I actually do have a bit of a liking for the hypotheses put forward by Mr. Svensmark. They're very elegant and tie (in theory) the cosmic ray flux and certain aspects of Earth's climate.
However, the link appears to be very weak so it may just be a mathematical artifact or (more likely) something else. The boys over at RealClimate don't seem to think much of it either- see this piece:
But having said that, the boffins at CERN have been investigating this and their results are there for anybody to see. Here's a quick missive on that:
"Dunne et al. (2016) have presented the main outcomes of 10 years of results obtained at the CLOUD experiment performed at CERN. They have studied in detail the physico-chemical mechanisms and the kinetics of aerosols formation. The nucleation process of water droplets/ice micro-crystals from water vapor reproduced in the CLOUD experiment and also directly observed in the Earth atmosphere do not only involve ions formation due to cosmic rays but also a range of complex chemical reactions with sulfuric acid, ammonia and organic compounds emitted in the air by human activities and by organisms living on land or in the oceans (plankton). Although they observe that a fraction of cloud nuclei is effectively produced by ionisation due to the interaction of cosmic rays with the constituents of Earth atmosphere, this process is insufficient to attribute all of the present climate modifications to the fluctuations of the cosmic rays intensity modulated by changes in the solar activity and Earth magnetosphere."
