Israeli scientist Nir Shaviv recently posted at his site an article on the effects of cosmic radiation on climate. At the end he summarizes:
The results have two particularly interesting implications. First, they bring yet another link between the galactic environment and the terrestrial climate. Although there is no direct evidence that cosmic rays are the actual link on the 32-million-year time scale, as far as we know, they are the only link that can explain these observations. This in turn strengthens the idea that cosmic ray variations through solar activity affect the climate. In this picture, solar activity increase is responsible for about half of the twentieth-century global warming through a reduction of the cosmic ray flux, leaving less to be explained by anthropogenic activity. Also, in this picture, climate sensitivity is on the low side (perhaps 1 to 1.5°C increase per CO2 doubling, compared with the 1.5 to 4.5°C range advocated by the IPCC), implying that the future is not as dire as often prophesied.
The second interesting implication is the actual value of the 32-million-year oscillation. The relatively short period indicates that there is more mass in the galactic plane than accounted for in stars and interstellar gas, leaving the remainder as dark matter. However, this amount of dark matter is more than would be expected if it were distributed sparsely in a puffed-up halo as is generally expected. In other words, this excess mass requires at least some of the dark matter to condense into the disk. If correct, it will close a circle that started in the 1960s when Edward Hill and Jan Oort suggested, based on kinematic evidence, that there is more matter at the plane than observed. This inconsistency and indirect evidence for dark matter was also advocated by John Bahcall, who for many years was a Faculty member here at the IAS.”
Read the entire post here.