Climate Change Poses a Hidden Challenge to NATO Nuclear Deterrence

Climate change stands to challenge the U.S. nuclear deterrent in increasingly serious ways. Sea level rise, extreme weather events, and warming temperatures could have mission-altering impacts on deterrence, significantly challenging the nuclear systems, activities, and operations at key bases in the United States that host nuclear weapons. But other bases hosting U.S. nuclear weapons overseas could also be challenged by climate change impacts.

As part of its extended deterrence efforts, the United States forward deploys nuclear bombs in Europe. An estimated one hundred warheads for dual-capable aircraft (DCA) are reported to be stored at six air bases in Belgium, Germany, Italy, the Netherlands, and Türkiye. As their name suggests, DCA serve both conventional and nuclear roles, the latter placing the DCA mission at the core of NATO’s nuclear sharing arrangement.

Climate change presents a challenge to this mission. Flash flooding, wildfires, and extreme heat could pose significant risks to the systems, infrastructure, and personnel that support the DCA mission. Greater efforts should be made to assess these risks and ensure NATO is prepared to effectively address the impacts of climate change on its nuclear deterrent.

A Gap in NATO’s Climate Security Work

NATO is committed to remaining a nuclear alliance so long as nuclear weapons exist. To maintain a robust deterrence posture, the alliance makes significant efforts to ensure its nuclear forces remain credible, especially in the face of “technological and geo-strategic evolutions.” Missing, though, is a careful evaluation of how geophysical evolutions prompted by climate change could also impact the credibility of NATO’s nuclear forces.

This gap is surprising given NATO’s efforts to address other climate risks. The alliance has set itself the goal of becoming the “leading international organisation” for understanding and adapting to the impacts of climate change on security and has made important progress toward that end. Take the Climate Change and Security Action Plan and the follow-on impact assessments from 2022 and 2023, initiatives aimed at assessing—and increasing members’ awareness of—the impacts of climate change on NATO’s security. The 2023 Impact Assessment summarizes just how expansive these impacts are:

“Overall, climate change risks are relevant to all components of NATO’s deterrence and defence posture, including situational awareness and strategic anticipation; training, exercises and operations; infrastructure and installations; capability development and equipment; as well as resilience and the enablement of the Area of Responsibility of the Supreme Allied Commander Europe.”¹

However, this work does not consider potential climate change challenges to the alliance’s nuclear forces, its DCA in particular.² In addition to the nuclear weapons deployed by the United States, allies provide supporting infrastructure as well as the aircraft themselves (specifically, F-16s and PA-200 Tornados, both of which are slated to be replaced by F-35As). While the nuclear weapons remain in the custody and control of U.S. Air Force personnel stationed at the European bases in peacetime, the DCA are equipped to carry those weapons in a conflict and are “available for nuclear roles at various levels of readiness.”

A lack of focus on the DCA mission in NATO’s public-facing climate security work is perhaps to be expected, considering the alliance does not even officially acknowledge where in Europe U.S. nuclear weapons are located. Moreover, allies may be reluctant to acknowledge the potential vulnerability of the alliance’s nuclear assets to climate change and thus potentially undermine the credibility of NATO’s nuclear deterrent. But a greater risk to the credibility of NATO’s nuclear deterrent may in fact be the potential impacts of climate change on the DCA mission—say, the destruction of a DCA base by a wildfire. Assessing and preparing for these impacts does not undermine the credibility of that deterrent. It enhances it.

Climate Change and the DCA Mission

Collectively, the European bases that host U.S. nuclear weapons—reportedly, Kleine Brogel in Belgium, Büchel in Germany, Aviano and Ghedi in Italy, Volkel in the Netherlands, and Incirlik in Türkiye—are projected to face flash flooding, wildfires, and extreme heat that could affect their capacity to deliver the DCA mission.³ Importantly, these climate change effects are projections, so they should be considered as potential future outcomes rather than predictions. The mere prospect of their impacts on the DCA mission, however, merits serious consideration.

Flash Flooding

The intensity and frequency of heavy rainfall events are projected to increase across Europe, which will in turn increase the risk of flash flooding. While projected changes in the severity of these events vary by region and under different emissions scenarios, any resulting flash flood could be “deadly and costly,” not least due to how rapidly these floods can overwhelm critical infrastructure.

