Heat stored in the Earth system: Where does the energy go? The GCOS Earth heat inventory team

Abstract

Abstract. Human-induced atmospheric composition changes cause a radiative imbalance at the top-of-atmosphere which is driving global warming. This Earth Energy Imbalance (EEI) is a fundamental metric of climate change. Understanding the heat gain of the Earth system from this accumulated heat – and particularly how much and where the heat is distributed in the Earth system – is fundamental to understanding how this affects warming oceans, atmosphere and land, rising temperatures and 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 international assessment of ocean warming estimates, and 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 past 58 years, with a total heat gain of 393 ± 40 ZJ, which is equivalent to a heating rate of 0.42 ± 0.04 W m−2. The majority of the heat gain (89 %) takes place in the global ocean (0–700 m: 53 %; 700–2000 m: 28 %; > 2000 m: 8 %), while it amounts to 6 % for the land heat gain, to 4 % available for the melting of grounded and floating ice, and to 1 % for atmospheric warming. These new estimates indicate a larger contribution of land and ice heat gain (10 % in total) compared to previous estimates (7 %). There is a regime shift of the Earth heat inventory over the past 2 decades, which appears to be predominantly driven by heat sequestration into the deeper layers of the global ocean, and a doubling of heat gain in the atmosphere. However, a major challenge is to reduce uncertainties in the Earth heat inventory, which can be best achieved through the maintenance of the current global climate observing system, its extension into areas of gaps in the sampling, as well as to establish an international framework for concerted multi-disciplinary research of the Earth heat inventory. Earth heat inventory is published at DKRZ (https://www.dkrz.de/) under the doi: https://doi.org/10.26050/WDCC/GCOS_EHI_EXP (von Schuckmann et al., 2020).

It’s the Heat and the Humidity: The Complementary Roles of Temperature and Specific Humidity to Recent Changes in the Energy Content of the Near‐Surface Atmosphere

“…Studying extremes highlights the major climate changes that have occurred in subtropical areas further still (Figure 4b). Despite our focus on the near‐surface atmosphere, global changes to this small but important part of the earth system remain a small fraction of changes to global energy content due to global change (Church et al., 2011; Peterson et al., 2011; von Schuckmann et al., 2020). Effectively conveying the magnitude of global energy change remains a challenge (Moser, 2010), but one that is surmountable if we continue to improve the ways in which we communicate global change to scientists and non‐scientists alike.…”

“…Global change is a change in the energy balance of the planet. It is usually communicated to the public as a change in near‐surface (2 m) air temperature ( T a ), but some 90% of the excess energy has entered the oceans (Church et al., 2011; von Schuckmann et al., 2020) and T a is only part of the energy balance of the near‐surface atmosphere (Peterson et al., 2011). The total energy ( E , J) of a representative kilogram of air is the sum of its enthalpy, latent heat, kinetic energy, and gravitational potential: $$$E=m{C}_{P}{T}_{a}+Lqm+\frac{1}{2}m{v}^{2}+mgz$$$ where C P is the specific heat of moist air at constant pressure (J kg −1 K −1 ), T a is in Kelvin, L is the latent heat of vapourization (J kg −1 ), q is the specific humidity (kg kg −1 ), v is the velocity (m s −1 ), g is the acceleration due to gravity (m s −2 ), z is the height (m), and air parcel mass ( m ) is 1 kg as noted.…”

“…We also study the ability of global models to simulate these changes with a focus on the period following the 1980 global temperature “regime shift” (Reid et al., 2016). We focus our discussion on the importance of communicating the roles of both enthalpy and latent heat as critical parts of energy changes in the Earth system due to global climate change (Church et al., 2011; von Schuckmann et al., 2020).…”

Past and future ocean warming

“…Currently, ~3,900 profiling floats constitute the array, providing a system to make near-global measurements of the Earth's open ocean 36 , with a target resolution of one profile every 3° × 3° every 10 days. However, the Argo data are much more limited in polar areas, shallow and coastal regions, in some major current systems, including the Indonesian throughflow (ITF), and in the water column below 2,000 m. Because the Argo network has incomplete global coverage, the global upper-2,000-m OHC rates based on Argo-only products can underestimate the rate of change by 10-20% [37][38][39] . Deep Argo has been developed to better capture measurements at 4,000-6,000 dbar (rEF.…”

“…Robust warming is apparent in the upper layers of the ocean since the late 1950s (Fig. 2a,c and 1), albeit with some variability in trends and uncertainty owing to differences in data selection, trend estimates and methodological approaches 6,38,82 (Supplementary Information). These warming rates have increased over time (Fig.…”