Treasury secretary Steven Kennedy has said his department had very little input into the modelling underpinning the federal government's plan for net zero.

Dr Kennedy told senators on Wednesday that Treasury had provided some technical advice on the risks some investors might face in a net zero world.

He said his department also seconded two staff to the Department of Industry, Science, Energy and Resources (DISER) — one in January, the other in August — to help with aspects of DISER's modelling.

But that was largely it.

Dr Kennedy's revelation comes a day after the Morrison government released its plan to achieve net zero emissions by 2050.

The government's document, found here, said its net zero plan was underpinned by economic modelling by DISER, and complementary  "analysis" by private consultancy McKinsey & Company.

Modelling part of 'cabinet-in-confidence'

On Wednesday morning during a senate estimates hearing, Dr Kennedy said Treasury's input into the modelling was minimal.

He said Treasury provided very "broad" advice on what would happen to various risk premia if Australia did, and did not, join the international consensus on the net zero target by 2050.

"It's that type of broad sense of um ... what are the risks that different companies might face in Australia if Australia wasn't seen to be fulsomely part of global consensus on climate change," he said.

He said that specific advice from Treasury was incorporated in the modelling, and if the government chose to release the modelling "it would all become apparent".

But Finance Minister Simon Birmingham said many of the details informing the economic modelling in the government's plan had passed through Cabinet, so it could be subject to "cabinet-in-confidence" — meaning it may not be made public.

"The inputs into the policy decisions that the government had made which are reflected in the plan which was released yesterday were all advice formulated for the consideration of the Cabinet in the making of those policy decisions," Senator Birmingham said.

"They have informed Cabinet deliberations and decisions and on those grounds, it's perfectly reasonable for the government to indicate that we have released a plan, a plan that is on the public record, it has many details and references within it, and obviously that the government is happy to take questions on that plan.

"But in terms of the inputs into those Cabinet deliberations then yes, they remain part of advice to government and cabinet-in-confidence," he said.

The government will decide if the modelling is released

According to the government's document, the "plan" to shift Australia to net zero by 2050 is underpinned by economic modelling from the Department of Industry, and "analysis" by McKinsey. 

Labor senator Jenny McAllister said she simply wanted to know what assumptions DISER used, informed by advice from Treasury, about the risk premia that Australian businesses could face if Australia did not commit to net zero by 2050.

Senator Birmingham said it was up to Angus Taylor, the Minister of Industry, Energy, and Emissions Reduction, to release the modelling.

Senator McAllister said: "Are you making a claim for public interest immunity?"

Senator Birmingham replied: "If you're seeking one, Senator, then yes at this time, given the processes that have been used in terms of very extensive Cabinet deliberations, as I say, in the adoption of this policy and this plan."

Senator McAllister said the government's net zero plan was very significant and it had implications for the entire economy.

She said it was reasonable to expect basic questions to be answered about the modelling in these senate estimates hearings, given they could be the last hearings before the federal election was held.

Treasury's input was minimal

Treasury's lack of input on a major economic plan that involves significant adjustment costs contrasts with past practice.

In the late 2000s, Treasury officials were heavily involved in modelling the economic costs of attempts to reduce greenhouse gas emissions.

In 2008, Treasury released detailed information about modelling they had performed.