A 2019 flood at Incirlik Air Base in Türkiye—the only base that hosts U.S. nuclear weapons but not DCA—illustrates the kind of impacts flash flooding can have on base personnel. Nearly 9.8 inches (248.9 millimeters) of rainfall inundated Incirlik over just two days. The rapid rainfall overloaded the base’s drainage system and flooded facilities at lower elevations, including the base’s water treatment plant. Water levels in the plant hit 5 feet (1.5 meters), making the plant inoperable and leaving personnel without clean water for the nearly twenty-four hours it took to repair the damage. Notably, it does not appear that the on-base vaults storing U.S. nuclear weapons were impacted by the flash flood, although it is conceivable that these underground facilities could experience water infiltration challenges during particularly severe flooding events.

Flash flooding may have even more direct impacts on the broader DCA mission at bases that host both U.S. nuclear weapons and DCA. According to our modeling, Volkel Air Base could see a 5 percent average annual increase of rain between 2020 and 2039 under a medium-high-emissions scenario (RCP6.0; see box 1) compared to the region’s historic annual average of 30.58 inches (776.73 millimeters). Even an apparently modest increase of annual rainfall can increase the likelihood of a flash flood—as the mean moves, extremes become more extreme. So although the base is relatively insulated from sea level rise—unlike most of the Netherlands—it may be increasingly vulnerable to flash flooding.

In a worst-case scenario, such flooding could rapidly inundate the base’s only runway, requiring the evacuation or forcible grounding of aircraft, similar to the incident that occurred at Offutt Air Force Base in Nebraska in 2019 when a record-setting flood inundated about a quarter of the base’s runway. Because Volkel is a DCA base, a flooded runway could mean that the nuclear weapons stored there may not be deployable in a nuclear mission—even if the weapons could be loaded onto DCA, those aircraft might not be able to take off. That could have serious implications for the overall readiness of the DCA mission. These issues would only be compounded if flash flooding prevented critical personnel from accessing the base, a plausible scenario as personnel at Volkel live off base. Büchel or Kleine Brogel could face similar challenges, especially given the record-setting floods that severely impacted regions near these bases in recent years.

Wildfires

Rising temperatures and more frequent, longer-lasting incidences of drought are exacerbating the risk of wildfires in Europe, as exemplified by the devastating fires that scorched much of the continent in 2022. Southern Europe will likely continue to face the greatest wildfire risk, a trend projected to be most pronounced at Incirlik and Ghedi Air Bases. Compared to averages from 1970 to 2005, Incirlik is projected to experience nearly seventeen more days and Ghedi nearly six more days of high fire danger by late century under a medium-emissions scenario (RCP4.5)—an optimistic scenario as, even if all countries stick to their current climate pledges, warming is expected to exceed this scenario by 2100.

A wildfire could significantly undermine a base’s ability to deliver the DCA mission. A fire that affects a base itself would pose obvious risks to infrastructure and personnel, entirely disrupting operations and requiring emergency efforts to secure facilities and key assets. U.S. nuclear weapons stored in underground vaults would likely be relatively insulated even if rendered inaccessible, but DCA would need to be evacuated. The risks involved suggest base personnel and local firefighters would undertake all possible measures to prevent a wildfire from reaching a DCA base in the first place. But even if a wildfire does not cross a base’s perimeter, operations could still be severely disrupted. Unhealthy air quality could require personnel to remain indoors for all but essential activities. Even assuming DCA activities are deemed essential, an encroaching wildfire would likely pose significant challenges to getting DCA personnel on and off base. And any efforts to evacuate DCA may be impeded by low visibility caused by smoke from the fire.

Beyond these direct challenges to the DCA mission, wildfires and other climate hazards could indirectly impact the mission. Namely, they could cause a significant strain on resources since military personnel are often called upon to supplement civilian disaster response efforts.

Extreme Heat

Europe is already experiencing more hot days per year, defined as days with temperatures above 86°F (30°C), compared to the twentieth century. By the end of the twenty-first century, the number of hot days is projected to double under a medium-emissions scenario (RCP4.5). Extreme temperatures are projected to be especially pronounced in Southern Europe, which may have a notable impact on Aviano and Ghedi Air Bases in Italy. In a medium-emissions scenario, the region is projected to face an average of fifty to seventy-five hot days per year by late century, compared to an average of thirty-two days from 1986 to 2005.

Extreme heat could disrupt operations at Aviano and Ghedi, with potential implications for the DCA mission. On the ground, extreme heat can severely affect personnel—excessive temperatures increase the risk of heat exhaustion and heat strokes. Consequently, the U.S. Air Force, for example, limits and even suspends some personnel activities under various extreme heat conditions defined according to the wet bulb globe temperature, a metric of heat stress in direct sunlight. If Northern Italy experiences such conditions, these limits and suspensions would affect the U.S. personnel tasked with maintaining the nuclear warheads stationed at Aviano and Ghedi. Extreme heat conditions may also affect pilots’ readiness by limiting on-the-ground cockpit times.

