A striking correlation has recently been observed between global cloud cover
and the flux of incident cosmic rays. The effect of natural variations in the
cosmic ray flux is large, causing estimated changes in the Earth's energy
radiation balance that are comparable to those attributed to greenhouse gases
from the burning of fossil fuels since the Industrial Revolution. However a
direct link between cosmic rays and cloud formation has not been unambiguously
established. We therefore propose to experimentally measure cloud (water
droplet) formation under controlled conditions in a test beam at CERN with a
CLOUD chamber, duplicating the conditions prevailing in the troposphere. These
data, which have never been previously obtained, will allow a detailed
understanding of the possible effects of cosmic rays on clouds and confirm, or
otherwise, a direct link between cosmic rays, global cloud cover and the
Earth's climate. The measurements will, in turn, allow more reliable
calculations to be made of the residual effect on global temperatures of the
burning of fossil fuels, an issue of profound importance to society.
Furthermore, light radio-isotope records indicate a correlation has existed
between global climate and the cosmic ray flux extending back over the present
inter-glacial and perhaps earlier. This suggests it may eventually become
possible to make long-term (10-1,000 year) predictions of changes in the
Earth's climate, provided a deeper understanding can be achieved of the
``geomagnetic climate'' of the Sun and Earth that modulates the cosmic-ray
flux.Comment: More information and higher resolution drawings at
http://cern.ch/Cloud Improved figure qualit