Time variability of high energy cosmic rays

Our model involving cosmic ray acceleration in supernova remnants has been used to predict cosmic ray intensities over long periods of time on a statistical basis. If, as is highly probable, extensive air showers caused by PeV cosmic rays are needed to initiate terrestrial lightning then past dramatic changes in PeV intensities may have had important biological effects. The model has been used to estimate the manner in which the PeV cosmic ray intensity at Earth has varied over the past tens of thousand years.