A study examines climate and vegetation changes in early modern human environments. Periods of wet climate are thought to have helped early modern humans spread from Africa to Eurasia, but water source reductions during dry periods may also have been important. John Kutzbach and colleagues examined the changing climate and vegetation in Africa, Arabia, and the Mediterranean Basin from 140,000 years ago to the present. Wet and dry extremes from Earth's orbital changes occurred between approximately 80,000 and 130,000 years ago. Orbital changes increased winter rains in the Mediterranean Basin and caused longer and stronger summer monsoon rains in the Arabian Peninsula and northern Africa at approximately 20,000-year intervals, resulting in increased vegetation and the narrowing of the Saharan-Arabian desert and semidesert zone. These wet periods alternated with dry intervals, when decreased summer insolation caused monsoon rains to decrease and the desert zone's width to increase. Between approximately 15,000 and 70,000 years ago, large ice sheets and lowered greenhouse gas concentrations increased Mediterranean winter precipitation, but the lowered greenhouse gas concentrations caused the tropics to become dry and reduced forest area. Variations in climate and vegetation patterns led to contractions and expansions of regional habitats, potentially influencing the dispersal of early modern humans, according to the authors.
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Article #19-17673: "African climate response to orbital and glacial forcing in 140,000-y simulation with implications for early modern human environments," by John E. Kutzbach et al.
MEDIA CONTACT: John E. Kutzbach, University of Wisconsin-Madison, WI; tel: 608-334-0745; email: < jek@wisc.edu >; Andrew S. Cohen, University of Arizona, Tucson, AZ, tel: 520-621-4691; email: < cohen@email.arizona.edu >
Proceedings of the National Academy of Sciences