IT’S 2020, and we are a decade into a huge experiment in which we are trying to convert our country to a sustainable or “steady-state” economy. We have two guiding principles: we don’t use natural resources faster than they can be replenished by the planet, and we don’t deposit wastes faster than they can be absorbed.

In our society, scientists set the rules. They work out what levels of consumption and emission are sustainable – and if they’re not sure they work out a cautious estimate. Then it’s up to the economists to work out how to achieve those limits, …