The world’s growing number of mega-cities could cause climate change. Atlanta (US), for example, of which the growth has destroyed 55 acres of trees a day for the last twenty years, has become a ‘heat island’, with its own weather. On five out of nine days during Summer 1996 it triggered its own local thunderstorms. The general increase in temperatures means that more air conditioning is used, increasing the production of greenhouse gases. NASA scientist, Dr. Dale Quattrochi, believes that these ‘heat islands’ can be cooled by promoting energy efficiency, tree planting, and installing reflective materials on roofs to stop buildings heating up so much in the summer.

Although the area’s higher than average temperatures have lengthened the growing season, satellite studies have detected reduced food-growing capacity by 20 days a year around Atlanta. NASA’s Dr. Marc Imhoff estimates that 3% of the US and Europe now counts as ‘urban sprawl’, which could have a huge impact as cities tend to site on the most productive land. He comments: “If the capacity of the landscape to carry out photosynthesis is substantially reduced, the ability of the planet to support human life must also be diminished”.