Despite the inevitably heavy redactions, the Department of Defence’s brief for the incoming government ^[1]makes for interesting reading, including its section on climate change.

The briefing, released under freedom of information laws, acknowledges that Defence’s cooperate with the Office of National Intelligence on an assessment of the national security implications of climate change. It also states that ‘Defence will continue to provide … support to disaster response within the context of climate risk’—but says this is placing increasing pressure on the Australian Defence Force’s capacity to fulfill its other missions.

Much ^[2] of the information outlined was already ^[3] known, but its reiteration among key points for the new government signals the seriousness with which Defence’s leaders are taking climate change.

An even stronger signal about these concerns is provided by the emissions-reduction targets the brief reveals:

Defence has initiated a range of investments to drive a 43 per cent reduction in Greenhouse Gas Emissions by 2030 and achieve net zero by 2040. The Defence Renewable Energy and Energy Security Program is delivering renewable energy and associated technologies, leading high-level feasibility assessments of low-emission technologies including hydrogen, battery energy storage, micro-grids and alternative liquid fuels.

Defence is matching the government’s overall 43% target ^[4] by 2030 (presumably relative to the same 2005 baseline, though that isn’t said in the brief). Moreover, it has apparently committed to a net-zero position a decade ahead of the government’s overall national target.

This is a remarkable commitment. Defence operates a range of capabilities that are very difficult to decarbonise because we don’t have viable replacements for things like powerful jet and marine engines, and nor do we yet have access to alternative fuels for such systems. Moving the defence estate to green electricity is one thing; getting the air force’s F-35 jets and the navy’s giant landing ships off legacy fuels is another.

Nevertheless, an ambitious approach to emissions reduction is entirely justified for Defence. First, it faces genuine social-licence concerns in the long term. While Australia lacks readily available data on the defence organisation’s contribution to public-sector or national emissions, the numbers from allied countries are significant and indicative.

The UK armed forces account for 50% of the UK government’s emissions ^[5]. The US military similarly accounts for 56% of US government emissions ^[6], is the world’s single largest ^[7] institutional petroleum user and carbon emitter, and would rank as the 55th largest CO₂ emitter if it were a country ^[8]. One widely cited estimate puts it at around 6% of total US emissions. Even if that estimate is on the high side, a single institutional user accounting for even 1% or 2% of national emissions is significant.

If underlying military emissions remain steady or even rise, their portion of public-sector and national emissions will increase significantly as decarbonisation proceeds in the broader economy. It is certainly true that criticism of military emissions ^[9] isn’t yet mainstream and that exemptions for militaries like the ADF are not domestically controversial. But we should expect that these issues will be increasingly contested as military emissions take on greater relative significance.

A second reason for taking an ambitious approach is that the legitimacy of those emissions is also likely to be increasingly contested as climate-change impacts deepen and worsen ^[10]. Without compromising its ability to deliver military power, Defence should be doing everything it can to avoid contributing to the climate-driven problems to which Defence itself will need to respond (for example, disaster responses at home and abroad, or increased regional instability). Avoided climate change ^[11] is not a mere footnote.

Third, there are numerous benefits of alternative energy sources from a military point of view. For example, Australian Army leaders placed great emphasis on the tactical benefits of the Bushmaster all-electric protected mobility vehicle when it was unveiled ^[12] last month in Adelaide: it is quieter, quicker and mechanically simpler than its conventionally fuelled sibling. Dependency on fossil-fuel supply chains ^[13] is a longstanding anxiety of some strategic thinkers. Military bases with independent renewable power supplies are more resilient and operationally useful than those that aren’t, which is another reason for the great emphasis in the defence brief on solar supplies at various bases.

At this point, it’s unclear how Defence will achieve these bold targets and what is wrapped up in the ‘Defence Renewable Energy and Energy Security Program’, though the briefing does indicate some of the technical priorities that will be required. In estimates of US Department of Defence energy use, ‘operational energy use’, defined as that ‘required for training, moving, and sustaining military forces and weapons platforms’, represents 70% ^[7] of the department’s energy consumption. More than two-thirds of that total is jet fuel.

If the ADF’s energy use and emissions profile (they are not same thing) are anything vaguely like the US military’s proportions, even complete decarbonisation of the defence estate and non-operational activities may not be enough to reduce emissions by 43% by 2030. Aggressive action to approach complete decarbonisation of that part of the portfolio will be required in parallel to work attacking the operational side of the problem.

As we outlined in our report, The Australian Defence Force and its future energy requirements ^[14], earlier this year, solving the more difficult technical problems required to shift away from legacy fuels at scale requires long-term thinking in partnership with industry.

Such partnerships could include collaboration among researchers, key industry players like Qantas and Virgin, and the defence organisation to realise promising technologies like ‘power-to-liquid’ ^[15] at a meaningful scale. The jet fuel example is also central because the ADF, Qantas and Virgin make up such a significant portion of the Australian consumer market that concerted action by this relative handful of players would have a potentially outsized effect.

Airport and port operators are other key partners in realising alternative fuel use at scale across the country. Defence is partly dependent on such commercial facilities, but they are also critical because they represent the physical nexus at which many of these technologies and inputs need to be pulled together.

Targeted but significant investment in research on hydrogen and battery technologies should also be in the policy mix, and hopefully that’s all part of what the department refers to when it cites these technologies in the brief.

How Defence’s efforts on this front are integrated with those of our allies, whose economies and militaries operate at significantly greater scale than our own, is another important open question.

Our conversations with major industrial and investment players in this space have indicated that there’s significant investment appetite remaining, beyond existing and high-profile initiatives like the Sun Cable venture. The right policy levers need to be pulled to ensure that a portion of this capital is allocated to potential technologies and capabilities with strategic military, not just economic, relevance. As much transparency as possible about Defence’s strategy to meet its targets should be part of such an approach, because it’s necessary to facilitate engagement with partners across the economy.

We now know that Defence has set itself remarkably ambitious emissions reductions targets. Modest innovations like the electric Bushmaster and investment in solar power across the defence estate are important steps forward. If a net-zero commitment for 2040 is to be met with more than huge purchases of carbon offsets, still larger policy steps will be needed without delay.