Diamonddavej writes "The BBC reports that researchers at the University of Edinburgh have found that Galactic Cosmic Rays (GCRs) somehow makes trees grow faster. GCRs vary according to the 11-year solar cycle, with more GCRs hitting the Earth during solar minimum when there is a lull in the solar wind, which normally acts to protect the inner solar system from external galactic radiation. The mechanism might have something to do with GCRs increasing cloud cover, which diffuses sunlight and increases the efficiency of photosynthesis. Nevertheless, the researchers remain mystified and are requesting further ideas and research collaboration to test hypotheses. (How about Radiation Hormesis, AKA 'Vitamin-R?')" Here is the paper's abstract at the journal New Phytologist. The researchers say: "The relation of the rings to the solar cycle was much stronger than to any climatological factors. ... As for the mechanism, we are puzzled."