Understanding of the periodicity of the past solar activity by radiocarbon measurements and the relation to the global environment

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We have measured the radiocarbon concentration in tree rings from the past 3,000 years and discussed the variation of cosmic-ray intensity and solar activity in the past. We found the increase of theSchwabe cycle lengths from the modern value of 11 years to 13-16 years during grand solar minima, which are characteristic periods of solar activity change. We also discovered the rapid increase of radiocarbon concentration at AD775 and AD993. These events indicate that extremely large solar flares occurred at the solar surface in these yearsand a lot of solar high-energy particles arrived at the global environment. These results largely contribute to solve the dynamo mechanism of solar activity and the understanding of its influence to the Earth.