The world is getting hotter, and increasing heat could exacerbate global instability and conflict. The US military views this situation as a “threat multiplier,” one of the global changes threatening national security and potentially contributing to the ever-evolving character of warfare. In response, the Department of Defense is adapting equipment and installations. Hardening infrastructure that supports warfighters makes sense—and measures like micro–power grids also make installations more resilient against direct threats like cyberattacks. At the same time, the US military services also feel acute pressure to reduce carbon emissions; the US military is the world’s largest institutional producer of greenhouse gases, emitting more each year than entire industrialized countries like Sweden or Denmark and accounting for some 80 percent of federal energy consumption. Climate-related challenges are most immediately apparent for the Navy and Air Force, which rely on weapons platforms deployed from fixed installations to fight. Newport, Virginia, home of the largest naval base in the world, faces increasing flooding even during sunny days when sea level rise combines with high tides. To fly in hotter, less dense air, Air Force aircraft need to significantly reduce their operational load or flight range.

However, in one critical area, there have been limited efforts to address the threat of increasing temperatures: the soldier. Army installations don’t face chronic flood risk like Navy facilities, and Army equipment may be better able to operate in extreme temperatures and weather than Air Force stock. But soldiers have the fundamental constraint of being human, and the human body has physiological limits to operating in heat. Human physiology also adapts to changes at timescales driven by evolution, not technological innovation. Already, parts of the world are experiencing hot temperature extremes approaching the limits of what a healthy human can work in. Considering the impact of climate change on the soldier and developing adaptations to deploy, fight, and win in future conflicts is as important as ensuring equipment and installations are prepared for a climate-altered future.

Soldier Thermal Physiology 101

Heat stroke is characterized by central nervous system dysfunction, typically when a body’s core temperature exceeds 104ºF, although it can occur at lower temperatures. True heat stroke generally requires treatment within ten minutes to minimize organ damage and thirty minutes to prevent death. Protecting against heat stroke is already challenging in the current climate; 2,103 US service member heat strokes occurred between 2018 and 2022, with rates highest for soldiers and Marines.

Preventing soldier heat stroke in a hotter operational environment will be complicated by the limits of human physiology. Human core temperature can stray only slightly from normal levels before heat-related illness occurs. Just maintaining basic life functions generates body heat. Without the ability to shed metabolic heat, a resting soldier (or any human) would experience a core temperature rise of around 2ºF per hour. Fortunately, humans sweat to keep the core temperature stable in hot conditions. When ambient temperature exceeds skin temperature (above approximately 95ºF), sweating is the only effective method to shed body heat.

Although human physiology is generally good at preventing heat stroke, two additional factors require consideration. First, soldiers engaged in physically laborious activities generate huge amounts of metabolic heat—up to ten times more than when resting. Heat generated from work can result in heat stroke if not dissipated fast enough. Second, sweating only works if it evaporates from the skin; dripping sweat does nothing to cool body core temperature. In high humidity environments, sweat doesn’t evaporate freely; the higher the humidity, the less effective sweating becomes. For soldiers, uniforms and equipment also reduce sweat evaporation. Little sweat evaporates from under body armor, and (by design) chemical suits are virtually impermeable.

What Do a Few Degrees Matter?

The US National Security Strategy, the secretary of defense, intelligence assessments, and DoD reports all note climate change threatens US national security. But for militaries, weather has always been strategically, operationally, and even tactically relevant. Aside from installation and equipment resiliency, few sources describe how to prepare militaries to operate in expected climate-altered conditions. This is true even of the Army Climate Strategy. Despite making “training” one of its three lines of effort, the strategy gives little consideration to the impacts of rising temperatures on soldiers. By contrast, carbon emission reduction features prominently in its discussion of the training line of effort, as it does in all service climate strategies. So how much will a few degrees of global warming really matter to the Army?

Climate change as it is currently occurring is characterized by the rapid increase in Earth’s temperature, but impacts differ at regional and local scales. Rising global temperatures increase the frequency and intensity of extreme events like heat waves, creating future conditions that will drastically change the operational environment. A few degrees of rapid global warming will destabilize the climate system, reducing the occurrence of average temperatures and increasing the occurrence of hot temperatures, as shown in Figure 1. Not only does the distribution of temperatures shift warmer (i.e., rightward), the right “tail” (i.e., hot extremes) gets bigger. This significantly increases the frequency of extremely hot days—by 2050 DoD projection tools anticipate a 375 percent increase in the number of days above 95ºF at Fort Liberty, North Carolina.

