It may seem strange to celebrate, but let’s hear it for oil-price shocks. Admittedly, there is little reason to rejoice in a disruption to the world’s energy system. The price of oil is linked to the price of all sorts of essentials, including food, so this crisis will be painful for billions of people. But the high price is the consequence of the energy shock, not the cause, and it is a healthy consequence too. Sharp price increases are like painful nerve impulses: we might wish them away, but they send an essential signal to remove ourselves from harm.

What sort of signal? First, and most obvious, the signal to consumers to cut back. Anything with oil in the supply chain — from petrol to plastic to fertilised crops to package holidays — will become more expensive. The signal is to reduce when you can, because carrying on as usual will cost money. Maybe holiday nearer home this year; maybe find someone to share car journeys with. Maybe pull on a cardigan and turn down the central heating.

Or maybe none of these things. Unlike ration books or speeches by Jimmy Carter, price signals don’t tell anyone what to do; they change the incentives and we are all free to act, or not, depending on our own circumstances and preferences.