Reflections on a hypothetical decentralized grassroots deployment solar geoengineering scenario

•Although decentralized grassroots SRM is unlikely to occur at scale, it usefully challenges common governance assumptions.•Multiple, redundant forms of independent data collection are essential to guide deployment efforts and governance responses.•The social movements behind decentralized deployment efforts require multidirectional considerations of public legitimacy.•Deployment rates may not be sustained by grassroots actors, potentially requiring states to guard against termination shock.•Grassroots efforts may ultimately lead to productive state-led discussions concerning geoengineering governance.