The airborne fraction is a scaling factor defined as the ratio of the annual increase in atmospheric CO
2 to the CO
2 emissions from anthropogenic sources. It represents the proportion of human emitted CO
2 that remains in the atmosphere. The fraction averages about 45%, meaning that approximately half the human-emitted CO
2 is absorbed by ocean and land surfaces. There is some evidence for a recent increase in airborne fraction, which would imply a faster increase in atmospheric CO
2 for a given rate of human fossil-fuel burning. Changes in carbon sinks can affect the airborne fraction.
- Forster, P, V Ramaswamy, P Artaxo, 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. et al. (eds.)]. Cambridge University Press, Cambridge, UK & New York, USA.
- Canadell, Josep G.; Corinne Le Quere; Michael R. Raupach; Christopher B. Field; Erik T. Buitenhuis; Philippe Ciais; Thomas J. Conway; Nathan P. Gillett; R. A. Houghton; Gregg Marland (November 20, 2007). "Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks" (PDF). PNAS. 104 (47): 18866–18870. doi:10.1073/pnas.0702737104. PMC 2141868. PMID 17962418. Retrieved 2010-01-02.