Urban growth is changing the condition of humanity and the face of the earth. Half the world's people now live in cities, with most of the other half depending on them for their economic survival. Mega-cities of ten million or more people are the largest, most complex structures ever made. They are the Central hubs of modern economies and their transport systems. The resource use and waste discharge of contemporary cities dominate the human presence on earth. Fossil fuel technology powers modern urbanisation, but in the coming decades many cities will become vulnerable to the rising tides of...