Don Pittis has reported on business for Radio Hong Kong, the BBC and the CBC.

Picture Barack Obama and Stephen Harper in a room with other world leaders, arguing over the strength of their respective currencies.

"My currency is crummier than yours," says Obama.

"Are you kidding?" says Russia, "The ruble is much worse."

"The ruble?" says Brazil, "Are you crazy? It's the Brazilian real that is really terrible. It should be much lower."

"Can you believe it? Ours is called a 'loonie,'" interrupts Harper. "Who would want to buy a currency called a loonie?"

It sounds like a bizarre joke, but that is exactly what world leaders - or their central bank governors - are doing. It is a race for the bottom, and they all want to have the worst currency.

Here at home we call it "talking down the dollar," and our own Mark Carney, governor of the Bank of Canada, is a prize-winner. With the Canadian dollar creeping toward parity with the U.S. dollar in late October, Mark Carney stepped up to the mic. His warning about the implications for the economy was severe.

It worked.

After the governor's remarks, the Canadian dollar plunged to 92 U.S. cents and fractions thereof (although it has been creeping up since).

It is strange for people who think of the money they spend as something real and hard, but the value of that cash you carry in your pockets or hoard in your bank accounts is a very flighty thing indeed. Every day, an army of paid speculators at banks all over the world do nothing but buy and sell money. The polite term is "currency trader," but paid speculator is more accurate.

The job of this mob is to guess which currency is going to rise, and buy it before it rises. But in the weird world of markets, buying something because you think it is going to rise actually makes it rise. Selling it makes the price go down.

All the others want it, too

So if Mark Carney is convincing enough when he says the Canadian dollar is overvalued and that a high dollar will knock the stuffing out of the Canadian economy, driving the dollar down, the currency traders will listen and say, "Wow, that that was tough. That is going to drive the Canadian dollar lower." And so the currency traders will rush to sell Canadian dollars before they fall, driving the Canadian dollar down.

Nice trick, Mark.

But here is the problem. In the current climate, all the other countries want a lower currency too. It is obvious to some, but there's no harm in quick explanation.

A lot of economists insist that having a low and falling currency is good for a country's economic health - at least in the short term. That's because, if most things inside your country - from a day's work to a dozen eggs - are priced in your own currency, having a lower currency makes your products cheaper in countries with higher currencies.

The classic example is China. It has done more than talk, however. The country actually intervenes in world currency markets in a big way, going out and buying dollars and euros, and selling its own currency, called the renminbi or yuan. By keeping its currency cheap, the price of China's goods is even more affordable in richer countries.

A lot of governments do that. It is one kind of protectionism. If you have the economic clout, it is stabilizing in unstable times. I remember during my years as an economics reporter in Hong Kong, through thick and thin, the HK dollar traded at 7.8 to the U.S. dollar. That's unnatural. China uses the same system.

Same argument used in Canada

This week, the Wall Street Journal reported on its front page that countries such as Thailand, Korea and Russia have been buying U.S. dollars hand-over-fist to keep the dollar up and their currencies down. They are terrified that their goods will become so expensive no one in other countries will want to buy them. They also fear their citizens will spend all their money on cheap foreign imports, further disrupting their struggling domestic economies.

It was the same argument used by those who believe the Bank of Canada should play that game too. CIBC chief economist Avery Shenfeld was one who advised Mark Carney to move beyond talking and intervene, selling loonies to drive the Canadian dollar down.

But wait, guys, wait! We can't all have a falling currency. It just doesn't work. If one currency falls, other currencies have to go up.

Just before the latest Asia Pacific Economic Co-operation (APEC) summit, China's central bank hinted it would gradually let the renminbi rise. But no one believes their powerful currency trading body is going to permit a sharp and sudden increase.

The U.S. has little interest in having its dollar rise. As well as stimulating exports, a falling dollar reduces the value of the country's huge debt.

Australia and Norway have decided a strong currency is better than runaway inflation, biting the bullet and raising interest rates. The world's central banks, however, can't all hold Australian dollars and Norwegian krone.

Everyone knows the competition for the bottom is no solution. There is some danger it could lead to chaos. It has certainly contributed to the rise in the price of gold. There is also a danger it could lead to a trade war.

I think everyone should go to their browser and search the term "Bretton Woods." We need a new one of those agreements.