Solar geoengineering poses existential threats, both in terms of the massive risks if deployed, but also in how the promotion of the false and dangerous ideas that it could be a “Plan B” or “emergency measure” defuse the pressure for transformative change and real solutions. The Non-use agreement effectively counters the attempts by pro-geoengineering actors (often portraying themselves as “neutral”) to normalise real-world research and move the world down a slippery slope. Solar geoengineering is ungovernable and hence must never be deployed.