The climate impact of war

War is first and foremost a human tragedy. It results in devastating and unnecessary loss of life, disruption of families and communities, and the fracturing of societies. As we continue to see a concerning escalation in conflict and war globally, it would be remis to not also talk about the often devastating but overlooked impact of conflict and war on the environment. Warfare wreaks devastation on human developments, but also on landscapes and wildlife – as images of desolated cities, rubble, and destroyed green spaces attest to. Conflict and war, as well as militaries, also have considerable carbon footprints, contributing to climate change. The climate impact of war and militarisation is rarely surfaced in decisions on warfare or climate policy, partly because of limited reporting and partly because it straddles concerns and priorities around national security and sovereignty. Nevertheless, ongoing research suggests that the climate implications of warfare are significant and growing. Understanding these impacts is increasingly important, not only for climate mitigation but also for anticipating how a changing climate may shape the conduct of warfare itself.

The global military sector is one of the world’s largest producers of greenhouse gas emissions. The US military alone has been described as the world’s largest institutional emitter of greenhouse gases. Recent estimates suggest that the carbon footprint of the world’s militaries (including personnel, operations, infrastructure, and supply chains) amounts to roughly 2.75 billion tonnes of carbon dioxide equivalent annually, or about 5.5% of global greenhouse gas emissions. If the world’s militaries were treated as a single country, they would rank amongst the largest emitters globally. These figures likely underestimate the true scale of emissions. Reporting on military emissions remains inconsistent and incomplete, and in many cases classified. Indeed, international climate agreements historically treated military emissions differently from other sectors. Under the Kyoto Protocol, for example, some military activities were exempted from national reporting requirements, and under the Paris Agreement disclosure remains voluntary. 

What are the sources of military emissions? Modern armed forces rely on energy-intensive equipment (e.g., fighter jets, naval vessels, tanks, and transport aircraft) that burn large quantities of fossil fuels. Large military institutions also maintain extensive infrastructure networks. The construction of fortified bases, airfields, bunkers, and defensive walls requires large volumes of cement, a material responsible for roughly 8% of global emissions in its own right. Studies of US military infrastructure during the Iraq war have shown that even a single category of defensive concrete barriers generated tens of thousands of tonnes of carbon dioxide. Once operating, these facilities, in addition to training facilities, logistics hubs, and surveillance systems, consume energy on a scale comparable to medium-sized cities. Beyond direct fuel use, the military supply chain contributes to emissions. The production of weapons systems, vehicles, electronics, and ammunition involves energy-intensive industrial processes and complex logistics systems. Steel, aluminium, and advanced composites used in military equipment carry substantial embodied carbon. Also rarely assessed is the climate heating due to military aviation emissions in the stratosphere. 

Alongside this, there are wider environmental impacts of war. Bombing campaigns damage energy systems, industrial facilities, and urban infrastructure, often triggering fires and chemical releases that increase atmospheric pollution. War can lead to large-scale deforestation and damage to other biological carbon stores, contamination of soil and water, and long-term ecosystem disruption. Importantly, emissions from rebuilding after conflict may exceed those produced during the fighting itself. Reconstruction requires vast amounts of cement, steel, and energy, often in regions where infrastructure is already strained. It has been estimated, for instance, that in the first seven months of the war on Ukraine, approximately 100 Mt carbon dioxide equivalents were released, largely due to post-conflict reconstruction, forest fires, and leakage of methane due to the Nord Stream gas pipeline.

The climate impact of warfare is worsening with increasing militarisation. Global military spending has increased steadily in recent years, reaching record levels amidst rising geopolitical tensions. Higher defence spending typically translates into greater procurement of energy-intensive equipment and expanded operational activity. Research also suggests that military expenditure has a disproportionate emissions footprint compared with other forms of public spending. Each dollar allocated to defence generates more greenhouse gas emissions than an equivalent dollar invested in civilian sectors such as health, education, or public infrastructure. 

Military spending can also indirectly influence climate outcomes by shaping investment priorities. Large defence budgets may crowd out funding for renewable energy and climate adaptation. Indeed, some studies have found that increases in military spending are associated with higher national emissions and slower progress towards decarbonisation. At the same time, geopolitical tensions and security concerns may drive governments towards more carbon-intensive energy policies. Conflicts that disrupt energy markets often lead countries to prioritise domestic fossil fuel production or short-term energy security over longer-term climate commitments.

Efforts to reduce military emissions

Fortunately, the climate implications of military activity are beginning to receive greater attention with some efforts to mitigate this. For instance, some militaries are investing in renewable energy systems, such as solar microgrids on bases, to reduce dependence on fossil fuels. Electrification of non-combat vehicles are also being explored, as are alternative fuel sources such as nuclear reactors in submarines or biofuels in aviation. Other areas of effort involve technological shifts in warfare. Unmanned systems, cyber operations, robotic vehicles, and satellite-based capabilities may in some contexts reduce the need for fuel-intensive equipment such as manned aircraft or armoured vehicles. Both the British and US Ministry of Defence has noted, for instance, the co-benefits of low-carbon technologies in gaining advantage in warfare, as less reliance of fuel mean armed forces can fight for longer. However, these developments do not necessarily guarantee lower emissions overall, particularly if they lead to expanded operations or new forms of military activity. Additionally, there are ethical concerns involved in some of these technologies, such as the reduction in accountability from using drones or the potential for nuclear radioactivity risk.

Obviously, avoiding war in the first instance will be the best mitigation method. Indeed, historical research on military emissions shows declines during periods of peace. Between 1990-2000, for instance, emissions from the US and UK military declined by 41% and 45% respectively. Engaging in diplomatic and non-violent measures of navigating nation-state differences, although inherently complicated (especially in a world run by ‘strong-men’), could avoid unnecessary loss of life while also having benefits for the environment. 

Warfare in a changing climate

While war contributes to climate change, the reverse relationship is also increasingly relevant. Climate change is altering the physical and geopolitical conditions in which conflicts occur. Rising temperatures and more frequent extreme weather events can intensify competition over land, water, and food resources. In fragile regions, these pressures may increase the risk of instability and conflict. At the same time, climate change can affect the operational environment for militaries themselves. Heat extremes can reduce the performance of personnel and equipment. Flooding and sea-level rise threaten coastal bases and naval facilities. Melting Arctic ice is opening new shipping routes and strategic competition in previously inaccessible regions. 

Humanitarian missions are also becoming more common in a changing climate. Armed forces are increasingly deployed in disaster response, supporting evacuations, rebuilding infrastructure, and delivering aid following climate-related events such as hurricanes, floods, and wildfires. As such, some analysts have argued that climate mitigation itself should be viewed as a security priority. Reducing global emissions can help limit the destabilising effects of climate change that ultimately shape conflict and warfare.

Bringing war into the climate conversation

Conflict and war remain underexamined contributors to global emissions. Compared with sectors such as transport, energy, or agriculture, military activity has historically received far less scrutiny within climate debates, despite available evidence suggesting its substantial impact. Addressing this gap does not diminish the appalling human costs of conflict, nor does it suggest that security concerns are secondary to environmental ones. Rather, recognising the environmental consequences of war broadens the understanding of how conflict affects societies and ecosystems. 

In an era defined by both geopolitical tension and accelerating climate change, integrating military emissions into climate governance will likely become increasingly necessary. Improved reporting, technological innovation, and greater alignment between security and climate goals may help reduce the carbon footprint of defence activities. At the end of the day, the most effective way to reduce the carbon footprint of war remains the same as reducing its human toll: preventing conflict where possible and pursuing peace where it can be achieved.

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