Reduction of radiation reflecting from earth per units of increase of a chemical component that causes this change in the atmosphere. The result is often used to compare the relative effect of greenhouse gases which can alter climate on earth. This means that components that are present in the atmosphere at low concentrations (e.g. methane at 1. 7 ppmv) but with high radiative forcing have a greater effect on global warming than higher concentration components with a lower radiative forcing.