"We often think of future wars in apocalyptic terms - nuclear weapons slamming into city centres and such like. But our modern cities are so brittle that far less spectacular attacks could bring them to ruination. In this they are very different from the London that withstood the blitz. Today's cities rely upon highly sophisticated and easily disrupted technology to deliver water, goods, fuel and power to populations of ten million or more, in a just-in-time manner. Imagine a city like New York or London without a functioning electricity grid. People living in high-rise buildings would probably be trapped. With water pumps not working, both the removal of sewage and the supply of clean water would immediately become problems. Communications would be cut, traffic flows and rail services paralysed, and with no refrigeration food would quickly spoil. At night the streets would be plunged into darkness. Local generators might keep hospitals and other vital infrastructure going for a while, but within weeks the city would have to be abandoned. Where would the millions go? If the disruption were sufficiently prolonged it's fair to question whether the city would ever be reoccupied."
- Tim Flannery, Here on Earth: An argument for hope
(Melbourne: Text Publishing, 2010), 230.
Flannery's illustration itself illustrates a lack of imagination in contemplating a more difficult future. Very large cities already face a range of problems in which they struggle under the weight of their own complexity and this is highly likely to increase in the bumpy decades ahead. No city prior to the widespread exploitation of fossil fuels supported a population much above a million. The fate of megacities in a world of increasingly expensive energy is unclear. However, the kind of scenario that Flannery paints is a lazy shorthand for the incredibly complex series of questions faced by political authorities, communities and individuals as our largest infrastructure investments - our cities - become increasingly problematic. The staggering sunk cost that cities represent means that decline or abandonment will likely be piecemeal rather than sudden.
Sunk costs of existing infrastructure also provide a very high incentive to make things work. For instance, in a future where just-in-time agribusiness-to-supermarket supply chains become less reliable and so threaten food security, I doubt it would take long for suburban lawns to be converted to gardens.
Even great catastrophes such as that experienced by New Orleans in 2005 do not suddenly wipe a city clear of inhabitants. It may well be the case that the population never recovers to pre-Katrina levels as the cost of building levees will rise faster than sea levels, making more and more of the city uninhabitable. And the precise conditions faced by each city are unique. Not every coastal city is as threatened as New Orleans by rising seas.
Whether it is wise to live in a very large city is a complex question. Yet such judgements are not aided by visions of the future based on simplistic assumptions or apocalyptic nightmares.