The intensity of cosmic rays changes climate
The mechanism by which cosmic rays might affect climate is as yet purely speculative and unquantified. While it has long been known that radiation could form ions and, in theory, ultimately lead to cloud formation, the importance of this process compared to all the other major sources of particles and cloud condensation nuclei has not been proven. Indeed, there is no evidence that the flux of cosmic rays has decreased over the last 30 years.
Even if cosmic rays have a detectable effect on climate (and this remains unproven), measured solar activity over the last few decades has not significantly changed and cannot explain the continued warming trend. In contrast, increases in CO2 are well measured and its warming effect is well quantified. It offers the most plausible explanation of most of the recent warming and future increases.
