Can cirrus cloud seeding be used for geoengineering?

Abstract

Cirrus cloud seeding has been proposed as a possible technique that might thin cirrus clouds leading to reduced heating. The technique was shown to be viable in one model evaluation. Here we use an updated version of the Community Atmosphere Model version 5 (CAM5) and reevaluate whether seeding is a viable mechanism for cooling. We explore different model setups (with and without secondary organic aerosols acting as heterogeneous ice nuclei). None of the updated versions of the CAM5 lead to a significant amount of negative climate forcing and hence do not lead to cooling. We only calculate a net negative cloud forcing (-0.74 ± 0.25 W m-2) if we restrict the modeled subgrid-scale updraft velocity during nucleation to <0.2 m s-1 and if the deposition of water vapor onto preexisting ice crystals during nucleation is not included. Hence, we do not find that cirrus cloud seeding is a viable climate intervention technique. Key Points Cirrus cloud seeding only works to cool climate for restricted model setup The most recent version of CAM5 predicts warming Mechanisms that attempt to restrict seeding to polar regions may not cool