Earth receives solar energy in multiple wavelengths. A significant part of this energy is either reflected or dissipated in the atmosphere, rest is absorbed by the earth’s surface. This energy warms the surface and the air near the surface. In the due process of cooling, earth radiates maximum amount of this energy back into space. Earth receives solar energy in the shorter wavelengths and radiates the longer wavelengths.
- Net radiation: It is defined as the difference between the solar radiation absorbed by the Earth-atmosphere system and the long-wave radiation emitted by the Earth atmosphere system to space. Net radiation influences the Earth’s climate because it determines the energy available for heating the atmosphere, ocean and land. Hence net radiation influences the seasonal variation of rainfall and the strength of the global circulation patterns.
- Radiative Forcing: The change in net radiation caused by changes in the concentration of greenhouse gas or aerosol concentrations are called Radiative forcing or climate forcing.
It is quantified at tropopause or the zone between troposphere and the stratosphere. The unit of radiative forcing is watts per square meter of the Earth’s surface. It is observed in two different trends
- Positive radiative forcing: It means that the amount of incoming solar energy is more than the number of radiations going out. It warms the earth atmosphere system.
- Negative radiative forcing: It means that the amount of outgoing energy is more than the amount of incoming energy. It cools the earth-atmosphere system.