An assessment of the infrastructural and temporal barriers constraining a near-term implementation of a global stratospheric aerosol injection program

Model of stratospheric aerosol injection deployment scenarios have often assumed that a global sunscreen could be applied to the earth on relatively short notice, perhaps in response to a climate emergency.  This emergency response framing confuse the time scales associated with the commencement of such a program.  Once deployed, stratospheric aerosols could cool the earth quite quickly, but such a deployment would require aircraft and other infrastructure that does not currently exist.  Given the span required to develop and certify a novel aircraft program and thereafter to build a fleet numbering in the hundreds, scenario builders should assume a roughly two-decade interval between a funded launch decision and the attainment of a target level of cooling.