Cosmic rays are not really cosmic rays at all, they are little cosmic particles. They are high-speed little bits and bobs which bombard us all the time from outer space and, by and large. they interfere only very little with the normal noiseless tenor of our way.
These little particles carry an electric charge and hence are liable to be affected if under the influence of a magnetic field. Earth has a magnetic field and there are occasional short periods when it is greatly disturbed and the compass needle shows unusual signs of liveliness.
Such occurrences are called magnetic storms; they are closely related to solar flares, spectacular eruptions visible from time to time on the surface of the sun. A magnetic storm is invariably detected on Earth just a few days after a solar flare has been observed.
About the end of the 1940s, an interesting discovery was made by a man called Scott Ellsworth Forbush about cosmic rays. For bush found a pattern when measuring the number of cosmic rays which find their way into the atmosphere. He found there was a low intensity when the sun was very active with a multitude of flares and when magnetic storms were occurring on Earth.
It was as if the disturbed magnetic field was blocking the path of particles that would otherwise have been able to penetrate into our atmosphere.
This line of inquiry has been carried a stage further recently by Henrik Svensmark of the Danish Research Institute. He has studied the relationship between the cloudiness of the weather on Earth and the intensity of cosmic radiation.
His work suggests that the more cosmic rays there are, the cloudier our planet seems to be. His inference is that these tiny charged particles, interacting electrically with the molecules of air, may indirectly play a part in cloud formation.
Many meteorologists will find this suggestion exciting and it could provide a missing link. For centuries, scientists have sought some connection between sunspots and variations in the global climate. Even where a relationship appeared to have been found, however, a difficulty was always the lack of any plausible mechanism by which it might have been brought about.
This might well be it - a more active sun, leading to a disturbed terrestrial magnetic field, fewer cosmic rays allowed into the atmosphere, less cloud on Earth and a consequent effect upon the climate of the world.