FIGURE 63.6 Estimating past greenhouse gas concentrations and past temperatures using ice cores. (a) Ice cores are extracted from very cold regions of the world such as this glacier on Mount Sajama in Bolivia. (b) Ice cores have tiny trapped air bubbles of ancient air that can provide indirect estimates of greenhouse gas concentrations and global temperatures.
(a: George Steinmetz/Corbis; b: Marc Steinmetz/Visum/The Image Works)