The biggest story in the world economy is the continuing fall of the U.S. dollar, or at least it is everywhere outside of Washington, D.C., the place most responsible for its declining value. For good reason, the world is wondering if America has cast the dollar adrift.

A passel of Asian central banks—South Korea, Taiwan, the Philippines and Thailand—intervened yesterday to stop the greenback's fall against their currencies. European Central Bank President Jean-Claude Trichet also tried to buoy the buck, telling reporters that "A strong dollar is extremely important in the given circumstances." Neither effort made much difference.

Meanwhile, the London Independent created a splash this week with a thinly sourced and not very credible story that several nations were working secretly to trade oil in currencies other than the dollar. The alleged conspirators all quickly denied it, but the tizzy the story created suggests the global mood of concern about holding American currency.

The attempts at intervention are probably futile, save for the short-term scare they give to currency traders. Currency interventions are typically "sterilized," which means that while a central bank extinguishes a currency (say, Thai baht) in the foreign-exchange markets it creates more baht through domestic monetary operations. Thus there's no underlying change in the relative supply of baht versus dollars. The point of intervention is to frighten traders about the risks of speculating and getting burned. Everything else is commentary.

The value of any currency is ultimately determined by the supply and demand for that currency. And the problem for the dollar at the moment is that there is a much larger supply of dollars than there is global demand for them. The solution rests not in Manila, Bangkok or Paris, but in Washington.