Английская Википедия:African humid period

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Файл:Sahara satellite hires.jpg
The Sahara was not a desert during the African humid period. Instead, most of northern Africa was covered by grass, trees, and lakes.

The African humid period (AHP; also known by other names) is a climate period in Africa during the late Pleistocene and Holocene geologic epochs, when northern Africa was wetter than today. The covering of much of the Sahara desert by grasses, trees and lakes was caused by changes in the Earth's axial tilt; changes in vegetation and dust in the Sahara which strengthened the African monsoon; and increased greenhouse gases. During the preceding Last Glacial Maximum, the Sahara contained extensive dune fields and was mostly uninhabited. It was much larger than today, and its lakes and rivers such as Lake Victoria and the White Nile were either dry or at low levels. The humid period began about 14,600–14,500 years ago at the end of Heinrich event 1, simultaneously to the Bølling–Allerød warming. Rivers and lakes such as Lake Chad formed or expanded, glaciers grew on Mount Kilimanjaro and the Sahara retreated. Two major dry fluctuations occurred; during the Younger Dryas and the short 8.2 kiloyear event. The African humid period ended 6,000–5,000 years ago during the Piora Oscillation cold period. While some evidence points to an end 5,500 years ago, in the Sahel, Arabia and East Africa, the end of the period appears to have taken place in several steps, such as the 4.2-kiloyear event.

The AHP led to a widespread settlement of the Sahara and the Arabian Deserts, and had a profound effect on African cultures, such as the birth of the Ancient Egyptian civilization. People in the Sahara lived as hunter-gatherers and domesticated cattle, goats and sheep. They left archaeological sites and artifacts such as one of the oldest ships in the world, and rock paintings such as those in the Cave of Swimmers and in the Acacus Mountains. Earlier humid periods in Africa were postulated after the discovery of these rock paintings in now-inhospitable parts of the Sahara. When the period ended, humans gradually abandoned the desert in favour of regions with more secure water supplies, such as the Nile Valley and Mesopotamia, where they gave rise to early complex societies.

Research history

Herodotus in 440 BC and Strabo in 23 AD discussed the existence of a greener Sahara, although their reports were at first questioned owing to their anecdotal nature. In 1850 the researcher Heinrich Barth discussed the possibility of past climate change leading to increased wetness in the Sahara after discovering petroglyphs in the Murzuq Desert, and further discoveries of petroglyphs led desert explorer László Almásy to coin the concept of a Green Sahara in the 1930s. Later in the 20th century, conclusive evidence of a past greener Sahara, the existence of lakes[1]Шаблон:Sfn and higher Nile flow levels was increasingly reportedШаблон:Sfn and it was recognized that the Holocene featured a humid period in the Sahara.Шаблон:Sfn

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.[1] At first it was believed that humid periods in Africa correlate with glacial stages ("pluvial hypothesis") before radiocarbon dating became widespread.Шаблон:Sfn

The development and existence of the African humid period has been investigated with archaeology, climate modelling and paleoproxies,Шаблон:Sfn with archaeological sites,Шаблон:Sfn dunes and deposits left by lakes, aeolian deposits and leaf wax in the sea and wetlands playing an important role.Шаблон:SfnШаблон:Sfn Pollen, lake deposits and former levels of lakes have been used to study the ecosystems of the African humid period,Шаблон:Sfn and charcoal and leaf impressions have been used to identify vegetation changes.Шаблон:Sfn The time 6,000 years ago has received particular attention, especially since that period of the AHP has been used as an experiment in the Paleoclimate Modelling Intercomparison Project.Шаблон:Sfn Most recently, the effects of the Sahara greening on other continents has drawn scientific attention.Шаблон:Sfn

Research issues

While the precipitation changes since the last glacial cycle are well established, the magnitude and timing of the changes are unclear.Шаблон:Sfn Depending on how and where measurements and reconstructions are made, different beginning dates, ending dates, durationsШаблон:Sfn and precipitation levelsШаблон:Sfn have been determined for the African humid period.Шаблон:Sfn The amounts of precipitation reconstructed from paleoclimate records and simulated by climate modelling are often inconsistent with each other;Шаблон:Sfn in general, the simulation of the Green Sahara is considered a problem for earth system models.Шаблон:Sfn Erosion of lake sediments and carbon reservoir effects make it difficult to date when they dried up.Шаблон:Sfn Vegetation changes by themselves do not necessarily indicate precipitation changes, as changes in seasonality, plant species composition and changes in land use also play a role in vegetation changes.Шаблон:Sfn Isotope ratios such as the hydrogen/deuterium ratio that have been used to reconstruct past precipitation values likewise are under the influence of various physical effects, which complicates their interpretation.Шаблон:Sfn Most records of Holocene precipitation in eastern Africa come from low altitudes.Шаблон:Sfn

Terminology

The term "African humid period" was coined in 2000 by deMenocal et al..Шаблон:Sfn Earlier humid periods are sometimes known as "African humid periods"Шаблон:Sfn and a number of dry/wet periods have been defined for the Central Africa region.Шаблон:Sfn In general, these types of climate fluctuations between wetter and drier periods are known as "pluvials" and "interpluvials", respectively.Шаблон:Sfn Because the AHP did not affect all of Africa, there have been calls to not use the term[2] also because it has supposedly colonial implications,[3] and some researchers have specified "North African humid period" and "Northern African humid period".Шаблон:Sfn

Other terms that have been applied to the Holocene AHP or correlative climate phases are "Holocene humid period", which also covers an analogous episode in Arabia and Asia;Шаблон:Sfn[4] "early to mid-Holocene humid episode";Шаблон:Sfn "Holocene Pluvial";Шаблон:Sfn "Holocene Wet Phase";Шаблон:Sfn "Шаблон:Lang" in Central Africa;Шаблон:Sfn "Makalian" for the Neolithic period of northern Sudan;Шаблон:Sfn "Nabtian Wet Phase"Шаблон:Sfn or "Nabtian period" for the 14,000–6,000 humid period over the Eastern Mediterranean and Levant;Шаблон:Sfn "Neolithic pluvial";[5] "Neolithic Subpluvial";Шаблон:Sfn "Neolithic wet phase";[6] "Шаблон:Lang" of the Western Sahara 6,500 – 4,000 years before present;Шаблон:Sfn "Subpluvial II"[6] and "Шаблон:Lang" in the Central Sahara 14,000 – 7,500 years before present.Шаблон:Sfn The terms "Шаблон:Lang"Шаблон:Sfn and Шаблон:Ill have been applied to the dry period in the last glacial maximum,Шаблон:Sfn the latter is equivalent to the "Kanemian";Шаблон:Sfn "Kanemian dry period" refers to a dry period between 20,000 and 13,000 years before present in the Lake Chad area.Шаблон:Sfn

Background and beginning

The African humid period took place in the late PleistoceneШаблон:Sfn and early-middle Holocene,Шаблон:Sfn and saw increased precipitation in Northern and Western Africa due to a northward migration of the tropical rainbelt.Шаблон:SfnШаблон:Sfn The AHP is the most profound climate change of the low latitudes during the last 100,000 yearsШаблон:Sfn and stands out within the otherwise relatively climatically stable Holocene.Шаблон:Sfn It is part of the so-called Holocene climatic optimumШаблон:Sfn and coincides with a global warm phase, the Holocene Thermal Maximum.Шаблон:SfnШаблон:Efn Liu et al. 2017Шаблон:Sfn subdivided the humid period into an "AHP I" which lasted until 8,000 years ago, and an "AHP II" from 8,000 years onward,Шаблон:Sfn with the former being wetter than the latter.Шаблон:Sfn

The African humid period was not the first such phase; evidence for about 230 older such "green Sahara"/wet periods exist going back perhaps to the first appearance of the Sahara 7–8 million years ago,[1] for example during Marine Isotope Stage 5 a and c.Шаблон:Sfn Earlier humid periods appear to have been more intense than the AHP of the Holocene,Шаблон:SfnШаблон:Sfn including the exceptionally intense Eemian humid period. This humid period provided the pathways for early humans to cross Arabia and Northern AfricaШаблон:Sfn and which, together with later moist periods, has been linked to expansions of the Aterian populationsШаблон:Sfn and the speciation of insect species.[7] Such humid periods are usually associated with interglacials, while glacial stages correlate to dry periods;Шаблон:Sfn they occur during precession minima, unless large ice sheets or insufficient greenhouse gas concentrations suppress their onset.[8]

The Bølling–Allerød warming appears to be synchronous with the onset of the African humid periodШаблон:SfnШаблон:SfnШаблон:Sfn as well as to increased humidity in Arabia.Шаблон:Sfn Later, in the Blytt–Sernander sequence the humid period coincides with the Atlantic period.Шаблон:Sfn

Conditions before the African humid period

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African vegetation during the last glacial maximum

During the Last Glacial Maximum, the Sahara and Sahel had been extremely dryШаблон:Sfn with less precipitation than todayШаблон:SfnШаблон:Sfn as reflected by the extent of dune sheets and water levels in closed lakes.Шаблон:Sfn The Sahara was much larger,Шаблон:Sfn extending Шаблон:Convert farther southШаблон:Sfn to about 12° northern latitude.Шаблон:Sfn Dunes were active much closer to the equator,Шаблон:SfnШаблон:SfnШаблон:Efn and rainforests had retreated in favour of afromontane and savannah landscapes as temperatures, rainfall, and humidity decreased.Шаблон:SfnШаблон:SfnШаблон:Sfn

There is little and often equivocal evidence of human activity in the Sahara or Arabia at that time, reflecting its drier nature;Шаблон:SfnШаблон:SfnШаблон:Sfn in the Acacus Mountains the last human presence was recorded 70,000-61,000 years ago and by the LGM humans had largely retreated to the Mediterranean coast and the Nile Valley.Шаблон:Sfn The aridity during the Last Glacial Maximum appears to have been the consequence of the colder climate and larger polar ice sheets, which squeezed the monsoon belt to the equator and weakened the West African Monsoon. The atmospheric water cycle and the Walker and Hadley circulations were weaker as well.Шаблон:Sfn Exceptional dry phases are linked to Heinrich eventsШаблон:Sfn when there are a large number of icebergs in the North Atlantic;Шаблон:Sfn the discharge of large amounts of such icebergs between 11,500 and 21,000 years before present coincided with droughts in the subtropics.Шаблон:Sfn

Before the onset of the AHP, it is thought that Lake Victoria, Lake Albert, Lake Edward,Шаблон:Sfn Lake TurkanaШаблон:Sfn and the Sudd swamps had dried out.Шаблон:Sfn The White Nile had become a seasonal riverШаблон:Sfn whose courseШаблон:Sfn along with that of the main Nile may have been dammed by dunes.Шаблон:Sfn The Nile Delta was partially dry, with sandy plains extending between ephemeral channels and exposed seafloor, and it became a source of sand for ergsШаблон:Efn farther east.Шаблон:Sfn Other lakes across Africa, such as Lake Chad and Lake Tanganyika, also had shrunkШаблон:Efn during this time,Шаблон:Sfn and both the Niger River and Senegal River were stunted.Шаблон:Sfn

Early humidity increases

Whether some parts of the desert such as highlands like the Red Sea Hills were reached by the westerliesШаблон:Sfn or weather systems associated with the subtropical jet streamШаблон:Sfn—and thus received precipitation—is contentious. It is only clearly supported for the Maghreb in northwestern Africa,Шаблон:Sfn though river flowШаблон:Sfn/terrace formationШаблон:Sfn and lake development in the Tibesti and Jebel Marra mountainsШаблон:SfnШаблон:Sfn and residual Nile flow may be explained in this way.Шаблон:Sfn The highlands of Africa appear to have been less affected by drought during the last glacial maximum.Шаблон:Sfn

The end of the glacial drought occurred between 17,000 and 11,000 years ago,Шаблон:Sfn with an earlier beginning noted in the Saharan mountainsШаблон:SfnШаблон:Sfn (possibly) 18,500 years ago.Шаблон:Sfn In southern and central Africa earlier starts 17,000 and 17,500 years ago, respectively, may be linked to Antarctic warming,Шаблон:SfnШаблон:Sfn while Lake Malawi appears to have been low until about 10,000 years ago.Шаблон:Sfn

High lake levels occurred in the Jebel Marra and Tibesti Mountains between 15,000 and 14,000 years agoШаблон:Sfn and the youngest stage of glaciation in the High Atlas mountains took place at the same time as the Younger Dryas and early African humid period.[9] Around 14,500 years ago, lakes started to appear in the arid areas.Шаблон:Sfn

Onset

The humid period began about 15,000Шаблон:SfnШаблон:Sfn-14,500 years ago.Шаблон:EfnШаблон:Sfn The onset of the humid period took place almost simultaneously over all of NorthernШаблон:Efn and Tropical Africa,Шаблон:Sfn with impacts as far as Santo Antão on Cape Verde.[10][11] In Arabia, wet conditions apparently took about two millennia to advance northward,Шаблон:SfnШаблон:Sfn a gradual advance is supported by tephrochronological data.[12] Likewise, in the Sahara there might have been a delay of about a millennium between the onset of the AHP and the full establishment of humid conditions, as vegetation growth and the filling of river systems took time.Шаблон:Sfn

Lake Victoria reappeared and overflowed;Шаблон:Sfn Lake Albert also overflowed into the White NileШаблон:Sfn 15,000–14,500 years agoШаблон:Sfn and so did Lake Tana, into the Blue Nile.Шаблон:Sfn The White Nile flooded part of its valleyШаблон:Sfn and reconnected to the main Nile.Шаблон:SfnШаблон:Efn In Egypt widespread flooding by the "Wild Nile" took place;Шаблон:Sfn this "Wild Nile" periodШаблон:Sfn led to the largest recorded floods on this river,Шаблон:Sfn sedimentation in floodplains,Шаблон:Sfn and probably also impacted human populations along the river.Шаблон:Sfn Even earlier, 17,000–16,800 years ago, meltwater from glaciers in Ethiopia – which were retreating at that time – may have begun to increase the flow of water and sediment in the Nile.Шаблон:Sfn In the East African Rift water levels in lakes began to rise by about 15,500/15,000Шаблон:Sfn-12,000 years ago;Шаблон:Sfn Lake Kivu began overflowing into Lake Tanganyika by about 10,500 years ago.Шаблон:Sfn

