Solar Radiation Change and Climatic Effects on Decennial–Centennial Scales

The causes of climatic effects associated with a change in orbital parameters at decennial–centennial scales are still being debated in the scientific community. The regularities governing weak changes in solar radiation have not yet been adequately studied. The amount of solar radiation at some point of the Earth depends on the latitude, season, position of the Earth in its orbit relative to the Sun, and solar activity, which determines total solar irradiance (TSI). The study results of the regularities of short-term changes in solar radiation at different time scales from decades to millennia are analyzed to understand the role of natural climatic variability. The evolution of orbital factors on such time scales can affect some physical processes of weather and climate, but the main contribution to the variations of insolation for 1–100 years is made by changes in TSI (1–8 W/m2 TSI vs 0–0.2 W/m2 orbital). If the millennial trend in the decrease of orbital-induced insolation in mid-latitudes is taken into account, it leads to some increase in the estimation of the relative contribution of the anthropogenic factor to global warming. It is necessary to take into account errors (up to 5%) in calculating the average daily insolation as a function of longitude, which is up to 2.5 W/m2 during the vernal equinox.