The "hot air" on the agenda is Russian: the term refers to Russian pollution that isn't happening any more because the country's smokestack economy has collapsed. America, the world's biggest polluter, would like to buy it.
It sounds, at first, like a sensible deal, this strange trading of something that has not yet taken place. At Kyoto last December, the industrialised nations committed themselves to limiting their emissions of greenhouse gases, such as carbon dioxide, from motor vehicles, factories and power stations, which are now accepted as inexorably changing the world's climate. If, the reasoning goes, as a result of this we both have pollution reduction targets to meet, and you have more than met yours and have a theoretical "pollution allowance" available, why not sell it to me? Especially if I am having terrible trouble meeting mine.
Unfortunately, much of the rest of the world will be deeply unhappy at just how much "hot air" the United States wishes to purchase. Russia and its former constituent republics such as Ukraine, whose heavy industries have also gone down the pan, have an awful lot to sell. Might the US buy so much that it could meet its greenhouse gas reduction targets on paper without in fact doing anything in practice?
Numerous nations suspect that this idea is not far from American minds, with a powerful US industrial lobby sounding the alarm at the thought of reining in the world's most dynamic economy for something so seemingly nebulous as a bit of atmospheric chemistry.
Kyoto surprised everyone by the mere fact of agreement between more than 150 countries with very different views of what, if anything, should be done about the the threat of climate change. And not least surprising was that the US, the country that would have to make the most sacrifices, joined in.
But it exacted a price: emissions trading. An essential part of the Kyoto protocol is that, at American insistence, a global system of trading permits to emit greenhouse gases should be set up and made available to help countries meet their targets, with those nations that eventually have a surplus pollution allowance being able to sell it on to those with a deficit.
America is attached to the idea for two reasons. One is that the principle of solving pollution problems with market mechanisms rather than with regulation is now better understood and better established across the pond than anywhere else.
Under the current US Acid Rain Program, for example, the 110 largest power stations in the country must cut their emissions of sulphur dioxide, the main pollutant causing acid deposition, by a total of 3.6 million tons a year between 1995 and 2000. But they are allowed to do it by a system of tradeable sulphur dioxide allowances. A power station that can easily make deep cuts can sell its surplus allowances to those having more difficulty, and the whole reduction is achieved at much lower total cost. A similar system is helping to tackle the serious air-quality problems of southern California, with trading taking place in emissions of nitrogen oxides as well as sulphur dioxide. The flexibility that these schemes provide is much liked by American industry.
The second reason is the sheer, awesome size of America's greenhouse gas reduction programme. By 2010, under the Kyoto protocol, it must reduce its carbon dioxide emissions to a figure of 70 per cent below what they were in 1990. In that year they were 4.9 billion tonnes annually. But they are growing rapidly: now they are about 5.3 billion tonnes; by 2000, they will be 5.6 billion; by 2010, with business as usual, they will be about 6.3 billion tonnes. It will need to get them down to about 4.6 billion tonnes. Where on earth is that reduction of 1.7 billion tonnes of American CO2 - nearly a quarter of the projected total - to come from? How many thousands of Cadillacs have to be banned from the roads? How many thousands of car-sharing schemes will have to be strictly enforced? How many scores of US power stations have to close, and how many wind farms must replace them? For American industrialists, especially in the energy and motor vehicle sectors, this is the stuff of nightmares.
But then, their eyes turn to Russia and its former client republics, and what do they see? They see that Russia's 2010 target is only to return to its 1990 emissions figure, 2.37 billion tonnes. And they see that by 1994, as the Russian economy imploded, these had already collapsed to 1.66 billion tonnes, and that even with some recovery, the latest UN estimate for 2000 puts them at only 1.75 billion tonnes. And that by 2010, whatever happens, they are likely to be substantially below the 1990 figure. A similar story can be told for Ukraine, Belarus and other such ex-Soviet republics.
Set up an emissions trading market, and this pollution surplus, hundreds of millions of tonnes of CO2, is suddenly worth hundreds of millions of dollars. The overwhelming temptation will be for the Russians to sell, and the Americans to buy, as much hot air as they can.
But how much should the Americans, who alone emit 25 per cent of the world's greenhouse gases, be allowed to purchase? The full amount of their allowance, so that they, the worst offenders, will then have contributed nothing to the global fight against climate change?
Surely not, think most of the undeveloped countries; surely not, thinks the European Union. The issue is likely to hang heavily over the Buenos Aires conference, and, at worst, may sabotage the drawing up of the complex rules under which an international emissions trading market could operate.
For rules are certainly needed, and soon. Where is the market to be located? Will it be done through a stock exchange? Who is to take part, companies or countries? Who would issue the "pollution permits"? Could speculators buy them? Who would validate them? Who would verify a country's CO2 emission figures? Who will take action if a country cheats? And what action?
These will be the issues before world politicians next month, with the row over America's intentions overshadowing the legal detail. Never mind the coffee in Brazil; there'll be an awful lot about hot air in Argentina.