21. Astronomical cycles correlate perfectly with glacial and interglacial periods , and their transitions, " inside " an ice age. 22. During the last interglacial period , the Red Sea coast of Eritrea was occupied by early anatomically modern humans. 23. Increases in greenhouse gases, such as by volcanic activity, can increase the global temperature and produce an interglacial period . 24. During the final stage of the Riss-Wurm interglacial period the shoreline was six meters above the present sea level. 25. From there they spread north during the interglacial periods , mainly as migrants, returning to the ancestral region in winter. 26. Kuhle explains the interglacial periods by the 100, 000-year cycle of radiation changes due to variations in Earth's orbit. 27. It is the current interglacial period , and it has proven to be a relatively stable environment of the Earth. 28. These conditions typically last for about 100, 000 years and are followed by brief interglacial periods of more temperate weather. 29. There is strong evidence that the Milankovitch cycles affect the occurrence of glacial and interglacial periods within an ice age. 30. Tree species spread outward from refugia during interglacial periods , but in varied patterns, with different trees dominating in different periods.
