The sun is the ultimate source of energy for the earth-atmosphere-ocean system. Since the earth is situated far away from the sun, with a mean distance of about 1.5 × 108km, radiation is the only method of energy transfer from the sun to the earth. The space between the topmost layer of the atmosphere and the sun is devoid of any matter. Hence, the other two methods of heat transfer, namely convection and conduction, are ineffective here. The atmosphere consists of gases, water vapour, and many other suspended particles. Due to physical processes, such as reflection, refraction, scattering, and absorption, the amount of solar radiation that reaches the top of the atmosphere changes when it reaches the earth and ocean surface. In order to understand the complex processes of climate change, it is important to have some basic knowledge of the physical processes that are responsible for the difference in solar radiation at different parts of the globe.

The complex processes of climate change are often explained with the help of a simple procedure called the ‘greenhouse effect’. The roofs of so-called greenhouses are made up of glasses or plastic sheets to create a warmer atmosphere, which is conducive for the growth of certain flowers, vegetables, and other plants. In such houses, the solar radiation can enter through the roof unhindered. However, the long wave radiation emitted within the enclosure, from the surface of its sides and from plants, cannot escape from the roof completely.