From an Aarhus University press release:

Scientists at Aarhus University (AU) and the National Space Institute (DTU Space) show that particles from space create cloud cover

New input to the United Nations climate model: Ulrik Ingerslev Uggerhøj, Physics and Astronomy, AU, along with others including Jens Olaf Pepke Pedersen and Martin Bødker Enghoff, DTU Space, have directly demonstrated in a new experiment that cosmic radiation can create small floating particles – so-called aerosols – in the atmosphere.