Introduction

When the earth was born, about 4.54 billion years ago, regularities in the behaviour of material and energy led to development of the properties of the atmosphere, land surface and oceans. Energy input by solar radiation soon became the dominating external influence on the planet. All material emits thermal radiation and its intensity increases with temperature. If the solar radiation remains unchanged for a prolonged period, and if the thermal radiation by the globe is smaller than the solar energy input, then the global temperature increases until it reaches the temperature at which the energy input from the sun and output of thermal radiation by the earth are equal. In principle, the same happens if the output by thermal radiation is larger than solar input, but the global temperature decreases in this case.

Solar energy input generates and drives a complex circulation of energy and material on the globe. This circulation of energy includes several rather different phenomena such as: absorption and emission of radiation, evaporation and condensation of water, heat exchange between solid and liquid material and gas, and convection by mass flow. The atmosphere buffers the diurnal exchange of energy and so reduces the temperature difference between day and night.