In the past year, the price of corn has risen 110 per cent while US stocks of the grain declined 15 per cent. That combination makes economic sense. Both the increase in price and the drawdown of inventories could be responses to a shortage of supply relative to demand. But Joseph Glauber at the US Department of Agriculture, has a different interpretation. He suggested on Thursday that high prices were having almost no effect on buyers: they wanted so much corn that inventories had fallen by a record amount.

This high price inelasticity of demand (the term for prices changing more dramatically than consumption) can be seen in most commodities; sharp price rises have increased producers’ and traders’ profits but not discouraged consumers. These days it seems only genuine shortages – for example of thermal coal – can actually slow down consumption.

The rule that prices are set where marginal demand meets marginal supply has not been suspended for commodities. But prices have been distorted by cheap funding, which allows many buyers to borrow, bid up the price to high levels – and not use any less. Even when supply is ample, cheaply financed inventories can absorb the slack.