Wetter climate stimulated human expansions after 70 ka?

PNAS 104:16416-21
East African megadroughts between 135 and 75 thousand years ago and bearing
on early-modern human origins
CA Scholz cs.2007

The environmental backdrop to the evolution and spread of early Homo sapiens
in East Africa is known mainly from isolated outcrops and distant marine
sediment cores. Here we present results from new scientific drill cores from
Lake Malawi, the first long and continuous, high-fidelity records of
tropical climate change from the continent itself. Our record shows periods
of severe aridity between 135 and 75 ka, when the lake's water volume was
reduced by at least 95 %. Surprisingly, these intervals of pronounced
tropical African aridity in the early late-Pleistocene were much more severe
than the Last Glacial Maximum, the period previously recognized as one of
the most arid of the Quaternary. From these cores and from records from
Lakes Tanganyika (East Africa) and Bosumtwi (West Africa), we document a
major rise in water levels and a shift to more humid conditions over much of
tropical Africa after c.70 ka. This transition to wetter, more stable
conditions coincides with diminished orbital eccentricity, and a reduction
in precession-dominated climatic extremes. The observed climate mode switch
to decreased environmental variability is consistent with terrestrial and
marine records from in and around tropical Africa, but our records provide
evidence for dramatically wetter conditions after 70 ka. Such climate change
may have stimulated the expansion and migrations of early modern human
populations.


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