But you have to admit that, so far, there is no indication in the commodity markets of overall pressure on the world's resources.There are, however, two problems with that. The first is that commodity prices do not reflect damage to the environment. It is a period of extraordinary growth in world output and population, in depression and inflation, and of course interspersed by two world wars. Yet the long- term trend of real commodity prices has been down.

The graph on the right shows what has happened to real commodity prices over the past century. You can make the case sketched above that this particular run in wheat and oil is a one-off, and I think it is. But it is perfectly possible to believe that, yet still worry: worry there will be more and more similar spikes in commodity prices in the next couple of decades, and that these spikes will become sharper and more damaging.Anyone faced with this concern has to acknowledge that so far there has been no general commodity crisis. But as a new paper by UBS points out, some research at the New York Federal Reserve Bank last year suggests that commodity prices are now much less likely to trigger inflation than they used to, partly because commodities are less important in the western developed economies, partly because they have lost their reputation as an inflation hedge and partly because any rise can be offset by monetary policy. (They might have added that any rise would be choked off by the bond markets too, but it is asking a lot of central bankers to acknowledge that one of the world's main bulwarks against inflation is the bond market, not themselves!)So, fingers crossed, a jump like this in a couple of commodity prices is not an inflationary danger signal.The other concern, about the longer-term pressure on world resources, is on the other hand a very real one.

The second is that there has been no significant increase in other commodity prices. True, there was a surge in metal prices last year, but this has largely unwound. Gold, traditionally an early-warning indicator of inflation, is flat. Even food prices, as measured by the Economist commodity index, are a shade lower than they were in April last year.The experience of the past 40 years has trained us to be extremely sensitive to any potential early-warning signal of rising inflation.