The Coalition government may have to cut Australia's greenhouse gas emissions by twice as fast as has been planned.

An analysis of international commitments following the latest report of the Intergovernmental Panel on Climate Change suggests Australia will be obliged to cut emissions to 10 to 15 per cent below 2000 levels by 2020, rather than the 5 per cent the Coalition had been promising.

The Coalition's policy document commits it to a 5 per reduction ''without the need for a great big new tax''. But it confirmed during the election campaign it would honour a commitment of the previous government to cut further if ''conditions relating to the extent of global action are met''.