The opposition leader - who has been fending off renewed speculation about the ambitions of Peter Costello - has seized on the government's emissions trading scheme (ETS) policy, flagging a Senate inquiry to replace the one the government axed last week.

But on Monday Liberal MPs were unwilling to define their policy with frontbencher Christopher Pyne telling ABC Television: "Everything's on the table."

Emissions trading spokesman Andrew Robb was also reluctant to provide more details.

"We will specify that in clearer terms later on," he said, when asked for a specific reduction target.

Queensland backbencher Stuart Robert was happy to attack the government, but unable to offer clear advice on where the opposition was heading.

"The government's ETS will cost jobs," Mr Robert told reporters in Canberra.

Mr Turnbull has also signalled a more ambitious greenhouse gas reduction target than the government's 5-15 per cent by 2020, and a less complex scheme for achieving the target.

The government has dismissed the new stance, saying it is a mirage.

Senator Wong says the government has always acknowledged the need for additional policies to its planned emissions trading scheme.

But turning Australia from one of the most carbon-intensive economies in the world to a low-pollution one requires the "hard" economic reform of an ETS.

"Mr Turnbull knows this," Senator Wong said.

The only reason he is walking away from the ETS is because of deep divisions in the Liberal Party, she said.

"Many ... simply do not want to take action on climate change."

Tasmanian Labor MP Dick Adams said he leant toward starting with a lower reduction target.

"We can't go about sending our capital offshore and therefore costing us one hell of a lot of jobs.

"I'm a minimalist in this debate, let's start, let's get a scheme out there and then let's deal with that over a period of years."

South Australian government backbencher Amanda Rishworth said it was hard to believe anything the opposition said about climate change.

"I don't believe what Malcolm Turnbull does say because he's dealing with a party that is filled with climate change sceptics."