Planetary-scale engineering schemes designed to cool Earth’s surface and lessen the effects of global heating are potentially dangerous and should be blocked by governments, more than 60 policy experts and scientists said on yesterday. Even if injecting billions of sulfur particles into the middle atmosphere — the most hotly debated plan for so-called solar radiation modification (SRM) — turned back a critical fraction of the sun’s rays as intended, the consequences could outweigh any benefits, they said in an open letter. The letter, supported by a commentary in the journal WIREs Cl...