Inhaltsangabe1. Brief Introduction.- 2. Astronomy.- 3. Spectral Analysis.- 4. Climate proxies.- 5. Time scale and timing.- 6. Mechanisms, models and theories.- 7. Accretion climate models.- 8. Evidence.- 9. Status of our understanding.- Appendix 1. Bispectral analysis.- Appendix 2. Matlab programs.- Appendix 3. Maximum entropy plots.- Appendix 4. Websites for data.