Cosmics Leaving Outdoor Droplets or the CLOUD is an experimental facility being run at CERN by Jasper Kirkby to investigate the microphysics between galactic cosmic rays (GCRs) and aerosols under controlled conditions. The experiment began operation in November 2009. But there are other important experiments taking place at CERN, including research designed to help resolve one of the biggest uncertainties of climate change — how clouds form and what role they play in regulating Earth’s temperature. The first results from the lab’s CLOUD experiment published in Nature in 2011 confirm that cosmic rays spur the formation of clouds through ion-induced nucleation. Current thinking posits that half of the Earth’s clouds are formed through nucleation. Ultimately it is desired to know the recipe for cloud formation, a phenomenon that is not fully understood.