After years in which $100 oil was the norm, the price of Brent crude is now around a third of that. Assume for a moment that Russia and Saudi Arabia fail in their efforts to get the price back up. Will $30 oil change the world? The answer is yes, of course. Everything is connected to everything else in economics, and that is particularly true when it comes to oil. For all the talk of the weightless economy, we’re not quite so post-industrial as to be able to ignore the cost of energy. Because oil is versatile and easy to transport, it remains the lubricant for the world’s energy system.

The rule of thumb has always been that while low oil prices are bad for the planet, they’re good for the economy. Last year a report from PwC estimated that a permanent fall in the price of oil by $50 would boost the size of the UK economy by about 1 per cent over five years, since the benefits — to most sectors but particularly to heavy industry, agriculture and air travel — would outweigh the costs to the oil production industry itself.

That represents the conventional wisdom, as well as historical experience. Oil was cheap throughout America’s halcyon years of the 1950s and 1960s; the oil shocks of the 1970s came alongside serious economic pain. The boom of the 1990s was usually credited to the world wide web but oil prices were very low and they soared to record levels in the run-up to the great recession. We can debate how important the oil price fluctuations were but the link between good times and cheap oil is not a coincidence.