  The lack of long and reliable time series of solar spectral irradiance (SSI)
measurements makes an accurate quantification of solar contributions to recent
climate change difficult. Whereas earlier SSI observations and models provided
a qualitatively consistent picture of the SSI variability, recent measurements
by the SORCE satellite suggest a significantly stronger variability in the
ultraviolet (UV) spectral range and changes in the visible and near-infrared
(NIR) bands in anti-phase with the solar cycle. A number of recent
chemistry-climate model (CCM) simulations have shown that this might have
significant implications on the Earth's atmosphere. Motivated by these results,
we summarize here our current knowledge of SSI variability and its impact on
Earth's climate. We present a detailed overview of existing SSI measurements
and provide thorough comparison of models available to date. SSI changes
influence the Earth's atmosphere, both directly, through changes in shortwave
(SW) heating and therefore, temperature and ozone distributions in the
stratosphere, and indirectly, through dynamical feedbacks. We investigate these
direct and indirect effects using several state-of-the art CCM simulations
forced with measured and modeled SSI changes. A unique asset of this study is
the use of a common comprehensive approach for an issue that is usually
addressed separately by different communities. Omissis. Finally, we discuss the
reliability of the available data and we propose additional coordinated work,
first to build composite SSI datasets out of scattered observations and to
refine current SSI models, and second, to run coordinated CCM experiments.
