For decades, the idea that governments would deliberately alter the weather was treated as the territory of cranks. The record says otherwise. In 1977, the United Nations opened a treaty for signature whose full name is a mouthful — the Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques. Everyone calls it ENMOD. Its existence is the plainest possible proof of a documented fact: states have modified the environment as an instrument of war, and the world's governments thought the practice serious enough to regulate it.
That much is on the record. What's less understood — and far more important for anyone asking questions about the sky today — is what ENMOD actually prohibits. Read closely, the treaty is narrower than its reputation. It is also a useful lesson in how to read a claim: precisely, and without importing more than the text will bear.
What the treaty says
ENMOD bars the "hostile use" of environmental modification techniques that have "widespread, long-lasting or severe effects" against another state party. Three words carry the entire weight of the prohibition, and each was given a specific meaning in the negotiating record. The ban is real. It is also bounded — by hostility, by scale, and by the relationship between states.
The hostility threshold
The treaty governs weather modification used as a weapon, against an adversary. It does not, on its face, address domestic programs, research, or commercial cloud-seeding conducted by a government within its own borders. That is not a loophole someone slipped in — it is the explicit scope of a Cold War arms-control instrument. But it means the treaty answers a much smaller question than the one most people bring to it.
A treaty that proves weather has been weaponized is not a treaty that tells you it is being weaponized now.
This is exactly the kind of distinction the Clear Skies Project exists to hold. The documented fact — that ENMOD exists, and why — is solid, sourced, and uncontested. The inference some draw from it — that a covert program is operating today — is a separate claim that the treaty neither establishes nor rules out. We keep those two things in different columns, on purpose.
The evidence, on the record
Governments have deliberately modified weather as an act of war.
Operation Popeye (1967–1972) seeded clouds over the Ho Chi Minh Trail to extend monsoon season. The disclosure helped drive the 1977 ENMOD treaty, which bans the hostile use of environmental modification between states.
Best available — for now
What it leaves open
Because ENMOD is scoped to hostile interstate use, three large categories of activity sit entirely outside it: domestic weather modification, peacetime research, and the fast-growing field of solar geoengineering. None of these are secret in principle. All of them raise the same questions of disclosure and oversight that the treaty was never designed to answer.
- Domestic cloud-seeding programs operate in multiple US states with varying disclosure requirements.
- Solar geoengineering research is funded and published, but governed by no binding international norm.
- The line between "research" and "deployment" is exactly where public oversight is weakest.
This is why our first demand is for the records, and our second is for the process. The history is documented. The present is not — not because the truth is necessarily sinister, but because the disclosure regime that should make it legible doesn't yet exist. We intend to help build it, in the open, and to publish what we find either way.