SAI and L1 Space Sunshading Mass Requirements for Climate Mitigation: Fictitious Aerosol Disk Validation of SAI and Sunshade Formula Corrections - Preprint

[Geoengineering News]

https://papers.ssrn.com/sol3/papers.cfm?abstract_id=6259580

Authors: Alec Feinberg

18 February 2026

Abstract

Mass deployment is a fundamental constraint in solar geoengineering and provides a consistent basis for comparing L1 space sunshading, stratospheric aerosol injection (SAI), and Earth brightening. Updated diagnostic estimates of deployment mass are presented for L1 sunshading and regionally targeted SAI under scenarios in which mass is the dominant limiting parameter. A key result is correction of a longstanding geometric error in legacy L1 sunshade formulations originating with Early (1989), which overstated required disk area. Using physically consistent geometry, required L1 sunshade area is reduced by ~30–40× relative to widely cited historical estimates. When combined with an Annual Solar Geoengineering (ASG) framework that offsets incremental yearly warming, effective area requirements decline by up to ~1600× compared to legacy formulations. Despite these reductions, mass requirements remain substantial. Under optimistic ultra-lightweight thin-film assumptions (5 g m⁻²), approximately 19,000 tonnes are required at L1 in the first year. Within the annual framework, incremental mass declines to ~100 tonnes yr⁻¹ under continued CO₂ growth. A 22-year, three-phase LEO-to-L1 deployment strategy is outlined to address mass constraints. For regionally targeted SAI, empirical aerosol–forcing relationships derived from volcanic observations yield nominal requirements of ~10³ tonnes SO₂ yr⁻¹, increasing ~0.6% annually under continued forcing. Inferred optical depths (τ ≈ 10⁻³–10⁻⁴) are well below those of major eruptions. An independent fictitious aerosol-disk framework produces comparable mass estimates, supporting the robustness of the diagnostics. Results identify mass as a central feasibility parameter for comparing complementary solar geoengineering pathways within a narrowing mitigation window (~75 years).

Source: SSRN