Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 141. This monograph presents a state-of-the-art description of the most recent results on solar variability and its possible influence on the Earth's climate and atmosphere. Our primary goal in doing so is to review solar energy flux variations (both electromagnetic and particle) and understand their relations to solar magnetic field changes and global effects, their impact on different atmospheric layers, and—as a collaboration of scientists working on solar-terrestrial physics—to note unresolved questions on an important interdisciplinary area.One of the highest-level questions facing science today is whether the Earth's atmosphere and climate system changes in a way that we can understand and predict. The Earth's climate is the result of a complex and incompletely understood system of external inputs and interacting parts. Climate change can occur on various time scales as a consequence of natural variability—including solar variability—or anthropogenic causes, or both. The Sun's variability in the form of sunspots and related magnetic activity has been the subject of careful study ever since the earliest telescopic observations. High precision photometric observations of solar-type stars clearly show that year-to-year brightness variations connected with magnetic activity are a widespread phenomenon among such stars. As our nearest star, the Sun is the only star where we can observe and identify a variety of structures and processes which lead to variations in the solar energy output, in both radiative and particle fluxes. Studying event tiny changes in solar energy flux variations may teach us about internal processes taking place in the Sun's convective zone and below.
