Labor's promise of a net zero public service by 2030 will need to exclude Defence and national security agencies or risk being unachievable, the party's climate spokesperson has conceded.
Senior opposition member Chris Bowen on Monday told a National Press Club audience the Coalition government's fear campaign against climate change had been "toxic" but Labor's turn in power would result in climate action progress.
It follows the announcement of a 43 per cent emissions reduction target by Labor on Friday as part of its $24 billion "Powering Australia" plan.
Forming part of the commitment is a goal to achieving a net zero bureaucracy by the decade's end with a few agencies being exempt.
But those exemptions, which include Defence, the Australian Border Force and the Australian Federal Police, represent more than half of the sector's emissions.
Mr Bowen said the promise to slash reductions by 2030 on just 40 per cent of the APS was made very clear in Friday's release and the accompanying economic modelling.
"It is harder to make that transition to net zero when you're running some very power-hungry aeroplanes and chips and military hardware," he said.
"What we will do is work very closely with Defence to try and get a plan in place for emissions reduction.
"But we will not bind Defence, in particular, to that net zero commitment because we are not sure it would be achievable, or implementable, in a reasonable timeframe."
He added the country's immediate national security would not be threatened in order to achieve the unrealistic target.
Instead, Mr Bowen said a Labor defence minister, along with the Defence chiefs, would increase accountability and transparency to their emissions reductions strategy.
"If Defence can do better, we'd like that," he said.
"But we're not claiming the emissions reduction [applies to Defence] or binding [Defence] to it."
No additional modelling had been completed by Labor on possible emissions reduction targets Defence and national security agencies.
A lack of climate change action, however, also presented national security risks Labor's defence spokesperson, and Mr Bowen's colleague, Brendan O'Connor said on Monday.
Referencing a speech made by former Australian Defence Force chief Admiral Chris Barrie, the Victorian MP said the issue represented the most significant threat to Australia's defence and national security.
"Labor understands that climate change is not only real, it has serious ramifications for global security and the Australian Defence Force," he said.
"We have already seen the response work the ADF has undertaken in climate-related disasters such as last year's bushfires.
"These national security threats, however, go beyond the domestic, with the 2020 Defence Strategic Update highlighting that threats to human security - including climate change - are likely to result in greater political instability and friction within and between countries and reshape our security environment.
"Australia is unable to achieve lasting national security without an effective response to climate change."