Earth's heat inventory from climate model simulations and observations

Cuesta Valero, Francisco José (2021) Earth's heat inventory from climate model simulations and observations. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Changes in the Earth system due to anthropogenic activities, such as emissions of greenhouse gases, have altered the response of the climate system to shortwave radiation received from the Sun. This response is mainly determined by several feedbacks that alter the amount of reflected shortwave radiation and emitted longwave radiation into the Space, resulting in a positive radiative imbalance at the top of the atmosphere. Such radiative imbalance causes heat storage within the climate system and modifies the evolution of several physical phenomena, such as permafrost thawing and sea level rise. Therefore, determining the response of the system to anthropogenic activities and the heat distribution among all climate subsystems is crucial to project future climate change. In this dissertation, I estimate a preindustrial surface temperature climatology over North America and global changes in surface temperature, surface heat flux and continental heat storage from borehole temperature profiles. These observational estimates are used to assess the Earth Heat Inventory (EHI) and the preindustrial climatology over North America represented in an ensemble of transient climate simulations performed by atmosphere-ocean Coupled General Circulation Models (CGCMs) from the fifth phase of the Coupled Model Intercomparison Project (CMIP5). The retrieved temperature climatology for North America based on borehole profiles is consistent with important features present in meteorological observations over a different period and the same spatial domain. Although the models were not tuned to match these temperatures, part of the analyzed CGCM preindustrial simulations agree with this climatology, while the rest of the models display lower temperatures. Estimates of ground surface temperatures and ground heat content indicates an average increase in land temperatures of 1⁰C since preindustrial times, and higher values of continental heat storage than previously reported. The assessment of the simulated and observed EHI shows that CMIP5 CGCMs constantly underestimate the heat storage in the continental subsurface, while overestimating the observed ocean heat content. These CMIP5 CGCM simulations also achieve values of atmosphere heat content and absorbed heat by sea ice melting similar to observations.

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