FIGURE 10-1 Evolution of atmospheric carbon dioxide and methane over the last 22,000 years. Left-hand axes show atmospheric concentrations (note the carbon dioxide scale does not start from zero), and right-hand axes show the radiative forcing relative to 1750 as calculated using the formulas given by Myhre et al. (1998) and Ramaswamy et al. (2001). Red arrows indicate the theoretical detection limit of a forcing (relative to Last Glacial Maximum and preindustrial conditions) within a climate system model, assuming an internal climate variability or detection threshold of 0.2°C, climate equilibrium, and a midrange climate sensitivity of 3°C for a carbon dioxide doubling. Dashed red lines indicate the uncertainty of the detection threshold associated with the climate sensitivity range of 1.5 to 4.5°C. SOURCE: Joos (2005). Reprinted with permission; copyright 2005.