Given their concentration of people, industry, and infrastructure, cities and built environments are generally expected to face significant impacts from climate change. Some of the most important impacts will be associated with changes in the frequency and intensity of extreme weather. Hurricane Katrina in 2005 illustrated the potential for extreme events to cause catastrophic damage to human well-being as well as urban infrastructure; likewise, temperature extremes in cities increasingly cause severe human and environmental impacts, even in the developed world (see Box 12.1). The impacts of warming are amplified in large urban conglomerations because of the heat island effect and the interaction of other environmental stressors (Grimmond, 2007; Hayhoe et al., 2004; Rosenzweig et al., 2005; Solecki et al., 2005). For example, the urban heat island of Phoenix raises the minimum nighttime temperature in parts of the city by as much as 12.6°F (7°C), generating serious water, energy, and health consequences (Brazel et al., 2000). The growth of the southwestern U.S. “sunbelt” as well as that of megacities throughout other arid regions of the world increases the populations at risk from extreme heat as well as their demand for energy and water (Rosenzweig et al., 2005).
In addition, CO2, nitrogen oxides, volatile organic compounds, particulate matter, and other pollutants and pollutant precursors react in the urban airshed to produce high levels of surface ozone and other potential health hazards (see Chapter 11). In a warmer future world, stagnant air, coupled with higher temperatures and absolute humidity, will lead to worse air quality even if air pollution emissions remain the same (e.g., Cifuentes et al., 2001a,b In many cases, air pollution plumes extend well beyond the urban area per se, affecting people and agriculture over large areas, such as the Ganges Valley (e.g., Auffhammer et al., 2006). In the developing world, such decreases in outdoor air quality come on top of poor indoor air quality—for example, from wood fuel heating (Zhang and Smith, 2003).
As discussed in Chapter 11, certain groups (such as the elderly) are especially vulnerable to intensive heat waves in cities worldwide, especially in temperate climates. Groups with preexisting medical problems, without air-conditioned living quarters, who are socially isolated, or who live on top floors are particularly vulnerable (Naugh-ton et al., 2002; Patz et al., 2005; Semenza et al., 1996). The elderly, as well as portions of the population with asthma and related problems, are also susceptible to poor air quality (e.g., Hiltermann et al., 1998). The U.S. population over age 65 is expected to reach 50 million (20 percent of the total U.S. population) by 2030, with the overwhelming majority living in cities. Cities throughout the nation and the world are differentially prepared (CCSP, 2008a), as illustrated by the relative success of Marseille in the