But the flood of more visible cosmic -ray data makes it difficult to pick them out.
He also finds that wobbles in the earth's temperature have followed those in the cosmic-ray flux for the past 60-odd years.
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.
His (as yet unpublished) research confirms, he says, that the variations in cloud cover seen by satellites match those in cosmic-ray flux better than anything else, such as the sun's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.
But, a detailed analysis of the lunar samples by Kuni Nishiizumi, from the University of California at Berkeley, and Marc Caffee, from Purdue University, suggests that far more beryllium exists in the soil than can be accounted for by cosmic-ray delivery alone.
Eichler thinks that such a sun-grazing comet may have triggered a large solar flare and cosmic ray-generating shockwaves as recently as 775 A.D.
FORBES: Sun-Grazing Comets As Triggers For Electromagnetic Armageddon
Or so says David Eichler, lead author of a forthcoming Astrophysical Journal Letters paper positing that a sun-grazing comet roughly the size of Hale-Bopp (with a nucleus some 30 kms in diameter), could trigger cosmic ray-generating shockwaves large enough to initiate a global electromagnetic Armageddon.
FORBES: Sun-Grazing Comets As Triggers For Electromagnetic Armageddon
And Giles Harrison believes climate sceptics need to apply the same scepticism to the cosmic ray theory as they do to greenhouse warming - particularly those who say there are too many holes in our understanding of how clouds behave in the man-made greenhouse.
Svensmark then teamed up with Friis-Christensen to review solar activity, cloud cover and cosmic ray levels recorded using satellite data available since 1979.
Although the probe would carry no cameras in the classic sense, its onboard instruments would include a low-energy charged particle experiment, a magnetometer, a cosmic ray detector, and an energetic neutral atom detector.
Interestingly, an April 18 paper in the journal Nature reported that upper limits for neutrinos measured from IceCube are low enough that gamma-ray bursts are unlikely to be the sole source of ultra-high energy cosmic rays.
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