Abstract

The CLOUD experiment was proposed to determine whether cosmic rays have a strong enough effect on clouds to influence the Earth’s climate. To achieve this requires a better understanding of the atmospheric aerosol particles that form the seeds for cloud droplets. Aerosol concentrations have changed substantially over the industrial era and as a result the effect of aerosols on clouds causes the largest uncertainty in projections of global temperature changes for the coming century. CLOUD measurements can be used to determine the rate at which cloud seeds form in the atmosphere in climate models, and this should help to constrain climate change predictions in the future. In addition, the role of ions from cosmic rays in cloud seed formation is now better understood. I will introduce the science, describe the experiment and related atmospheric modelling, and outline the important advances in this field CLOUD has published in the last two years.