[211], Closed lakes in East Africa rose, sometimes by hundreds of metres. In October of 2000, Paul Sereno led a small group of paleontologists into the Tnr desert in Niger, in search of dinosaur fossils. [2][8] Pollen, lake deposits and former levels of lakes have been used to study the ecosystems of the African humid period,[9] and charcoal and leaf impressions have been used to identify vegetation changes. [265] Skeletons of elephants, hippos and hominins have been found in the Angamma delta, which is the dominant shoreline feature of northern Lake Chad. [700] The effects of grazing on vegetation cover are context-dependent and hard to generalize over wider region. [718], The warm episode and coinciding drought may have triggered animal and human migration to less inhospitable areas[661] and the appearance of pastoralists where previously fishery-dependent societies had existed, as happened at Lake Turkana. According to Wikipedia, the Sahara covers a vast area of some 9.2 million square kilometers. [553] During spring, the increased vegetation forces anomalous atmospheric circulations that direct moisture transport from the Mediterranean, the Red Sea and eastern tropical Africa into the Middle East, increasing precipitation[554] and agricultural productivity there. This would prompt quite significant changes in [608] Some changes in climate possibly extended into southeastern Australia,[609] Central America[610] and into South America. [60] North Africa together with East Asia is one of the first places where pottery was developed[317] probably under the influence of increased availability of resources during the AHP. [408] One study has estimated that the amount of rainfall in the Red Sea did increase to no more than 1 metre per year (39in/year). [395] Episodes of increased river discharge occurred in Yemen[396] and increased precipitation is recorded in the caves of Hoti, Qunf in Oman, Mukalla in Yemen and Hoq cave in Socotra. Green Saharas Ancient Rainfall Regime Revealed by Scientists, Milankovitch cycles, people. [617] Finally, sometimes the 4.2 kiloyear event - the transition from the Northgrippian to the Meghalayan stage of the Holocene -[575] is considered to be the true end of the AHP,[579] especially in central Africa. [531] The net effect could be a global increase in tropical cyclone activity and a westward shift. Becky Oskin, OurAmazingPlanet Staff Writer . [723] Such human migrations towards more hospitable conditions along rivers and the development of irrigation also took place along the Euphrates, Tigris and Indus, leading to the development of the Sumerian and Harappan civilizations. [106][107] In Arabia, wet conditions apparently took about two millennia to advance northward,[104][108] a gradual advance is supported by tephrochronological data. [634] It shrank to about 5% of its former size,[256] with the deeper northern Bodele basin drying up entirely about 2,000[263]-1,000 years ago[635] as it was disconnected from the southern basin where its major tributary, the Chari River, enters Lake Chad. [157] Among the proposed mechanisms are decreased seasonality of precipitation[158] due to increased dry season precipitation,[159] shortening of the dry season, increased precipitation[160] and increased inflow of moisture from the Atlantic and Indian Oceans. [159] Particular changes occurred in central southern Africa, where a dry period co-occurred with an expansion of Lake Makgadikgadi; presumably increased wetness over the Okavango River catchment in the Angolan Highlands due to the AHP nourished the lake during a dry interval. [357] These favourable conditions for human populations may be reflected in paradise myths such as the Garden of Eden in The Bible and Elysium and the Golden Age in Classical Antiquity,[358] and in the spread of the Nilo-Saharan languages. [270] Wetlands also expanded during the AHP, but both their expansion and subsequent retreat were slower than that of lakes. [506], The end of the humid period appears to reflect the changes in insolation during the Holocene,[105] as a progressive decrease of summer insolation caused the insolation gradients between Earth's hemispheres to decrease. [315], Conditions and resources were ripe for first hunter-gatherers, fishermen[316] and, later, pastoralists. [669] Such a change took also place in Benin and Nigeria between 4,500 and 3,400 calibrated years ago. Paleoclimate Modelling Intercomparison Project, Atlantic meridional overturning circulation, Special Report on Global Warming of 1.5 C, "Early North African Cattle Domestication and Its Ecological Setting: A Reassessment", "Decadal cyclicity of regional mid-Holocene precipitation: Evidence from Dominican coral proxies", "Heat-flow and subsurface temperature history at the site of Saraya (eastern Senegal)", "Late Holocene environmental change and the anthropization of the highlands of Santo Anto Island, Cabo Verde", "Implications of S1 tephra findings in Dead Sea and Tayma palaeolake sediments for marine reservoir age estimation and palaeoclimate synchronisation", "Intra-tooth stable isotope profiles in warthog canines and third molars: Implications for paleoenvironmental reconstructions", "Sea Level Change Controlled the Sedimentary Processes at the Makran Continental Margin Over the Past 13,000 yr", "Wet phases in the Sahara/Sahel region and human migration patterns in North Africa", "Interaction of Fire, Vegetation, and Climate in Tropical Ecosystems: A Multiproxy Study Over the Past 22,000 Years", "Species delimitation in the African tree genus Lophira (Ochnaceae) reveals cryptic genetic variation", "Lactuca