Cities have always been great engines of pollution – sinks of bad air and poisoned water – and the environmental harm they do generally extends well beyond their borders. Large numbers of people gathering together with the ambition of improving their living standards have razed surr­ounding forests, ruined seas and rivers and exhausted local farmland. Cities and their inhabitants are a major and growing source of greenhouse gases.

It doesn’t have to be this way. Ecological science has found that cities often harbour a surprising variety of wildlife, especially when contrasted to the arid, silent, denatured rural landscapes produced by modern farming techniques. Inhabitants of cities tend to use less energy than country dwellers, not least because urban buildings are generally better insulated and travel is less reliant on cars. And good policies can do much to help cities become sustainable – and even better than sustainable.

This edition focuses on London’s natural environment and its contribution to global efforts to combat climate change. London is widely perceived as a green city.