English: Historic and predicted climate change (Average Global Temperature (°C) Relative to 1986-1995 Average).

Source: Congressional Budget Office. Historical data are from the Hadley Centre for Climate Prediction and Research, available at www.met-office.gov.uk/research/ hadleycentre/CR_data/Annual/land+sst_web.txt and described primarily in C.K. Folland and others, “Global Temperature Change and Its Uncertainties Since 1861,” Geophysical Research Letters, vol. 28 (July 1, 2001), pp. 2621-2624. The projection is based on data provided by Mort Webster, University of North Carolina at Chapel Hill, in a personal communication, December 11, 2002; the results are discussed in Mort Webster and others, Uncertainty Analysis of Climate Change and Policy Response, Report no. 95 (Cambridge, Mass.: Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change, December 2002).

Note: The projection, which is interpolated from decadal averages beginning in 1995, shows the possible distribution of changes in average global temperature as a result of human influence, relative to the 1986-1995 average and given current understanding of the climate. Under the Webster study’s assumptions, the probability is 10 percent that the actual global temperature will fall in the darkest area and 90 percent that it will fall within the whole shaded area. However, actual temperatures could be affected by factors that were not addressed in the study (such as volcanic activity and the variability of solar radiation) and whose effects are not included in the figure.