About the same time that the AHP started, the cold glacial climate in Europe associated with Heinrich event 1 endedШаблон:Sfn with climate changing as far as Australasia.Шаблон:Sfn A warming and retreat of sea ice around Antarctica coincides with the start of the African humid period,Шаблон:Sfn although the Antarctic Cold Reversal also falls into this timeШаблон:Sfn and may relate to a drought interval recorded in the Gulf of Guinea.Шаблон:Sfn

Causes

The African humid period was caused by a stronger West African MonsoonШаблон:Sfn directed by changes in solar irradiance and in albedo feedbacks.Шаблон:Sfn These led to increased moisture import from both the equatorial Atlantic into West Africa, as well as from the North Atlantic and the Mediterranean Sea towards the Mediterranean coasts of Africa.Шаблон:SfnШаблон:Sfn There were complex interactions with the atmospheric circulation of the extratropics and between moisture coming from the Atlantic Ocean and the Indian Ocean,Шаблон:Sfn and an increased overlap between the areas wetted by the monsoon and those wetted by extratropical cyclones.Шаблон:Sfn

Climate models indicate that changes from a dry to a green Sahara and back have threshold behaviour, with the change occurring once a certain level of insolation is exceeded;Шаблон:Sfn likewise, a gradual drop of insolation often leads to a sudden transition back to a dry Sahara.Шаблон:Sfn This is due to various feedback processes which are at work,Шаблон:Sfn and in climate models there is often more than one stable climate-vegetation state.Шаблон:Sfn Sea surface temperature and greenhouse gas changes synchronized the beginning of the AHP across Africa.Шаблон:Sfn

Orbital changes

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Milankovich cycles over the past one million years

The African humid period has been explained by increased insolation during Northern Hemisphere summer.Шаблон:Sfn Due to precession, the season at which Earth passes closest to the Sun on its elliptical orbit – the perihelion – changes, with maximum summer insolation occurring when this happens during Northern Hemisphere summer.Шаблон:Sfn Between 11,000 and 10,000 years ago, Earth passed through the perihelion at the time of summer solstice, increasing the amount of solar radiation by about 8%,Шаблон:Sfn resulting in the African monsoon becoming both stronger and reaching farther north.Шаблон:Sfn Between 15,000 and 5,000 years ago, summer insolation was at least 4% higher than today.Шаблон:Sfn The obliquity also decreased during the HoloceneШаблон:Sfn but the effect of obliquity changes on the climate is focused on the high latitudes and its influence on the monsoon is unclear.Шаблон:Sfn

During summer, solar heating is stronger over the North African land than over the ocean, forming a low pressure area that draws moist air and precipitation inШаблон:Sfn from the Atlantic Ocean.Шаблон:Sfn This effect was strengthened by the increased summer insolation,[13] leading to a stronger monsoon that also reached farther north.Шаблон:Sfn The effects of these circulation changes reached as far as the subtropics.Шаблон:Sfn

Obliquity and precession are responsible for two of the foremost Milankovich cycles and are responsible not only for the onset and cessation of ice agesШаблон:Sfn but also for monsoon strength variations.Шаблон:Sfn 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.Шаблон:Sfn The precession change increased seasonality in the Northern Hemisphere while decreasing it in the Southern Hemisphere.Шаблон:Sfn

Albedo feedbacks

Шаблон:See also

According to climate modelling,[1] orbital changes by themselves cannot increase precipitation over Africa enough to explain the formation of the large desert lakes such as Шаблон:Convert Lake MegachadШаблон:EfnШаблон:Sfn or the northward expansion of vegetationШаблон:SfnШаблон:SfnШаблон:Sfn unless ocean and land surface changes are factored in.Шаблон:Sfn

Decreasing albedo resulting from vegetation changes is an important factor in the precipitation increase.Шаблон:Sfn Specifically, increased precipitation increases the amount of vegetation; vegetation absorbs more sunlight and thus more energy is available for the monsoon. In addition, evapotranspiration from vegetation adds more moisture, although this effect is less pronounced than the albedo effect.Шаблон:Sfn Heat fluxes in the soil and evaporation are also altered by the vegetation.Шаблон:Sfn

Reduced dust generation from a wetter Sahara,Шаблон:Sfn where major dust-generating regions were submerged by lakes, influences the climateШаблон:Sfn by reducing the amount of light absorbed by dust. Decreased dust emissions also modify cloud properties, making them less reflective and more efficient at inducing precipitation.[1]Шаблон:SfnШаблон:Sfn In climate models, reduced amounts of dust in the troposphere together with vegetation changes canШаблон:SfnШаблон:Sfn often but not always explain the northward expansion of the monsoon.Шаблон:SfnШаблон:Sfn There is not universal agreement on the effects of dust on precipitation in the Sahel, however,[1] in part because the effects of dust on precipitation may be dependent on its size.Шаблон:Sfn

In addition to raw precipitation changes, changes in precipitation seasonality such as the length of dry seasons need to be considered when assessing the effects of climate change on vegetation,Шаблон:Sfn as well as the fertilizing effects of increased carbon dioxide concentrations in the atmosphere.Шаблон:Sfn

Other sources of albedo changes:

Intertropical Convergence Zone changes

Warmer extratropics during summer may have drawn the Intertropical Convergence Zone (ITCZ) northward,Шаблон:Sfn resulting in precipitation changes.Шаблон:Sfn Sea surface temperatures off North Africa warmed under orbital effects and through weaker trade winds, leading to a northward movement of the ITCZ and increasing moisture gradients between land and sea.Шаблон:Sfn Two temperature gradients, one between a cooler Atlantic during spring and an already warming African continent, the other between warmer temperatures north of 10° latitude and cooler south, may have assisted in this change.[14] In Eastern Africa, ITCZ changes had relatively little effect on precipitation changes.Шаблон:SfnШаблон:Sfn The past position of the ITCZ in Arabia is also contentious.Шаблон:Sfn

Precipitation changes in East Africa

The African humid period that took place in East Africa appears to have been caused by different mechanisms.Шаблон:Sfn Among the proposed mechanisms are decreased seasonality of precipitationШаблон:Sfn due to increased dry season precipitation,Шаблон:Sfn shortening of the dry season, increased precipitationШаблон:Sfn and increased inflow of moisture from the Atlantic and Indian Oceans. The Atlantic moisture inflow was in part triggered by a stronger West African and Indian monsoon, perhaps explaining why the effects of the AHP extended into the Southern Hemisphere.Шаблон:SfnШаблон:Sfn The behaviour of the easterly trade winds is unclear; increased moisture transport by easterly trade winds may have aided in the development of the AHPШаблон:Sfn but alternatively a stronger Indian Monsoon that draws easterly winds away from East Africa may have occurred.Шаблон:Sfn

Changes in the Congo Air BoundaryШаблон:EfnШаблон:Sfn or increased convergence along this boundary may have contributed;Шаблон:SfnШаблон:Sfn the Congo Air Boundary would have been shifted east by the stronger westerly windsШаблон:Sfn directed by lower atmospheric pressure over Northern Africa,Шаблон:Sfn allowing additional moisture from the Atlantic to reach East Africa.Шаблон:Sfn The parts of East Africa that were isolated from Atlantic moisture did not become significantly wetter during the AHPШаблон:Sfn although at one site in Somalia the seasonality of precipitation mayШаблон:Sfn or may not have decreased.[15]

Various contributing factors may have led to the increased humidity in East Africa, not all of which were necessarily operating simultaneously during the AHP.Шаблон:SfnШаблон:Sfn That the "African humid period" reached this part of Africa has been doubted.[16] Finally, increased greenhouse gas concentrations may have been involved in directing the onset of the AHP in tropical southeastern Africa;Шаблон:Sfn there, orbital changes would be expected to lead to climate variations opposite to those in the Northern Hemisphere.Шаблон:Sfn The pattern of humidity changes in south-eastern Africa are complex.Шаблон:Sfn

Additional factors

Effects

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Vegetation and water bodies in the Eemian (bottom) and Holocene (top)

The African humid period extended over the Sahara as well as eastern,Шаблон:Sfn southeastern and equatorial Africa. In general, forests and woodlands expanded through the continent.Шаблон:Sfn A similar wet episode took place in the tropical Americas,Шаблон:Efn China, Asia,Шаблон:EfnШаблон:SfnШаблон:SfnШаблон:SfnШаблон:SfnШаблон:SfnШаблон:Sfn India,Шаблон:Sfn the Makran region,[21] the Middle East and the Arabian PeninsulaШаблон:SfnШаблон:SfnШаблон:SfnШаблон:SfnШаблон:Sfn and appears to relate to the same orbital forcing as the AHP.Шаблон:Sfn An early Holocene monsoonal episode extended as far as the Mojave Desert in North America.[22] In contrast, a drier episode is recorded from much of South America where Lake Titicaca, Lake Junin, the discharge of the Amazon River and water availability in the Atacama were lower.Шаблон:Sfn

The discharge of the Congo, Niger,[23] Nile,[24] Ntem,Шаблон:Sfn Rufiji,Шаблон:Sfn and Sanaga rivers increased.[23] Runoff from Algeria,[25] equatorial Africa, northeastern Africa and the western Sahara was also larger.Шаблон:Sfn Changes in the morphology of the river systems and their alluvial plains occurred in response to the increased discharge,Шаблон:SfnШаблон:Sfn and the Senegal River expanded its riverbed,Шаблон:Sfn breached dunes and re-entered the Atlantic Ocean.Шаблон:Sfn

Flora and fauna of the Sahara

During the African humid period, lakes, rivers, wetlands and vegetation including grass and trees covered the Sahara and Sahel[13]Шаблон:SfnШаблон:Sfn creating a "Green Sahara"Шаблон:Sfn with a land cover that has no modern analogues.Шаблон:Sfn Evidence includes pollen data, archaeological sites, evidence of faunal activity such as diatoms, mammals, ostracods, reptiles and snails, buried river valleys, organic-rich mats, mudstones, evaporites as well as travertines and tufas deposited in subaqueous environments.Шаблон:Sfn

Файл:Tarangire-Natpark800600.jpg
A present-day savannah, Tarangire National Park, Tanzania

The vegetation cover then extended over almost all of the SaharaШаблон:Sfn and consisted of an open grass savannah with shrubs and trees,Шаблон:SfnШаблон:Sfn with a moist savanna vegetation getting established in the mountains.Шаблон:Sfn In general, the vegetation expanded northwardШаблон:Sfn to 27–30° northern latitude in West AfricaШаблон:SfnШаблон:Sfn with a Sahel boundary at about 23° north,Шаблон:Sfn as the Sahara was populated by plants that today often occur about Шаблон:Convert[26]Шаблон:Sfn farther south.Шаблон:Sfn The northward movement of vegetation took some time and some plant species moved faster than others.Шаблон:Sfn Plants that perform C3 carbon fixation became more common.[27] The fire regime of the vegetation changed;[28] in the desert the expansion of vegetation facilitated fire activity, while in the savanna the increased prevalence of woody vegetation reduced fire activity.Шаблон:Sfn

Forests and plants from the humid tropics were concentrated around lakes, riversШаблон:Sfn and the Atlantic Ocean coast of Senegal;[29] waterbodies were also settled by aquatic and partially aquatic plantsШаблон:Sfn and the Senegalese coast by mangroves.[19] The landscape during the AHP has been described as a mosaic between various vegetation types of semi-desert and humid originШаблон:Sfn rather than a simple northward displacement of plant species,Шаблон:Sfn and some brown or yellow vegetation communities persisted.[1] There was no southward displacement of Mediterranean plants during the HoloceneШаблон:Sfn and on the Tibesti Mountains cold temperatures may have restricted the expansion of tropical plants.Шаблон:Sfn Pollen data often show a dominance of grasses over humid tropics trees.Шаблон:Sfn The tree Lophira alata and others may have spread out of the African forests during the AHP,[30] and the Lactuca plants may have split into two species under the effects of the AHP and other climate changes in Africa during the Holocene.[31]

The Sahara climate did not become entirely homogeneous; its central-eastern parts were probably drier than the western and central sectorsШаблон:Sfn and the Libyan sand sea was still a desert[1] although pure desert areas retreated or became arid/semiarid.Шаблон:Sfn An arid belt may have existed north of 22° latitude,Шаблон:Sfn or the vegetationШаблон:Sfn and the African monsoon might have reached 28–31° northern latitude;Шаблон:Sfn in general conditions between 21° and 28° northern latitude are poorly known.Шаблон:Sfn Dry areas may have persisted in the rain shadows of mountains and could have supported arid climate vegetation, explaining the presence of its pollen in sediment cores.Шаблон:Sfn In addition, north–south gradations in vegetation patterns have been reconstructed from charcoal and pollen data.Шаблон:Sfn

Fossils record changes in the animal fauna of the Sahara.Шаблон:Sfn This fauna included antelopes,Шаблон:Sfn baboons, cane rats,Шаблон:Sfn catfish,Шаблон:SfnШаблон:Sfn clams,Шаблон:Sfn cormorants,Шаблон:Sfn crocodiles,Шаблон:Sfn elephants,Шаблон:Sfn frogs,Шаблон:Sfn gazelles,Шаблон:Sfn giraffes,Шаблон:Sfn hartebeest,Шаблон:SfnШаблон:Sfn hares,Шаблон:Sfn hippos,Шаблон:SfnШаблон:Sfn molluscs, Nile perches,Шаблон:Sfn pelicans,Шаблон:Sfn rhinoceroses,Шаблон:Sfn snake-eagles,Шаблон:Sfn snakes,Шаблон:Sfn tilapia,Шаблон:Sfn toads,Шаблон:Sfn turtlesШаблон:Sfn and many more animals,Шаблон:Sfn and in Egypt there were African buffaloes, spotted hyenas, warthogs, wildebeest and zebra.Шаблон:Sfn Additional birds include brown-necked raven, coot, common moorhen, crested grebe, glossy ibis, long-legged buzzard, rock dove, spur-winged goose and tufted duck.Шаблон:Sfn Large herds of animals lived in the Sahara.Шаблон:Sfn Some animals expanded over the whole desert, while others were limited to places with deep water.Шаблон:Sfn Earlier humid periods in the Sahara may have allowed species to cross the now-desert.Шаблон:Sfn A reduction in open grasslands at the beginning of the AHP may explain the decline of the populations of some mammals during[32] and a population bottleneck in cheetahs at the start of the humid period,[33] while leading to the expansion of the population of other animals such as Hubert's multimammate mouse[34] and Natal multimammate mouse.[35]

