The broader lesson from booming copper prices

BLESSED ARE the cheesemakers. A revival in restaurant visits in America has fed demand for one of the more obscure financial instruments—cheese futures. The number of contracts traded on the Chicago Mercantile Exchange surged last month. It is not only cheese that has melted up. A year-long rally in broader commodity markets shows few signs of cooling. Iron-ore prices are at record highs. A boom in American housing has driven timber prices to a new peak. Corn and soyabean prices are at their highest since 2013.