In its third and final key findings, the IPCC panel reports:

■ A cost of $US20-50 a tonne of atmospheric carbon would have a big impact on cutting harmful emissions. "It could lead to a power generation sector with low greenhouse gas emission by 2050."

■ This would allow renewable energy to have a 30 to 35 per cent share of total electricity supply by 2030.

■ Nuclear power would provide only an additional 2 per cent of the world's electricity supply by 2030 because it is too expensive, and "safety, weapons proliferation and waste remain as constraints".

■ Clean coal technology has the potential to make an important contribution by 2030.

■ Improving efficiency of energy supply and use would play a key role in reducing emissions by up to 30 billion tonnes a year by 2030.