Lakes and rivers of the Sahara

Файл:Megatschad GIS.PNG
Lake Megachad, with present-day Lake Chad highlighted in green

A number of lakes formedШаблон:Sfn or expanded in the Sahara[18] and the Hoggar and Tibesti Mountains.Шаблон:Sfn The largest of them was Lake Chad which increased to at least ten times its present-day sizeШаблон:Sfn to form Lake Megachad.Шаблон:Sfn This enlarged Lake Chad reached dimensions of Шаблон:Convert in north–south and east–west direction respectively,Шаблон:Sfn covering the Bodélé DepressionШаблон:Sfn and perhaps as much as 8% of the present-day Sahara desert.Шаблон:Sfn It influenced the climate itself;Шаблон:Sfn for example rainfall would have been reduced at the centre of the lake and increased at its margins.[1] Lake Chad was possibly fed from the north by rivers draining the Hoggar (Taffassasset drainage)Шаблон:Sfn and Tibesti Mountains, from the Ennedi Mountains in the east through the "Eastern palaeorivers"[36] and from the south by the Chari-Logone and Komadugu Rivers.Шаблон:Sfn The Chari River was the main tributaryШаблон:Sfn while the rivers draining the Tibesti formed alluvial fansШаблон:Sfn/the Angamma river delta at their entry into northern Lake Chad.Шаблон:Sfn Skeletons of elephants, hippos and hominins have been found in the Angamma delta, which is the dominant shoreline feature of northern Lake Chad.Шаблон:Sfn The lake overflowed into the Niger RiverШаблон:Sfn during highstand through the Mayo Kebbi and the Benue River, eventually reaching the Gulf of Guinea.Шаблон:Sfn Older dune systems were submerged by Lake Chad.Шаблон:Sfn

Among the largeШаблон:Sfn lakes which may have formed in the Sahara are Lake Megafezzan in LibyaШаблон:Sfn and Lake Ptolemy in Sudan.Шаблон:SfnШаблон:Sfn[37]Шаблон:Sfn Quade et al. 2018 raised some doubts about the size and existence of some of these lakes such as Lake Ptolemy, Lake Megafezzan, Lake Ahnet-Mouydir;Шаблон:Sfn it is possible that giant lakes only formed in the southern part of the Sahara.Шаблон:Sfn Other lakes are known from Adrar Bous in Niger,Шаблон:Sfn Era Kohor and Trou au Natron in the Tibesti Mountains,[38] I-n-Atei in the Hoggar, at Ine SakaneШаблон:Sfn and in TaoudenniШаблон:Efn in Mali,Шаблон:Sfn the Garat Ouda and Takarkori Lakes in the Acacus Mountains,Шаблон:Sfn Chemchane in Mauretania,[39] at Guern El Louläilet in the Great Western Erg[40] and Sebkha Mellala close to Ouargla, both in Algeria,Шаблон:Sfn at Wadi Shati and elsewhere in the Fezzan in Libya,Шаблон:Sfn at Bilma, Dibella, FachiШаблон:Sfn and Gobero in the Ténéré,Шаблон:Sfn Шаблон:Lang in NigerШаблон:Sfn and at "Eight Ridges",Шаблон:Sfn El Atrun,Шаблон:Sfn Lake Gureinat, Merga,Шаблон:Sfn "Ridge",Шаблон:Sfn Sidigh,Шаблон:Sfn at Wadi Mansurab,Шаблон:Sfn Selima and Oyo in Sudan.Шаблон:Sfn The lakes of Ounianga merged into two large lakesШаблон:Sfn and overflowed, either above surface or underground.Шаблон:Sfn Mosaics of small lakes developed in some regions,[37] such as the Grand Erg Occidental.Шаблон:Sfn Wetlands also expanded during the AHP, but both their expansion and subsequent retreat were slower than that of lakes.Шаблон:Sfn The Niger River, which had been dammed by dunes during the LGM, formed a lake in the Timbuktu region that eventually overflowed and drained at some point during the AHP.Шаблон:Sfn

In some parts of the Sahara ephemeral lakes formed such as at Abu Ballas, Bir Kiseiba, Bir Sahara, Bir Tarfawi and Nabta PlayaШаблон:Efn in Egypt,Шаблон:SfnШаблон:Sfn which may relate to later Egyptian religions,Шаблон:Sfn or swamp-lakes such as at Adrar Bous close to the Air Mountains.Шаблон:Sfn Ephemeral lakes developed between dunes,Шаблон:Sfn[41] and a "freshwater archipelago" appears to have existed in the Murzuq basin.Шаблон:Sfn All these lake systems left fossils such as fish, limnic sedimentsШаблон:Sfn and fertile soils that were later used for agriculture (El Deir, Kharga Oasis).Шаблон:Sfn Finally, crater lakes formed in volcanic fields[42] such as Trou au Natron and Era Kohor in the Tibesti,Шаблон:Sfn and sometimes survive to this day as smaller remnant lakes such as Malha craterШаблон:Sfn in the Meidob volcanic field.[42] Potentially, the increased availability of water during the AHP may have facilitated the onset of phreatomagmatic eruptions such as maar formation in the Bayuda volcanic field, although the chronology of volcanic eruptions there is not well known enough to substantiate a link to the AHP.[43]

The large Tamanrasset River[44] flowed from the Atlas Mountains and Hoggar westward towards the AtlanticШаблон:Sfn and entered it in the Bay of Arguin in Mauretania.[45] It once formed the 12th largest watershed in the world[46] and left a submarine canyon and riverine sediments.Шаблон:Sfn Together with other rivers it formed estuaries and mangroves in the Bay of Arguin.[45] Other rivers in the same area also formed submarine canyons,Шаблон:Sfn and sediment patterns in marine sediment coresШаблон:Sfn and the occurrence of submarine landslides in the area have been related to the activity of these rivers.Шаблон:Sfn

Rivers such as the Irharhar in Algeria, Libya and TunisiaШаблон:Sfn and the Sahabi and Kufra rivers in Libya were active during this timeШаблон:Sfn although there is some doubt that they had perennial flow;Шаблон:Sfn they appear to have been more important in earlier humid periods.Шаблон:Sfn Small watersheds,Шаблон:Sfn wadisШаблон:Sfn and rivers discharging into endorheic basins such as Wadi Tanezzuft also carried water during the AHP.Шаблон:SfnШаблон:Sfn In Egypt, some rivers active during the AHP are now gravel ridges.Шаблон:Sfn In the Air, Hoggar and Tibesti Mountains, the so-called "Middle Terrace" was emplaced at this time.Шаблон:Sfn The rivers of the Sahara,Шаблон:Sfn lakes and their watersheds may have acted as pathways for the spread of humans and animals;Шаблон:SfnШаблон:Sfn the rivers were often connected to each other by alluvial fans.Шаблон:Sfn Proposed examples of animals that spread through rivers are the Nile crocodile and the fish Clarias gariepinus and Tilapia zillii.Шаблон:Sfn It is possible that the name Tassili n'Ajjer, which means "plateau of the rivers" in Berber, is a reference to past river flows.[47] On the other hand, intense flows of these rivers may have made their shores dangerous to humans and thus created additional impetus for human movement.[48]Шаблон:Sfn Now-dry river valleys from the AHP in the eastern Sahara have been used as analogues for former river systems on Mars.[49]

Humans of the Sahara

Conditions and resources were ripe for first hunter-gatherers, fishermenШаблон:Sfn and, later, pastoralists;Шаблон:Sfn the exact chronology - when humans returned in the Sahara after the onset of the AHP - is disputed.Шаблон:Sfn They may have come either from the north (Maghreb or Cyrenaica)Шаблон:SfnШаблон:Sfn where the Capsian cultureШаблон:Efn was located,[50] the south (Sub-Saharan Africa), or the east (Nile Valley).Шаблон:Sfn The human population in the Sahara increased at the beginning of the AHP.Шаблон:Sfn Traces of human activity have been found in the Acacus MountainsШаблон:Sfn where caves and rock shelters were used as basecamps for humans,Шаблон:Sfn such as the Uan Afuda caveШаблон:Sfn and the Uan Tabu and Takarkori rock shelters.Шаблон:Sfn The first occupation in Takarkori took place between 10,000 and 9,000 years ago;Шаблон:Sfn about five millennia of human cultural evolution are recorded there.Шаблон:Sfn At Gobero in the Ténéré desert a cemetery has been found, which has been used to reconstruct the lifestyle of these former inhabitants of the Sahara,Шаблон:Sfn and at Lake Ptolemy in Nubia humans settled close to the lake shore, using its resources and perhaps even engaging in leisure activities.Шаблон:Sfn At that time, many humans appear to have depended on water-bound resources, seeing as many of the tools left by the early humans are associated with fishery; hence this culture is also known as "aqualithic"[18]Шаблон:Sfn although substantial differences between the cultures of various places have been found.Шаблон:Sfn The greening of the Sahara led to a demographic expansion[51] and especially in the Eastern Sahara human occupancy coincides with the AHP.Шаблон:Sfn Conversely occupation decreased along the Nile valley, perhaps due to the expansion of wetlands thereШаблон:Sfn and frequent large-scale flooding of the Nile delta.[52]

Humans were hunting large animals with weapons that have been found in archaeological sitesШаблон:Sfn and wild cereals occurring in the Sahara during the AHP such as brachiaria, sorghum and urochloa were an additional source of food.Шаблон:Sfn Humans also domesticated cattle,Шаблон:Sfn goats and sheep.[53] Cattle domestication may have occurred especially in the more environmentally variable Eastern Sahara,Шаблон:Sfn where the lack of lakes (cattle having high requirements of drinking water) may however have limited the occurrence of cattle.Шаблон:Sfn Animal husbandry picked up in earnest around 7,000 years ago when domestic animals came to the Sahara, and a population boom may be linked to this change in cultural practice;Шаблон:SfnШаблон:Sfn cattle and goats spread southwestwards from northeasternmost Africa from 8,000 years before present.Шаблон:Sfn Dairying has been demonstrated in some locationsШаблон:Sfn and cattle-husbandry is supported by the frequent depiction of cattle in rock paintings.Шаблон:Sfn The Dufuna canoe, one of the oldest known ships in the world,Шаблон:Sfn appears to date to the Holocene humid period and implies that the waterbodies of that time were navigated by humans.Шаблон:Sfn The cultural units "Masara" and "Bashendi" existed in Dakhleh Oasis during the AHP.[54] In the Acacus Mountains, several cultural horizons known as Early and Late Acacus and Early, Middle, Late and Final Pastoral have been identifiedШаблон:Sfn while in Niger the Kiffian culture has been related to the beginning of the AHP.[55] Ancient civilizations thrived,Шаблон:Sfn with farming and animal husbandry taking place in Neolithic settlements.[39]Шаблон:Sfn Possibly, the domestication of plants in Africa was delayed by the increased food availability during the AHP, it only took place around 2,500 BC.Шаблон:Sfn[56]

Файл:WadiSuraSwimmers.jpg
Images of swimming people in the Cave of Swimmers

Шаблон:Further

Humans created rock art such as petroglyphs and rock paintings in the Sahara, perhaps the largest density of such creations in the world.Шаблон:Sfn Scenes include animalsШаблон:Sfn and everyday lifeШаблон:Sfn such as swimming which supports the presence of past wetter climates.[43] One well-known such petroglyph location is the Cave of Swimmers in the Gilf Kebir mountains of Egypt;[57] other well known sites are the Gabal El Uweinat mountains also of Egypt,Шаблон:Sfn ArabiaШаблон:Sfn and the Tassili n'Ajjer in Algeria where rock paintings from this time have been discovered.Шаблон:Sfn Humans also left artifacts such as FesselsteineШаблон:Efn and ceramics in what today are inhospitable deserts.Шаблон:Sfn North Africa together with East Asia is one of the first places where pottery was developedШаблон:Sfn probably under the influence of increased availability of resources during the AHP. The humid period also favoured its development and spread in West Africa during the 10th millennium BC;Шаблон:Sfn the so-called "wavy line" or "dotted wavy-line" motif was widespread across Northern AfricaШаблон:Sfn and as far as Lake Turkana.[58]

These populations have been described as Epipaleolithic, Mesolithic and NeolithicШаблон:Sfn and produced a variety of lithic tools and other assemblages.Шаблон:Sfn In West Africa, the cultural change from the African Middle Stone Age to the Late Stone Age accompanied the beginning of the AHP.[59] Genetic and archaeological 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;Шаблон:Sfn this may be reflected in the northward spread of Macrohaplogroup L and Haplogroup U6 genomic lineages.[60] In return, the AHP facilitated the movement of some Eurasian populations into Africa,[61] and bidirectional travel across the Sahara more generally.[62] 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,Шаблон:Sfn and in the spread of the Nilo-Saharan languages.Шаблон:SfnШаблон:Sfn

Additional manifestations in the Sahara

The expanded vegetation and soil formation stabilized previously active dunes,Шаблон:Sfn eventually giving rise to the present-day draa dunes in the Great Sand Sea of Egypt for example,[41] although there is uncertainty about whether this stabilization was widespread.Шаблон:Sfn Soil development and biological activity in soils are attested in the Acacus MountainsШаблон:Sfn and the Mesak Settafet area of Libya,Шаблон:Sfn but evidence of soil formationШаблон:Sfn/pedogenesisШаблон:Sfn such as bog ironШаблон:Sfn are described from other parts of the Sahara as well.Шаблон:Sfn In the Selima Sand Sheet, the landscape underwent erosional truncation and bioturbation.Шаблон:Sfn The Central and Southern Sahara saw the development of alluvial deposits[18] while sebkha deposits are known from the Western Sahara.Шаблон:Sfn Lightning strikes into soil left lightning-altered rocks in parts of the Central Sahara.Шаблон:Sfn

