The CPFC project generalized established methods of climate-feedback analysis to decompose cloud radiative feedbacks by cloud-top phase. This facilitates a rigorous assessment of radiative feedbacks from changes in the optical properties of clouds that are caused by cloud-phase changes. The method was developed for use with satellite observations and global climate models. Both satellite and model results indicate that ice-to-liquid conversions cause clouds to become more opaque, causing them to reflect more solar radiation. This is a negative feedback, which dampens climate warming. However, ice-to-liquid conversions also increase the greenhouse effect of clouds and enhance the fraction of incident solar radiation that is scattered in the forward direction by cloud particles. These are positive feedbacks, which amplify climate warming. The CPFC project quantified these feedback components and identified the scattering-direction component for the first time. These results clarify the importance of cloud-phase changes for climate feedbacks and provide a more complete physical explanation of the mechanism.
The observational methods developed in CPFC were also adapted to study the climate forcing from interactions between anthropogenic aerosol particles and low-level liquid clouds. This approach disentangled the radiative perturbations caused by aerosol-driven changes in cloud-droplet size, condensed water path, and cloud amount. The research indicates that aerosol pollution causes cloud amount to increase substantially. This provides new observational constraints for aerosol radiative forcing of climate change.
The results of the project have been published or submitted for publication in three peer-reviewed scientific journal articles, and they have been communicated in international scientific conferences. New computer code and data for the analysis have been published with open access online so that others can freely implement the methods. The results were also communicated to the public in a popular-science article that was published on a website that promotes science in Norway.
