Sensitivity and linearity of surface temperature response to solar irradiation changes

During the last millennia, prior to the industrialization, long-term climatic variations correlate with low-frequency total solar irradiance (TSI) changes. This long-term correlation does, however, not prove or disapprove a causal relationship. An additional natural forcing is the volcanic activity. The exact magnitudes of these two natural forcings are not known because reconstructions are based on proxy data which include substantial uncertainty. The Maunder Minimum, a period between roughly 1600 and 1700 A.D., is characterized by lower temperatures, low solar activity, and relatively high volcanic activity. There is still a debate on how forcing, i.e., solar vs. volcanic, influenced the climate and to which extend during that time. The amplitude of the TSI decrease is especially uncertain and suggestions range from a few W/m² to a few tens of W/m² lower than today’s value. Here we present simulations with the chemistry-climate model SOCOL where different solar forcings ranging from +10 W/m² to -20 W/m² in TSI terms are applied. On a global scale, changes in temperature are linear with changes in TSI. On a regional scale, however, the temperature response can be non-linear especially at high latitudes. The mechanisms leading to the non-linear behavior are explored.