Файл:Ounianga Lakes from ISS.jpg
The Lakes of Ounianga are recharged from fossil groundwater that originated partly during the AHP

The increased precipitation also resulted in recharged aquifersШаблон:SfnШаблон:Sfn such as the Nubian Sandstone Aquifer; presently, water from this aquifer maintains several lakes in the Sahara, such as the Lakes of Ounianga.Шаблон:Sfn Other groundwater systems were active at that time in the Acacus Mountains, Air Mountains, in the FezzanШаблон:Sfn and elsewhere in LibyaШаблон:Sfn and the Sahel.[63] Raised groundwater tables provided water to plants and was discharged in depressions,Шаблон:Sfn lakesШаблон:Sfn and valleys, forming widespread carbonate depositsШаблон:Efn and feeding lakes.Шаблон:Sfn

The formation of lakesШаблон:Sfn and vegetation reduced the export of dust from the Sahara. This has been recorded in marine cores,Шаблон:SfnШаблон:Sfn including one core where dust export decreased by almost half,[64] and in Italian lakes.[65] In coastal places, such as in Oman, sea level rise also reduced the production of dust.Шаблон:Sfn In the Mediterranean, a decreased dust supply was accompanied by increased sediment input from the Nile, leading to changes in marine sediment composition.Шаблон:Sfn Conversely, the increased vegetation may have yielded more volatile organic compounds in the air.Шаблон:Sfn

Whether the strengthening of the monsoon enhanced or reduced upwelling off Northwestern Africa is debatable,[66] with some research suggesting that the strengthening in upwelling decreased sea surface temperatures[67][68]Шаблон:Sfn and increased the biological productivity of the sea,[66] while other research suggests that the opposite occurred; less upwelling with more moisture.Шаблон:Sfn However, regardless of whether upwelling increased or decreased, it is possible that the strengthening of the monsoon boosted productivity off the coasts of Northern Africa because the increased river discharge delivered more nutrients to the sea.[67][68]Шаблон:Sfn The decline of dust input may have caused the cessation of deep-water coral growth in the eastern Atlantic during the AHP by starving them of nutrients.[69]

Arabia

Precipitation in Dhofar and southwestern Arabia is brought by the African monsoon,Шаблон:Sfn and a change to a wetter climate resembling Africa has been noted in southern ArabiaШаблон:Sfn and Socotra from cave and river deposits.[70] It possibly reached as far as Qatar.[71] Holocene paleolakes are recorded at Tayma, Jubbah,Шаблон:Sfn in the Wahiba Sands of OmanШаблон:SfnШаблон:Sfn and at Mundafan.Шаблон:SfnШаблон:Sfn In the Rub al-Khali lakes formed between 9,000 and 7,000 years agoШаблон:Sfn and dunes were stabilized by vegetation,Шаблон:Sfn although the formation of lakes there was less pronounced than in the Pleistocene.Шаблон:Sfn The Wadi ad-Dawasir river system in central Saudi Arabia became active againШаблон:SfnШаблон:Sfn with increased river runoff into the Persian Gulf.Шаблон:Sfn Wadis in Oman eroded across LGM dunesШаблон:Sfn and formed accumulation terraces.Шаблон:Sfn Episodes of increased river discharge occurred in YemenШаблон:Sfn and increased precipitation is recorded in the caves of Hoti, Qunf in Oman, Mukalla in Yemen and Hoq Cave in Socotra.Шаблон:Sfn Increased precipitation resulted in increased groundwater flow, generating groundwater-fed lakes and carbonate deposits.Шаблон:Sfn

Forests and wildfire activity expanded across parts of Arabia.Шаблон:Sfn Freshwater sources in Arabia during the AHP became focus points of human activityШаблон:Sfn and herding activity between mountains and lowlands occurred.Шаблон:Sfn In addition, karstic activity took place on exposed coral reefs in the Red Sea and traces of it are still recognizable today.Шаблон:Sfn Increased precipitation has been also invoked to explain decreased salinities in the Red SeaШаблон:Sfn and increased river inflow, while dust input decreased.[72] Rock art depicts wildlife that existed in Arabia during the humid period.[73] Archaeological sites such as cairns appeared with the beginning of the humid period.Шаблон:Sfn

The humid period in Arabia did not last as long as in Africa,Шаблон:Sfn deserts did not retreat as muchШаблон:Sfn and precipitation may not have reached the centralШаблон:Sfn and northern part of the peninsulaШаблон:Sfn past OmanШаблон:Sfn and the Yemen Highlands;Шаблон:Sfn northern Arabia remained somewhat drier than southern Arabia,Шаблон:Sfn droughts were still commonШаблон:Sfn and the land and still produced dust.Шаблон:Sfn One study has estimated that the amount of rainfall in the Red Sea did increase to no more than Шаблон:Convert.Шаблон:Sfn Whether some former lakes in Arabia were actually marshes is contentious.Шаблон:Sfn

East Africa

Nile discharge was higher than today[24] and during the early African humid period, the Nile in Egypt flooded up to Шаблон:Convert[24] higher than it did recently before flood control.Шаблон:Sfn The increased flooding may have turned the Nile Valley marshy and inhospitableШаблон:Sfn and could explain why many archaeological sites along the Nile were abandoned during the AHP, with violent conflicts reconstructed from the Jebel Sahaba archaeological site.Шаблон:SfnШаблон:Sfn Early after the Younger Dryas, the Blue Nile would have been the major source of waters for the Nile.[74] Waters from the NileШаблон:Efn filled depressions like the Fayum DepressionШаблон:Sfn to form a deep lake with anoxic bottom watersШаблон:Sfn and reaching Шаблон:Convert above sea level,Шаблон:Sfn probably once a geomorphic barrier was breached.Шаблон:Sfn Wetlands and anastomosing channels developed in the Nile DeltaШаблон:Sfn as sediment supply increased.[75] In addition, Nile tributaries in northwestern Sudan[76] such as Wadi Al-Malik,[24] Wadi HowarШаблон:EfnШаблон:Sfn and Valley of the Queens became active during the AHP[77] and contributed sediments to the Nile.Шаблон:Sfn Wadi Howar was active until 4,500 years ago,Шаблон:Sfn and at the time often contained dune-dammed lakes, swamps and wetlands;Шаблон:SfnШаблон:Sfn it was the largest Saharan tributary of the NileШаблон:Sfn and constituted an important pathway into sub-Saharian Africa.[24] Conversely it appears that Lake Victoria and Lake Albert were not overflowing into the White Nile for all of the AHP,Шаблон:Sfn and the White Nile would have been sustained by overflow from Lake Turkana.Шаблон:Sfn There appears to be a tendency over the course of the AHP for the discharge of the Blue Nile to decrease relative to that of the White Nile.Шаблон:Sfn The Blue Nile built an alluvial fan at its confluence with the White Nile, and incision by the Nile reduced flooding risk in some areas which thus became available for human use.[24]

Файл:Kenya Rift Valley volcanoes and lakes.svg
Some lakes formed or expanded during the African humid period

Closed lakes in East Africa rose, sometimes by hundreds of metres.Шаблон:Sfn Lake Suguta developed in the Suguta Valley, accompanied by the formation of river deltas where rivers such as the Baragoi River entered the lake.Шаблон:Sfn In turn, Lake Suguta overflowed into the Kerio River, this adding water to Lake TurkanaШаблон:Sfn where increased discharge by the Turkwel River led to the formation of a large river delta.Шаблон:Sfn The Omo River remained its principal inflow but the relative role of other water sources increased compared to present-day conditions.[78]Шаблон:Sfn Lake Chamo, Lake Abaya and the Chew Bahir basins formed a river system flowing into Lake Turkana,Шаблон:Sfn which itself overflowed on its northwestern side through the Lotikipi Swamp into the White Nile.Шаблон:SfnШаблон:Sfn Deposits from this lake highstand form the Galana Boi Formation.Шаблон:Sfn The increased water depth reduced water mixing in Lake Turkana, allowing organic material to build up.Шаблон:Sfn This overflowing large lake was filled with freshwater and was populated by humans,Шаблон:Sfn typically in bays, along capes and protected shorelines;Шаблон:Sfn the societies there engaged in fisheryШаблон:Sfn but could probably also fall back on other resources in the region.Шаблон:Sfn

The EthiopianШаблон:Sfn Lake Abhe expanded to cover an area of Шаблон:Convert, much larger than the present-day lake, in the "Abhe IV"-"Abhe V" lake cycle.Шаблон:Sfn The enlarged lake covered a large area west of the present-day lake, present-day lakes Afambo, Gamari and Tendaho, reducing Borawli, Dama Ale and Kurub to islands.Шаблон:Sfn The maximum water level was reached during the early Holocene as river discharge increased, but was later limited by partial overflow and did not rise above Шаблон:Convert again.Шаблон:Sfn Deep thermal groundwater recharge occurred in the region.[79] About 9,000 years of human occupation are documented at the lake.Шаблон:Sfn Archaeological sites indicate that people obtained resources from the lake and followed its riseШаблон:Sfn and decline.Шаблон:Sfn The cultural traditions at Lake Abhe appear to be unusual by AHP/African standards.Шаблон:Sfn

Lake Zway and Lake Shala in Ethiopia joined with Lake Abiyata and Lake Langano to form a large waterbodyШаблон:Sfn which began overflowing into the Awash River.Шаблон:Sfn Other lakes that expanded include Lake AshengeШаблон:Sfn and Lake Hayq also in Ethiopia,[80] Lake Bogoria, Lake Naivasha[18] and Lake Nakuru/Lake Elmenteita all in Kenya,Шаблон:Sfn and Lake Masoko in Tanzania.Шаблон:Sfn Lakes formed in the caldera of the Menengai volcano[81]Шаблон:Sfn and in the Chalbi region east of Lake Turkana; the lake covered an area of about Шаблон:Convert.[82] A Шаблон:Convert large and Шаблон:Convert deep Lake Magadi formed in the early Holocene,Шаблон:Sfn generating the "High Magadi Beds" sediments.Шаблон:Sfn This lake was fed by now-dry waterfalls and possibly from the neighbouring lake Koora.Шаблон:Sfn In the Danakil Depression of Ethiopia freshwater conditions became established.[18] Lakes formed in depressions on the mountains around Lake Kivu.[83] Some of these lakes became connected through overflow: Lake Nakuru-Elmenteita drained northward through the Menengai caldera,Шаблон:Sfn Baringo-BogoriaШаблон:Efn, Suguta into Lake Turkana and from there into the Nile, carving gorges along the way. Lake Naivasha drained south through Lake SiriataШаблон:Sfn into Lake Magadi-Natron.Шаблон:Sfn Overflow of several of these lakes allowed animals including Nile crocodiles and fish to propagate to the individual lake basins,[84] but at the same time hindered the propagation of many land-based mammals.Шаблон:Sfn

Файл:KiliGlacier.JPG
A glacier on Mount Kilimanjaro. The oldest now present ice of Kilimanjaro formed during the African humid period

Glaciers stopped retreating or briefly expanded in East Africa at the beginning of the AHP before continuing retreat.[85] On Mount Kilimanjaro they may have expanded during the AHPШаблон:Sfn after a phase during the Younger Dryas where the mountain was ice free,[86] but the tree line also rose at that time, accompanied by soil formation.[87] The wetter climate may have destabilized the neighbouring Mount Meru volcano, causing a giant landslide that removed its summit.[88]

Erosion in catchments of East Africa increased with the beginning of the humid period but then decreased even before its end,Шаблон:Sfn as the increased weathering led to the formation of soils, these in turn to the establishment of a vegetation cover that subsequently reduced additional erosion.Шаблон:Sfn Increased weathering resulted in the increased consumption of [[atmospheric CO2|atmospheric Шаблон:Chem]] during the AHP.[89]

Surprisingly, and contrary to the patterns expected from precessional changes, the East African Rift also experienced a wetter climates during the AHP,Шаблон:Sfn reaching as far south as Lake Rukwa and Lake Cheshi into the Southern Hemisphere.Шаблон:SfnШаблон:Sfn In the region of the African Great Lakes, pollen evidence points to the occurrence of forests including rainforest vegetationШаблон:Sfn due to the increased precipitation,Шаблон:Sfn while today they occur only in limited areas there.Шаблон:Sfn Denser vegetation also occurred at Lake Turkana,Шаблон:Sfn with wooden vegetation covering almost half of the dry landШаблон:Sfn although grasslands remained dominant.[31] Development of forest vegetation around the African Great Lakes created an interconnected environment where species spread, increasing biodiversity with effects on the future when the environment became fragmented.Шаблон:Sfn Vegetation cover also increased in the Afar regionШаблон:Sfn and Ericaceae plants spread at high elevations.Шаблон:Sfn Forests and moisture-requiring vegetation expanded in the Bale Mountains.Шаблон:Sfn Different types of vegetation, including dryland vegetation, existed at Lake Malawi and Lake Tanganyika however,Шаблон:Sfn and vegetation did not change much.Шаблон:Sfn A wetter climate is recorded from a soil in the Afar region.[90]

In East Africa, the AHP led to improved environmental conditions in terms of food and water supply from large lakes, allowing early human populations to survive and grow in size without requiring major changes in food gathering strategies.Шаблон:Sfn Pottery techniques such as the "dotted wavy line" and "Kanysore" are associated with fishing and foraging communities.[58] Earlier wet and dry periods in East Africa may have influenced the evolution of humansШаблон:Sfn and allowed their spread across the SaharaШаблон:Sfn and into Europe.[91]

