4. Conclusions

[12]  Analysis of the effect of long-term solar activity variations on climatic parameters on the time scales from 40,000 to 10,000 years BP (the Pleistocene) and from the modern times to 10,000 years BP (the Holocene) has been carried out. A comparative analysis of temperature and solar activity variations (variations in the contents of cosmogenic 10Be isotopes in Greenland ice and 14C in tree rings) has revealed two kinds of solar forcing of climate. On the one hand, deep solar minima create conditions for abrupt climate change manifesting themselves in the most pronounced manner in the Holocene with a 2400-2300-year periodicity. On the other hand, a high level of solar activity and, hence, solar irradiance give rise to conditions for the development of dynamic processes at the Earth's surface, such as ice-rafting events in the North Atlantic. Simulation has shown that ice-rafting events can be stimulated by an increase in the ocean surface temperature, i.e., the conditions produced by a high solar activity level and a high level of solar irradiance. Ice-rafting events sharply change the character of the North Atlantic overturning circulation (NAOC) by moving the northern edge of the Gulf Stream southwards, which leads to abrupt climate change of the global nature.

[13]  Analysis of experimental data has revealed that a high solar activity level stimulated development of ice-rafting events in both the Pleistocene and the Holocene. Thus, it can be concluded that both deep solar minima and a high solar activity level can create conditions for abrupt climate change.


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