Cosmic Rays and Cloud Cover

Galactic cosmic rays (GCRs) play an important role in controlling global cloud cover on Earth, according to recent studies by researchers at the Danish Space Research Institute in Copenhagen (Nigel D. Marsh, 011-45-35325740). GCRs, consisting principally of energetic protons emitted from stars within our galaxy, are a primary source of the atmospheric ionization which affects cloud formation. Because cloud cover has an impact on both the reflection of solar radiation and the retention of heat in the atmosphere, correlation between GCRs and low level clouds suggests a link between global climate changes and cosmic ray flux (see figure at Physics News Graphics).

The discovery reveals a convoluted connection between solar variability and climate change. Fluctuations in the sun's radiative output are generally dismissed as too small to account directly for global warming and other climate variations. Periods of intense solar activity, however, lead to powerful solar winds which shield the atmosphere from cloud-forming GCRs, potentially modulating the global climate. (N. D. Marsh; H. Svensmark, Physical Review Letters, 4 December.)

Researchers at the University of Leeds (UK), on the other hand, have observed a direct and rapid connection between atmospheric chemistry and ultraviolet light from the sun (Dwayne E. Heard, 44-113-233-6471, dwayneh@chem.leeds.ac.uk). During the 97% eclipse of the sun over Ascot, England, local ozone concentrations fell to 60% of typical daytime levels, and quickly returned to normal after the event. The study demonstrates the dynamic connection between sunlight and the photochemistry of atmospheric gasses which may contribute to global warming, smog formation, and acid rain. (J. P. Abram; et al, Geophysical Research Letters, 1 November.)