Sun-dimming risks putting the planet’s thermostat under Donald Trump’s control. Better to adopt the precautionary principle with high-stakes science

It is fitting that this week’s UN environment talks are in Nairobi, with Africa shaping the global climate conversation. The continent’s diplomats are dealing with the vexed question of whether it is wise to try to cool the planet by dimming the sun’s rays. While not on the formal summit agenda, on the sidelines they are arguing that it’s time to stop promoting solar geoengineering technology as a solution to global heating. It’s hard to disagree.

African nations have acted because they don’t want their continent to become a test bed for unproven schemes to spray particles into the high atmosphere to reflect sunlight away from Earth for a small, uncertain cooling gain. They point to environmental, ethical and geopolitical risks . That’s why the continent is pushing for a global “ non-use ” agreement that would rule out public funding, outdoor experiments, patenting and official promotion of these technologies.

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