Most city dwellers are familiar with the concept of the urban heat island. The concrete that covers a city, along with the dark asphalt on the roads, absorbs the sun’s heat and reflects it back into the streets. On a sunny day, a city can be several degrees warmer than the surrounding countryside. The extra warmth persists after sunset, when ambient daytime heat is still being reflected. As the climate in general gets warmer, those few extra degrees can pose potentially fatal health risks. Aware of the danger, cities have been experimenting with a variety of techniques to cool things down. One New York City councilman recently proposed coating the streets with a reflective material designed to deceive spy satellites.

“Cool materials” are especially promising, and there is evidence that they work. A multi-year study in Athens, Greece, by A. Synnefa, A. Dandou, M. Santamouris, M. Tombrou, and N. Soulakellis modeled the impact of simply using lighter-colored building materials. They discovered that the heat island could be reduced by two degrees celsius. Their study proved that light materials can increase the reflectivity of the city, or albedo, so less heat is stored. Furthermore, as the ambient temperature lowers, less energy is used for central air and other cooling measures, increasing air quality and reducing the use of heat-producing machinery. The study only considered the impact of lightening the city’s rooftops; lightening other surfaces such as walls or roads would presumably be even more effective.

Of course, not every source of urban heat can be mitigated through building materials. In the Athens study, one of the biggest sources of urban heat was traffic. According to Sachiho A. Adachi et al., creating more compact urban centers with accessible public transportation should lead to reduced urban heat islands. Not only would there be less traffic, but compact living quarters would require less energy to cool than large suburban homes. Unfortunately, while compact cities have lower per capita emissions, simply having so many people in such close quarters immediately increases the heat island effect compared to suburban design. Accordingly, Adachi et al. recommend planning future development with an eye toward mitigating heat islands by setting aside space for trees and green spaces in compact cities.

Of course, implementing these strategies is easier said then done. To truly make heat island mitigation a reality, urban planning scholar Jason Corburn suggests re-thinking our entire approach to climate change science. Corburn argues that preparing for climate change at a local scale, rather than globally, is more likely to result in immediate action. Climate scientists can work with builders and urban planners at the local level in a way that’s basically impossible at the global level.



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American Meteorological Society
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