Sweltering Cities

US urban areas are heating up faster than rest of world

Many major U.S. cities are warming up about twice as fast as the overall planet, and current climate action plans are not enough to ward off extreme heat, researchers conclude in Landscape and Urban Planning.

Most talk of climate change is about effects on the entire planet, rather than on individual cities or regions. But in addition to global warming due to greenhouse gas emissions, cities experience what’s known as the “urban heat island effect”: the tendency for surfaces such as asphalt to capture and emit heat. The team wondered if the heat island effect was growing more intense and if cities were warming faster as a result.

The study authors examined temperature data from weather stations in 50 U.S. metropolitan areas, as well as data from nearby rural stations. The rural areas heated up by 0.16 degrees Celsius per decade between 1961 and 2010, comparable to the overall planet’s rate of warming. But the temperature in cities rose by 0.24 degrees Celsius per decade, the team reports. In about three-quarters of the cities, where the heat island effect appeared to be growing due to more development of rural land, the average rate of warming was 0.31 degrees Celsius per decade.

Next, the team studied 50 cities’ climate action plans, programs developed by local and state agencies to stave off and adapt to climate change. The plans included emission-reducing actions such as using more energy-efficient lighting, encouraging walking and biking, and improving the fuel efficiency of municipal vehicles. But only about 25 percent of cities were planning strategies that would combat the heat island effect, such as planting vegetation or making roads and roofs more reflective. These plans “may fail to adequately protect human health and welfare from rapidly rising temperatures,” the team concludes, noting that “a reduction of the urban heat island effect would more effectively slow ongoing warming trends in cities than emissions reductions alone.” — Roberta Kwok

Source: Stone, B., J. Vargo, and D. Habeeb. 2012. Managing climate change in cities: Will climate action plans work? Landscape and Urban Planning doi: 10.1016/j.landurbplan.2012.05.014.

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