Estimating Continental Energy Storage from CMIP5 Simulations

Abstract:

The Earth's energy imbalance is a critical metric for understanding the current state of the Earth's climate system and its future evolution. Although much of the energy gained by the climate system over the last century has been stored in the oceans, the energy stored in the continental subsurface is important because climate feedback processes such as thawing permafrost and soil carbon stability depend on the energy stored in the ground. We use 32 General Circulation Models (GCMs) from the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5) to assess the ability of the current generation of GCMs to account for the energy storage in the continental subsurface. The estimated heat from the ground temperatures in each GCM indicates an underestimation of the simulated heat stored in the continental subsurface in comparison with estimations from borehole temperature profiles for the period 1950-2000. The CMIP5 GCMs present a broad spectrum of results with maximum values of 6×10²¹ J, while the borehole estimations range from 6×10²¹ J to 8×10²¹ J in the same spatial domain. Using a one-dimensional purely conductive model we asses the effect of the near-surface climate on the heat storage estimates of each GCM, as well
as expand the depth of the models to 500 m depth. The analysis of all results shows that the main cause of the underestimation of the stored energy in the subsurface by the CMIP5 GCMs may be due to the shallow depth of the land surface models and the nature of the bottom boundary condition that they apply. These underestimates of continental energy storage have important implications for the modelling of climate
dependent near-surface processes.