The SOLCHECK Project: A State-of-the-Art Investigation into the Imprints of Solar Variability Across Multiple Timescales

Abstract. The project Solar Contribution to Climate Change on Decadal to Centennial Timescales (SOLCHECK) investigated the influence of solar variability on the atmosphere from the pre-industrial era to the present and future. Variations in the Sun’s output, ranging from weeks to millennia, leave distinct imprints on the climate system. Assessing these imprints is challenging due to limited observations, incomplete representation of feedbacks in climate models, and computational constraints. By exploiting a large ensemble of simulations with advanced chemistry–climate models incorporating realistic solar forcing, SOLCHECK particularly aimed at reducing prevailing uncertainties of the atmospheric solar imprints, and to assess the sensitivity of the atmospheric response to solar forcing on different time scales and in different climate states. One key result of SOLCHECK is that although the initial radiative and chemical response to the 11-year solar cycle is consistent across models in the upper tropical stratosphere, the tropospheric climate response in northern winter is highly sensitive to the dynamical state of the stratosphere, thus impeding a robust assessment of surface solar signatures and decadal climate prediction skill. Another important finding suggests that the climate system reacts differently to solar forcing under past, present, and future conditions, showing a stronger response to external solar variations in the tropical upper troposphere and the Arctic as anthropogenic warming progresses. SOLCHECK further highlighted potential impacts of extreme solar storms in a future climate, as such events, although occurring extremely seldom, may have substantial effects on surface UV with potential consequences for ecosystems and human health.