The document also recommends embracing the climate authority's suggested reductions to the emissions intensity of new cars, pushing up prices which motorists would then gain back in savings over the life of the vehicle.

Mr Butler said, however, that the paper simply contained ideas still up for discussion and the proposal had not yet been considered by shadow cabinet.

"This is just one of a series of papers that have been prepared over the period of time and there is not even been the beginning of a discussion yet in Shadow Cabinet about this," he said.

While Mr Shorten had flagged campaigning for a trading scheme last year, there had been some doubt over what sort of climate policy Labor would take to the next election, with Mr Butler signalling in June it might not be an ETS.

"[We are] not going to indicate one way or the other what we're going to do because we will do that in a deliberative way," he said.

Coalition jump to 'kill Bill'

Prime Minister Tony Abbott jumped on the news of early this morning, labelling the ETS proposal a "triple whammy carbon tax".

"Now we know from this leaked shadow document that the carbon tax will be back not just in one guise but a triple whammy carbon tax if Labor comes back," he said.


Federal Environment Minister Greg Hunt said the leak to News Corp was aimed at "killing Bill", considering the damage the carbon Tax had on Former Prime Ministers Julia Gillard and Kevin Rudd.

"This is a spectacular leak of a major Labor party policy of not one but two new carbon taxes. There is a question of who leaked it and why, are they trying to kill the tax or kill Bill," Mr Hunt said.

Mr Butler denied this: "No, of course not. How this paper ended up in News Limited hands is obviously unfortunate...I don't think too much should be read into it as all," he said.

Treasurer Joe Hockey told the ABC this morning it would be "madness" for Labor to adopt a carbon tax after it brought down two Labor leaders, "but obviously someone wants to kill Bill".

Carbon stance 'no surprise': Labor

Labor have said their position on carbon should not come as a surprise to the Australian public, pointing to speeches and interviews last year when Mr Shorten said they would be backing emissions trading in an election.

On Wednesday Mr Shorten did not deny Labor was working on a new ETS, saying action was simply part of believing in climate change.

"We believe climate change is real and we believe there are sensible measures we can make with the rest of the world and focussing on had market-based system and also focussing upon renewable energy," he said.