| definition |
- Radiative forcing (measured in Watts per square meter) can be estimated in different ways for different components. For the case of a change in solar irradiance (i.e., "solar forcing"), the radiative forcing is simply the change in the average amount of solar energy absorbed per square meter of the Earth's area. Since the cross-sectional area of the Earth exposed to the sun (πr2) is equal to 1/4 of the surface area of the Earth (4πr2), the solar input per unit area is one quarter the change in solar intensity. This must be multiplied by the fraction of incident sunlight that is absorbed, F=(1-R), where R is the reflectivity, or albedo, of the Earth, equal to approximately 0.7. Thus, the solar forcing is the change in the solar intensity divided by 4 and multiplied by 0.7.
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