It is a measure (expressed in W/m˛) of the influence that a factor has in altering the balance of incoming and outgoing energy in the Earth's atmosphere system and is an index of the importance of the factor as a potential climate change mechanism.
Positive forcing tends to warm the surface while negative forcing tends to cool it.
"A change in average net radiation (in W/m˛) at the top of the troposphere resulting from a change in either solar or infrared radiation due to a change in atmospheric greenhouse gases concentrations; perturbance in the balance between incoming solar radiation and outgoing infrared radiation."
(IPCC 1999, Special report on "Aviation and the global atmosphere")
Remark : Since RFs are measured at the moment the perturbation is present in the atmosphere, they do not take into account the fact that GHGs may have different lifetimes in the atmosphere. Scientists try to tackle this problem by using Global Temperature Potential.
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