Heat stored in the Earth system: where does the energy go?

Abstract

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).

Long-term global ground heat flux and continental heat storage from geothermal data

“…These new estimates of continental heat storage and ground heat flux from BTP inversions have implications for the assessment of the Earth's heat inventory and for comparison with general circulation model simulations. The ocean heat flux is still much larger than the ground heat flux, with an ocean flux of ∼ 900 ± 100 mW m −2 (von Schuckmann et al, 2020) in contrast to the ∼ 129±28 mW m −2 ground heat flux (Fig. 4) for the period 1993-2018 CE.…”

Review article: Earth's ice imbalance

“…Although the initial temperature is poorly constrained, the fractional energy required for warming is a small (0.7 % • C −1 ) percentage of the total energy imbalance. Altogether, the ice sheet, glacier, ice shelf and sea ice loss amounts to an 8.9 ± 0.9 × 10 21 J sink of energy, or 3.2 ± 0.3 % of the global imbalance over the same period (von Schuckmann et al, 2020).…”

Alkalinization Scenarios in the Mediterranean Sea for Efficient Removal of Atmospheric CO2 and the Mitigation of Ocean Acidification

“…The ocean plays a particular role in the climate system acting as significant sink of atmospheric heat and CO 2 due to its greater heat capacity, solubility, and inertia. Recent estimates suggest that the ocean has taken up more than 90% of the excess heat in the climate system since 1970 and 20-30% of anthropogenic carbon since the 1980s (IPCC, 2019;von Schuckmann et al, 2020). This has caused the additional hazard of ocean acidification lowering the average pH of the ocean surface by approximately 0.017-0.027 units per decade.…”