Cosmic Rays, Particle Formation, Natural Variability of Global Cloudiness, and Climate Implications

Via its role in aerosol formation, cosmic ray may affect the global cloudiness and hence climate. Here we show that an increase in cosmic ray fluxes may lead to an increase in particle production in the lower troposphere but a decrease in particle production in the upper troposphere. In addition to the reported positive correlation between cosmic ray variations and low cloudiness, our analysis of satellite-based cloud cover data reveals that high cloudiness may be anti-correlated with cosmic ray variations if volcano and El Niño impacts are excluded. The observed different correlations between cosmic ray variations and low, middle and high cloud anomalies are consistent with the predicted different sensitivities of particle production to cosmic ray changes at various altitudes. The influence of the solar-modulated cosmic ray fluxes on global cloudiness, if confirmed, may provide the external forcing needed to reconcile the apparent differences between observed surface and troposphere temperature trends.