Energy Balance of the Earth

Abstract

In this Chapter the energy transformations on Earth are described. The surface temperature, which is a key variable for the climate, is on the one hand determined by the global energy balance between radiative energy coming from the Sun and radiative energy emitted back to space by the Earth (Fig. 3.1a). On the other hand, the atmosphere has a strong impact on the global energy balance as it efficiently absorbs infrared radiation coming from the surface of the Earth. As a consequence, the surface temperature is much higher than it would be without the atmosphere.

The basis for life on Earth is the ability to convert energy received from the Sun into energy-containing chemical components via photosynthesis. The Earth’s biosphere has been evolving over long periods of time and is capable of changing energy-relevant properties of the Earth and altering the energy balance on a global scale.

From an engineering point of view, the Earth is an energy converter like the technical converters described in the subsequent Chapters of this book (Fig. 3.1b). Shortwave radiation from the Sun is transformed into longwave radiation that is re-emitted by Earth, but also into latent heat contained in the atmosphere and the ocean, as well as into mechanical energy in wind, rivers, and ocean currents. The complexity of the Earth system is tremendous and a full understanding of the processes taking place in it has not yet been achieved. However, several general properties, limiting cases, and typical phenomena occurring within the Earth system can be derived from relatively simple energetic analyses.