Living with the City

With the fossil fuel consumption that accompanies them, and the resulting air pollution, noise and heat island effect, our daily urban activities have caused changes in climate and air quality that threaten the environmental sustainability of cities. Researchers have been reporting on heat-island observations at different urban centres for some thirty years. A discussion of some of the underlying phenomena is given by Barry and Chorley. ¹ They also quote values of mean minimum urban temperatures as being 5–6 K higher than those of the surrounding countryside, with differences rising to 6–8 K in large cities on calm and clear nights. The maximum difference between urban and rural temperatures has been found to correlate with population size. ² For North America, such a correlation yields an estimated urban–rural difference of 2.5 K for a town of one thousand inhabitants, rising to 12 K for a city with a population of one million. For European cities, the correlation was reported to yield smaller differences, suggesting heat island effects of lesser intensity; this has been explained as being due to lower buildings and wider street canyons compared to North America. Surely, however, the lower European energy consumption per capita must also be a factor, since energy use is the main anthropogenic contributor to the heat island, in this instance from heat exhausted from buildings and cars.