Writing in 1931, the great economist, John Maynard Keynes, thought the major problem of this generation (that of his possible grandchildren) would be how to entertain ourselves, how to live ‘wisely and agreeably and well’ because he thought ‘the economic problem’ would have been solved: we would have enough material goods.  He was talking about Europe, not the poor colonies, of course.

And we do have enough: for example, average income in the UK is  around £25,000 or nearly three times the world average, and 60 times that in Afghanistan. We have enough, but Afghanistan and  most developing countries clearly do not.  That we have enough is shown by surveys showing we – in rich countries – don’t get happier when we get richer.

More important is the environmental issue: growth eats up the world’s resources and generates carbon with seemingly inevitable and catastrophic effects on the climate.

There is a simple tautology:  world carbon use depends on the size of the global population multiplied by the amount of carbon required to generate output (or income) – depending on the available technology – multiplied by income per head.  We are already at the edge of the precipice in terms of the safe amount of carbon in the atmosphere. To save ourselves and secure and sustain a planet which is livable in we have to work on all three variables in the tautology: there are limits to changes in population growth over the medium term, although the rate of increase of world population is decelerating; and we are making some progress in developing and adopting new carbon-saving techniques, but not nearly enough to ensure a sustainable planet. That leaves growth in output. World growth has to slow down.  Yet clearly this slowdown should not come from poor countries that need growth to reach tolerable living standards for all. Given that the world has a limited amount of resources, we must share them fairly across the global population.