Effect of the chosen solar irradiance dataset on simulations of a Future Grand Minimum: Results from a state-of-the-art Chemistry-Climate Model

Abstract:

The long-lasting minimum of Solar Cycle 23 as well as the overall weak maximum of Cycle 24 reveal the possibility for a return to Grand Solar Minimum conditions within the next decades. The past 1,000 years featured at least 5 excursions (lasting 60–100 years) of exceptionally low solar activity, induced by a weak magnetic field of the Sun. The last Grand Solar Minimum (the Maunder Minimum, 1645–1715) coincides with the Little Ice Age in Europe, a time of severe cold and hardship. The quantification of the implications of such a projected decrease in solar forcing is of ultimate importance, given the on-going public discussion of the role of carbon dioxide emissions for global warming, and the possible role a cooling due to decreasing solar activity could be ascribed to. However, existing model simulations that aim to answer these questions suffer from simplifications in the included parameterizations (e.g., no spectral radiation scheme), missing coupling with ocean models, or too low model tops. In addition, there is still no clear consensus about the actual strength of the Maunder Minimum, which is reflected in a range of spectral reconstruction datasets available. To estimate the range of climate response to different Maunder Minimum reconstructions, we compared 3 acknowledged solar datasets that show significant differences in both, total solar irradiance (TSI) and spectral irradiance (SSI) in a single model, first-time. For our purposes we choose to use the ECHAM/MESSy Atmospheric Chemistry Model (EMAC) coupled to a mixed-layer ocean. EMAC incorporates interactive ozone chemistry, a high-resolution shortwave radiation scheme as well as a high model top (0.01 hPa). To get a clean climate signal, all simulations were conducted in time slice mode under 1960 conditions. The experiments show distinct differences in near surface temperatures and reveal the important role of stratospheric processes for the response of surface climate to solar irradiance variations.