Senior Nationals MPs say they will refuse to consider a net zero by 2050 emissions target without seeing a plan for how much it will cost and who will pay.

But despite leading the Nationals and being the Deputy Prime Minister, Barnaby Joyce was unable to say what work his own government was actually doing on such a plan, or when it might be released.

Mr Joyce’s Senate colleague, Bridget McKenzie, said flatly “it’s not up to us to come up with the plan”.

The net-zero issue threatens to again tear a climate rift in the Coalition, with the three most senior Nationals politicians conducting a media blitz on Wednesday to challenge their Liberal partners to come up with more detail before the regional party agrees.

“Nobody is telling us exactly what’s in the plan,” Mr Joyce complained in a Radio National interview on Wednesday morning.

Host Fran Kelly countered “with respect, you’re the Deputy Prime Minister of this government”.

“It’s your government you’re asking to come up with a plan. Where are you at with a plan?” she said.

"We don't come up with the plan. The CSIRO, other competent people come up with the plan," says @Barnaby_Joyce, Deputy Prime Minister.

— RN Breakfast (@RNBreakfast) August 10, 2021

The Coalition government has come under renewed pressure to commit formally to the net zero by 2050 target – long-embraced by nearly all Australia’s main trading partners and allies – following the latest United Nations climate warning.

The IPCC report, released on Tuesday, warned of catastrophic climate change, intensifying natural disasters and irreversible damage to global food systems without urgent action on emissions and pollution.

Prime Minister Scott Morrison waved away questions about whether Australia would now commit to net zero, but his junior Coalition partners haven’t been as restrained.

The Nationals’ three most senior politicians – Mr Joyce, deputy leader David Littleproud and Senate leader Senator McKenzie – were all singing from the same song sheet on Wednesday, saying they wouldn’t sign up to net zero without firmer commitments and projections from the Liberals on how the target would be achieved.

“We don’t believe in legislating until we have a clear understanding of exactly where the costs are. Otherwise you just have an open book,” Mr Joyce told Radio National.

It echoed bizarre comments made last month, utilising a restaurant metaphor to ask “what’s on the menu and what the price is”.

On Wednesday, Mr Joyce brushed aside questions on why the government he was is a senior member of is yet to share a plan to reach net zero.

“We don’t come up with the plan. The CSIRO, other competent people come up with the plan,” he said.

“You’re making an answer to the equation without telling the people the numbers that got there.”

David Littleproud, Mr Joyce and Bridget McKenzie. Photo: AAP

But in a press conference later, Mr Littleproud, the Nationals’ deputy and Agriculture Minister, said the plan was in the works, and that he and Energy Minister Angus Taylor had been part of the team working on it.

“The government is working through this. Obviously, Angus Taylor has taken a leading role and this will obviously come through at some point with the Prime Minister and then obviously through cabinet and through our party rooms,” Mr Littleproud said.

“This isn’t just one single solution. This is a range of solutions that have to be fed in and modelled. So this isn’t just pull it out of the back pocket and put it on the back of an envelope sort of stuff.”

However, he too was critical that there was “not a lot of detail”.

When asked why the Coalition – which has been in government since 2013 – hadn’t yet shared its plan, Mr Littleproud said it had been focused on meeting emissions goals from the Paris agreement.

He also noted that plans needed to have “currency”.

“That is exactly what the Prime Minister and the government is working through, to make sure that not only can they show the National Party party room, but they can say to the Australian public, this is how we get there and who pays for it,” Mr Littleproud said.

“Agriculture has an opportunity to be part of the solution. That is being fed into the modelling. So this is bringing together a number of portfolios, a range of portfolios: resources, agriculture, energy, transport. This is an opportunity.”

“I know everyone’s keen and eager, but it’s got to be done properly.”

Asked when he expected such modelling to be available, Mr Littleproud said only: “I haven’t got that detail for you.”

Later, on Sky News, Senator McKenzie also called for the government to “show us the detail so we can be convinced and encouraged”.

“That’s fair enough, that’s actually the responsible thing for us to do as the National Party,” she said.

“We won’t be signing a blank cheque.”

Senator McKenzie said rural and regional industries such as beef and mining wanted certainty, to “understand the role we can play positively in lowering emissions”.