Only months after an effusive Tony Abbott compared him to Jesus Christ, free-market think tank leader John Roskam has dumped on the government's direct-action policy and accused the Prime Minister of not being a true believer in the need for climate change action.

''I don't think we should have direct action because the Coalition hasn't explained what, if any, changes to the world's temperature it will provide,'' said Mr Roskam, who is the executive director of the Institute of Public Affairs.

"I've yet to be convinced that Tony Abbott is doing any of this for anything other than political purposes": John Roskam. Credit:Matthew Bayard

Asked whether Mr Abbott's earlier position on the science of climate change - namely, as he notoriously declared in 2009, that it was ''absolute crap'' - suited the PM better than direct action, Mr Roskam agreed.

''Yes, and isn't it interesting how climate change gets people to say things they don't really believe? I've yet to be convinced that Tony Abbott is doing any of this for anything other than political purposes. I think he would be much better off, as any politician would, telling us what he genuinely believed.''