The Arctic is warming several times faster than the global mean, driving rapid sea ice loss and raising concern about regional and global climate impacts. This has motivated growing interest in cooling interventions targeted specifically at the Arctic. One proposed approach is mixed-phase cloud thinning (MCT), which would seed wintertime Arctic clouds with ice nucleating particles to promote glaciation and weaken their strong wintertime longwave warming effect.

But could MCT cool the Arctic enough to matter? I will first place MCT in the broader context of proposed Arctic interventions and discuss the physical constraints on regional cooling. I will then present observational evidence from meteorologically matched Arctic and Southern Ocean clouds showing differences in cloud phase, optical properties, occurrence, and radiative effects that are consistent with the hypothesized response to enhanced ice nucleating particles. Finally, I will use satellite observations and idealized CESM2 simulations to constrain the maximum radiative and climate response achievable by wintertime MCT. These results suggest that MCT can produce moderate surface cooling and a modest increase in sea ice extent. I will discuss what these bounds imply for the viability of MCT and for the broader challenge of targeted Arctic climate intervention.