As the world has urbanized rapidly since 1950, per capita carbon footprint has declined, and so has carbon intensity in economic output, defined as the amount of energy used to produce a unit of economic growth. But gross material throughputs and greenhouse gas production during this same period skyrocketed. Global natural capital – fisheries, topsoil, freshwater supply, etc. – has plummeted. This is because, as we pack into cities, we are consuming more materials as measured by absolute volume. The totality of the chopping up of mother earth into little bloody pieces has become more intense, not less.
These facts would appear to undermine one of the central tenets of green orthodoxy: that urbanization always leads to sustainability.
Three characteristics common to large-scale 21st century cities augur an unpleasant future.
The first is that, though they are already metastatically overgrown, cities seek always to grow more. There is not a city on earth that has for official policy a ceiling on population, no city that has said, We shall have only so many people. Lewis Mumford in The City in History described this as patholopolis, the city as cancer.
The second is that, from an ecological vantage, cities produce nothing of value. “In ecological terms,” writes William Rees, a population ecologist at the University of British Columbia and the originator of the ecological footprint concept, “the city is a node of pure consumption existing parasitically on an extensive resource base.” (By contrast with the modern city — to take one example of difference — the medieval city produced night-soils that fed nutrients back into the surrounding agricultural land-base; the modern city removes its feces from ecological cycling, and reduces it to “treated sewage.")