evidence: Among other concerns, critics argue it’s far too dangerous to consider tinkering with the global climate system. But the field, and Keith’s research in particular, has also gotten ensnared in conspiracy theories about "chemtrails." Proponents assert that the condensation trails created by aircraft are actually evidence that the military, or someone, is already spraying chemicals into the sky for wide-scale weather modification, mind control, or other nefarious purposes. [...] Though chemtrail theories have been repeatedly debunked, they’re surprisingly widespread. A study published in Nature found that up to 40 percent of Americans believe these theories are "completely" or "somewhat" true. Such "conspiratorial views" also accounted for around 60 percent of the conversation about geoengineering on social media. Keith himself regularly receives hateful messages, and even threats of physical violence, as a result of his research. [...] But I am worried, full stop, that chemtrail concerns are bleeding over into solar geoengineering in a way that will make it much harder to have a sensible conversation.