Dear Ben, this is how you spot a bubble

A year into the greatest downturn since the Great Depression of the 1930s, there is still no real consensus on what caused the sudden collapse in the financial system. Greedy bankers? Lax regulations? Global imbalances? You can take your pick from an intellectual buffet table laden down with different theories.

But one thing seems to unite just about every shade of opinion. In the years running up to the credit crunch, the US Federal Reserve, along with other central banks, ran far too loose a monetary policy. They kept interest rates too low for too long, inflating asset bubbles in everything from houses to credit derivatives to fine art. Everyone agrees on this, except probably the most important figure in global finance the Fed chairman Ben Bernanke.

Reading Bernanke's remarks to an audience in New York earlier this month, it was impossible not to be transported straight back to the era of his predecessor, Alan Greenspan. "It is inherently extraordinarily difficult to know whether an asset's price is in line with its fundamental value," he said. "It's not obvious to me in any case that there's any large misalignments currently in the US financial system." The best approach, he argued, was to regulate the financial players in the markets properly and "make sure the system is resilient in case an asset-price bubble bursts in the future."

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It was very reminiscent of Greenspan's argument all through the dotcom era, and the property and credit bubble that followed it, that it was not the job of central bankers to go around spotting bubbles. Nor was it their job to prick them. All they should try and do was clear up the mess afterwards. With varying shades of enthusiasm, that argument was followed by central bankers the world over. Our own Mervyn King, the Governor of the Bank of England, fretted publicly about the level of house prices in the run up to the crash. But he never actually raised interest rates to stop prices rising further. Was property a bubble or not? Too hard to tell, decided the Governor.

In fairness, there is an intellectual case to be made for that argument. In a free market, it's hard to tell the difference between a bubble and a shift in prices. So, for example, if the price of oil doubles, that might be a bubble. Then again, it might be a rational response to a shift in supply and demand. If the world really is running out of oil, it makes sense for the price to soar: in response, we'll find ways of using less of the stuff, and the exploration companies will invest more money finding new sources of supply. It is not a bubble it's just prices changing. In a free market, that happens all the time. Try and stop it, and the market won't work anymore.

On top of that, it isn't obvious that we're in a bubble right now. Bernanke referred to the 63% rise in US stocks since the depths of the crisis last March. That was just getting back to normal prices, he argued. And he has a point. At a cyclically adjusted p/e ratio of 20, US stocks aren't cheap but they are well below the p/e ratio of 44 they hit at the peak of the dotcom boom. That said, there are clear signals that what the financial markets are experiencing right now is indeed a bubble and one caused by record low interest rates, and central banks printing money like crazy.

It might not be evident in stock prices yet. But there are lots of signs elsewhere. Commodity prices are soaring, even as industrial production remains subdued. Take aluminium, for example. Its price is up by 33% so far this year, even though there is enough of the stuff sitting in warehouses to build 69,000 Boeing jumbo jets. How can you explain that, except that there is too much speculative money flowing into the system?

Bankers are paying themselves huge bonuses. There isn't much sign of a pick-up in basic lending, or in the profitability of past loans, but they are minting a fortune from their trading operations. Even hedge-fund launches are picking up once more. Again, sure signs of a frothy financial system. The carry trade borrowing in a cheap currency and investing in an expensive one is booming just as it did for much of the noughties. Last time round, firms borrowed in yen, and invested in the US or UK. Now they borrow in pounds or dollars and invest in emerging markets. The result is the same asset prices soaring on the back of borrowed money. Even luxury, trophy assets are fetching record prices another sure sign there is a lot of hot cash swilling around the system.

The real issue is not whether we are in a bubble right now. There are arguments on either side of that question. The point is whether central bankers in both the US and Europe are prepared to look for bubbles and try and stop them. It isn't enough to argue that central banks should just wait until a bubble has burst before they deal with it. They tried that last time around and the results were hardly encouraging.

True, spotting bubbles is tough. Deflating them is hard work. But that is no excuse for not trying. And if the world's central bankers haven't grasped that yet, there isn't much hope of avoiding another crisis a few years down the line.