This paper explores what kind of uncertainty a research program governing solar climate engineering through Stratospheric Aerosol Injection (SAI) needs to account for. Specifically, it tries to answer two central issues with regards to SAI research and it’s ethical evaluation: One, what irreducible uncertainties remain throughout the decision-process, and, two, how do these remaining uncertainties affect the ethical evaluation of SAI research. The main assumption is that decisions on SAI research governance will be made under normative uncertainty, i.e. situations under (...) irreducible knowledge-constraints that arise in concrete, practical decision-contexts. These decision-contexts are multi-lateral and empirically ambiguous, and the decision-makers need to reconcile a plurality of values. While normative uncertainty complicates the ethical evaluation of policy decisions, I argue that moral considerations can be accommodated through the inclusion of recognitional, participatory justice approaches, as well as adaptive and anticipatory governance methods. (shrink)