Americans paused at Thanksgiving yesterday for the traditional annual audit of their blessings. If they'd been listening at all closely to the morose lucubrations of their opinion leaders, however, it would have been pretty slim pickings.

The pundits have finally run out of bad news to report from Iraq, where, unmolested by the morbid fascination of misery-seeking reporters, the locals actually seem to be belatedly enjoying the first fruits of their liberation. So attention has turned again, as it has tended to do from time to time these past 50 years, to the inevitable collapse of the American economy.

The declining dollar is for many an ominous indication that the long period of US economic supremacy is at an end. In the past month especially, a nation that usually remains in blissful ignorance of the daily fluctuations of the foreign exchange markets has been repeatedly reminded that the dollar now buys a fraction of what it used to — down 35 per cent against the pound in the past six years and 40 per cent against that fledgeling monetary superpower, the euro.

Much has been written about the eschatological symbolism of the dollar's fall and the financial problems that have accompanied it. The apparent consensus among commentators here in America and especially in Europe is that the US has become a kind of Third World country, awash in debt and sinking fast because of a collapsing housing market and a banking system in meltdown. And all this is supposed to reflect in turn a seismic shift in the balance of global economic power away from the US and towards Mighty Europe and Emerging Asia.

Let me take a moment in this season of cheer to raise a few objections. The first and most obvious point is that there are many reasons why currencies move against each other, often in quite dramatic fashion. Seismic, epochal, geopolitical shifts are not usually the best explanation.

Rather, more prosaic facts such as differentials in countries' short-term interest rates, the rebalancing of temporary financial and economic imbalances and sudden changes in demand for and prices of commodities such as oil produced by particular countries — all of these help explain the dollar's recent decline.

US interest rates are on a downward trend, while European rates are steady and might even rise. The US still has a vast trade deficit, which is being reduced by a continuing fall in the value of the dollar. Countries such as Canada, which has seen the largest increase in its currency against the dollar, have been beneficiaries of the steep increase in the energy products they export. Another factor behind the current movements is the sensible shift by the world's central banks to a more balanced portfolio of foreign exchange reserves.

For the historically short-sighted, let's remember we have been here before. Between 1985 and 1995, the dollar declined by 43 per cent against the world's big currencies — somewhat more than it has in the past six years. That period was also marked by dire proclamations of the end of US economic power. But it turned out that in those years the foundations were laid for the strongest period of US economic growth in the past 35 years.

If you're still sceptical, ask yourself this: is it probable that the shift in the relative value of the dollar and the euro represents a bet by the world's investors that Europe — strike-torn, productivity-challenged, demographically doomed Europe — is the world's economic future, rather than the US, or, let's say, China? All right, but this is different, say the Cassandras. The US has been living on borrowing for years now. The world has finally woken up to America's addiction to debt — all that growth has been bought on the never-never and now, at last, the bill has come due.

The first thing to be said is that the level of public sector borrowing in the US is very small. The fiscal deficit, at just over 1 per cent of national income, is smaller than in most major European countries. It's true that America faces a large long-term fiscal challenge from an ageing population. But it's a smaller challenge than that faced by most of Europe, Japan or even China.

So if government borrowing isn't the problem, it must be the private sector that's neck-deep in debt, right? The general view is that Americans have irresponsibly fattened themselves up on widescreen televisions and gas-guzzling four-wheel drives, all paid for with easy credit.

If you look at a simple measure such as the savings rate — the proportion of income that is saved rather than spent — Americans do look pretty spendthrift. It is close to zero in the US, compared with 10 per cent in Europe and much higher in Asia. But focusing on this one measure distorts the full picture of America's household balance sheets. The reality is this: why save when the value of the investments you own is increasing at rapid rates? The total value of mortgage and consumer debt is indeed up by a massive $5 trillion since 2001, according to the latest figures published by the Federal Reserve.

But consider the increases in the wealth of Americans during that period. The aggregate value of houses alone is up $8 trillion. The increase in the value of stocks held either directly or through pension funds and other investment instruments is higher by another $8 trillion. That's an increase in net wealth of American households of $11 trillion in less than six years. That's about $90,000 for every household in the country. As someone once said, 11 trillion dollars here and 11 trillion dollars there and pretty soon you're talking serious money.

All right, but isn't the US going into recession, you say? Maybe, but so what? The US is overdue a recession by the standards of the business cycle in the past 60 years. It's possible the housing market and related problems will tip America into another one. Provided the people responsible get policy right, it doesn't have to be a depression.

So the dollar is falling for good, sound reasons that do not require a millenarian view of the global economy. It is yet another thing Americans should be thankful for.

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