Most efforts to rein in climate change have so far focused on curbing carbon dioxide emissions from cars, power plants and heavy industry.

But Robert Aisi, Papua New Guinea's delegate at the 190-nation seminar which aims to widen the UN Kyoto protocol on slowing climate change said: "Forests are our assets and should be valued."

Under the extension plan, farmers in the developing world would get a cash incentive to preserve trees - which soak up greenhouse gases as they grow - rather than sell them to loggers or cut them down to make way for crops.

"The loggers come in and tell villagers we'll give you $10 (£5.44) for your tree - then they cut it down and sell it for $1,000. Who wins? We lose because we get land degradation. The whole world loses," Mr Aisi told Reuters. "The commercial value of cutting down our forests is now far higher than retaining them."

He added that Papua New Guinea's rainforest was third biggest in the world after those in the Amazon and Congo.

A new system would give farmers credits for averting deforestation which could then be traded on the international market, and mirrors a European Union scheme to reduce industrial emissions of greenhouse gases, he said. The details of the credit scheme have yet to be worked out.

But the scientific panel which advises the United Nations has estimated 20-25% of global greenhouse gases in the 1990s stemmed from land-use changes, mainly deforestation, Mr Aisi said.

Carbon constitutes about half the weight of a tree, and wood and roots begin to release carbon dioxide, the main gas blamed for warming the planet, as soon as they start to rot.