8.1 The Earth's thermal regime

This chapter discusses the Earth’s thermal regime. The conditions under which geothermal energy can be exploited strongly depend on both the origin of geothermal heat and the environment in which it is stored. Therefore, the chapter examines the internal structure of the Earth. It discusses the energy budget of the Earth and the contributions of the various external and internal sources and sinks of heat. The thermal regime of the Earth's crust structure, the magnitudes of heat storage and transport, and the associated physical properties specific heat capacity, thermal conductivity, and thermal diffusivity are explained. The heat is stored in the Earth by virtue of the heat capacity of its rocks and fluids. The heat transport in the Earth is governed mainly by three mechanisms: radiation, advection, and transient diffusion or steady-state conduction. The Earth's energy budget is determined by its thermal income and expenditure.