CERN is home to lots of experiments and collaborations, most notably the Large Hadron Collider. http://lhc.web.cern.ch/lhc/
CLOUD is an experiment that uses a chamber to study the possible link between cosmic rays and cloud formation.
The experiment is based at the Proton Synchrotron; this is the first time a high-energy physics accelerator has been used in the study of atmospheric and climate science.
CLOUD's results could greatly modify our understanding of our planet's climate.