IT WAS only a decade or so ago that Scotland was hit by the “Great Drain Robbery”, the disappearance of 50 manhole covers in Fife. It gave an inkling of the emergence of a new era in commodity markets, spurred by insatiable demand from China. Scrap-metal prices—and so scrap-metal thefts—soared. Africa was over-run by Chinese engineers; Australia elected a Mandarin-speaking prime minister; and emerging markets from Argentina to Zambia relished the rising values of their farmland and mines. The boom was fanned by a weak American dollar, the currency in which most stuff that comes out of the ground is priced.

The gears have now gone into reverse. A resurgent dollar has hammered commodity prices: many have recently fallen below their levels of a decade ago. That is a fate not shared by other tradeable assets: not since the late 1990s have commodity prices been so weak compared with shares (see chart 1). The American economy is strengthening, but by no means enough to encourage thieves to filch bronze bells from Chinese temples to send as scrap to the United States. The impact of its recovery is dwarfed by slowing demand in China, which still consumes about half the world’s metals such as iron, aluminium, and zinc.

The real curse for producers is over-supply in almost all raw materials. Yet they continue to act as if they are blithely unaware of it. Capital is still pouring into holes in the ground, creating a hangover that may last at least a decade. Jeff Currie of Goldman Sachs, a bank, says past cycles suggest it can take up to 15 years to work through the over-investment. “The world has just flip-flopped,” he says.

Analysts point out that not all commodities act the same way. Coal prices started falling in 2011; crude oil hung on until mid-2014; agricultural prices hinge on the weather. But a generalised whiff of fear about China’s economic prospects has re-emerged in recent weeks, partly caused by sliding stockmarkets and by the unexpected devaluation of the yuan this month. So far this year, almost all major commodities—energy, industrial metals and agriculture—have fallen in a 10-20% range, a fairly homogenous performance. What’s more, the supply glut is being fed by three common factors. Cost-cutting has led producers to think they can bear the pain of falling prices for longer. Heavy hitters, whether OPEC princes or global miners, still yearn to increase market share. And funding is still available.

The cost cuts are part of a self-reinforcing downward spiral. Outside America, cheap currencies vis-à-vis the dollar have made domestic inputs, such as manpower, appear less pricey. Ironically, cheaper energy and steel help, too. In Australia, for example, Gina Rinehart, a mining tycoon, uses low costs to justify opening a $13 billion mine in the outback that is expected to produce 55m tonnes of iron ore a year—as much as America’s annual output.

In the oil world, cost cuts have come from producers once thought likely to be wiped out by falling oil prices: shale producers. “Frackers” have slashed a third off their cost bases, and continue to pump enough black stuff to depress prices. Lower costs may give them a false sense of security about where prices will go: when crude prices temporarily ticked higher in America this spring, the number of drilling rigs rose for the first time since December. Shortly afterward prices fell again.

Among drilling titans, efforts to recoup market share from fracking upstarts can appear counterproductive. Led by Saudi Arabia, OPEC is pumping well above its 30m barrel-a-day quota, helping push crude prices to below $47 a barrel on August 19th, just about the lowest level since March 2009. But if it intended to strangle American shale producers, its plan has backfired, instead pushing frackers to become more efficient. Meanwhile global miners such as BHP Billiton and Rio Tinto have continued to increase iron-ore production, despite plunging prices. Analysts say they are trying to drive higher-cost competitors in China and elsewhere out of business.

Funding avenues have not closed down, however. Tomás Gutiérrez of Kallanish Commodities, an industry watcher, notes that in China steel output has only recently peaked. Yet rather than facing bankruptcy, many inefficient steel producers are limping along thanks to local-government support. Their surpluses are exported, adding to the pressure on global steel prices (see chart 2).