Other parts of Africa and the rainforest realm

Lake Bosumtwi in Ghana rose during the AHP.Шаблон:SfnШаблон:Efn Evidence there also suggests a decrease in wildfire activity took place.Шаблон:Sfn Tropical forests expanded in Cameroon HighlandsШаблон:Sfn and the Adamawa Plateau of CameroonШаблон:Sfn[92] and moved upward at Lake Bambili also in Cameroon.[93] The core of the rainforest was probably unaltered by the African humid period, perhaps with some changes in speciesШаблон:Sfn[94] and an expansion of their area.Шаблон:Sfn There is some evidence that an "Equatorial humid period", mechanistically linked to equatorial insolation and extending into the Amazon, may have taken place in the eastern Congo region at the same time as the AHP.Шаблон:Sfn The peatlands of Central Congo started developing during the African humid period and peat continues to accumulate there to this day,[95] albeit with a slowdown in the Cuvette Centrale after the end of the African humid period.[96]

On São Nicolau and Brava in the Cape Verde Islands, precipitation and erosion increased.Шаблон:Sfn In the Canary Islands, there is evidence of a moister climate on Fuerteventura,[97] the laurel forests changed perhaps as a consequence of the AHP.[11] Recharge of groundwater levels have been inferred from Gran Canaria also in the Canary Islands, followed by a decrease after the end of the AHP.[98] Choughs may have reached the Canary Islands from North Africa when the latter was wetter.[99]

Levant and Mediterranean

High latitude Africa has not undergone large scale changes in the past 11,700 years;Шаблон:Sfn the Atlas Mountains may have blocked the monsoon from expanding further north.Шаблон:Sfn However, river valleyШаблон:Sfn and cave deposits showing a moister climate in southern Morocco,Шаблон:Sfn vegetation changes in the Middle Atlas,Шаблон:Sfn several floods in Tunisian rivers[100] and ecosystem changes which impacted steppe-dependent rodents of Northern Africa have been linked to the AHP.[101]

In the Pleistocene and Holocene humidity in the Mediterranean is often correlated to humidity in the Sahara,Шаблон:Sfn[102] and the early-mid Holocene climate of Iberia, Italy, Negev and Northern Africa was wetter than today;[103] in Sicily wettening correlates with ITCZ changes in Northern Africa.[104] Mediterranean precipitation is brought by Mediterranean cyclones and the westerlies;Шаблон:Sfn either increased precipitation from the westerlies,[105] northward moisture transport from Africa[106] or monsoonal precipitation extending into the Mediterranean may have rendered it wetter.[107] The connection between the African Monsoon and Mediterranean precipitation is unclear[108]Шаблон:Sfn and it was winter rainfall that increased predominantly,[109] although separating monsoonal and non-monsoonal precipitation can be difficult.Шаблон:Sfn

The Mediterranean Sea became less saline during the AHP, in part due to increased precipitation from the westerlies[105] but also from increased river discharge in Africa, leading to the formation of sapropel layers when the increased runoff led to the Mediterranean becoming more stratifiedШаблон:EfnШаблон:SfnШаблон:Sfn and eutrophied,[110] with changes in the main water masses of the sea.[111] The S1 sapropel layer is specifically associated with the AHPШаблон:Sfn and with increased discharge of the Nile and other African rivers.Шаблон:Sfn These processes together with decreased dust transport by wind led to changes in the sediment patterns of the Mediterranean,Шаблон:Sfn and increased marine nutrient availability[110] and food web productivity in the Mediterranean,[112] which impacted the development of deep-sea corals.[113]

In the Levant, wetter conditions during the AHP are recorded from Jeita Cave in Lebanon and Soreq Cave in IsraelШаблон:Sfn while the Dead Sea and other southern European lakes were low during this period. This is unlike some earlier wet periods in the Sahara; possibly the stronger winter-summer insolation gradient in these earlier wet periods created a different moisture pattern than during the Holocene.[114] The northern Mediterranean may have been drier, with more wildfire activity, during the AHP.[115]

Southern Africa

The effects, if any, of the African humid period on Southern Africa have been unclear. Originally it was proposed that the orbitally driven changes would imply a dry period in Southern Africa which would have given way to moister conditions as the northern AHP ended,Шаблон:SfnШаблон:Sfn as the ITCZ should shift its average position between the two hemispheres.Шаблон:Sfn However, the lack of paleoclimatology data with sufficient time resolution from Southern Africa has made it difficult to assess the climate there during the AHP.Шаблон:Sfn More recently obtained paleoclimate data have suggested however that southern Africa was actually wetter during the AHP rather than drier,[116]Шаблон:Sfn reaching as far as north-northwest MadagascarШаблон:SfnШаблон:Sfn 23° southШаблон:Sfn and as far as the catchment of the Orange River.[117] The area between Lake Tanganyika and Lake Malawi has been interpreted as the limit of the AHP's influence.[118]

Conversely, and consistent with the opposite reaction pattern of the Southern Hemisphere, the Zambezi River reached its lowest discharge during the AHP,[119] and the AHP did not reach southernШаблон:Sfn or southeastern Africa.Шаблон:Sfn There may have been opposite changes in precipitation between southeast Africa and tropical East Africa,Шаблон:Sfn separated by a "hinge zone".Шаблон:Sfn Particular changes occurred in central southern Africa, where a dry period co-occurred with an expansion of Lake Makgadikgadi; presumably the lake during this dry interval was nourished by increased wetness over the Okavango River catchment in the Angolan Highlands due to the AHP;Шаблон:Sfn peatlands formed in Angola during the AHP.[120] In general there is little consistency between Northern and Southern Africa in terms of hydrological changes during the Holocene,Шаблон:Sfn and nowhere are both the start and end of the AHP apparent.Шаблон:Sfn Orbitally-mediated changes in Northern Hemisphere climate affected the Southern Hemisphere through oceanic pathways involving sea surface temperatures.Шаблон:Sfn Additionally, wetter periods unrelated to the AHP may have occurred after deglaciation in Southern Africa.[121]

Numerical estimates

Estimates of the exact amount of increased precipitation vary widely.Шаблон:Sfn During the African humid period, Saharan rainfall increased to Шаблон:Convert,Шаблон:Sfn and values exceeding Шаблон:Convert may have spread to 19–21° northern latitude.Шаблон:Sfn In the eastern Sahara, a gradient from Шаблон:Convert increment in the north to Шаблон:Convert in the south has been identified.Шаблон:Sfn An area with less than Шаблон:Convert may have remained in the Eastern Sahara however,Шаблон:SfnШаблон:Sfn although its driest parts may have received 20-fold more precipitation than today.Шаблон:Sfn Precipitation in the Sahara probably reached no more than Шаблон:Convert,Шаблон:Sfn with large uncertainty.Шаблон:Sfn

Other reconstructed values of the precipitation increase indicate an annual increase of about Шаблон:Convert in Africa,Шаблон:Sfn with strong regional variation.Шаблон:Sfn From lake levels precipitation increases of 20–33%Шаблон:Sfn or 50–100%[18]/40-150% have been inferred for East Africa,[89] with an increase of 40% reconstructed for Northern Africa.Шаблон:Sfn In the early Holocene, there appears to have been an eastward- and northward-decreasing trend of humidity.Шаблон:Sfn Additionally, at Tayma in Arabia a threefold increase appears to have occurredШаблон:Sfn and precipitation in the Wahiba Sands of Oman may have reached Шаблон:Convert.Шаблон:Sfn

Effect on other climate modes

The El Niño–Southern Oscillation is a major climate variability mode. Paleoclimatology records from Ecuador and the Pacific Ocean indicate that during the early and middle Holocene ENSO variability was suppressed by about 30–60%, which can be only partially explained through orbital forcing.Шаблон:SfnШаблон:Sfn The Green Sahara may have suppressed ENSO activity, forcing a La Niña–like climate state,Шаблон:SfnШаблон:Sfn in a climate model this is accompanied by decreased upwelling and deepening of the thermocline in the Eastern Pacific as the Walker circulation shifts westward.Шаблон:SfnШаблон:Sfn Easterly winds in the western Pacific Ocean increase, while they decrease in the eastern.Шаблон:Sfn In addition, Atlantic Niño sea surface temperature patterns develop in the Atlantic Ocean.Шаблон:SfnШаблон:Sfn

Remote effects of the AHP on climate have also been studied,Шаблон:Sfn although many changes are model-dependent and may also be inaccurate due to incorrect depictions of atmospheric dust distribution.Шаблон:Sfn Whether the reduced albedo of the Sahara during the AHP contributed to, or increased cloud cover counteracted, the warming of the Holocene thermal maximum is model-dependent;Шаблон:Sfn dust changes did not have a major effect.Шаблон:Sfn The AHP would also influence SSTs in the Indian Ocean, although there is not much evidence about the mid-Holocene sea temperatures there.Шаблон:Sfn

The AMOC transports heat from the Southern into the Northern HemisphereШаблон:Sfn and is implicated in starting the Holocene AHP an earlier AHPs after the end of an ice age.Шаблон:Sfn Various studies have been conducted to determine which effects reduced dust supply and the greening of the Sahara would have had on its intensity,Шаблон:Sfn with conflicting results on which effects would predominate.Шаблон:Sfn Increased heat transport either through the atmosphere or the ocean would result in warming in the Arctic.Шаблон:Sfn

Remote precipitation and the AHP

The Sahara greening intensified the Indian and Asian monsoons,Шаблон:Sfn warmingШаблон:Sfn and increased precipitation across most of the Tibetan PlateauШаблон:Sfn especially late in the monsoon season, and climate simulations including a green Sahara reproduce the reconstructed palaeoclimates there better than these without.Шаблон:Sfn In a climate model, there is a shift in precipitation from snow to rain.Шаблон:Sfn The strengthened and expanding monsoons of Africa and Asia alter the atmospheric circulation of the planet, inducing a wetter East Asian Monsoon and drying across tropical South America and central-eastern North America.Шаблон:SfnШаблон:SfnШаблон:Sfn The reduced dust emission warms the North Atlantic and increases westerly flow into the North American Monsoon, strengthening it.Шаблон:Sfn The far-field precipitation changes reach as far as Europe and Australia.Шаблон:Sfn Discrepancies between modelled and reconstructed northward extensionШаблон:SfnШаблон:Sfn and precipitation in the Asian monsoon regions and the North American Monsoon area may be explained through these remote effects.Шаблон:Sfn

Sun et al. 2020 proposed that the greening of the Sahara during the AHP can increase precipitation over the Middle East even if neither the African nor the Indian monsoons reach it.Шаблон:Sfn 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 precipitationШаблон:Sfn and agricultural productivity there.Шаблон:Sfn This could explain increased precipitation in the Middle East during the AHP:Шаблон:Sfn A wet climate occurred in the Middle East during the early Holocene, leading to the Ubaid period of settlement in Mesopotamia, followed by dry phases around 5,500 years agoШаблон:Sfn and a concomitant reduction in simulated wheat yield.Шаблон:Sfn

Hurricanes and the AHP

One climate model has indicated that a greener Sahara and reduced dust output would have increased tropical cyclone activity, especially over the Atlantic but also in most other tropical cyclone basins. Changes in the intensity of the storms, decreases in wind shear, changes in atmospheric circulation and less dust in the atmosphere, which results in warmer oceans, are responsible for this phenomenon,Шаблон:Sfn while tropical wave activity may have increased[20] or decreased.Шаблон:Sfn The net effect could be a global increase in tropical cyclone activity, a westward shift within the ocean basinsШаблон:Sfn and in the Atlantic Ocean a shift towards later dates.Шаблон:Sfn While there are no good paleotempestology data for the time of the African humid period that could confirm or refute this theoryШаблон:SfnШаблон:Sfn and many of these records are specific for particular locations,Шаблон:Sfn hurricane activityШаблон:Sfn including past strikes in Puerto RicoШаблон:Sfn and in Vieques appear to correlate with the strength of the West African MonsoonШаблон:Sfn and increased precipitation on the northern Yucatan Peninsula during the middle Holocene could be explained by increased hurricane activity during the AHP.[122] On the other hand, at Grand Bahama Bank and the Dry Tortugas of South Florida a decrease of hurricane activity took place during the AHPШаблон:Sfn and dust emission is not always anti-correlated to hurricane activity.Шаблон:Sfn Finally, the northward movement of the ITCZ during the AHP may have caused a corresponding northward movement of tropical cyclogenesis areas and storm tracks in the Atlantic Ocean,Шаблон:SfnШаблон:Sfn which could also explain decreased hurricane activity in the Bahamas and Dry Tortugas.Шаблон:Sfn

Fluctuations

Шаблон:See also

Файл:Younger Dryas and Air Temperature Changes.jpg
Temperatures in Greenland during the Younger Dryas

Some gaps with less precipitation took place during the late glacial and the Holocene.Шаблон:Sfn During the Younger Dryas 12,500–11,500 years ago, the North Atlantic and Europe became much colder again and there was a phase of drought in the area of the African humid period,Шаблон:SfnШаблон:Sfn extending over both East Africa,Шаблон:EfnШаблон:Sfn where lake levels dropped in many places,Шаблон:SfnШаблон:Sfn southern AfricaШаблон:Sfn and West Africa. The dry interval extended to IndiaШаблон:Sfn and the MediterraneanШаблон:Sfn where dune activity occurred in the Negev.Шаблон:Sfn At the end of the Younger Dryas, precipitation, lake levels and river runoff increased again, although south of the equator the return of humid conditions was slower than the relatively abrupt change to its north.Шаблон:SfnШаблон:Sfn

Another dry phase took place about 8,200 years ago, spanning East AfricaШаблон:SfnШаблон:Sfn and Northern AfricaШаблон:Efn as documented by various lines of evidenceШаблон:Sfn such as decreased water levels in lakes.Шаблон:Sfn It coincided with cooling in the Northern Atlantic,Шаблон:Sfn in surrounding landmasses such as GreenlandШаблон:Sfn and around the world;Шаблон:Sfn the drought may be related to the 8.2 kiloyear eventШаблон:Sfn which separates the Greenlandian and Northgrippian stages of the Holocene[123] and lasted for about one millennium.Шаблон:Sfn The 8,200 year event has also been noted in the Maghreb, where it is associated with a transition of the Capsian culture[124] as well as with cultural changes both in the Sahara and the Mediterranean;Шаблон:Sfn at the Gobero cemetery a population change occurred after this dry interruptionШаблон:Sfn but the occurrence of widespread cultural changes appears to be questionable.[2] This episode appears to have been caused by the draining of ice-dammed lakes in North America Шаблон:Sfn although a low latitude origin has also been suggested.Шаблон:Sfn

