Mr Butler's comments came as the UN's Intergovernmental Panel on Climate Change warned of irreversible global warming damage due to the high level of global emissions and followed a Labor-led Senate committee last week calling for deeper cuts. It demonstrates the Labor Left faction leader's preparedness to take on the hard-heads in the Labor Right over emissions targets.

Australia's current policy is for an unconditional 5 per cent reduction in emissions by 2020 against 2000 levels, but with room to move to a target of 15 per cent to 25 per cent depending on global action.

The independent Climate Change Authority, which the government plans to abolish, said in February Australia should adopt a minimum target of 15 per cent by 2020 and its 5 per cent target was out of step with countries including China and the United States.

Mr Butler said: ''It [the authority report] does make the point that the conditions for 15 per cent have been met.

''For example, similar countries have targets of 15 per cent. It's quite clear 20 per cent hasn't been met but it is strongly arguable 15 per cent has been met.'' A spokesman for Mr Shorten said the climate authority had said a 15 per cent reduction in emissions was achievable with the right policy settings.