Solar Irradiance Variability and Climate

Abstract

The brightness of the Sun varies on all timescales on which it has been observed, and there is increasing evidence that this has an influence on climate. The amplitudes of such variations depend on the wavelength and possibly the timescale. Although many aspects of this variability are well established, the exact magnitude of secular variations (going beyond a solar cycle) and the spectral dependence of variations are under discussion. The main drivers of solar variability are thought to be magnetic features at the solar surface. The climate response can be, on a global scale, largely accounted for by simple energetic considerations, but understanding the regional climate effects is more difficult. Promising mechanisms for such a driving have been identified, including through the influence of UV irradiance on the stratosphere and dynamical coupling to the surface. Here, we provide an overview of the current state of our knowledge, as well as of the main open questions.