Abstract
<p>Energy exchanges among climate subsystems are of critical importance to determine the climate sensitivity of the Earth's system to changes in external forcing, to quantify the magnitude and evolution of the Earth's energy imbalance, and to make projections of future climate. Additionally, climate phenomena sensitive to land heat storage, such as permafrost stability and sea level rise, are important due to their impacts on society and ecosystems. Thus, ascertaining the magnitude and change of the Earth's energy partition within climate subsystems has become urgent in recent years. </p><p>Here, we provide new global estimates of changes in ground surface temperature, ground surface heat flux and continental heat storage derived from geothermal data using an expanded database and new techniques developed in the last two decades. This new dataset contains 253 recent borehole profiles that were not included in previous estimates of global continental heat storage. In addition, our analysis considers additional sources of uncertainty that were not included in previous borehole studies. Results reveal markedly higher changes in ground heat flux and heat storage within the continental subsurface during the second half of the 20th century than previously reported, with a land mean temperature increase of 1 K and continental heat gains of around 12 ZJ relative to preindustrial times. Half of the heat gained by the continental subsurface since 1960 have occurred in the last twenty years. These results may be important for estimates of climate sensitivity based on energy budget constrains, as well as for the evaluation of global transient climate simulations in terms of the Earth’s heat inventory and energy-dependent subsurface processes. Our estimate of land heat storage is included in the new assessment of the components of the Earth’s heat inventory recently released (von Schuckmann et al. 2020), together with the oceans, the atmosphere and the cryosphere.</p>
Highlights
Climate change is a consequence of the current radiative imbalance at the top of the atmosphere, which delivers an excess amount of energy to the Earth’s system in comparison with preindustrial conditions (Hansen et al, 2011; Stephens et al, 2012; Lembo et al, 2019)
Ground surface temperature histories estimated using a 25year inversion model, together with the standard approach and the new GST_PPIT ensemble, show temperature increases that are large during the second half of the 20th century in comparison with preindustrial conditions (Fig. 3a)
This is in agreement with meteorological observations of surface air temperatures and with previous studies using both borehole temperature profiles and proxy data (Pollack et al, 1998; Huang et al, 2000; Beltrami, 2002a; Pollack and Smerdon, 2004; Fernández-Donado et al, 2013; Masson-Delmotte et al, 2013)
Summary
Climate change is a consequence of the current radiative imbalance at the top of the atmosphere, which delivers an excess amount of energy to the Earth’s system in comparison with preindustrial conditions (Hansen et al, 2011; Stephens et al, 2012; Lembo et al, 2019). The energy imbalance presents an interhemispheric asymmetry that is larger in the Southern Hemisphere (Loeb et al, 2016; Irving et al, 2019). This asymmetry causes an increase in the heat uptake by the ocean surface in the Southern Hemisphere in comparison with the ocean heat uptake in the Northern Hemisphere.
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