Understanding solar irradiance variability is essential for grasping the Sun's impact on Earth's climate system. Direct measurements of solar irradiance have only been available since 1978, necessitating longer records and reconstructions for studying long-term solar variability. The sunspot number has been directly observed for the last four centuries, while earlier periods rely on indirect proxies like cosmogenic isotopes 10Be and 14C found in terrestrial archives. These isotopes are produced in the upper atmosphere by galactic cosmic rays, whose flux is influenced by the heliospheric magnetic field, leading to similarities in isotope signals, though local climate and systematic effects can cause short-term discrepancies. To address these challenges, a consistent multi-isotope composite was created from one global 14C and six regional 10Be datasets using a new Bayesian approach. This composite aids in reconstructing solar irradiance over the past 9000 years with the SATIRE-M model. However, due to the sampling of cosmogenic isotope data, the reconstructions are limited to decadal resolution, averaging out solar cycle information. To overcome this, a statistical method was developed to simulate the quasi 11-year solar cycle from observed decadally-averaged sunspot numbers. The final solar irradiance reconstruction serves as a solar forcing input for climate models, enhancing our understanding of solar influence on Earth's cli
