By Roger Harrabin
Environment analyst, BBC News
Rich nations should be absolved from the need to cut emissions if they pay developing countries to do it on their behalf, a senior UN official has said.
The controversial suggestion from Yvo de Boer, head of the UN Framework Convention on Climate Change (UNFCCC), has angered environmental groups.
They say climate change will not be solved unless rich and poor nations both cut emissions together.
But Mr de Boer said the challenge was so great that action was needed now.
The UN's binding global climate agreement, the Kyoto Protocol, currently requires industrialised nations to reduce the majority of emissions themselves.
But Mr de Boer said this was illogical, adding that the scale of the problem facing the world meant that countries should be allowed to invest in emission cuts wherever in the world it was cheapest.
"We have been reducing emissions and making energy use more efficient in industrialised countries for a long time," he told BBC News.
"So it is quite expensive in these nations to reduce emissions any more.
"But in developing nations, less has been done to reduce emissions and less has been done to address energy efficiency," Mr de Boer observed.
"So it actually becomes economically quite attractive for a company, for example in the UK, that has a target to achieve this goal by reducing emissions in China."
Mr de Boer's views were personal ones, he said, and not those of the UNFCCC. He added that rich nations should be able to buy their way out of 100% of their responsibilities - though he doubted that any country would want to do so.
Green groups said the proposal was against the spirit of the UN, which agreed that wealthy countries - who were responsible for climate change - should do most to cure it.
Mike Childs from Friends of the Earth said: "This proposal simply won't deliver the cuts we need in time. The scientists are telling us that we need to cut carbon dioxide (CO2) by 50-80% by 2050.
"Unless rich countries start to wean themselves off fossil fuels right away this won't happen."
Doug Parr of Greenpeace was equally critical of Mr de Boer's suggestion.
"The current trading system is not delivering emissions reductions as it is," he said. "Expanding it like this to give rich countries a completely free hand will simply not work."
But Mr de Boer further explained: "The atmosphere does not care where emissions are reduced as long as they are reduced.
"Most of the cheapest emissions reduction possibilities are in developing countries. The carbon market can be used to catalyse these. So in terms of the maximum result at the lowest possible cost, it does not matter where emissions are reduced.
"Rich countries have the responsibility to take the lead by substantially reducing emissions at home."
Rich countries that reduced emissions at home were investing in their own clean energy future, rather than someone else's, he added.