Labor leader Bill Shorten says it's "stupid" not to take action on climate change, as a question mark continues to hover over the cost of his emissions reduction plan.
He says the coalition's $25 billion costing of his policy is a lie, accusing the government of running a scare campaign.
"There will never be enough figures to satisfy the climate sceptics," he told reporters in Darwin.
"If you don't believe in the science of climate change, no amount of evidence will ever convince you. Because fundamentally, it's a stupid position not to take action."
Under Labor's plan companies will buy international offsets if they can't adequately reduce their pollution.
Mr Shorten is under pressure to flesh out the detail and outline the cost it would have on businesses.
The coalition's $25 billion estimate relies on a series of assumptions, including that the offsets would cost an average of $50 a tonne.
Current figures show the most expensive offsets, in the European market, cost about $33 a tonne.
The opposition has proposed a target to cut emissions by 45 per cent by 2030 on 2005 levels, compared to the coalition's 26 per cent reduction.
Prime Minister Scott Morrison has budgeted $3.5 billion for his plan, which extends a scheme that has so far increased emissions.
Mr Morrison wants a clear answer from his rival on the cost of a higher target.
"He still can't tell Australians what the cost of his emissions reduction policy is on Australians," Mr Morrison told reporters in Tasmania.
Mr Shorten quoted Josh Frydenberg in 2017 saying it didn't matter whether a tonne of carbon was reduced in Australia or another country.
"The government is now scaring you about policies they used to have and support," he said.
A day after refusing to answer questions on the economic impacts of Labor's climate and energy policies, Mr Shorten on Wednesday said they won't cost the economy but will help it to grow.
He pointed to findings by ANU economist Warwick McKibbin that under both the coalition's target and that proposed by Labor, Australia will rack up 23 per cent worth of economic growth through the 2020s.
"Our economy is going to grow, I don't accept the characterisation that it's a cost," he told reporters in Perth.
