As the twelve-day United Nations Climate Conference in Argentina nears its end on Friday, there's little agreement on how to achieve its principal aim -- reducing pollution leading to global warming.

The main dispute is between the United States and Europe over what's know as emissions trading -- the right of countries which fulfil their commitment to cut pollution to sell their excess allowances to nations struggling to meet their objectives.

While the US argues that such trade should operate under free market principles, European countries favour a tax to make it harder for rich countries to buy permits abroad to avoid making cuts at home.

The BBC Environment Correspondent says many countries also fear they could lose out to competitors if they adopt potentially expensive pollution controls and others don't.

The conference in the Argentine capital, Buenos Aires, follows last year's meeting in Kyoto, where developing nations made a pledge to cut the emission of so-called greenhouse gases.