Cooling of the Northern Atlantic during Heinrich event 1 and the Younger Dryas associated with a weaker Atlantic meridional overturning circulation leads to atmospheric pressure anomalies that shift the Tropical Easterly Jet and precipitation belts south, making Northern Africa drier. Шаблон:SfnШаблон:SfnШаблон:Sfn Storm tracks shift north away from the Mediterranean.Шаблон:Sfn Earlier Heinrich events were also accompanied by drought in North Africa.Шаблон:Sfn Likewise, a weakening of moisture transport and a less eastward position of the Congo Air Boundary contributed to reducing precipitation in East AfricaШаблон:Sfn although some parts of southern Africa at Lake Malawi were wetter during the Younger Dryas.[125]

Many humidity fluctuations in the early Holocene appear to be caused by the discharge of meltwater from the Laurentide Ice Sheet into the Atlantic, which weakens the Atlantic meridional overturning circulation.Шаблон:Sfn Some dry periods in marine cores in the Gulf of Guinea appear to coincide with events recorded in Greenland ice cores.Шаблон:Sfn Other variations in precipitation observed in records have been attributed to solar activity changes,Шаблон:Sfn water levels of Lake Turkana for example appear to reflect the 11-year solar cycle.Шаблон:Sfn

In Lake Turkana, water level fluctuations took place between 8,500 and 4,500 years before present, with highstands before 8,400, around 7,000 and between 5,500 and 5,000Шаблон:Sfn and lowstands around 8,000, 10,000 and 12,000 years before present.Шаблон:Sfn In total, five separate highstands are recorded in desert varnish around the lake.[126] The highstands appear to be controlled by sea surface temperature patterns in the Atlantic and Indian Oceans, but also by overflow of water from Lake SugutaШаблон:Sfn and Chew Bahir and upstream lakes into Lake Turkana..Шаблон:Sfn Volcanic and tectonic phenomena occur at Lake Turkana, but do not have the magnitude required to explain large changes in lake level.Шаблон:Sfn Water level fluctuations have also been inferred for Lake Chad on the basis of pollen data, especially towards the end of the AHP.Шаблон:Sfn In the Taoudenni lake fluctuations of about a quarter-millennium have been recordedШаблон:Sfn and frequent droughts occurred in the Eastern Sahara.Шаблон:Sfn

Other variations appear to have occurred 9,500–9,000 and 7,400–6,800Шаблон:Sfn as well as 10,200, 8,200, 6,600 and 6,000 years before present; they were accompanied by decreased population density in parts of the Sahara,Шаблон:Sfn and other dry interludes in Egypt have been noted 9,400–9,300, 8,800–8,600, 7,100–6,900 and 6,100–5,900 years ago.Шаблон:Sfn The duration and severity of dry events is difficult to reconstructШаблон:Sfn and the impact of events like the Younger Dryas is heterogeneous even between neighbouring areas.[127] During dry episodes, humans might have headed to waterbodies which still had resources,Шаблон:Sfn and cultural changes in the central Sahara have been linked to some dry episodes.Шаблон:Sfn Aside from fluctuations, a southward retreat of the humid period may have been underway after 8,000 years agoШаблон:Sfn with a major drought around 7,800 years ago.Шаблон:Sfn

End

Шаблон:See also

The African humid period ended about 6,000–5,000 years ago;Шаблон:SfnШаблон:Sfn an ending date of 5,500 years before present is often used.Шаблон:Sfn After vegetation declined,Шаблон:Sfn the Sahara became barren and was claimed by sand.Шаблон:Sfn Wind erosion increased in northern Africa,Шаблон:Sfn and dust export from the now-desertШаблон:Sfn and from dried up lakesШаблон:Sfn such as the Bodélé Basin grew; Bodélé today is the largest single source of dust on Earth.Шаблон:Sfn The lakes dried up, mesic vegetation disappeared, and sedentary human populations were replaced by more mobile cultures.Шаблон:Sfn The transition from the "green Sahara" to the present-day dry Sahara is considered to be the greatest environmental transition of the Holocene in northern Africa;Шаблон:Sfn today almost no precipitation falls in the region.Шаблон:Sfn The end of the AHP but also its beginning could be considered a "climate crisis" given the strong and extended impact.Шаблон:Sfn Drying extended as far as the Canary Islands[128]Шаблон:Sfn and southeastern Iran,[129] and there is evidence of climate change on São Nicolau, Cape Verde.[130]

The Piora Oscillation cold period in the AlpsШаблон:Sfn coincides with the end of the AHP;Шаблон:SfnШаблон:Sfn the period 5,600–5,000 years ago was characterized by widespread cooling and more variable precipitation changes around the worldШаблон:Sfn and was possibly forced by changes in solar activity and orbital parameters.Шаблон:Sfn Some changes in climate possibly extended into southeastern Australia,[131] Central America[132] and into South America.[133] The neoglacial began.Шаблон:Sfn

A major pan-tropical environmental change took place about 4,000 years ago.Шаблон:Sfn This change was accompanied by the collapse of ancient civilizations, severe drought in Africa, Asia and the Middle East and the retreat of glaciers on Mount KilimanjaroШаблон:Sfn and Mount Kenya.Шаблон:Sfn

Chronology

Whether the drying happened everywhere at the same time and whether it took place in centuries or millennia is unclearШаблон:SfnШаблон:SfnШаблон:Sfn in part due to disagreeing recordsШаблон:Sfnand has led to controversy,Шаблон:SfnШаблон:Sfn and such a disagreement on timing also exists with respect to the expected vegetation changes.Шаблон:SfnШаблон:Sfn Marine cores usually indicate an abrupt changeШаблон:SfnШаблон:Sfn but not without exceptionsШаблон:Sfn while pollen data do not, perhaps due to regional and local differences in vegetation.Шаблон:Sfn Africa is a diverse landscapeШаблон:Sfn and groundwater and local vegetation can modify local conditions;Шаблон:Sfn groundwater-fed water bodies for example persisted longer than those nourished by rain.Шаблон:Sfn The debate on how quickly the Sahara formed goes back to 1849, when the Prussian naturalist Alexander von Humboldt suggested that only a quick drying could form the desert.Шаблон:Sfn

Most recently, the idea has taken hold that the end of the African humid period occurred from north to south in a stepwise fashion.Шаблон:SfnШаблон:SfnШаблон:Sfn In northeastern Asia,Шаблон:Sfn the western Sahara and east Africa it ended within 500 yearsШаблон:Sfn with a one-step drying 6,000 – 5,000 years ago north of the present-day monsoon belt. Farther south, precipitation decrease was more protractedШаблон:SfnШаблон:SfnШаблон:Sfn and closer to the equator the AHP ended between 4,000 and 2,500 years ago.Шаблон:SfnШаблон:Sfn In East Africa, pronounced drying occurred between 4,500 and 3,500 years ago, centered on 4,000 years ago;Шаблон:Sfn Egypt during the Old Kingdom was still wetter than today.Шаблон:Sfn A later end in northeast Africa about 4,000 years ago may reflect the different configuration of landmasses and thus monsoon behaviour,Шаблон:Sfn while other research has found a westward propagating drying trend.Шаблон:Sfn

Some evidence points to a two-phase change in climate with two distinct dry transitionsШаблон:Sfn caused by the existence of two different steps of insolation decrease at which climate changes.Шаблон:Sfn Distinct environmental changes may have occurred in Central Africa, Western Africa and East Africa.Шаблон:Sfn Finally, sometimes the 4.2 kiloyear event - the transition from the Northgrippian to the Meghalayan stage of the Holocene -[123] is considered to be the true end of the AHP,Шаблон:Sfn especially in central Africa.Шаблон:Sfn

Increased variability in precipitation may have preceded the end of the AHP; this is commonly observed before a sudden change in climate.Шаблон:Sfn In Gilf Kebir, between 6,300 and 5,200 years ago apparently a winter rainfall regime became established as the AHP ended.Шаблон:Sfn Later fluctuations in climate that produced brief humid spells also took place,Шаблон:Sfn such as a moister period between 500 BCE – 300 CE in Roman Northern Africa and along the Dead SeaШаблон:Sfn and an earlier one 2,100 years before present in the western Sahel.[11] By 2,700 years ago the central Sahara had become a desert and remained one until the present-day.Шаблон:Sfn

Sahara and Sahel

After a first brief lake level drop between 5,700 and 4,700 calibrated years ago that might reflect climate variability towards the end of the African humid period,Шаблон:Sfn water levels in Lake Megachad decreased quickly after 5,200 years before present.Шаблон:Sfn It shrank to about 5% of its former size,Шаблон:Sfn with the deeper northern Bodele basin drying up entirely about 2,000Шаблон:Sfn-1,000 years agoШаблон:Sfn as it was disconnected from the southern basin where its major tributary, the Chari River, enters Lake Chad.Шаблон:Sfn The dried out basin was now exposed to the Harmattan winds, which blow dust out of the dry lake bed,Шаблон:Sfn making it the single largest source of dust in the world.Шаблон:Sfn Dunes formed in the dried-up SaharaШаблон:Sfn or began moving again after stabilizing during the AHP.Шаблон:Sfn

The tropical vegetation was replaced by desert vegetation, in some places suddenly and in others more gradually.Шаблон:Sfn Along the Atlantic coast, the vegetation retreat was slowed by a stage of sea level rise that increased soil moisture levels, delaying the retreat by about two millennia.Шаблон:SfnШаблон:Sfn A gradual decline has been noted in the Tibesti.Шаблон:Sfn In Libya at Wadi Tanezzuft the end of the humid period was also delayed by leftover water in dune systems and in the Tassili mountains until 2,700 years ago, when river activity finally ceased.Шаблон:Sfn[134] A brief moist pulse between 5,000 – 4,000 years ago in the Tibesti led to the development of the so-called "Lower Terrace".Шаблон:Sfn The Egyptian Sahara might still have been vegetated until 4,200 years ago, based on depictions of savanna environments in Fifth Dynasty tombs in Egypt.Шаблон:Sfn

At Lake Yoa, which is groundwater-fed, vegetation decreased and became desert vegetation between 4,700–4,300 and 2,700 years ago, while the lake became hypersaline 4,000 years ago.Шаблон:SfnШаблон:SfnШаблон:Sfn Lake Teli dried out completely about 4,200 years ago.Шаблон:Sfn However, the climate of the Ounianga lakes may have been affected by the Tibesti Mountains and the end of the AHP thus delayed,Шаблон:Sfn and fossil groundwater left by the AHP nourishes the lake to this day.Шаблон:Sfn In the central Sahara, water resources in the mountains persisted longer.Шаблон:Sfn

East Africa and Arabia

In northern East Africa, water levels dropped rapidly about 5,500 years agoШаблон:Sfn while in Hoti cave in Arabia a southward retreat of the Indian Monsoon took place about 5,900 years ago.Шаблон:Sfn Drying is also documented from Oman,Шаблон:Sfn and rivers and lakes of Arabia became intermittent or entirely dry.Шаблон:Sfn The Blue Nile basin became less moistШаблон:Sfn with a noticeable decrease of Nile discharge about 4,000 years ago.Шаблон:Sfn Decreased discharge of the Nile led to the cessation of sapropel deposition and turbidite activity off its delta,Шаблон:Sfn the abandonment of river channels in its delta and upstream[135] and increased seawater influence in the delta.Шаблон:Sfn

Some data from Ethiopia and the Horn of Africa indicate that drying there may have begun already 7,000–8,000 years ago or earlier.Шаблон:Sfn[70] Reconstructions from Lake Abiyata in Ethiopia suggest that the end of the African humid period took the form of severe droughts rather than a gradual decrease of precipitation.Шаблон:Sfn Drying in Arabia commenced about 7,000 calibrated years agoШаблон:Sfn and there are large disparities in the timing between various parts of ArabiaШаблон:Sfn but a tendency towards an arid climate between 6,000 and 5,000 years ago has been observedШаблон:SfnШаблон:Sfn which continued until 2,700 years ago.Шаблон:Sfn In the Bale Mountains and the Sanetti Plateau of Ethiopia vegetation changes signalling a drier climate took place around 4,600 years ago.Шаблон:Sfn

Forest cover in the area of the African Great Lakes decreased between 4,700 and 3,700 years ago,Шаблон:Sfn although drying at Lake Victoria had begun around 8,000 years ago,Шаблон:Sfn at Lake Rukwa 6,700 years ago,Шаблон:Sfn at Lake Tanganyika about 6,000 years agoШаблон:Sfn and at Lake Edward major changes in lake chemistry consistent with drying are noted 5,200 years ago. There a minor recovery in vegetation took place between 2,500 and 2,000 years ago, followed by a much more rapid appearance of grasses accompanied also by substantial wildfire activity. This might have been the most severe drought of the Lake Edward region in the Holocene, with many lakes such as Lake George dropping significantly or drying up altogether.Шаблон:Sfn Other lakes such as Nakuru, Turkana, Lake Chew Bahir, Lake Abbe and Lake Zway also dropped between 5,400 and 4,200 years ago.Шаблон:Sfn Decreased vegetation cover in the catchment of the Blue Nile has been correlated with increased sediment transport in the river beginning 3,600 – 4,000 years ago.Шаблон:Sfn

The end of the AHP at Lake Turkana occurred about 5,000[126]-5,300 years before present, accompanied by a lake level declineШаблон:Sfn and the cessation of overflow from other lakes in its area into Lake Turkana.Шаблон:Sfn Between 5,000 and 4,200, Lake Turkana became more saline and its water levels decreased below the level of outflow to the Nile.Шаблон:Sfn Towards the end of the AHP water temperatures in the lake and in other regional lakes appear to have increased, followed by a drop after its endШаблон:Sfn possibly resulting from the insolation seasonality pattern that was in force at the time of the end of the AHP.Шаблон:Sfn The decrease of water levels in Lake Turkana also impacted the Nile and the Predynastic societies dependent on it.Шаблон:Sfn

