The Morrison government has spent nearly $13 million promoting its climate credentials to voters while refusing to release modelling underpinning its plan to cut emissions.
The $12.9 million spend includes more than $488,000 looking at public attitudes towards climate change and market testing the coalition's "positive energy campaign" launched in September.
Labor wants government officials to hand over findings of market research into the campaign.
"It's subject to cabinet consideration so I need to check on that," the head of the industry department's climate change division, Helen Bennett, told a Senate estimates hearing on Monday.
The campaign, including TV and radio ads, was developed because "the public wanted to hear more about what the government is doing to reduce emissions".
Meanwhile, the government has refused to release modelling underpinning a 2050 target, begrudgingly agreed to by the Nationals, on the grounds of cabinet confidentiality.
Energy Minister Angus Taylor flagged a public interest immunity claim on the modelling requested last week by Nationals senator Matt Canavan because it informed or was the subject of cabinet deliberations.
Appearing on the minister's behalf, Senator Zed Seselja told the hearing the plan was based on existing policies and would be detailed ahead of the COP26 summit starting in six days.
"What you're asking for is for this committee to be able to effectively interrogate the internal deliberations of cabinet and that has not been the approach in the past," he said.
The Climate Change Authority was not asked to advise the government about updating its 2030 or 2050 targets.
"It was, once upon a time, part of our statutory responsibilities to advise on these matters but that is not presently the case," the authority's chief executive Brad Archer told the hearing.
Its involvement in COP26 will be limited to running two events, one around global trade and investment trends and another on building carbon offset markets in the Indo-Pacific.
Industry department deputy secretary Jo Evans confirmed Australia was not changing its 2030 target from a 26 to 28 per cent reduction on 2005 levels.
"That target which was set at 2015 and which is for 2030, is not changing," she said.
Greens senator Sarah Hanson-Young described the in-principle deal for net-zero emissions by 2050 as hostage negotiations between Prime Minister Scott Morrison and Nationals leader Barnaby Joyce.
"It seems to everybody else that the prime minister has no idea what he's doing and Barnaby Joyce is calling all the shots," she said.
A majority of the junior coalition partner agreed on Sunday to in-principle support for net-zero emissions by 2050 after vetoing an increase to the 2030 target.
Australian Associated Press