Opposition Leader Bill Shorten has come out swinging against "propaganda" modelling of the cost of his climate change policies, likening its author to doctors shilling for tobacco giants.
Former federal government economist Brian Fisher, managing director of BAEconomics, estimated Labor's carbon reduction targets could wipe up to $542 billion from the nation's growing economy.
"This fellow and his report remind me of the doctors that big tobacco companies used to roll out in the '70s and '80s to say that smoking was healthy for you," Mr Shorten told reporters in Tasmania on Thursday.
"We will file this report under 'P' for propaganda."
Dr Fisher estimated Labor's plan to cut carbon emissions by 45 per cent by 2030 could shrink economic growth by 0.8 per cent over the decade.
However, he said allowing heavy polluters to offset more of their emissions using international credits would slash the negative impacts in half.
"It's not disastrous, but it is a drop-off," Dr Fisher told ABC Radio.
Mr Shorten says it's impossible to cost Labor's plan as businesses would decide how to reduce their pollution.
Prime Minister Scott Morrison likened Labor's "reckless" policy to a scene in movie The Castle.
"The only person, frankly, who's trying to sell a pair of jousting sticks to the Australian people at this election is Bill Shorten - the only difference is the guy selling the jousting sticks would tell you what the price was," Mr Morrison told reporters in Tasmania.
Labor's climate change spokesman Mark Butler rubbished the "dodgy" modelling.
"This is a complete crock of rubbish, this modelling, by a fellow who has spent 20 years building a career fighting every single climate policy," he said
Dr Fisher is an agricultural economics professor and former executive director of the Australian Bureau of Agricultural and Resource Economics, .
His modelling relies on a quarter of the emissions reductions being achieved by allowing big companies to buy international carbon credits to offset their pollution.
If big polluters could instead meet half their targets through international permits, Dr Fisher predicted economic growth would slow by just 0.2 per cent, or $276 billion.
"The more ambitious you are with your target, the higher the cost is going to be, unless you can defray that cost in some way," he said.
Labor has promised to consult with business over what level of international permits would be allowed.
Under the Gillard government's carbon price, polluters were allowed to offset 12.5 per cent of their emissions with credits from overseas.
The coalition government wants to reduce carbon emissions by 26 per cent by 2030, although its plans to use credits from exceeding Australia's Kyoto commitments drops this to about 15 per cent.
Dr Fisher's modelling does not factor in the economic cost of climate inaction.
"If we leave the problem of climate change any longer, it's going to cost more to fix," Mr Shorten said.