A specialised delivery system for stratospheric sulphate aerosols (part 2): financial cost and equivalent CO₂ emission

Temporary stratospheric aerosol injection (SAI) using sulphate compounds could help avoid some of the adverse and irreversible impacts of global warming, but comprises many risks and uncertainties. Among these, the direct financial cost and carbon emissions of potential SAI delivery systems have hitherto received only modest attention. Therefore, this paper quantifies the initial and operating financial costs and initial and operating equivalent CO₂ (CO₂eq) emissions of the specialised aircraft-based SAI delivery system developed with relatively high-fidelity tools in part 1 of this series. We analyse an interval of operating conditions, within which we devote special attention to four injection scenarios outlined in part 1: Three scenarios where H₂SO₄ vapour is directly injected at several dispersion rates and one SO₂ injection scenario. We estimate financial cost through Raymer’s adjustment of Rand Corporation’s Development and Production Costs for Aircraft (DAPCA) model, augmented by additional data. CO₂eq emission is computed from existing data and the computed fuel consumption for each of the scenarios. The latter estimates include an emission weighting factor to account for non-CO₂ aircraft combustion products at altitude. For direct H₂SO₄ injection, both financial cost and CO₂eq emission are sensitive to the design dispersion rate. For scenarios where higher dispersion rates are achieved, the delivery system’s cost and CO₂eq are relatively small compared with the presumed benefits of SAI. The most optimistic H₂SO₄ scenario is found to have a financial cost and CO₂eq emission similar to that of SO₂ injection, while potentially allowing for reductions in the annual mass of sulphur injected to achieve a target negative radiative forcing. The estimates of financial cost and CO₂eq emission were subjected to sensitivity analyses in several key parameters, including aircraft operational empty weight, engine specific fuel consumption, fuel price and aerosol price. The results indicate that the feasibility of the considered scenarios is robust.