Figure 1: Global temperature distribution changes. The y-axis is the frequency of temperature occurrences. Between 1962 and 2022, the distribution curve peaks—the most frequently observed temperature—shifted by about 2ºF warmer (rightward), while the number of occurrences at the hottest (right) end of the distribution (beyond 4.0ºC, or 7.2ºF, higher than the distribution peak) also increased significantly. (Data source: NASA)

Increasingly frequent and severe heat waves will significantly affect land operations. Heat waves in the United States are already twice as common as they were forty years ago, and record-breaking heat is occurring more commonly across the globe. A RAND report on the Middle East finds that in a pessimistic scenario, by 2050, Iran may experience 120 days of extreme heat (up from seventy-six historically) and thirty more days of “extreme danger” temperatures each year, defined according to the National Weather Service heat index. Already, temperature and humidity combinations in select regions are approaching the limit of tolerance even for humans resting in shade; such conditions will expand to more regions, occur more frequently, and be more intense as the climate warms.

Military Operations in the Heat: Vulnerabilities and Opportunities

Throughout history, climatic conditions have never been merely the “backdrop to human events,” especially in warfare. While shifting climatic conditions do not determine human decisions, they nonetheless limit or expand choices available to combatants. In the era of rapid climate change, military professionals must recognize the environment’s influence on warfare. Environmental conditions undoubtedly impact how, when, and where countries fight. Over the long history of states and interstate conflict, Earth’s average temperature changed only modestly. It was often only when empires dispatched armies to hot climates—Roman legionnaires around the border of present-day Syria, for example, or British redcoats in today’s Haiti—that extreme heat played a substantial role in military history. Local and regional variations in temperature did occasionally affect military campaigns, influencing the progress of Spanish forces in the seventeenth-century Low Countries, for instance, but there is no historical analogue for the magnitude of warming in the coming century or its probable impact on soldiers. Earth is likely to  soon be hotter than it has been in millions of years, and armies will surely find it hard to cope, but emerging climatic conditions also provide opportunities for resilient and adaptive armies. As the climate changes at an increasingly rapid pace, the ability to adapt to changing conditions may influence who wins and who loses on future battlefields. While climatic threats are threats without passports that do not respect the sovereignty of nation-states, national decisions can influence where states end up in the race to harness the heat, with some countries already starting to adapt their armies to hotter conditions.

  • Singapore has a history of policies to prevent soldier heat stroke. Recruits are grouped by fitness levels and prescribed appropriate training programs; less fit recruits attend an eight-week physical training phase prior to the nine-week vocational training program. Thermoregulatory profiling is implemented to determine return-to-duty status and profile soldiers undertaking highly demanding (e.g., commando) training.
  • The Indian Army, operating in the intense heat of the subcontinent, has incorporated research into educating its soldiers on the need for the gradual increase of rigorous training to acclimatize units to perform military functions in extreme heat.
  • China’s military, along with others, has tried to optimize its uniforms and lighten its troop equipment, although climate concerns are generally missing from national and strategic military documents, exposing a potential area of vulnerability if the People’s Liberation Army is slow to adapt to changing environmental conditions.

Harnessing the Heat for Operational Advantages

Anyone who deployed to Afghanistan, Iraq, or Kuwait during the summer months in the past twenty years will remember that feeling of exiting the plane in what feels like an oven. As the world heats up, armies may find themselves fighting in extreme temperatures more often. They must consider how to prepare soldiers to maintain lethality in the face of challenging climatic circumstances.

First, soldiers must embrace fitness in the heat. Unlike in past contingencies such as Operation Desert Storm, future crises will be unlikely to provide soldiers with time and safe areas to acclimate, necessitating options to do so at home stations. One solution would be establishing heated bubble gyms to train activities such as ruck marches, individual movement techniques, medical evacuations, battle drills, and functional fitness. Training in such an environment would be particularly beneficial in the two weeks prior to deployment by enabling physiological heat acclimatization processes to take place. There are additional benefits to training in hot environments, such as blood plasma volume increase enhancing cardiovascular fitness, a reduction of core temperature when exercising, and increased skeletal muscle force. Some studies also indicate heat training is superior to altitudinal training, providing enhanced aerobic power.