Mediterranean

The southern Aegean,[136] Libya and the Middle Atlas became gradually more dry,Шаблон:Sfn and drying in Morocco took place about 6,000 radiocarbon years ago,Шаблон:Sfn 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.Шаблон:Sfn[137][138] More complicated changes have been found for the northern margin of the Mediterranean,Шаблон:Sfn and winter rainfall increased in the Levant at the end of the AHP.[139] A 4.2 kiloyear event is recorded in dust records from the MediterraneanШаблон:Sfn and might have been caused by changes in the circulation of the Atlantic Ocean.Шаблон:Sfn

Tropical West Africa

In Lake Bosumtwi the African humid period ended about 3,000 years agoШаблон:Sfn after a brief moistening between 5,410 ± 80 years ago that ended 3,170 ± 70 years ago. This, earlier but similar changes off western Senegal and later but similar changes in the Congo Fan appear to reflect a southward shift of the precipitation zone over time.Шаблон:Sfn Some drying occurred simultaneously between the Sahel and the Gulf of Guinea.Шаблон:Sfn Some lakes in the Guineo-Congolian region dried out, while others were relatively unaffected.Шаблон:Sfn

A general tendency towards a drier climate is observed in West Africa at the end of the AHP.Шаблон:Sfn There, dense vegetation became progressively thinner between 5,000 and 3,000 years ago,Шаблон:Sfn and major perturbations of the vegetation took place around 4,200 and 3,000–2,500Шаблон:SfnШаблон:Sfn /2,400 calibrated years ago.Шаблон:Sfn A brief return of moister conditions took place 4,000 years agoШаблон:Sfn while a substantial dry phase occurred between 3,500 and 1,700 years ago.Шаблон:Sfn Aridity became established between 5,200 and 3,600 years ago in the Sahara.Шаблон:Sfn In Senegal mangroves collapsed 2,500 years ago[19] and modern-type vegetation arose about 2,000 years ago.Шаблон:Sfn

Central Africa

Farther south at the equator between 6,100 and 3,000 calibrated years before present savannah expanded at the expense of forests, with the transition possibly lasting until 2,500 calibrated years before present;Шаблон:Sfn a different time course estimate for the area between 4° southern and 7° northern latitude states that forest cover decreased between 4,500 and 1,300 years ago.Шаблон:Sfn In the Adamawa Plateau (CameroonШаблон:Sfn), the Ubangui Plateau (Central African RepublicШаблон:Sfn) and the Cameroon Volcanic Line montane forests disappeared at the end of the African humid period.Шаблон:Sfn In the Adamawa Plateau savanna has continuously expanded since 4,000 calibrated years ago.Шаблон:Sfn Such a change took also place in Benin and Nigeria between 4,500 and 3,400 calibrated years ago.Шаблон:Sfn In the Congo Basin, there were changes in the composition and density of the forests rather than their extent,Шаблон:Sfn and along the equator precipitation may have increased around 4.2 ka.Шаблон:Sfn Many vegetation changes in the tropical regions were probably caused by a longer dry seasonШаблон:Sfn and perhaps a smaller latitudinal range of the ITCZ.Шаблон:Sfn

Southern Hemisphere Africa

In the Southern Hemisphere at Lake Malawi drying began later – 1,000 years before present – as did the African humid period which there began only about 8,000 years ago.Шаблон:Sfn Contrarily, increased water levels in Etosha Pan (Namibia) appear to relate to a southward movement of the ITCZ at the end of the AHP[140] although stalagmite growth data in Dante Cave also in Namibia has been interpreted as indicating a wetter climate during the AHP.[116] Several records indicate that 5,500 years ago, precipitation changed in an east-west dipole-like wayШаблон:Sfn with drying in the west and moistening in the east.Шаблон:Sfn This pattern was probably driven by shifts in atmospheric moisture transport and of rain belt width.Шаблон:Sfn

Mechanisms

The end of the humid period appears to reflect the changes in insolation during the Holocene,Шаблон:Sfn as a progressive decrease of summer insolation caused the insolation gradients between Earth's hemispheres to decrease.Шаблон:Sfn However, the drying appears to have been much more abrupt than the insolation changes;Шаблон:Sfn it is not clear whether non-linear feedbacks led to abrupt changes in climate and it is also unclear whether the process, driven by orbital changes, was abrupt.Шаблон:Sfn Also, the Southern Hemisphere warmed and this resulted in a southward shift of the ITCZ;[141] orbitally-driven insolation has increased over the Holocene in the Southern Hemisphere.Шаблон:Sfn

As precipitation decreased, so did vegetation, in turn increasing the albedo and further decreasing precipitation.[13] Furthermore, vegetation may have responded to increased variations in precipitation towards the end of the AHPШаблон:Sfn although this view has been challenged.Шаблон:Sfn This could have directed sudden changes in precipitation, although this view has been cast in doubt by the observation that in many places the end of the African humid period was gradual rather than sudden.Шаблон:Sfn Plants at higher and lower latitudes might respond differently to climate change; for example more diverse plant communities might have slowed down the end of the AHP.Шаблон:Sfn

Other proposed mechanisms:

The orbitally-induced changes of precipitation may have been modified by the solar cycle; specifically, solar activity maxima during the ending phase of the AHP may have offset the orbital effect and thus stabilized precipitation levels, while solar activity minima compounded the orbital effects and thus induced rapid decreases in water levels of Lake Turkana.Шаблон:Sfn At Lake Victoria on the other hand, solar variations appear to sometimes lead to drought and sometimes lead to wetness, probably due to changes in the ITCZ.[141]

Potentially human-mediated changes

Major changes in vegetation in East Africa about 2,000 years ago may have been caused by human activity, including large-scale deforestation for iron production during the Iron Age.Шаблон:Sfn Similar changes have been observed on the Adamawa PlateauШаблон:Sfn (CameroonШаблон:Sfn) but later dating of archaeological sites has found no correlation between human expansion in Cameroon and environmental degradation.Шаблон:Sfn Similar rainforest degradation across Western African took place between 3,000 and 2,000 years agoШаблон:Sfn and the degradation is also known as "third millennium rainforest crisis".Шаблон:Sfn Climate-mediated processes may have increased the impact of land use changes in East Africa.Шаблон:Sfn In the Sudanian and Sahelian savannah on the other hand human activity seems to have had little impact,Шаблон:Sfn and in Central Africa forest changes were clearly triggered by climate change with little or no evidence of anthropogenic changes.Шаблон:Sfn The question has led to intense debate among paleoecologists and archaeologists.Шаблон:Sfn

While humans were active in Africa during the end of the African humid period, climate models analyzed by Claussen and colleagues 1999 indicate that its end does not need any human activity as an explanationШаблон:Sfn although vegetation changes may have been induced by human activity.Шаблон:Sfn Later it was suggested that overgrazing may have triggered the end of the AHP around 5,500 years ago;Шаблон:Sfn human influence might explain why the Sahara became a desert without the accompanying onset of an ice age; usually the existence of a Sahara desert is associated with the expansion of high latitude glaciers.Шаблон:Sfn Later research has on the contrary suggested that human pastoralism may have actually delayed the end of the AHP by half a millenniumШаблон:Sfn as moving herds of animals driven by humans seeking good pasture conditions may lead to more balanced impacts of pastures on the vegetation and thus to greater vegetation quality.Шаблон:SfnШаблон:Sfn However, increased grazing has been invoked to explain the increase in dust emissions after the end of the AHP.Шаблон:Sfn The effects of grazing on vegetation cover are context-dependent and hard to generalize over wider regions.Шаблон:Sfn

Global

A general drying tendency is observed in the northern tropicsШаблон:Sfn and between 5,000 – 4,500 calibrated years ago the monsoons weakened.Шаблон:Sfn Perhaps as a consequence of the end of the AHP,Шаблон:Sfn[4] Asian monsoon precipitation declined between 5,000 and 4,000 years ago.Шаблон:Sfn A drought 5,500 years ago is recorded in Mongolia[142] and eastern America, where drought conditions around 5,500–5,000 years ago occurred in places like Florida and between New Hampshire and Ontario.[143][144] A drying tendency is also noted in the Caribbean and the Central Atlantic.[145] The final retreat of vegetation from the Sahara may have helped cause the 4.2 kiloyear event.[146]

Conversely, in South America there is evidence that the monsoon behaves in an opposite fashion consistent with precessional forcing;Шаблон:Sfn water levels in Lake Titicaca were low during the middle Holocene and began to rise again after the end of the AHP.[147] Likewise, a trend towards increased wetness took place in the Rocky Mountains at this time[148] although it was accompanied by a drier phase around Lake Tahoe, California and in the Western United States.[149]

Consequences

Humans

As observed in archaeological sites, settlement activity decreased in the Sahara after the AHP.Шаблон:Sfn Population in Northern Africa decreased between 6,300 and 5,200 years agoШаблон:Sfn over less than a millennium,Шаблон:Sfn beginning from the north.Шаблон:Sfn In inner Arabia many settlements were abandoned about 5,300 years ago.Шаблон:Sfn Some Neolithic people in the desert persisted for longer thanks to the exploitation of groundwater.Шаблон:Sfn

Different human populations responded to the drying in diverse manners,Шаблон:Sfn with responses in the Western Sahara being distinct from those in the Central Sahara.Шаблон:Sfn In the Central Sahara, pastoralism replaced hunter-gatherer activityШаблон:Sfn and a more nomadic lifestyle replaced semi-sedentary lifestylesШаблон:Sfn as observed in the Acacus Mountains of Libya.Шаблон:Sfn Nomadic lifestyles also developed in the Eastern Sahara/Red Sea Hills in response to the end of the AHP.[150] There was a shift in domestic animal use from cattle to sheep and goats as these are more suited in arid climates, a change reflected in rock art from which cattle disappeared at this time.Шаблон:Sfn

The development of irrigation systems in Arabia may have been an adaptation to the drying tendency.Шаблон:Sfn The decreased availability of resources forced human populations to adapt,Шаблон:Sfn in general fishing and hunting declined in favour of farming and herding.Шаблон:Sfn However, the effects of the end of the AHP on human food production have been subject to controversy.Шаблон:Sfn

Файл:All Gizah Pyramids.jpg
The pyramids of Giza, the most recognizable trace left by the Egyptian civilization

The warm episode and coinciding drought may have triggered animal and human migration to less inhospitable areasШаблон:Sfn and the appearance of pastoralists where previously fishery-dependent societies had existed, as happened at Lake Turkana.Шаблон:Sfn Humans moved to the Nile,Шаблон:Efn where the society of Ancient Egypt with pharaohs and pyramids was eventually forged by these climate refugeesШаблон:SfnШаблон:SfnШаблон:Sfn perhaps reflecting renewed exuberance;Шаблон:Sfn thus the end of the AHP can be considered responsible for the birth of Ancient Egypt.Шаблон:SfnШаблон:Sfn[1] Lower water levels in the Nile also aided the settlement of its valley as has been observed at Kerma.Шаблон:Sfn A similar process may have led to the development of the Garamantian civilization.Шаблон:Sfn 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.Шаблон:SfnШаблон:Sfn Population shifts into mountain areas have also been reported for the Air Mountains, Hoggar and Tibesti.Шаблон:Sfn In other places, such as the Acacus Mountains populations conversely remained in oasesШаблон:SfnШаблон:Sfn and hunter-gatherers also stayed in the Horn of Africa.Шаблон:Sfn

The Nile itself was not totally unaffected however;Шаблон:Sfn the 4.2 kiloyear eventШаблон:Sfn and the end of the AHP may be linked to the collapse of the Old Kingdom in EgyptШаблон:Sfn when the Nile floods failed for three decades around 4,160 years before presentШаблон:Sfn and the final drying occurred.Шаблон:Sfn The ongoing decrease of precipitation after the end of the AHP could be the cause of the end of the Akkadian Kingdom in Mesopotamia.[151] The end of the Garamantian civilization may also relate to climate change although other historical events were probably more important;Шаблон:Sfn at Tanezzuft oasis after 1,600 years ago it certainly relates to the drying trend.Шаблон:Sfn

In Central Africa, forests became discontinuous and savannahs formed in some places, facilitating the movement and growth of Bantu speaking populations;Шаблон:Sfn these in turn may have affected the ecosystem.Шаблон:Sfn The vegetation changes may have aided in the establishment of agriculture.Шаблон:Sfn The relatively slow decline of precipitation gave humans more time to adapt to the changing climate conditions.Шаблон:Sfn In East Africa, the beginning of the "Pastoral Neolithic" and the appearance of Nderit pottery have been attributed to the climatic changes at the end of the AHP.[152]

Cultural changes may also have occurred as a consequence of climate change, such asШаблон:Sfn changes in gender roles, the development of elites,Шаблон:Sfn the increased presence of human burials where formerly cattle burials predominated,Шаблон:Sfn as well as an increase of monumental architecture in the Sahara may have also been a response to increasingly adverse climates.Шаблон:Sfn A spread in cattle domestication at the time of climate changeШаблон:Sfn and as herders escaped the drying Sahara southwards[153][154] may also relate to these events, although the details of the exact process by which cattle domestication spread are still controversial.Шаблон:SfnШаблон:Sfn Finally, changes in agricultural practices at the end of the AHP may be associated with the propagation of malaria and one of its causative pathogens Plasmodium falciparum; in turn these may correlate with the origin of human genome variants such as sickle cell disease that are linked to malaria resistance.[155]

