Do Solar/Heliospheric Changes Affect the Earth’s Climate?

Ilya G. Usoskin

Sodankyla Geophysical Observatory (Oulu unit), University of Oulu, Finland

An important factor affecting the terrestrial environment is the flux of cosmic rays permanently impinging on Earth. Energetic cosmic rays initiate a nucleonic-electromagnetic cascade in the atmosphere, affecting its physical-chemical properties. In particular, cosmic rays form the dominant source of ionization in the atmosphere, especially in the troposphere. Therefore, a detailed knowledge of processes leading to the cosmic ray induced ionization makes a solid basis for a quantitative study of the outer space influence upon Earth. Via the variable heliospheric modulation of cosmic rays, this provides an indirect solar-terrestrial link. Because of the additional shielding effect of the geomagnetic field, regional ionization is greatly affected by the geomagnetic dipole migration, making it possible to disentangle direct (radiance) and indirect (cosmic ray) effects on the Earth’s climate. We present here a review of atmospheric effects of cosmic rays, including both physical modelling and phenomenological relations to the climate changes, on different time scales.