If Tony Abbott and Malcolm Turnbull were women there would be invariable calls of "catfight" being shouted across the schoolyard.

But Turnbull's third intervention in less than a week to blast Abbott on climate change policy — via his blog — is bigger than that. It is a direct attack on his new leader's environmental and economic credentials.

And moreover he is probably right.

That is not to say Turnbull's latest intervention is not full of personal, Latham-esque spite. He after all promised to be "measured" in his comments from the backbench on the day he was deposed as leader.

"The Liberal Party is currently led by people whose conviction on climate change is that it is 'crap' and you don't need to do anything about it," Turnbull wrote instead.

"Any policy that is announced will simply be a con, an environmental figleaf to cover a determination to do nothing.

"So any suggestion that you can dramatically cut emissions without any cost is, to use a favourite term of Mr Abbott, 'bullshit.' Moreover he knows it."

But despite the personal malice that appears frequently throughout his post, Turnbull is reflecting mainstream economic wisdom and a disbelief in many circles that the alternative government would dump a carbon price in its climate change policy.

First, let's clear up one fudge in Turnbull's latest blog. Abbott has never claimed he could reduce emissions without any cost. Abbott, and now the opposition spokesman for climate change Greg Hunt, say their new policies will reduce emissions at a lower cost than the Rudd Government's proposed emissions trading scheme.

Abbott has now ruled out a carbon tax, and an emissions trading scheme is off the agenda for the next election. Instead the Liberals will pursue policies of energy efficiency, green carbon such as biochar, and cleaning up coal power plants. Abbott claims that these policies could reach the Government emissions target range of 5-25 per cent on 2000 levels by 2020.

These policies would require regulation of some form or another — though we are not yet sure exactly what form that will take because there are no policy details yet.

Nor are we sure what they will cost, though shadow treasurer Joe Hockey is reported to have told Abbott in a shadow cabinet meeting that $50 billion would be the price. To be honest, we have to wait for the detail of the policy to make a full assessment. But we can make broad statements about a carbon price.

The Opposition's former economic adviser on emissions trading, the chief executive of free-market leaning Centre for International Economic, David Pearce, said he was surprised that the Liberals dumped a carbon price as policy.

Pearce added that a carbon price is far more efficient, and less costly, than regulation would ever be. Pearce's view is backed by Garnaut Review economists Frank Jotzo and Stephen Howes among others.

As another expert, Andrew Macinotsh, environment law and policy expert from ANU, said last week the Liberal "policy" is verging on ludicrous.

"The great irony of this is that the Greens are arguing for a rational economics, which the Liberal have reverted to picking winners and command and control," Mr Macintosh said.

Turnbull this morning put it like this: "The whole argument for an emissions trading scheme as opposed to cutting emissions via a carbon tax or simply by regulation is that it is cheaper — in other words, electricity prices will rise by less to achieve the same level of emission reductions."

Abbott, in an old-fashioned attempt to detract attention away from the Liberals policy switch on a carbon price, challenged the Prime Minister to a debate on climate change at the weekend.

Kevin Rudd was never going to accept — prime ministers never do. But wouldn't it now be even more interesting to see Abbott and Turnbull instead debate each other.

After this latest outburst the future for Turnbull is also unclear.

"Not that anyone would doubt it, but I will be voting for the ETS legislation when it returns in February and if my colleagues have any sense they will do so as well," Turnbull wrote this morning.

The question is now will Turnbull remain a Liberal? Is this him positioning himself to run as an independent in Wentworth? Or instead take another shot at the Liberal leadership by rallying the moderates?

Or maybe, though many find it hard to believe as cynical as we are, Turnbull's words are just a simple expression of his true beliefs.

If so, even though Turnbull appears to be heading down a dark path of bitterness, he is starting to sound like the last sane man in the Liberal Party on climate change.