Assessment of land energy uptake in the industrial period from observational and model products

Abstract

<p>Land-air interaction occurs at the ground surface at a wide range of time scales in the form of mass, momentum, and energy exchange. As a result of the water and heat fluxes, the land acts as a water and mostly energy storehouse for the climate system. Last estimates based on multimodel comparisons quantify the land contribution to terrestrial energy budget at about 2 % in the last four decades, whilst other studies based on borehole temperature profiles (BTPs) scale it up to be a 6 %. This uncertainty makes it necessary to explore other data sources to determine the land energy uptake, mostly under the increasing energy imbalance due to the ongoing anthropogenic-induced climate change.</p><p>State-of-the-art land surface models (LSMs) resolve a subsurface whose bottom boundary condition placement (BBCP) is not deep enough to correctly represent its thermal structure. This results both in a constrained capability to store energy, and an overestimation of temperature variability and industrial trends with increasing depth. A 2000-year-long forced simulation using a version of the Max Planck Institute (MPI) Earth System Model (ESM), MPI-ESM, including a very deep version of the LSM (BBCP at 1417 m), allows for assessing the behavior of subsurface temperatures and heat storage at long term scales, with a particular focus on the land response to the last century global warming. The analysis also allows for extending the assessment to CMIP6 historical simulations and climate reanalysis data.</p><p>Preliminary results show the energy uptaken by the MPI-ESM simulation with a deep version of the LSM is well above the range of values provided by CMIP6 model-based estimates and much closer to the observations. This underlines the great importance of BBCP depth in correctly representing the role of the land component in the terrestrial energy budget.</p>