Cirrus clouds trap outgoing LW radiation and so warm the planet. SAI could either increase or decrease cirrus cloud cover, both directly through aerosol interactions and indirectly through changes to the vertical temperature profile. These competing processes (direct and indirect impacts), and limited understanding of cirrus cloud microphysics mean there is uncertainty in the response.
Metric
The range of the potential RF effects of cirrus cloud changes is great enough to impact projected injection amounts by more than 25%
Uncertainty
We don't know the sign of the effect, or if it is linear/non-linear in injection magnitude. However, the 25% threshold, selected in order to make this a consequential uncertainty, is high relative to modeled impacts.
Decision relevance
Effect is likely small, but not negligible, compared to the direct aerosol forcing of SAI (e.g. 10% in Visioni et al., 2018).