What matters more, supply or demand? This is a key question for investors as they watch metals prices bounce around. It may seem as though the risks are on the downside, as many expect a downturn in the turbo-charged cycle - a picture reinforced by Alcoa's profits warning.

Certainly, rising energy costs and weaker upstream prices make for an unpleasant squeeze. But the industry picture is not homogeneous. There is a greater threat of an impending supply surge in copper, nickel and steel than in aluminium or zinc. Then there is the complex impact of rising energy prices.