Discussing cities is like talking about the knots in a net: they’re crucial, but they’re only one part of the larger story of the net and what it’s supposed to do. It makes little sense to talk about knots in isolation when it’s the net that matters.
Cities are part of the system we’ve invented to keep people alive on Earth. People tend to like cities, and have been congregating in them ever since the invention of agriculture, 10,000 or so years ago. That’s why we call it civilisation. This origin story underlines how agriculture made cities possible, by providing enough food to feed a settled crowd on a regular basis. Cities can’t work without farms, nor without watersheds that provide their water. So as central as cities are to modern civilisation, they are only one aspect of a system.
There are nearly eight billion humans alive on the planet now, and that’s a big number: more than twice as many as were alive 50 years ago. It’s an accidental experiment with enormous stakes, as it isn’t clear that the Earth’s biosphere can supply that many people’s needs – or absorb that many wastes and poisons – on a renewable and sustainable basis over the long haul. We’ll only find out by trying it.
Right now we are not succeeding. The Global Footprint Network estimates that we use up our annual supply of renewable resources by August every year, after which we are cutting into non-renewable supplies – in effect stealing from future generations. Eating the seed corn, they used to call it. At the same time we’re pumping carbon dioxide into the atmosphere at a rate that is changing the climate in dangerous ways and will certainly damage agriculture.
This situation can’t endure for long – years, perhaps, but not decades. The future is radically unknowable: it could hold anything from an age of peaceful prosperity to a horrific mass-extinction event. The sheer breadth of possibility is disorienting and even stunning. But one thing can be said for sure: what can’t happen won’t happen. Since the current situation is unsustainable, things are certain to change.