A reconstruction of total solar irradiance since 1700

The irradiance of the Sun is reconstructed from 1700 to the present, whereb y the contributions of active regions and the quiet Sun are modelled separa tely. A method is proposed which allows the contribution of active-region f aculae and sunspots to irradiance changes to be isolated even when only a s ingle proxy of solar activity, such as sunspot relative number, R-z, is ava ilable. The resulting reconstruction explicitly takes the non-linear relati onship between R-z and irradiance variations into account. Nevertheless, du e to the decreasing accuracy of the solar proxy data the accuracy of the re construction decreases at earlier epochs. The main uncertainty, however, li es in the reconstruction of the quiet-sun irradiance variations.