A few seconds later, a device resembling a snow maker began to rumble, then produced a great and deafening hiss. A fine mist of tiny aerosol particles shot from its mouth, traveling hundreds of feet through the air. The scientists wanted to see whether the machine that took years to create could consistently spray the right size salt aerosols through the open air, outside of a lab. If it works, the next stage would be to aim at the heavens and try to change the composition of clouds above the Earth’s oceans. That has pushed the idea of deliberately intervening in climate systems closer to reality.

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Persons: Matthew Gallelli crouched Locations: San Francisco Bay, United States