The variability of the Sun is well established, as well as that of the Earth's climate. To what extent the two are connected, in the sense that solar variability drives climate, is the subject of considerable research and, in some cases, controversy. After an earlier workshop at the International Space Science Institute (ISS!) on Solar Composition and its Evolution, two ofthe participants came up with the idea to initiate a similar project on the topic of Solar Variability and Climate, a work shop aimed at obtaining an overview of the current knowledge of the variability of the Sun and of the Earth's Climate, and of their possible connections. A further, equally important objective was the strengthening of the interaction between the two, often diverse communities of solar physicists and climatologists. ISSI took up this idea and invited six convenors, E. Friis-Christensen, C. Froh lich, J. Haigh, J. Hansen, M. Schussler, and S. Solanki, who subsequently formu lated the aims and goals of the workshop, nominated a list of invitees, drafted a programme of introductory talks, and structured the workshop into three sections. For each section there was a concluding discussion session moderated by two co chairs. Moreover, there was a number of contributed poster papers for which there were two viewing sessions. The main intent of this format was to leave ample time for open, informal discussions, which is one of the principal aims of ISSI.

Zusammenfassung
Proceedings of an ISSI Workshop, 28 June - 2 July 1999, Bern, Switzerland

Inhalt
Solar Variability and the Earth's Climate: Introduction and Overview.- Solar Variability.- Observations of Irradiance Variations.- Observations of Variability in Cosmic Rays.- Short Term, Direct Indices of Solar Variability.- Long-term Indirect Indices of Solar Variability.- Extreme Solar Cycle Variability in Strong Lines Between 200 and 400 nm.- Data from the Precision Solar Photometrie Telescope (PSPT) in Hawaii from March 1998 to March 1999.- Variations of Solar Ultraviolet Irradiance Observed by the UARS SOLSTICE 1991 to 1999.- Solar Variability Observations (Discussion Session la).- Physical Causes of Solar Activity.- Theory of Solar Irradiance Variations.- Reconstruction of Past Solar Irradiance.- Modelling Short-term Spectral Irradiance Variations.- Modelling Solar Irradiance Variations: Comparison with Observations, Including Line-ratio Variations.- Resonance in a Coupled Solar-Climate Model.- A Least-squares Solution for the Effective Conductivity of the Solar Convection Zone.- Using Precise Solar Limb Shape Measurements to Study the Solar Cycle.- Physical Causes of Solar Variability (Discussion Session lb).- Influences.- The Influence of Total Solar Irradiance on Climate.- The Effect of Solar UV Irradiance Variations on the Earth's Atmosphere.- Cosmic Rays, Clouds, and Climate.- Influence of Solar Wind on the Global Electric Circuit, and Inferred Effects on Cloud Microphysics, Temperature, and Dynamics in the Troposphere.- The Influence of the 11-Year Solar Cycle on the Stratosphere Below 30 km: a Review.- Amplification of the Influence of Solar Flux Variations on the Winter Stratosphere by Planetary Waves.- The Impact of Solar Forcing on the Variability in a Coupled Climate Model.- Solar Variability and the Search for Corresponding Climate Signals.-Climate.- Climate Observations The Instrumental Record.- Long Term Climate Records from Polar Ice.- Anthropogenic and Natural Causes of Twentieth Century Temperature Change.- Observations of Climate Variability (Discussion Session 3a).- The Sun's Role in Long-Term Climate Change.- Climate Modelling (Discussion Session 3b).- Radiative Forcing of Climate Change.- What Can Cloud Observations Teil Us About Climate Variability?.- Cloud Formation and the Possible Significance of Charge for Atmospheric Condensation and Ice Nuclei.- Solar Variability and Clouds (Discussion Session 3c).- Solar Variability and Climate A Summary.- Press Release.- Author Index.- List of Participants.