


These changes have allowed more marginal homebuyers to clamber on to the housing ladder. But if interest rates rise as economists expect, many of those buyers will find it difficult to keep up their payments. And with many putting so little down—a fifth of American mortgages in 2003 were for more than 90% of the purchase price—any fall in house prices could leave a lot of them with negative equity, forcing them to default.

The increasing riskiness of mortgages is not the only sign that America is experiencing a housing bubble. The ratio of house prices to rents is well above its historical average, as is the ratio of prices to median incomes. And people seem increasingly to be basing their house-buying decisions on the notion that the large capital returns of the past few years—house prices in America are up by 65% since 1997—will continue indefinitely. As with a stockmarket bubble, if this confidence is shaken, prices could begin to fall rapidly.

Not merely an American folly

America is not the only country that has been experiencing a big run-up in prices. Its market isn't even the most frothy. Between 1997 and 2004, house prices more than doubled in Australia, Britain and Spain, and nearly tripled in South Africa and Ireland (see table). And while America's ratio of house prices to rents is 32% higher than its average value from 1975 to 2000, by that metric houses are even more overvalued elsewhere: by at least 60% in Britain, Australia and Spain, and by 46% in France.

Inflated house prices may have been a key factor in helping these countries weather the global slowdown in 2001. When household wealth is increasing, particularly housing wealth, consumers respond by saving less and spending more; economists call this the “wealth effect”. Explosive house-price growth thus encouraged consumers to keep their spending steady despite external shocks. It is probably not a coincidence that Germany, one of the few European countries where house prices have not been rising, fared far worse during the slowdown than its neighbours or America.

Unfortunately, when housing markets decline, the same process works in reverse: consumers have to cut back their spending and save more to compensate for lost home equity. Lower consumer demand generally means a slowdown in GDP. The sharper the correction, the greater the effect on the overall economy.

But how far will the market really fall? Prices have already begun to soften in places like London and New York, particularly at the high end, but it is possible that in most places price increases could simply moderate, giving incomes and rents time to catch up. An IMF study on asset bubbles estimates that 40% of housing booms are followed by housing busts, which last for an average of four years and see an average decline of roughly 30% in home values. But given how many homebuyers in booming markets seem to be basing their purchasing decisions on expectations of outsized returns—a recent survey of buyers in Los Angeles indicated that they expected their homes to increase in value by a whopping 22% a year over the next decade—nasty downturns in at least some markets seem likely.

A fall in American house prices could be bad news not just for American homeowners, but for the rest of the world. Robust American demand has supported export-driven growth in many economies, particularly emerging markets and Asia. If American consumers have to raise their abysmal savings rate, exporting nations will feel the pinch. And given the parlous state of the Japanese and European economies, it seems unlikely that they will be able to pick up the slack—particularly if many European countries are coping with the fallout from their own housing bubbles.

Most worryingly, a collapse in American export demand could trigger a vicious cycle. In order to keep their currencies low against the dollar, and thus boost exports to America, Asian central banks have been accumulating dollar reserves, which they have poured into Treasury bonds. This has increased the supply of capital in America, and thus been at least partly responsible for the borrowing binge that fuelled the housing boom. If house prices fall, and suddenly poorer Americans have to cut back on their purchases, this will shrink the supply of cheap credit from Asian central banks, pushing up interest rates and causing house prices to fall even further. Those who thought that housing was a haven may be in for a nasty surprise.