Most of the world's leading economies agreed at the Kyoto Climate Conference to limit emissions of carbon dioxide. The move opened the way for any countries that did not use all their agreed "quota" of pollution to sell the spare capacity to those which did.

As a result, some businesses in richer, highly-industrialised countries like the US are offering huge sums of money to buy the pollution permits of poorer, less-industrialised nations.

At the Chicago Board of Trade, the already charged atmosphere on the world's largest trading floor has a new sense of urgency.

A market in hot air - the right to buy and sell carbon dioxide pollution - which officials expect to be worth between $30bn and $100bn annually is slowly taking shape.

A valuable commodity

Richard Sandor: Air could be worth billions

Richard Sandor of The Chicago Board of Trade said: "What is more plentiful and the most valuable commodity we have?

"It is not corn, it is not wheat, it is not fish. It is the air we breathe. It is simply the most important commodity."

Successful economies like the USA's generate increasing amounts of carbon dioxide pollution, which comes mainly from power stations and cars. Any agreement to cut such emissions is seen as a threat to economic growth.

Worldwide, carbon dioxide pollution stands at 20bn tonnes per year. A 5% cut on 1990 levels was agreed at Kyoto.

The USA, which in 1990 produced 4.4bn tonnes, increased pollution in 1995 to 5.2bn tonnes and the figure continues to rise.

Meanwhile Russia emitted 2.4bn tonnes in 1990 with a fall by 1995 to 1.6bn tonnes.

Cashing in

Pollution is a global problem, so why not a global market?

Economic stagnation in the former Soviet Union has allowed Russia and other Eastern bloc countries to meet their Kyoto pollution targets with hundreds of millions of tonnes of carbon dioxide to spare.

The USA, with continued growth, is keen to buy it.

The Chicago Board of Trade has a head start. It is already trading pollution permits in sulphur dioxide, the power station pollutant that causes acid rain.

US power generators must now buy the right to pollute with sulphur and there are not enough permits to go around.

As a result, US industry has chosen to clean up its emissions.

David Kee, of the US Environmental Agency, said: "By using the market we achieve the goal of reducing pollution but we do it in the most cost-effective way."

At Kyoto, the world's leaders agreed a similar "capped trade" in carbon permits was inevitable but could not agree how it would work or when it could be introduced.

However, the US government is threatening to go it alone within two years.

'Anything can be sold'

Melinda Kimble, of the US Department of State said: "We can sell anything in our markets.

"The president of the United States has said that domestically we will have a cap and trade system, which means we would operate exactly as we do on sulphur dioxide."

A US market would be too big for the rest of the world to ignore, although the traders have yet to win support from Congress.

While the politicians continue to talk, the first tentative deals trading in carbon dioxide have already been struck in Chicago.