As cloud-seeding expands and extremes intensify, ENMOD struggles to deter weaponised weather

The notion of armies turning the sky into a theatre of war—weaponising rain, fog or frost to hinder enemies—has a long lineage. Yet as weather‑modifying technologies have spread and climate extremes intensify, worries that the atmosphere could be weaponised have resurfaced, pushed along by researchers, former military advisers and media commentary. The debate sits at the crossroads of science, law and geopolitics: what is feasible today, what remains science fiction, and how should the international community respond if states or non‑state actors push weather manipulation into a tool of coercion?

At its most basic level, the charge of weaponised weather involves deliberate attempts to alter precipitation, fog, hail or other atmospheric conditions to gain military advantage—for instance, extending rains to hamper supply routes, clearing skies to allow a parade to proceed, or seeding clouds to trigger localized floods. Cloud seeding, first developed in the mid‑20th century and still used for civil aims, works by releasing particles (commonly silver iodide or dry ice) into supercooled clouds to promote ice‑crystal formation and precipitation. According to scientific syntheses, the method needs suitable natural cloud conditions and cannot conjure rainfall from clear skies. Operational results remain uncertain and heavily dependent on local meteorology. The US National Oceanic and Atmospheric Administration warns that efficacy is limited, and many experiments have yielded inconclusive results; it also notes that silver iodide is largely insoluble and, at operational concentrations, poses minimal ecological risk as far as current assessments show.

There is, however, historical precedent for military interest. During the Vietnam War the US pursued Project Popeye, a covert programme aimed at extending the monsoon season over the Ho Chi Minh Trail to slow enemy movement. Declassified government memoranda from that era describe plans to prolong rains in targeted areas and record tests that supposedly increased rainfall in seeded clouds, yet they also warned of unpredictable spill‑over effects beyond the target zones and raised legal and ethical questions. Britain conducted weather‑modification experiments after World War II: Project Cumulus in the late 1940s and early 1950s involved RAF flights dropping chemicals over clouds. Those experiments later surfaced in public debate after the catastrophic Lynmouth floods in August 1952—when around 229mm of rain fell in 24 hours, killing 34 people—though subsequent inquiries and meteorologists have remained skeptical that the experiments caused the disaster.

Today more than 50 countries operate weather‑modification programmes in some form, often framed as civil efforts to reduce hail, boost rainfall for agriculture, or disperse fog at airports. China has been among the most ambitious, openly investing in a nationwide cloud‑seeding and hail‑suppression programme that officials say could cover millions of square kilometres, with aims to broaden capability by 2035. Such large‑scale schemes have prompted concern from neighbouring states and independent experts about transboundary impacts: as the World Meteorological Organization has repeatedly emphasised, “the atmosphere has no walls”—what is added in one place may move elsewhere.

That transboundary risk underpins the international legal response. In 1976 states concluded a convention prohibiting military or other hostile uses of environmental modification techniques; the treaty came into force on 5 October 1978. The convention—often called ENMOD—has purposely narrow key terms. It bars environmental modification with “widespread, long‑lasting or severe” effects; in practice, that “troika” threshold makes the treaty harder to apply in disputes where attribution and scale are contested. The convention also established review and consultative mechanisms intended to prevent hostile uses of environmental manipulation and to encourage transparency.

Experts and former military figures cited in media pieces stress two contrasting truths. On one hand, small, local interventions—such as seeding clouds to tweak short‑term precipitation, or burning fuel to disperse fog around airfields—are technically feasible and have been used for decades. “If you can control the weather, you can control the world,” a veteran meteorologist told a national paper, echoing a Cold War maxim that still sticks. Former military advisers warn that even hit‑and‑miss techniques could be effective at creating fear or disruption if deployed without regard for civilian harm.

On the other hand, leading atmospheric scientists stress the limits and unpredictability of such operations. Cloud seeding requires specific atmospheric conditions and cannot conjure storms from nothing; independent analyses of high‑impact events, such as the severe 2024 floods in Dubai, have cautioned that seeding cannot plausibly account for the scale of extreme rainfall observed. In that case, national meteorological authorities and external analysts pointed to a slow‑moving, moisture‑rich weather system intensified by a warming climate as the primary drivers, rather than deliberate seeding. Researchers also warn that deliberate manipulation can trigger cascading and unintended effects—flooding one basin while drying another—precisely because the climate system is interconnected and only partly understood.

The legal ban provides some protection, but enforcement is tricky. Proving intent and linking environmental effects to deliberate action is technically and politically challenging, especially in an era of pervasive atmospheric data and private actors with access to advanced technologies. The UN convention’s high threshold for prohibited effects means many interventions of concern may fall short of the legal definition of a banned “weapon.” That ambiguity, together with rising capabilities among sophisticated states and the diffusion of weather‑modification tools, is why a number of scientists and diplomats argue for renewed scrutiny.

There are also ecological and ethical questions. Some scientists warn of unknown consequences for ecosystems and agriculture, while public health experts have voiced concerns about potentially toxic additives, even though current assessments suggest commonly used agents do not persist or bioaccumulate at harmful levels in routine operations. Beyond toxicity, the ethical dilemma is stark: deliberately shifting rainfall patterns to favour one region inherently risks disadvantaging another.

What, then, is the practical risk of “weather wars”? For the moment, the consensus among many specialists is that large‑scale, sustained geoengineering of the kind imagined in popular scenarios—essentially a planetary thermostat set by a single actor—remains out of reach without enormous resources and multilateral coordination. But smaller‑scale uses that create disruption, economic damage or fear are feasible and have real strategic implications. The mix of technical uncertainty, legal ambiguity and growing capability means the question isn’t whether the sky can be weaponised in principle, but how states and international institutions will update rules, transparency mechanisms and scientific monitoring to lower risk.

If the past is any guide, governance will matter most going forward. The 1976 convention established an early norm against hostile environmental modification; experts now argue that it should be complemented by stronger verification tools, clearer attribution mechanisms, and routine transparency about civil weather‑modification activities. Without that, the very technologies designed to reduce climate and weather‑related harm could be repurposed in ways that amplify instability—intentionally or through unintended knock‑on effects—at a moment when the world’s weather is becoming more volatile. It’s pretty clear that we need robust governance, and soon.

Source: Noah Wire Services