Let me briefly sum up Svensmark’s theory. The temperature of the Earth, he argues, is regulated by the intensity of solar radiation, but not in the obvious way. It is not that the increase is solar radiation heats the Earth directly. (It does, of course, but not to a sufficient degree to explain climate variations.) Rather, an increase in solar radiation extends the Sun’s magnetic field, which shields Earth from cosmic rays (highly energetic, fast-moving charged particles that come from deep space). How does this affect the climate? Here is the crux of Svensmark’s argument. When cosmic rays hit the atmosphere, he argues, their impact on air molecules creates nucleation sites for the condensation of water vapor, leading to an increase in cloud-formation. Since clouds tend to bounce solar radiation back into space, increased cloud cover cools the Earth, while decreased cloud cover makes the Earth warmer.
So if Svensmark is right, lower solar radiation means more cosmic rays, more clouds, and a cooler Earth, while higher solar radiation means fewer cosmic rays, fewer clouds, and a warmer Earth.
Those who have followed the global warming controversy over the years may recall that cloud-formation is one of the major gaps in the computerized climate “models” used by the consensus scientists to predict global warming. They have never had a theory to explain how and why clouds form or to account accurately for their effect on the climate. Svensmark has smashed through this glaring gap in their theory.