Climate change’s threat to national security has been widely examined by security agencies, researchers and thought leaders across the world. Much of this analysis has focused on adaption and operational considerations associated with the destabilisation of societies, the impact of climate change on military assets or the potential for conflict over resources. By contrast, the Defence Establishment’s role in climate mitigation has historically been overlooked. It notably received almost no coverage during the recent COP28 in Dubai—although the conference took place in the context of major conflicts in Ukraine and Gaza.

Given climate change is a well understood national security issue, it stands to reason that Defence has a role in mitigating climate change by reducing its own emissions. Globally, there is increasing awareness of the contributions of national defence to global greenhouse emissions. One widely cited estimate suggests militaries are responsible for around 5% of global emissions and the International Military Council on Climate and Security has acknowledged that defence forces are the ‘largest single institutional consumer of hydrocarbons in the world’.

As a founding member of the global Net-Zero Government Initiative (NZGI), Australia has made global commitments to achieve net zero in government operations by 2030. Yet security agencies such as Defence do not explicitly form part of the commitment or other climate commitments such as the 2015 Paris Agreement. This is notable given defence is typically a major contributor to governments’ greenhouse gas emissions. The Ministry of Defence accounts for 50% of UK Government emissions, the Department of Defense (DoD) accounts for 76% of total US Government emissions (equivalent to around 1% of total US emissions) and Australia’s Department of Defence accounts for around 73% of public sector emissions according to the most recent Net Zero in Government Operations annual progress report.

For this reason, governments across the world are setting emissions reduction targets for their militaries such as the US Army’s aim of achieving a 50% reduction by 2030 and net-zero army emissions by 2050. Britain’s Royal Air Force aims to become the first net zero air force by 2040.

In 2009, the US Navy modified a carrier strike group to use advanced biofuels to demonstrate energy-saving technologies. This ‘Great Green Fleet’ completed its year-long deployment in 2010 and demonstrated the feasibility of alternative fuels and energy efficiency measures. The lessons learned have since been integrated into Navy operations.

We have previously reported that Australia’s Department of Defence is matching the government’s overall 43% target by 2030 and committed to a net-zero position a decade ahead of the government’s overall national target.

We welcome this ambition but we also recognise the operational complexities associated with reducing defence emissions. As we have explored in a previous article, Defence operates a range of capabilities that are very difficult to decarbonise because we lack viable alternatives for things like powerful jet and marine engines. It is widely acknowledged that emissions reduction should not comprise defence operational and capability requirements. It is therefore helpful to distinguish operational emissions from those of the defence estate (referred to as ‘military installations’ by the US DoD) and their relationship with mission-critical capabilities. Notably, US military installations account for 37% of DoD emissions which are primarily attributed to fossil fuel used for on-site electricity and heat generation, grid-sourced electricity derived in part from fossil-fuel generation sources, and non-tactical transportation fleets that run on fossil fuels.

Assuming the emissions associated with Australia’s defence estate are broadly consistent with the US military installation emissions (unfortunately, Australia’s emissions reporting does not currently offer the same level of detail), there are meaningful opportunities to reduce emissions across Defence’s estate of 700 owned and leased properties. These include critical infrastructure and facilities such as military bases, wharves, ports, airbases, training ranges, fuel and explosive ordnance infrastructure.

The decarbonisation of the defence estate poses a significant opportunity for Australia’s climate mitigation efforts as well as broader national security objectives. To drive emissions reductions in an efficient, cost effective, safe and systematic way, we believe Defence should:

• Measure and report on emissions—you can’t improve what you don’t measure. The US DoD is a leader in this and demonstrates how greater reporting and transparency can lead to improved decision making and increased ambition in emissions reduction
• Develop an updated, data-driven sustainability strategy and delivery program for the defence estate that sequences projects to manage costs, minimise operational impacts and aligns with wider policy and strategic objectives. Australia’s 2016-2036 Defence Environmental Strategy is already dated and mostly overlooks climate mitigation
• Embed sustainability and climate mitigation in defence estate sustainment and investment decision making including consideration of how rationalising the estate could result in reduced emissions and the role for the National Australian Built Environment Rating System or the green Star Rating System
• Prioritise onsite energy production and storage to improve resilience and energy security and cost effectiveness, and reduce impact on civilian energy networks
• Use Defence’s scale, expertise and purchasing power to investigate use of cost effective, innovative low emission alternatives, such as microgrids, modular reactors and hydrogen
• Leverage the defence estate to reduce and offset operational emissions such as the deployment of additional energy production, electric vehicle charging infrastructure, reforestation initiatives, carbon capture and sequestration
• Pursue knowledge sharing initiatives with our military partners in other jurisdictions as well as the private sector (as in port or airport operators) to ensure we are adopting best practice and sharing what we learn.

In contrast to military operations, the decarbonisation of the defence estate presents low hanging fruit easily harvested for Australia to reduce emissions associated with government operations. That would make a meaningful contribution to achieving the government’s commitment to achieving net zero emissions by 2050. By reducing emissions in a systematic, cost-effective way that minimises operational disruption, the defence estate can sustainably provide the infrastructure and services our defence personnel need now and into the future.