dregeana DC. [393] Wadis in Oman eroded across LGM dunes[394] and formed accumulation terraces. [18], Earlier humid periods are sometimes known as "African humid periods"[19] and a number of dry/wet periods have been defined for the Central Africa region. [646][647][648] However, the climate there may have been affected by the Tibesti Mountains and the end of the AHP thus delayed,[634] and fossil groundwater left by the AHP nourishes the lake to this day. [629], Increased variability in precipitation may have preceded the end of the AHP; this is commonly observed before a sudden change in climate. [133] This effect was strengthened by the increased summer insolation,[134][135] leading to a stronger monsoon that also reached farther north. [217] The 8,200 year event has also been noted in the Maghreb, where it is associated with a transition of the Capsian culture[576] as well as with cultural changes both in the Sahara and the Mediterranean;[323] at the Gobero cemetery a population change occurred after this dry interruption[577] but the occurrence of widespread cultural changes appears to be questionable. [662], Libya and the Middle Atlas became gradually more dry,[640] and drying in Morocco took place about 6,000 radiocarbon years ago,[627] Drier conditions in Iberia accompanied the end of the African humid period between 6,000 and 4,000 years ago, perhaps as a consequence of increasingly frequent positive North Atlantic Oscillation episodes and the shift of the ITCZ. The Amazon rain forest is a dense green mass of humid jungle that covers northeast South America. [284] Mosaics of small lakes developed in some regions. [532] While there are no good paleotempestology data for the time of the African humid period that could confirm or refute this theory[533] and many of these records are specific for particular locations,[534] hurricane activity[535] including past strikes in Puerto Rico[536] and in Vieques appear to correlate with the strength of the West African Monsoon. This will cause a greening of the Sahara. Get the specs and dimensions of the LC200 range. [752] Carbon dioxide concentration then increased after about 7,000 years as the biosphere began releasing carbon in response to increasing aridity. [173], The African humid period extended over the Sahara as well as eastern,[48] southeastern and equatorial Africa. [526] In other places, such as the Acacus Mountains populations conversely remained in oases[725][631] and hunter-gatherers also stayed in the Horn of Africa. [59] Later, in the BlyttSernander sequence the humid period coincides with the Atlantic period. Our knowledge of rainfall rates and the spatiotemporal extent of wet conditions has suffered from a lack of continuous sedimentary records. [143], Warmer extratropics during summer may have drawn the Intertropical Convergence Zone (ITCZ) northward,[147] resulting in precipitation changes. [4], The idea that changes in Earth's orbit around the Sun influence the strength of the monsoons was already advanced in 1921, and while the original description was partly inaccurate, later widespread evidence for such orbital controls on climate was found. It was 10 times as wet as today, said lead authorJessica Tierneyof the University of Arizona. [119], As precipitation decreased, so did vegetation, in turn increasing the albedo and further decreasing precipitation. [432], The Ethiopian[433] Lake Abhe expanded to cover an area of 6,000 square kilometres (2,300sqmi), much larger than the present-day lake, in the "Abhe IV"-"Abhe V" lake cycle. [392] The Wadi ad-Dawasir river system in central Saudi Arabia became active again[389][390] with increased river runoff into the Persian Gulf. [295], The large Tamanrasset River[296] flowed from the Atlas Mountains and Hoggar westward towards the Atlantic[297] and entered it in the Bay of Arguin in Mauretania. [132] Southern Hemisphere monsoons are expected to have the opposite response of Northern Hemisphere monsoons to precession, as the insolation changes are reversed; this observation is borne out by data from South America. [162], Changes in the Congo Air Boundary[k][163] or increased convergence along this boundary may have contributed;[160][163] the Congo Air Boundary would have been shifted east by the stronger westerly winds[161] directed by lower atmospheric pressure over Northern Africa,[164] allowing additional moisture from the Atlantic to reach East Africa. During the preceding last glacial maximum, the Sahara contained extensive dune fields and was mostly uninhabited. The last question is answered by assuming they fled to the Nile area and jump started Egypts civilization. The Sahara was once green. [86], During the African humid period, lakes, rivers, wetlands and vegetation including grass and trees covered the Sahara and Sahel[134][215][130] creating a "Green Sahara"[216] with a land cover that has no modern analogues. The history of how the fertile green Sahara lost its vegetation and animal life to become the barren Sahara desert dates back to about 40 million years ago when the Northern tip of Africa was submerged in an Ocean. [105], The African humid period has been explained by increased insolation during Northern Hemisphere summer. [354] Genetic and archeological data indicate that these populations which exploited the resources of the AHP Sahara probably originated in Sub-Saharan Africa and moved north after some time, after the desert got wetter;[355] this may be reflected in the northward spread of Macrohaplogroup L and Haplogroup U6 genomic lineages.

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