Climate Change Goal
Human activity now contributes to both global and local-scale climate change. It reinforces global warming through the release of heat-trapping gases such as carbon dioxide, water vapor, and methane into the atmosphere. These gases produce the greenhouse effect by reradiating back to earth energy that might otherwise escape into space. In addition to this global change, cities experience localized warming known as the "urban heat island effect." This phenomenon of increased air and surface temperatures in urban areas stems from loss of vegetation cover, expansion of surface area covered by mineral-based construction materials (asphalt, cement, and roofing tile), and waste heat emissions from industry, transportation, and air conditioning systems. While the urban heat island effect is not a direct consequence of the greenhouse effect, the localized warming drives up energy consumption during the summer months, resulting in further greenhouse gas emissions.
The specific impacts of global climate may be different from region to region. Here in the Great Lakes Region, maximum temperatures may increase, with the frequency of hot days and heat waves rising. These higher temperatures will drive up evaporation rates and decrease water levels in the Great Lakes. Locally, cities could see increased levels of heat exhaustion and heat-related deaths. Urban residents might also become more susceptible to health problems associated with combustion-related air pollution. A hotter climate generates greater energy demand for cooling purposes, which in turn requires more combustion of fossil fuels to generate electricity. Higher temperatures can also take a greater toll on urban infrastructure and services.
Municipal level strategies can help combat global and local climate change to reduce or prevent the harmful effects of this change. Planning strategies in particular can be effective in addressing three issues: surface albedo, evapotranspiration, and energy conservation.
Albedo is the ratio of the amount of light reflected by certain material to the amount of light hitting the material, and it is thus a measure of surface reflectivity. Surfaces that have a low albedo experience more heating from sunlight than those with a high albedo. Increasing the albedo of city surfaces, therefore, will decrease the amount of heat they retain, helping to mitigate the urban heat island effect. Roofs and pavements are two major contributors to surface warming in cities. Retrofitting standard roofs with reflective roofing material can result not only in cooler temperatures but also in a longer service life of those roofs. Rather than standard black asphalt paving for roads, driveways, and parking lots, a city can encourage the use of light-colored aggregates to be used in the asphalt or alternatives to asphalt such as granite slab, colored concrete, or terracotta bricks. Studies have shown that the aggressive albedo-enhancing strategies can result in a regional climate impact of 2¡ to 10¡ F. It has also been shown that in warmer climates, albedo enhancement can produce energy savings in buildings of up to 70 percent.
Evapotranspiration, a key component of the hydrologic cycle, is the combined process of evaporation and transpiration. It involves the uptake of water in soil by plants, the transport of water through the plant, and its eventual evaporation from leaves and other surfaces. Evapotranspiration is an important natural cooling process because water droplets absorb surface-level heat and, through evaporation, convey this energy away from the earth's surface. Accommodating the process of evapotranspiration in dense urban areas can be a useful approach to mitigating the urban heat island effect. Protection of peripheral green space, preserving and expanding natural areas and parks, and increasing tree canopy on city streets are all effective ways of encouraging evapotranspiration through land use planning.
Street trees and green space not only provide cooling through evapotranspiration, they can also reduce energy consumption by lowering demand for air conditioning. As discussed above, higher albedo roofing can produce energy savings in buildings. In fact, opportunities for energy conservation can be found in many places, including the built environment and transportation systems. Reducing the number of vehicle- miles traveled (VMT) in the city can go far in combating climate change; in Madison, an estimated 17 percent of greenhouse gas emissions is attributed to transportation. Numerous methods to decrease VMT include the development of new bicycle and pedestrian paths and expansion of transit service. Transit-oriented development (TOD), by promoting mixed-use and higher density development, is now widely recognized as an important strategy for making cities more energy efficient in the long term.
Air quality is a key element of a healthy, livable city environment, yet one that is easily taken for granted. Madison is fortunate to be free of serious, local air quality problems (although increasing ground level ozone concentrations could become a concern in the future). Climate change, on the other hand, has not been recognized as a major environmental problem until recently, and therefore, has not traditionally been a focus of cities' land use plans. Our recommendations for achieving other ecological goals--reducing stormwater runoff and providing more space for natural areas and green space--are largely consistent with the goal of reducing climate change, since these problems are interconnected. Still, thinking about climate change and addressing it directly can contribute new ideas and motivation to a land use plan for sustainability.