The pledges it has made to cut its emissions of greenhouse gases such as carbon dioxide are simply too enormous to be achieved, Robert Reinstein, a former senior official in the US State Department, said.
Ministers from 180 countries, including Britain's Deputy Prime Minister, John Prescott, are meeting in Buenos Aires to try to take forward the Kyoto agreement .
"The Americans made a mistake at Kyoto," Mr Reinstein said. "They signed up to something that is impossible to fulfil."
The result, he said, was that the Kyoto accord would eventually fail amid worldwide recriminations and embarrass ment, and the international process of trying to find an answer to global warming would be discredited.
Mr Reinstein, 58, who is attending the conference as a representative of the Canadian Electricity Association, was the US State Department's senior environmental official from 1990 to 1993. In 1992 he was the chief US negotiator on the UN's Framework Convention on Climate Change, which was signed at the Earth Summit in Rio de Janeiro. The Kyoto agreement is a protocol to this treaty.
America, the world's biggest polluter, agreed at Kyoto to cut its emissions of carbon dioxide from cars and power stations, and five other greenhouse gases, to a figure 7 per cent below their 1990 level, by 2010.
But that figure, Mr Reinstein said, would represent up to a 30 per cent cut from where the US economy will have grown to a decade from now, which would simply not be deliverable.
In 1990, he said, the US emitted about 5.8 billion tonnes of greenhouse gases and it had promised to cut that back to 5.4 billion. But by 2010, it would be emitting about 7.2 billion tonnes if business continued as usual, and even with the best efforts of the whole country at energy efficiency, it would still be emitting about 6.6 billion.
The shortfall of 1.2 billion tonnes could not even be covered by the US buying greenhouse gas emission credits from other countries, he said - the so called "hot air" which is one of the principal points of contention at Buenos Aires.
America would like to buy as much as possible of the notional "pollution allowances" available to countries such as Russia and Ukraine, whose CO2 emissions are already well below the targets given to them at Kyoto because in the Nineties their smokestack economies have collapsed.
The European Union and the world environment movement all want a firm ceiling on how much hot air the US can buy, so that it does not avoid taking steps to deal with its greenhouse gas emissions at home.
Britain's Kyoto target is to cut back to 12.5 per cent below its 1990 levels of greenhouse gas emissions by 2010. This looks likely to be achieved, largely because of the "dash for gas" - the widespread replacement of coal-fired power stations by gas fired ones, which emit less CO2.
The evidence for the approach of global warming is continuing to mount. This year is already certain to be the hottest year in the 150-year-long record of world temperatures.
Mr Prescott said last night of Mr Reinstein's comments: "That's all if if ifs ... what is clear is that to do nothing is not acceptable, and even if the Americans were only to achieve half their target that's got to be an advance."Reuse content