The Greens have accused Treasurer Wayne Swan of "bad faith" in releasing Treasury modelling on the carbon tax before showing it to them.

Deputy Greens leader Christine Milne accused Mr Swan of "breaking ranks" from the multi-party climate change committee by releasing Treasury figures that show the cost of the tax will be negligible.

The modelling predicts that real national income per person will grow by 1.1 per cent a year under a carbon price, only 0.1 per cent a year less than it would if no tax was in place.

But Senator Milne says the multi-party committee - which will decide on details of the tax this month - expected to see the modelling first.

"I think it is an act of bad faith from the Treasurer to go out and selectively release the Treasury modelling outside the multi-party climate committee context," Senator Milne told ABC Radio News.

"To go out and selectively put out bits and pieces doesn't show a great deal of respect for the process."

Mr Swan was unapologetic.

"I don't accept that. The modelling has been prepared by the government. We are working with the multi-party committee. We will work with them and are working with them in good faith and we will continue to do that," he told Radio National.

Key independent committee member Tony Windsor was also angered, saying the government should make up its mind if it wants the committee to work.

The Treasury modelling is based on a carbon price of $20 a tonne but the Greens are arguing the price should be much higher to encourage investment in renewable energy.

Mr Swan says incomes will rise significantly due to strong growth of the economy, but there will be a minor hit to wages.

"It would be slightly more without the impact of a carbon tax but a very small difference. A carbon price makes very little difference in terms of overall income levels," he said.