The meteoric growth of megacities - there are now 20 in total (see Map) -
has brought with it huge environmental and social problems. Cities occupy
just 2 per cent of the land surface of the Earth but consume three-quarters
of the resources that are used up each year, expelling the half-digested
remains in clouds of greenhouse gases, billions of tonnes of solid waste
and rivers of toxic effluent. Their inhabitants are making ruinous demands
on soils and water supplies for food, and on forests for timber and paper.
For example, London needs 125 times its own area to provide the
resources it consumes (see "London's annual metabolism"), and if the new
megacities in the developing world are allowed to grow in the same way
that cities did in the west, their environmental impact will be catastrophic.