evidence: Reports that cloud seeding caused this week’s flooding were likely erroneous, but the reaction they inspired "represents a healthy kind of skepticism about what happens when we interfere with natural systems," Laura Kuhl, a public-policy professor at Northeastern University who studies climate adaptation, told me. That’s particularly true, she said, when you consider forms of geoengineering premised on producing large-scale effects. Scientists have proposed injecting sulfur dioxide into the stratosphere to reflect some sunlight back into space, preventing it from reaching Earth’s surface. The resulting aerosols could linger in the stratosphere for years, shifting at the whims of the wind. Similar concerns surround another geoengineering technique that involves spraying salt compounds into the air to brighten clouds, which would in turn bounce sunlight back into space. This month, scientists conducted a secretive test of this technology, the first of its kind in the United States. The field is "moving a lot faster than it used to," Juan Moreno-Cruz, a climate-policy researcher at the University of Waterloo, told me.