Radiative Forcing

Excerpt from the Southwest Climate Change Network, written by Zack Guido, University of Arizona

Radiative forcing measures the influence that climate-altering factors have on the energy balance of the Earth. Examples of factors that can alter the Earth’s energy balance include atmospheric concentrations of greenhouse gases, aerosols from volcanoes and air pollution, and the amount of solar radiation delivered to the Earth by the Sun.

In a state of equilibrium, solar radiation entering the atmosphere equals the radiation that leaves the atmosphere. Figure 1 illustrates this energy balance. The radiative forcing of a particular factor, such as atmospheric concentrations of carbon dioxide (CO2), is the change in the energy balance that results from a change in the factor, such as an increase in CO2 concentrations. When the radiative forcing of a factor is positive, increases in the factor cause warming of the atmosphere. In contrast, for a negative radiative forcing, increases in the factor ultimately cause cooling (Forster et al. 2007).

Figure 1. Estimate of the Earth’s annual and global mean energy balance. Over the long term, the amount of incoming solar radiation absorbed by the Earth and the atmosphere is balanced by the Earth and atmosphere releasing the same amount of outgoing longwave radiation.

Adapted for eXtension.org by Michael Crimmins, University Arizona

References Cited
Forster, P., et al. 2007. Changes in atmospheric constituents and in radiative forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

External Links
Southwest Climate Change Network

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