Science To Support Limiting Future Climate Change

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Just as cities loom large in driving and being affected by climate change, they also have important roles to play in limiting the magnitude and ameliorating the impacts of climate change (Grove, 2009). The largest opportunities for reducing GHG emissions from urban centers lie in the transportation, construction, commercial, and industrial sectors, which typically lead in energy consumption and GHG emissions. Reducing industrial and transportation emissions provides a potential for multiple co-benefits to cities in limiting future climate change, reducing the urban heat island effect, and also improving air quality (e.g., NRC, 2009e).

The design and geometry of cities and metropolitan areas afford various means for reducing emissions as well as surface reflectivity. The urban form of most cities has grown in an ad hoc way, through piecemeal planning, development, and control under multiple, independent decision-making units (Batty, 2008). Many, if not all, of these decision-making entities respond foremost to considerations other than climate change, and they rarely consider environmental spillovers beyond their area of control or concern. Yet, the development of cities has profound impacts on infrastructure, travel behavior, and energy consumption (e.g., Ewing and Rong, 2008; Filion, 2008; NRC, 2010g), all of which offer opportunities for interventions that could offset the role of cities in driving climate change. These interventions are only beginning to be explored and appreciated.

One potential response option is altering the reflectivity of surface structures by whitening roofs and road surfaces or employing green rooftop and landscaping options (Akbari et al., 2001; Betsill, 2001). Roofs and paved surfaces typically comprise about 25 and 35 percent, respectively, of dense urban areas (Akbari et al., 2009), so increasing the reflectivity of these surfaces offers the potential to offset some of the urban heat island effect and influence global climate (see Chapter 15). Green rooftops and landscaping options not only reduce urban and regional heat islands but can also improve local and regional air quality (Taha et al., 1997) and provide recreational opportunities and other nonclimate benefits. Alternative city designs or configurations can also lower the heat island effect (Eliasson, 2000; Unger, 2004), although with varying impacts on water and energy consumption that introduce a new suite of trade-offs to consider. "Smart" or "green" redesigns of cities that foster less use of automobiles, among other factors, could reduce GHG emissions from urban areas (Ewing et al., 2007).

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