English: Illustration of the carbon cycle. Reservoirs of carbon are in billions of metric tons (shown in parentheses); flows of carbon (shown as arrows) are in billions of metric tons per year. Source: Congressional Budget Office adapted from D. Schimel and others, "Radiative Forcing of Climate Change," Chapter 2 in J.T. Houghton and others, eds., Climate Change 1995: The Science of Climate Change (Cambridge, U.K.: Cambridge University Press, 1996). The figure draws on data from Mustafa Babiker and others, The MIT Emissions Prediction and Policy Analysis (EPPA) Model: Revisions, Sensitivities, and Comparisons of Results, Report no. 71 (Cambridge, Mass.: Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change, 2001); Department of Energy, Energy Information Administration, Annual Energy Review 2000, DOE/EIA-0384(2000) (November 2001); P. Falkowski and others, “The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System,” Science, vol. 290, no. 5490 (October 13, 2000), pp. 291-296; J.T. Houghton and others, eds., Climate Change 2001: The Scientific Basis (Cambridge, U.K.: Cambridge University Press, 2001); R.A. Houghton and David L. Skole, “Carbon,” in B.L. Turner II and others, eds., The Earth as Transformed by Human Action: Global and Regional Changes in the Biosphere over the Past 300 Years (Cambridge, U.K.: Cambridge University Press, 1990), pp. 393-408; Keith A. Kvenvolden, “Potential Effects of Gas Hydrate on Human Welfare,” Proceedings of the National Academy of Sciences, vol. 96 (March 1999), pp. 3420-3426; Bert Metz and others, eds., Climate Change 2001: Mitigation (Cambridge, U.K.: Cambridge University Press, 2001); Edward D. Porter, Are We Running Out of Oil? Discussion Paper no. 81 (Washington, D.C.: American Petroleum Institute, December 1995); and World Energy Council, Survey of Energy Resources, 19th ed. (London: World Energy Council, 2001), available at www.worldenergy.org/wec-geis/publications.