Since we're past the point where emissions cuts alone can keep long term warming below 2 C, I do expect active geoengineering efforts later this century. Solar radiation management with aerosols is not a long term fix but could keep positive feedback effects damped while slower long term fixes (like emissions reduction plus accelerated silicate weathering) roll out.<p>The attractive thing about sulfate aerosols is that they could be formed from sulfur dioxide, which is cheap to form via sulfur combustion and disperses excellently because it's a gas. Delayed oxidation reactions cause SO2 to form nuclei for aerosols. Even though calcium carbonate is also inexpensive, I don't think there is a comparably cheap/easy way to deliver a fluid precursor for it to the upper atmosphere. The closest I can think of is aerosolizing a calcium hydroxide solution that would carbonate <i>in situ</i> via reaction with atmospheric CO2... but calcium hydroxide is only slightly soluble in water. You'd need to lift a lot of extra water mass.