Solar Variability, Galactic Cosmic Rays and Climate: A Review

Climate is among the most important natural resources for all living beings. The main external and internal driver for climate change is variability of the Sun. The Sun is the ultimate source of the energy on the Earth and play a key role in its climate change. What is still not known and needs to be found is the extent to which these variations in solar behavior affect the total energy that the Sun emits. The small variation in the solar irradiance and changes in its spectral distribution leads to a large variation in climate. An attempt has been made to report the present understanding of the solar variability and its consequences on the variability of solar irradiance which exhibits 11-year cyclic variation and modulation on higher time scale. Galactic Cosmic Rays (GCR) reaching the Earth's atmosphere is modulated by the solar wind and geomagnetic field, which also exhibit 11-year cyclic variation. In the present paper, we have reviewed our current understanding on physics of solar variability, galactic cosmic rays and their effects on the Earth's climate.