Mexico has not set a date for implementing its (geoengineering) ban, a spokeswoman for the environmental ministry said.

And it's unclear what effect a ban might have. Keith argues a ban is unenforceable. "You can't write legislation that says you can't put sulfur in the stratosphere since every commercial flight does that," he told Reuters.

Others note that a ban on geoengineering on Mexico's territory would offer no protection from the planet-scale impact of future experiments by any of its neighbors.

“It could happen literally next door. In terms of impacts on the world, it's the same," Pasztor said.

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