Using stratospheric aerosol injection to alleviate global warming: when?

Stratospheric aerosol injection (SAI), a type of solar radiation modification (SRM), has the potential to reduce global warming caused by excessive greenhouse gases in the atmosphere. However, there is currently widespread opposition to it, because deploying it would entail a number of uncertainties and risks. Here, we present a decision framework to help policymakers consider using SAI. Such a framework would be necessary if concrete evidence is found that SAI can contribute to reducing warming and that its related risks are acceptable. Of particular importance is the establishment of strict criteria for when SAI may or should be started, and when it should be stopped.