into areas of
gaps in the sampling, and the establishment of an international framework for
concerted multidisciplinary research of the Earth heat inventory as
presented in this study. This Earth heat inventory is published at the German Climate Computing Centre (DKRZ, https://www.dkrz.de/, last access: 7 August 2020) under the DOI
https://doi.org/10.26050/WDCC/GCOS_EHI_EXP_v2
(von Schuckmann et al., 2020).