Behind the crash - the commodities bubble

FIRST was the dotcom bubble, then the housing bubble. Now comes the commodities bubble. We don't fully understand the stock market's current turmoil, but we do know it's driven at least in part by a bubble of raw material prices. Their collapse weighs on world stock markets through fears of slower economic growth and large financial losses.

All bubbles share similar characteristics. There's a strong, enthusiastic demand for some object (whether stocks, homes, oil or tulips). High demand pushes up prices, which inspires more demand. Prices ultimately reach unsustainable levels so that when spending slows, the bubble implodes. Commodities have now traced this familiar path.

As The Economist reminds, raw material prices respond to different influences. Weather affects crops; technology (aka "fracking") affects oil recovery. Still, despite these variations, prices of many commodities - not just oil - have followed roughly similar trajectories in recent years. They have dropped steeply, according to figures from the International Monetary Fund.