ABSTRACT
That cities alter the climate experienced by inhabitants, often creating uncomfortable and/or unhealthy conditions is indisputable. As early as 1818, Luke Howard wrote on London’s impact on air temperature, concluding that the Mean Temperature of the Climate, ‘is strictly about 48.50°Fahr.: but in the denser parts of the metropolis, the heat is raised, by the effect of the population and fires, to 50.50°; and it must be proportionately affected in the suburban parts.’1 This is the first account of what is known as the urban heat island, a phenomenon that has been detected in innumerable subsequent studies. Urban areas also have effects on wind, humidity, precipitation and, of course, air quality. While the effects are greatest in cities themselves, the impact on the overlying atmosphere extends downwind so that the urban ‘signature’ is present in places distant from cities. In fact, the urban plumes extending from the largest cities are now detectable many thousands of miles away, albeit in a diluted form. Taken together, the cities of the world, as the foci of human activity, of resource consumption and of waste generation (including greenhouse gas emissions), have a global impact. As urban living becomes the norm on the planet, managing cities is a key to achieving global sustainability.2
