Urban heat

In life, as in boxing, the combined effects of a one-two punch are often more devastating than either blow alone. Imagine, then, the devastation from a triple whammy that city dwellers might suffer this century as three unfavorable trends converge to afflict an already warming world.

First, there’s temperature. According to the Intergovernmental Panel on Climate Change, Earth’s average global temperature has risen about 0.74 degrees Celsius in the past century (SN: 2/10/07, p. 83), an increase almost certainly linked to the rising concentrations of carbon dioxide and other heat-trapping greenhouse gases that human activities have released into Earth’s atmosphere. IPCC scientists suggest this warming trend will continue, and indeed accelerate: In the next 20 years, average global temperature will rise another 0.4 degrees C or so, they estimate.

Then, there’s population growth. Now home to more than 6.6 billion people, Earth will see its population increase by about 25 percent, or 1.65 billion, by the year 2030 (SN: 10/13/07, p. 235). Even with substantial increases in energy efficiency, this dramatically larger population will likely trigger a rise in total energy consumption, further boosting emissions of greenhouse gases.

Third, there’s urbanization. Much of the world’s population growth in coming decades will occur within cities, where residents are exposed to warmer-than-average conditions due to the “urban heat island” effect. People living in large, well-developed areas typically experience temperatures several degrees warmer than do residents of the rural areas nearby.

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