Role of the Radiation Factor in Global Climatic Events of the Late Holocene

On the basis of calculations of insolation and insolation characteristics, taking into account changes in solar activity, the causes of global climatic events in the late Holocene have been determined. The main reasons for the Little Ice Age (LIA) are the long and deep minimum of summer insolation and insolation seasonality (IS) in the Northern Hemisphere. The values of the minimums are fixed in the range of approximately 1400–1750. The depth of the minimum over the past 5000 years, taking into account the change in solar activity, is about 8.0 W/m 2 for summer insolation and about 13.3 W/m 2 for IS in the Northern Hemisphere. The medieval climatic optimum is associated with the winter maximum of insolation contrast (IC) in the Northern Hemisphere, reflecting an increase in the meridional heat transfer in the winter half of the year from the equatorial region to the polar regions, as well as with a maximum of interhemispheric heat transfer. The increase in winter IC at maximum (1118) relative to 3000 BC is 28.4 W/m 2 . The difference between the hemispheric radiative heat transfer at the maximums (881, 940, and 976) increases by 5.0 W/m 2 relative to 3000 BC. Thus, global events of the late Holocene are associated with extremes of insolation characteristics (incoming radiation, IC, and IS of the Earth), but the temporal structure of the extrema themselves is determined by variations in solar activity. It follows from the above that, when reconstructing and predicting global climatic events, it is important to take into account not only variations in the incoming radiation, but also the associated changes in insolation characteristics (IC and IS of the Earth), reflecting the mechanisms of heat transfer. The IC regulates the meridional transfer of radiation heat; its cause is a change in the tilt of the axis and precession. The IS of the Earth determines the intensity of interhemispheric heat transfer. The noted characteristics of insolation, reflecting not only variations in the arrival of solar radiation, but also variations in the mechanisms of heat transfer, are not taken into account in the general astronomical theory of climate. Taking these indicators into account will help obtain more complete information about climate changes in past eras and will allow the more accurate forecasting of the future climate.