Second, the US Army should examine efforts to keep soldiers cool through personal equipment adaptation, especially by innovating uniforms and body armor and developing means to better assist with load bearing. The ideal improvement may be the development of a uniform similar to the “Fremen stillsuits” depicted in the film Dune to extend the range of environments humans can work in. A whole-body cooling suit may seem like the stuff of science fiction now, but we can generally imagine what it might look like. Progress in materiel sciences and energy storage may result in advances leading to such cooling suits and research along such lines should continue to be pursued. Such equipment could recycle body moisture or use a cooling agent to augment the body’s ability to shed metabolic heat. More immediately, modifications can be made to the current Army uniform by drawing inspiration from traditional indigenous practices such as Bedouin dress, which uses breathable fabrics to allow maximum airflow. Another example is innovative armor that stops bullets and assists with temperature regulation or incorporates biosensors to help prevent heat injuries. On this front, the US Army has made inroads in its work on an initial biomonitoring device. Further developing self-cooling systems compatible with body armor would optimize performance in extreme temperatures. Additional adaptations include reducing load-bearing requirements for soldiers by emphasizing lightweight weapons and radios and by incorporating robotics, such as robotic mules or exoskeletons, to aid soldiers in carrying supplies, thus reducing their physical burden.

Third, the US Army must consider climate impacts on partner nations, assessing their forces’ ability to operate alongside US personnel in future hotter environments. Many nations will increasingly rely on militaries—including US forces—to respond to humanitarian crises and instability exacerbated by climate change. Focused internally, partner militaries may train less for warfighting, degrading readiness for combined operations, especially with US forces. Partner nations must also have resilient infrastructure to host US forces. Climate-resilient barracks and buildings, or heat casualty treatment facilities, may be needed as US soldiers acclimatize to local extreme heat.

To facilitate partner nation adaptations, combined summer training should encourage experimentation. A subset of these training exercises must assess how partners operate in the heat, potentially adopting local techniques. Although partner militaries may be more accustomed to locally hotter temperatures, increasingly frequent record heat means even militaries in tropical regions will struggle to operate during extreme heat waves. Heat casualty transportation and treatment should be exercised and evaluated during combined training and extreme temperatures included in operational planning. Seemingly mundane considerations like generating and transporting potable water and ice will be critically important during heat waves no matter if they occur during training, a humanitarian response, or hot conflict.

While ensuring infrastructure and equipment are ready to face the challenges of climate change is crucial, the US military must not forget its most important asset: its people. Even in an age of drones, cyberattacks, and AI, humans are still required to fight in challenging environments that are becoming more inhospitable with increasing temperatures. Threats presented by climate change are not abstract; they are real, are increasing in severity and frequency, and can be no less lethal than enemy fire. The US Army especially must continue research and investment to provide the best training, policy, and individual equipment to counter this threat. The warriors on the front line against enemy combatants will increasingly also face a very hostile force of nature, but by incorporating adaptations that allow them to operate despite extreme heat, these soldiers will gain a distinct advantage over their adversary.

Erik Patton, PhD, RG, is an active duty Army major assigned to the Advanced Strategic Planning and Policy Program at Duke University with a research focus on the implications of climate change on military training. He has sixteen years of service, including assignments with the 1st Infantry Division, 1st Armored Division, 25th Infantry Division, and Army Corps of Engineers, and has led soldiers in Iraq. He has published on the impact of increasing extreme heat on Army training programs.

Antonio Salinas is an active duty Army lieutenant colonel and PhD student in the Department of History at Georgetown University, where he focuses on the history of climate and conflict. Following his coursework, he will teach at the National Intelligence University. Salinas has twenty-five years of military service in the Marine Corps and the US Army, where he led soldiers in Afghanistan and Iraq. He is the author of Siren’s Song: The Allure of War and Boot Camp: The Making of a United States Marine.

Dagomar Degroot is an associate professor of environmental history at Georgetown University and the incoming Baruch S. Blumberg NASA/Library of Congress Chair in Astrobiology, Exploration, and Scientific Innovation. His first book, The Frigid Golden Age, was published by Cambridge University Press in 2018 and named by the Financial Times as one of the ten best history books of that year. His forthcoming book, Ripples on the Cosmic Ocean, is under contract with Harvard University Press and Viking, and he is editing several books on past climate change—including the Oxford Handbook of Resilience in Climate History. Degroot publishes equally in historical and scientific journals, including Nature and the American Historical Review, and writes for a popular audience in, for example, the Washington Post, Aeon magazine, and The Conversation. He maintains popular online resources on the history of climate change and has shared the unique perspectives of the past with policymakers, corporate leaders, and journalists in many cities, from Wuhan to Washington, DC.

The views expressed are those of the authors and do not reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.

Image credit: Spc. Steven Alger, US Army