A new cost analysis of various stratospheric aerosol injection (SAI) systems provides additional, up-to-date evidence that deploying such systems looks to be a relatively cheap proposition. Using cost models adapted from the aerospace industry, the study's authors calculate cost estimates for six potential delivery systems: existing airplanes, new airplanes, blimps, rockets, guns, and pipe-balloon platforms (as considered by the SPICE project). Based on a dispersion rate of 1 million metric tonnes of sulfur dioxide per year, new airplanes specifically designed for SAI payload delivery appear to be the most cost-effective technology option, with yearly costs estimated at between $1 billion and $2 billion (existing aircraft would cost slightly more, in the range of $1 billion to $3 billion). Pipe-balloon systems are estimated to cost between $4 billion and $10 billion per year, while rocket-powered gliders are estimated to be the most expensive (and least feasible) option costing approximately $390 billion per year.
Aside from these various estimates, which the authors are careful to note reflect many uncertainties, the overarching point of the analysis is that the costs of SAI geoengineering are likely to represent a tiny fraction of the costs associated with either unmitigated climate change or a program of robust emissions abatement. As the authors put it, "When SRM is considered as one element of climate strategy that also includes mitigation and adaptation, it is meaningful to compare costs and in this sense one can conclude that the cost of SRM deployment of quantities sufficient to alter radiative forcing by an amount roughly equivalent to the growth of anticipated GHG forcing over the next half century is low ..." (pp. 6-7). This is not to say that SAI or other forms of geoengineering should be pursued at the expense of mitigation, but rather that SAI and other technologies offer complementary strategies that policymakers cannot afford to ignore.