Solar irradiance variations and climate

The irradiance of the Sun is observed to vary in phase with the solar cycle at an amplitude of similar to0.1% and a period of roughly 11 years. There is indirect evidence that the irradiance also exhibits a larger secular variation. Direct measurements only cover the last 2(1)/(2) solar cycles and a longer record is needed to study the possible coupling with climate. Therefore, it is necessary to develop successful models of solar irradiance variations and to reconstruct it back into the past. In the present paper, the current observational knowledge and the state-of-the-art of the modelling are introduced and reviewed. (C) 2002 Published by Elsevier Science Ltd.