Government officials have acknowledged that Australia’s 2030 greenhouse gas emissions reductions pledged at Paris in 2015 were made without any modelling to show whether existing policies could achieve those targets.

They also admitted the government did not have any modelling revealing when Australia’s emissions would peak.

The admissions, made in a parliamentary committee under questioning from Labor Senator for New South Wales Jenny McAllister, fly in the face of advice from the Department of Foreign Affairs and Trade, telling the government it had “existing legislation, policies and measures to enable it to achieve” the the reductions.

They also follow a string of independent modelling exercises showing current policies will not achieve the emissions reductions committed to in Paris. Last week energy advisory firm RepuTex released modelling showing Australia’s emissions wouldn’t fall much at all between now and 2030, under current policies.

When asked about whether Australia would meet targets laid out in the Paris agreement, Patrick Suckling, the Australian ambassador for the environment, responded that the government had said it would meet those targets and its track record showed it met internationally agreed targets.

“On the basis of past performance, where we’ve met and exceeded Kyoto 1 and Kyoto 2, that’s the track record,” Suckling said.

When pushed on the issue by the committee, Suckling referred further questions to Brad Archer from the international climate change and energy innovation division in the Department of Environment and Energy.

Under extended questioning, Archer pointed to various analyses of individual policies but wasn’t able cite any modelling that would have informed government if the current set of policies would achieve the 2030 targets.

He said the government was paying polluters to pollute less under the Emissions Reduction Fund. “So we can take into account what is being achieved under the Emissions Reduction Fund.” But he couldn’t identify any analysis that looked at the overall impact of current policies.

Archer said: “It’s not the case that we have modelling capacity available on-tap to continually undertake analyses.” At another point he added: “There are inherent challenges in making projections over long periods of time.”

Kushla Munro from the international branch of the Department of Environment and Energy later told the committee that the government’s “latest emissions projections go to 2020” and that 2030 projections were being prepared.

When asked by McAllister when Australia’s emissions would peak, Archer said “that’s a very interesting question,” and that modelling done so far didn’t include analysis of current policies.

McAllister told Guardian Australia the Turnbull government needed to “own up and admit that their climate policies just aren’t credible”.

“These officials have confirmed Australia’s worst kept secret – that the Turnbull government has no idea how it will meet our 2030 emission reduction targets,” she said.

“They can’t say when Australia’s emissions will peak and begin to decline, and they wouldn’t confirm that the government’s current policy settings will see us meet the target without adjustment.”