Long-term Changes in Total Solar Irradiance and Their Predictions

Abstract

The Total Solar Irradiance (TSI) index of solar activity attracts the attention of a wide scientific audience due to its direct influence on the Earth’s climate. A number of reconstructions of inter-decadal TSI variability have been extended back to the early Holocene but these estimates still remain uncertain and depend on the model and proxy data used for the particular reconstruction. Here we compare the accuracy of nonlinear forecasts for different reconstructions, confirmed by the global Hurst exponent and pointwise Hölder regularity estimates with the only persistent, regular and predictable reconstruction. The deterministic reconstruction identified predicts a further slow decrease in average TSI level in Cycle 25. We applied the empirical mode decomposition to determine major TSI modes which mainly describe long-term changes in the Sun’s radiative output. We found a crucial role of ~100- and ~200-yr cycles in the occurrence of long-term TSI depressions related to grand minima in the Sun’s magnetic activity. A necessary condition for grand minima occurrence is established in terms of the major TSI modes. Based on the relationship, we conclude that a moderate TSI depression is possible in future decades without a grand minimum.