Extreme heat can also strain local energy grids, whether due to high demand for cooling or due to damaged or overheated critical infrastructure. While the bases could likely rely on emergency generators in the worst-case scenario of a blackout, base operations—including activities related to the DCA mission—might have to be reduced to conserve energy. (The risk of stress to energy grids is another argument for renewable energy generation and energy storage on NATO bases.)

The DCA themselves may also be challenged by extreme heat conditions. Hotter temperatures mean warmer, less dense air that makes it harder for aircraft to generate lift, which could pose problems for takeoff and landing. It could also reduce the aircraft’s fuel or payload capacity, with implications for the duration and scope of DCA operations in a nuclear contingency. And these impacts would only be exacerbated by any additional wear and tear caused by warmer temperatures, including damage caused by overheated engines or other mechanical parts.

A Deterrence Challenge Deserving of Attention

Importantly, there is some inherent resiliency in the DCA mission. The distribution of the mission across six bases in five countries means that even in a worst-case scenario, it is highly unlikely that any one climate hazard could significantly impact all bases’ capacities to deliver the DCA mission.

Nevertheless, NATO should devote more attention to assessing and preparing for the challenges climate change could pose to the DCA mission. NATO is rhetorically committed to remaining a nuclear alliance as long as nuclear weapons exist, a status that rests significantly on this nuclear sharing arrangement. Moreover, allies have also made quite costly investments to ensure the alliance can rely on the DCA mission for decades to come—namely, the significant political and economic costs associated with acquiring F-35As to replace the current DCA. Experts have already expressed concerns about these systems being overstretched given their dual-hatted role; if a handful of DCA were rendered unusable or inoperable by climate change effects, that would have significant impacts on both conventional and nuclear operations. The alliance therefore has a vested interest in ensuring climate change does not undermine the credibility of the DCA mission.

In its more general climate security work, NATO itself acknowledges the need to consider “widespread adaptive measures” to deal with the impacts of climate change, including runway length extensions, reduced payload capacity, and engineering modifications and upgrades. To prepare for potential impacts on the DCA mission, NATO should conduct comprehensive risk assessments of all relevant installations, operations, and activities, as well as implement various risk mitigation and adaptation measures. The risk assessments should include an examination of possible climate change effects at DCA bases under various emissions scenarios. Unlike some recent NATO analyses that are primarily based on a worst-case, high-emissions scenario (roughly comparable to RCP8.5)—which is considered unlikely due to foreseeable emissions cuts—the alliance would be better served by assessing climate effects under medium- and medium-high-emissions scenarios (RCP4.5 and 6.0) that are more widely accepted as plausible outcomes. Importantly, these analyses should be dynamic, that is, regularly updated to ensure they account for the latest climate modeling research.

As part of its mitigation and adaptation efforts, the alliance should identify both built and natural infrastructure solutions—such as floodwalls or fire-resistant vegetation—to better insulate the DCA bases from climate change effects. Moreover, it should consider various measures for further insulating nuclear vaults from extreme weather hazards. The alliance should prepare for more regular maintenance of DCA and related systems and infrastructure stressed by extreme climate conditions. It may also consider how measures taken to address other challenges at DCA bases could simultaneously help make them more resilient to climate change challenges. For example, the security upgrades at Incirlik and Volkel, which involved installing and burying cables that connect the nuclear vaults, may also make the base communications systems more resilient to storms or other extreme weather events. Similarly, the Aviano Renewable program, which aims to help NATO achieve its emissions reduction goals, could help make the base less reliant on local electricity grids that could be strained by climate hazards.

But more work must be done. Dedicated efforts will be needed to prepare the alliance for mitigating and adapting to climate change challenges to the DCA mission. So long as NATO relies on nuclear weapons to deter the most acute dangers, the alliance has a vested interest in ensuring its nuclear capabilities are not impeded by one of the world’s greatest chronic challenges—climate change.

Notes

¹ In this context, “enablement” refers to support for the transport and sustainment of deployed NATO forces.

² In addition to the DCA mission, NATO’s nuclear deterrence relies on U.S. strategic forces that act as the “supreme guarantee” of the alliance’s security as well as UK and French strategic forces that contribute to the overall security of the alliance.

³ All of these bases, with the exception of Incirlik, also host DCA and are currently assigned an active nuclear strike role in NATO nuclear missions. The DCA stationed at Aviano Air Base are under the command of the U.S. Air Force.