The EU's Seventh Framework Programme has granted EUR 2.3 million over the next three years to an experiment that examines the influence of cosmic radiation on the Earth's climate. The collaboration, entitled 'Cosmic rays leaving outdoor droplets - Initial Training Network' (CLOUD-ITN), began this August and is coordinated by Germany's Goethe University of Frankfurt am Main. It supports eight PhD and two postdoctoral positions at nine partner institutions across Europe; work will largely be carried out at the European Centre for Nuclear Research (CERN). The observed climate warming since 1900 is largely attributed to greenhouse gases in the atmosphere that are generated by human activity. Changes in solar irradiance are assumed to contribute relatively little to climate change. However, the effects of changes in UV (ultra-violet) radiation or galactic cosmic rays have not yet been quantified. Experiments to be conducted at CERN, a facility that sits astride the Franco-Swiss border, will seek to quantify the interactions of cosmic rays, UV radiation, aerosols and clouds. This in turn should improve our understanding of a so-called 'solar indirect' contribution to climate change. Cloud formation is one of the largest uncertainties in the climate change equation. But how do clouds form? When highly energetic galactic cosmic rays (which are generated by supernovas) enter the Earth's atmosphere, they pull electrons out of the gasses they encounter, leaving a trail of charged molecules (ions) in their wake. New aerosol particles can then form and grow around these ions; water droplets use these particles as 'condensation nuclei' to form a cloud. The CLOUD collaboration has developed an aerosol chamber which, when exposed to an elementary particle beam, can simulate the effects of cosmic rays on aerosol and cloud formation. The first prototype was developed in 2006 and the new, improved chamber will be used to carry out experiments on ion-induced nucleation and ion-aerosol interaction. This will lead to an improved understanding of the mechanisms of cloud formation. The cloud chamber is a stainless-steel construction which measures 3m by 3.7m and is filled with all of the components thought to make up a cloud (air, water vapour, trace amounts of gases). These are continuously analysed with myriad analysing instruments. One of the analysers is a chemical ion mass spectrometer that can measure sulphuric acid concentrations at less than 0.1 parts per trillion; CLOUD is one of only three groups in the world that operates such an instrument. Galactic cosmic rays are simulated by a Proton Synchrotron accelerator. The current prototype (called Mk2) will be used to carry out a broad range of important physics experiments over the next few years, after which it will be replaced by a final CLOUD facility that incorporates performance improvements and a newly developed aerosol pressure chamber. The CLOUD-ITN project provides funds for eight PhD candidates to carry out work and write their theses on this research. A comprehensive training programme for the PhD candidates and postdoctoral fellows has been set up, featuring annual summer schools and workshops on topics such as aerosol chemistry and physics, ion-induced aerosol nucleation and the influence of galactic cosmic rays on the climate in the past. The first summer school took place at Hyytiälä Forestry Field Station, Finland, this August. All of the analysing instruments are provided by the partner institutes and supported by national funding agencies. Project participants include CERN, the Paul Scherrer Institute (Switzerland), the Universities of Helsinki (Finland), Leeds (UK), Reading (UK) and Vienna (Austria), the Institute for Tropospheric Research in Leipzig (Germany) and Ionicon Analytik in Innsbruck, Austria. The University of Lisbon in Portugal and the Institute for Nuclear Research and Nuclear Energy in Sofia, Bulgaria have recently joined the collaboration. Russia's Lebedev Physical Institute has also been awarded a research grant to support CLOUD activities by the Russian Foundation for Basic Research (RFBR) under the CERN-RFBR agreement on scientific cooperation. The design manpower for the CLOUD Mk2 facility is provided by PSI, CERN and the University of Lisbon. The construction costs of the CLOUD Mk2 facility will be paid from a common fund shared among the partner institutes and by in-kind contributions.