Just how much cosmic rays affect cloud formation has, however, remained elusive.
And thus the debate stood, until a Danish scientist named Henrik Svensmark suggested something outrageous that cosmic rays might seed cloud formation.
Svensmark then teamed up with Friis-Christensen to review solar activity, cloud cover and cosmic ray levels recorded using satellite data available since 1979.
If either is right, Drs Close and Kirkby hope to be able to tell just how big an effect cosmic rays should have on cloud formation.
But when sun spot activity is low, a condition that can sometimes persist over decades and longer, the increased cosmic ray bombardment produces more cloud cover, hence cooling influences.
The first particle physicists detected their subatomic subjects, including cosmic rays, using devices called cloud chambers.
It has been proposed that reduced cosmic rays may lead to reduced cloud formation, causing global temperatures to rise.
This is predicted due to important modulating cloud-forming influences of cosmic rays throughout periods of reduced sunspot activity.
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Many prominent scientists predict that this is likely due to important modulating cloud-forming influences of cosmic rays throughout periods of reduced sunspot activity.
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As noted in the paper, the IPCC models also fail to incorporate climate modulating effects of solar changes such as cloud-forming influences of cosmic rays throughout periods of reduced sunspot activity.
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But if Svensmark was correct, it would mean that periods of high solar output should coincide with reduced cloud formation (due to reduced cosmic ray incidence), which in turn would have a warming effect on the Earth, since less sunlight would be reflected back into space by clouds.
Again, the two measures kept closely in step with each other, with the cloud cover swinging from 65% when cosmic rays were weakest, to 68% when they peaked.
His (as yet unpublished) research confirms, he says, that the variations in cloud cover seen by satellites match those in cosmic-ray flux better than anything else, such as the sun's total brightness.
They compared the cosmic-ray flux with the proportion of the world's skies obscured by cloud, a figure that has been available from satellite photographs since 1979.
Using a particle accelerator, he demonstrated that cosmic rays colliding with molecules in the atmosphere can, in fact, cause gaseous water vapor to condense into cloud-forming droplets.
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