SCIENTIFIC AMERICAN September, 2011, p. 66 How Green Is My City David Biello SAVING ENERGY A KEY PRIORITY for cities adapting to a world transformed by global warming is increasing energy efficiency and reducing greenhouse gas emissions to stave off even more catastrophic climate change. "As the primary centers of economic activity globally, cities are significant consumers of energy and emit nearly three quarters of the world's carbon emissions." New York City mayor Michael Bloomberg told a recent conclave of mayors at a meeting of C40, a planning group for 59 major cities engaged in efforts to combat climate change.
A major focus of C40 is equipping old buildings with energy-efficient features. In the U.S. the average building - whether skyscraper, house or church - was built in the 1970s. Replacing their black-tar roofs with white roofs that reflect sunlight to keep buildings cooler in the summer or installing solar thermal hot-water heaters, for example, can translate into major energy savings: healing hot water accounts for 17 percent of the energy used by buildings in the U.S. according to the Department of Energy. C40 has thus partnered with the World Bank to ensure funding for such retrofitting projects, among other climate action plans for cities.
Existing cities might also benefit from installing transportation .systems originally conceived of for planned eco-cities. Tailpipes in the U.S. spew 1.7 billion metric tons of carbon dioxide a year, along with a host of noxious fumes. In contrast, the electric car system proposed for Fujisawa City in Japan would produce no tailpipe emissions. Electric car systems require infrastructure, though, particularly to ensure that people can charge the cars. In Tokyo a company called Better Place has had success in testing a system of electric vehicles powered by batteries that, when depleted, can be quickly and easily swapped out for recharged ones at battery switch stations. In the near term, simple changes, such as converting buses to run on compressed natural gas rather than diesel, can both clean up the air and improve efficiency. Already such efforts have helped Denver save more than 24 million gallons of gasoline between 2005 and 2009.
Cities must no not only conserve energy and limit emissions but also diversify their energy supply. New York City recently mandated a switch from heavy heating oils to lighter, cleaner-burning fuels, such as natural gas, in a bid to improve air quality. Yet even such seemingly straightforward decisions can demand difficult trade-offs: David Bragdon, director of Bloomberg's Office of Long-Term Planning and Sustainability notes that New York is struggling to reconcile this increase in the use of natural gas with its desire to prevent hydraulic fracturing, or fracking - a process for producing natural gas from deep rock -in its watershed because fracking can contaminate water supplies.
WATER AND WASTE ENSURING THAT sustainable supplies of freshwater continue flowing to growing urban populations is another daunting task facing the international community. Large swathes of the world are already pushing the limits of water availability. Cities throughout the western U.S., from Denver to Phoenix, for instance, are using up more than the normal flow of the Colorado River. And the International Food Policy Research Institute estimates that about half of global grain production will be at risk because of limited water by 2050. Tо help cities conserve, С40 has developed a list of best practices based on case studies of strategies employed by cities ranging from Austin, Tex. to Tokyo. Austin, which launched its water-efficiency program in 1983 in response to a housing and commercial boom, offers а number of incentives to curb water use, including rebates for installing rainwater-harvesting .systems and water-conserving toilets. Tokyo, meanwhile, is the world leader in detecting and controlling leaks in its waterworks. It has earned this distinction by systematically checking, repairing and replacing pipes and by fixing leaks on the same day that they are identified.