Is audacity the better part of economic forecasting? In an essay entitled Economic Possibilities for Our Grandchildren, published in 1930 as share prices were tumbling all over the world, John Maynard Keynes conjectured that “mankind is solving its economic problem”. He predicted “that the standard of life in progressive countries one hundred years hence will be between four and eight times as high as it is today”.

As far as Britain is concerned, Keynes will be right. Consumption per head today is about five times higher than it was in 1930. If the next 22 years enjoy the same rate of material progress, our “standard of life” in 2030 will be roughly eight times that of our grand­parents.

But what can we say about our grand­children? Keynes’ essay was silent on one theme that we cannot avoid. As he was writing, it was not only stock markets that were falling month by month. The prices of all commodities were also sliding, driven by over-production and falling demand. Shortages of energy and basic materials did not seem possible, even looking ahead to 2030 for one’s grandchildren and great-grandchildren after a huge multiplication of output in the intervening century. Anyone proposing that “the earth is running out of resources” would have been regarded as daft.