The Mousterian Pluvial is a mostly obsolete term for a prehistoric wet and rainy period in North Africa. It was described as beginning around 50,000 years before the present, lasting roughly 20,000 years, and ending ca. 30,000 B.P. In Africa the Mousterian industry was an archaeological term for a category of Middle Stone Age stone tool production. During the time that archaeological dates were determined by radiocarbon decay, the production of these tools was once thought to have occurred just before the limit of radiocarbon datingat 40 – 35 thousand years ago. In Europe Mousterian tools are made by archaic Neanderthals. In Africa these tools are made by early anatomically modern Homo sapiens. Similar people also made similar tools which are categorized as Alterian. To avoid confusion about the makers, the Mousterian and Alterian tools are now sometimes grouped as Aterian. With more recent dating methods, these tools are now understood to have been mostly produced during the humid Eemian interglacial and later phases of MIS 5, from 130 kybp to 72 kybp. Mousterian tools are frequently older than the Aterian tools. During the dry period that followed in Northern Africa, from 71 to 14.5 kybp, recent research has found that there were 3 semi-humid interruptions: 65–61 kybp, 52.5–50.5 kybp and 37.5–33 kybp. The later 2 have sometimes been grouped to constitute a “Mousterian Pluvial.” They are not associated with strong “Green Sahara” events line the ones of the Eemian in early MIS 5; the late MIS 5 humid period ; or the early Holocene. Few, if any, Mousterian or Aterian tool makers survived in North Africa to witness them. Some older descriptions of the Mousterian Pluvial described it as a strong African Humid period. During earlier strong African Humid periods, the now-desiccated regions of northern Africa were well-watered, bearing lakes, swamps, and river systems that no longer exist. What is now the Sahara desert supported typical African wildlife of grassland and woodland environments: herbivores from gazelle to giraffe to ostrich, predators from lion to jackal, even hippopotamus and crocodile, as well as extinct forms like the Pleistocene camel. The humid periods of 52.5–50.5 kybp and 37.5–33 kybp were not has strong as those of the earlier Eemian humid period. The old theory was that the Mousterian Pluvial was caused by large-scale climatic changes during the last ice age. By 50 kybp, the Wisconsin glaciation was well-advanced; growing ice sheets in North America and Europe displaced the standard climatic zones of the northern hemisphere southward. The temperate zones of Europe and North America acquired an Arctic or tundra climate, and the rain bands typical of the temperate zones dropped to the latitudes of northern Africa. Curiously, the same influences that created the Mousterian Pluvial were thought to have brought it to a close. In the period of its fullest development, c. 30 to 18 kybp, the Laurentide Ice Sheet not only covered an enormous geographic area, but increased its altitude to 1750 meters. It generated its own long term weather patterns, which affected the jet stream passing over the North American continent. The jet stream effectively split in two, creating a new dominant weather pattern over the northern hemisphere that brought harsher conditions to several regions — changes that included an end to the Mousterian Pluvial and a return to a more arid climate in northern Africa. It is now understood that the major African Humid period events are caused by increased insolation in the northern hemisphere and the impact of continental surface warming on the tropical monsoons.
