urban ecological footprint (Rees and Wackernagel, 2008). This footprint involves land use changes in, and resource extraction from, not only the immediate city hinterland but also in distant areas as a result of globalization (DeFries et al., 2010). Thus, energy consumption, indirect land use change (e.g., deforestation), and ecosystem impacts (e.g., ground-level air pollution) beyond the city’s boundaries play important roles in climate change (e.g., Auffhammer et al., 2006).
Urbanized or built-up areas directly change reflectivity (Sailor and Fan, 2002), especially through the concentration of roads and other dark surfaces, and so can affect global radiative forcing even though they cover only 1 to 2 percent of the land surface of the Earth (Akbari et al., 2009). The urban heat island effect is relatively well understood (see Figure 12.2) and also has consequences for regional and global climate (e.g., Jin et al., 2005; Lin et al., 2008); for example it may have amplified the effects of the 2003 heat wave in western Europe (Stott et al., 2004). Sustained research demonstrates that urbanization also affects precipitation, including its variability and intensity over and on the leeward side of cities (e.g., Changnon, 1969; Jauregui and Romales, 1996; Shem and Shepherd, 2009). In addition, large built-up areas affect the global carbon balance via their configuration, which affects vegetation and soils (Pickett et al., 2008), and their almost inevitable spread over prime croplands (Angel et al., 2005; Seto and Shepherd, 2009).