Cosmic rays and climate

Climate change and global warming is generally attributed to increases in greenhouse gases in the atmosphere. Other possible contributing effects are constantly being sought. Because of the importance of solar irradiance as a driver of climate, and because the widely known effect of the solar cycle on cosmic rays, it has been speculated for more than 50 years that cosmic ray variations may have an impact on climate. The question has been how. A proposed mechanism would be through the effect of ionization from cosmic rays on the rates of nucleation of cloud condensation nuclei. The result would be an impact of the rate of cosmic rays on cloud formation that would subsequently impact the reflection of incoming short wavelengths and the trapping of outgoing long radiation; more cosmic rays would lead to more clouds and a net cooling of the planet (and visa-versa). This paper concludes that while the effect may operate, it is not sufficiently robust to be a significant contributor to the current warming of the planet. (C) 2017 COSPAR. Published by Elsevier Ltd. All rights reserved.