Non-human

In the Sahara, animal and plant populations were fragmented and restricted to certain favoured areas such as moist areas of mountain ranges; this happened for example to fish and crocodiles which only persist in isolated water bodies. Mediterranean plantsШаблон:SfnШаблон:Sfn such as cypresses too persist only in mountains,[156] along with some reptiles that may have also been stranded in mountains by the drying.[157] The whip spider Musicodamon atlanteus is probably also a relic of past wetter conditions.[158] The development of human-specific populations of the malaria-transmitting mosquito Aedes aegypti coincides with the end of the AHP.[159] The buffalo species Syncerus antiquus probably went extinct from the increased competition of pastoralists triggered by the climate drying.[160] Goat populations in Ethiopia shrunk during the droughts that followed the end of the AHP[161] and lion habitat declined across Africa.[162] The drying of the African Great Lakes region split gorilla populations into western and eastern populations,Шаблон:Sfn and a similar population split between the insect species Chalinus albitibialis and Chalinus timnaensis in Northern Africa and the Middle East may have also been caused by the expansion of deserts there.[163] Some aquatic species disappeared from the Sahara.Шаблон:Sfn Giraffes, widespread in the Sahara during the AHP, may have been forced to migrate into the Sahel; this together with the separating effect of Lake Megachad may have influenced the development of giraffe subspecies.[164] Climate change together with human impacts may have led to the extinction of a number of large mammals in Egypt.Шаблон:Sfn In northern Madagascar, wildlife declined after the end of the AHP even before the arrival of humans.Шаблон:Sfn On the other hand, the decline of tree cover may have grown the niche available to domestic animals[165] and some drought-tolerant plant species may have expanded their range.[166]

The Dahomey GapШаблон:Efn formed 4,500–3,200 years before present, correlative to the end of the AHP.Шаблон:Sfn The harbour porpoise declined in the Mediterranean due to a switch to oligotrophic conditions as discharge from African rivers decreased.[112] Desert varnish formed on exposed rocks in the SaharaШаблон:Sfn and at Lake Turkana in East Africa.[126]

Global climate

The shrinkage of subtropical wetlands probably led to a drop in atmospheric methane concentrations between 5,500 and 5,000 years ago, before boreal wetlands expanded and offset the loss of subtropical wetlands, leading to a return of higher atmospheric methane concentrations.Шаблон:Sfn Conversely, increases in atmospheric methane concentrations, detected in Greenland ice cores about 14,700 years ago,Шаблон:Sfn and atmospheric carbon dioxide decreases in the early Holocene may relate to the vegetation expansion caused by the AHP.Шаблон:Sfn Carbon dioxide concentration then increased after about 7,000 years as the biosphere began releasing carbon in response to increasing aridity.[151]

Файл:Dust Storms from Africa's Bodele Depression, Natural Hazards DVIDS848674.jpg
Dust originating in the Bodele depression

A sudden increase in the amount of land-originating dust in an oceanic drill core off Cape Blanc, Mauritania, has been interpreted as reflecting the end of the AHP 5,500 years ago occurring in only a few centuries.Шаблон:Sfn Increased African dust deposition took place at Ciomad[167] and the Durmitor Massif, both in Europe.[168] Potentially, alluvialШаблон:Efn sediments emplaced during the AHP[169] and dried up lake basins became an important source for dustШаблон:SfnШаблон:Sfn and silt-sized particles.Шаблон:Sfn Today, the Sahara is the single largest source of dust in the world, with far ranging effects on climate and ecosystems,Шаблон:Sfn such as the growth of the Amazon rainforest.[170]

In one climate model, the desertification of the Sahara at the end of the AHP reduces the amount of heat transported in the atmosphere and ocean towards the poles, inducing cooling of Шаблон:Convert especially in winter in the Arctic and an expansion of sea ice. Reconstructed temperatures in the Arctic indeed show a cooling, although less pronounced than in the climate model.Шаблон:Sfn Further, this climate transition in the climate model is accompanied by increased negative Arctic Oscillation states, a weaker subpolar gyre and increased precipitation and cold air outbreaks in much of Europe; such changes have also been observed in paleoclimate data.Шаблон:Sfn These findings imply that the vegetation state of the Sahara influences the Northern Hemisphere climate.Шаблон:Sfn In turn, this high latitude cooling may have further reduced precipitation over Africa.Шаблон:Sfn

Present-day situation

Presently, the African Monsoon still influences the climate between 5° south and 25° north latitude; the latitudes around 10° north receive the bulk of their precipitation from the monsoonШаблон:Efn during summer, with smaller amounts of rainfall occurring farther north. Thus farther north deserts can be found while the moister areas are vegetated.Шаблон:Sfn In the Central Sahara, annual precipitation reaches no more than Шаблон:Convert.Шаблон:Sfn Even farther north, the margin of the desert coincides with the area where the westerlies bring precipitation;Шаблон:Sfn they also influence southernmost Africa.Шаблон:Sfn Subsidence of air over parts of Northern Africa is responsible for the existence of deserts, which is further increased by the radiative cooling over the desert.[1] Climate variability exists to this day, with the Sahel suffering from droughts in the 1970s and 1980s when precipitation decreased by 30% and the flow of the Niger River and Senegal River even more,Шаблон:Sfn followed by an increase of precipitation.[1] The droughts are one of the most significant climate anomalies of the 20th century.Шаблон:Sfn Sea surface temperatures and feedbacks from land surface conditions modulate the strength of the monsoonШаблон:Sfn and the droughts may have been triggered by sea surface temperature changes forced by anthropogenic aerosols.Шаблон:Sfn A large increase in dust fluxes after 1800 AD has been explained with changed agricultural practices.Шаблон:Sfn

In East Africa the monsoon leads to two rain seasons in the equatorial area, the so-called "long rains" in March–May and the "short rains" in October–NovemberШаблон:Sfn when the ITCZ moves northward and southward over the region, respectively;Шаблон:Sfn in addition to the Indian Ocean-sourced precipitation there is also AtlanticШаблон:Efn- and Congo-sourced precipitation west of the Congo Air Boundary.Шаблон:SfnШаблон:Sfn In Arabia, the monsoon does not penetrate far from the Arabian Sea and some areas are under the influence of winter precipitation brought by cyclones from the Mediterranean Sea.Шаблон:Sfn East Africa is also under the influence of monsoon circulations.Шаблон:Sfn South Africa has both monsoonal climates, winter precipitation climates and climates without clear precipitation seasonality.Шаблон:Sfn

Implications for future global warming

Файл:Greening Sahel 1982-1999.jpg
Greening of the Sahel between 1982 and 1999

Some simulations of global warming and increased carbon dioxide concentrations have shown a substantial increase in precipitation in the Sahel/Sahara.Шаблон:Sfn This and the increased plant growth directly induced by carbon dioxideШаблон:Sfn could lead to an expansion of vegetation into present-day desert, although it would be less extensive than during the mid-HoloceneШаблон:Sfn and perhaps accompanied by a northward shift of the desert, i.e. a drying of northernmost Africa.Шаблон:Sfn Such a precipitation increase may also reduce the amount of dust originating in Northern Africa,Шаблон:Sfn with effects on hurricane activity in the Atlantic and increased threats of hurricane strikes in the Caribbean, the Gulf of Mexico and the East Coast of the United States of America.Шаблон:Sfn

The Special Report on Global Warming of 1.5 °C and the IPCC Fifth Assessment Report indicate that global warming will likely result in increased precipitation across most of East Africa, parts of Central Africa and the principal wet season of West Africa, although there is significant uncertainty related to these projections especially for West Africa.Шаблон:Sfn In addition, the end of the 20th century drying trend may be due to global warming.Шаблон:Sfn On the other hand, West Africa[171] and parts of East Africa may become drier during given seasons and months.[171]Шаблон:Sfn Currently, the Sahel is becoming greener but precipitation has not fully recovered to levels reached in the mid-20th century.Шаблон:Sfn

Climate models have yielded equivocal results about the effects of anthropogenic global warming on the Sahara/Sahel precipitation. Human-caused climate change occurs through different mechanisms than the natural climate change that led to the AHP,Шаблон:Sfn in particular through increased inter-hemispheric temperature gradients.Шаблон:Sfn The direct effect of heat on plants may be detrimental.Шаблон:Sfn Non-linear increases in vegetation cover are also possible,Шаблон:Sfn with several climate models showing abrupt increases when global temperatures rise by Шаблон:Convert.[172] One study in 2003 showed that vegetation intrusions in the Sahara can occur within decades after strong rises in atmospheric carbon dioxideШаблон:Sfn but would not cover more than about 45% of the Sahara.Шаблон:Sfn That climate study also indicated that vegetation expansion can only occur if grazing or other perturbations to vegetation growth do not hamper it.Шаблон:Sfn On the other hand, increased irrigation and other measures to increase vegetation growth such as the Great Green Wall could enhance it.Шаблон:Sfn A 2022 study indicated that while increased greenhouse gas concentrations by themselves are not sufficient to start an AHP if greenhouse gas-vegetation feedbacks are ignored, they lower the threshold for orbital changes to induce Sahara greening.Шаблон:Sfn

Plans to geoengineer the Sahara to increase its vegetation cover and precipitation have been proposed since the 19th century.Шаблон:Sfn The mechanisms and consequences of the AHP are important context to evaluate such proposals and their ramifications;Шаблон:Sfn precipitation may increaseШаблон:Sfn but the consumption of carbon dioxide would be small and there could be detrimental impacts on climate and dust fluxes in the far-field.Шаблон:Sfn Building large solar farms in the Sahara desert would also act to decrease its albedo and may trigger similar climate responses.[173]

A greening of the Sahara on the one hand may allow agriculture and pastoralism to expand into hitherto unsuitable areas, but increased precipitation can also lead to increased water borne diseases and flooding.Шаблон:Sfn Expanded human activity resulting from a wetter climate may be vulnerable to climate reversals as demonstrated by the droughts that followed the mid-20th century wet period.Шаблон:Sfn

See also

Шаблон:Portal

Notes

Шаблон:Notelist

References

Шаблон:Reflist

Sources

Шаблон:Refbegin

Шаблон:Refend

External links

Партнерские ресурсы
Криптовалюты
Магазины
Хостинг
Разное

  1. ↑ 1,00 1,01 1,02 1,03 1,04 1,05 1,06 1,07 1,08 1,09 1,10 1,11 1,12 1,13 Ошибка цитирования Неверный тег <ref>; для сносок Bader2017 не указан текст
  2. ↑ 2,0 2,1 Ошибка цитирования Неверный тег <ref>; для сносок Garcea2020 не указан текст
  3. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Pickering2023 не указан текст
  4. ↑ 4,0 4,1 Ошибка цитирования Неверный тег <ref>; для сносок DeckerFalkenroth2021 не указан текст
  5. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Brass2018 не указан текст
  6. ↑ 6,0 6,1 Ошибка цитирования Неверный тег <ref>; для сносок Reed1959 не указан текст
  7. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Yunakov2022 не указан текст
  8. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Armstrong2023 не указан текст
  9. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Hughes2011 не указан текст
  10. ↑ Ошибка цитирования Неверный тег <ref>; для сносок StokesGomes2019 не указан текст
  11. ↑ 11,0 11,1 11,2 Ошибка цитирования Неверный тег <ref>; для сносок Castilla-Beltrán2019 не указан текст
  12. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Neugebauer2017 не указан текст
  13. ↑ 13,0 13,1 13,2 Ошибка цитирования Неверный тег <ref>; для сносок Renssen2006 не указан текст
  14. ↑ 14,0 14,1 Ошибка цитирования Неверный тег <ref>; для сносок Springer2004 не указан текст
  15. ↑ Ошибка цитирования Неверный тег <ref>; для сносок YangUno2020 не указан текст
  16. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Johnson2007 не указан текст
  17. ↑ Ошибка цитирования Неверный тег <ref>; для сносок MarksWelc2019 не указан текст
  18. ↑ 18,0 18,1 18,2 18,3 18,4 18,5 18,6 Ошибка цитирования Неверный тег <ref>; для сносок BowmanNyamweru1989 не указан текст
  19. ↑ 19,0 19,1 19,2 Ошибка цитирования Неверный тег <ref>; для сносок Grouard2023 не указан текст
  20. ↑ 20,0 20,1 Ошибка цитирования Неверный тег <ref>; для сносок Bian2023 не указан текст
  21. ↑ Ошибка цитирования Неверный тег <ref>; для сносок HeLiu2020 не указан текст
  22. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Hiner2015 не указан текст
  23. ↑ 23,0 23,1 Ошибка цитирования Неверный тег <ref>; для сносок Flögel2008 не указан текст
  24. ↑ 24,0 24,1 24,2 24,3 24,4 24,5 Ошибка цитирования Неверный тег <ref>; для сносок Usai2016 не указан текст
  25. ↑ Ошибка цитирования Неверный тег <ref>; для сносок CoussinPenaud2020 не указан текст
  26. ↑ Шаблон:Harvnb (lower estimate).
  27. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Castañeda2009 не указан текст
  28. ↑ Ошибка цитирования Неверный тег <ref>; для сносок RuanMohtadi2020 не указан текст
  29. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Lézine2023 не указан текст
  30. ↑ Ошибка цитирования Неверный тег <ref>; для сносок EwédjèJansen2020 не указан текст
  31. ↑ 31,0 31,1 Ошибка цитирования Неверный тег <ref>; для сносок Sochor2020 не указан текст
  32. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Quinn2022 не указан текст
  33. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Cooper2017 не указан текст
  34. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Mouline2008 не указан текст
  35. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Hánová2023 не указан текст
  36. ↑ Ошибка цитирования Неверный тег <ref>; для сносок JewellDrake2021 не указан текст
  37. ↑ 37,0 37,1 Ошибка цитирования Неверный тег <ref>; для сносок Duringer2010 не указан текст
  38. ↑ Ошибка цитирования Неверный тег <ref>; для сносок AbdallahNassour2021 не указан текст
  39. ↑ 39,0 39,1 Ошибка цитирования Неверный тег <ref>; для сносок Hillaire-Marcel1990 не указан текст
  40. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Yahiaoui2023 не указан текст
  41. ↑ 41,0 41,1 Ошибка цитирования Неверный тег <ref>; для сносок BubenzerBoleten2008 не указан текст
  42. ↑ 42,0 42,1 Ошибка цитирования Неверный тег <ref>; для сносок Franz1997 не указан текст
  43. ↑ 43,0 43,1 Ошибка цитирования Неверный тег <ref>; для сносок Lenhardt2018 не указан текст
  44. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Armitage2017 не указан текст
  45. ↑ 45,0 45,1 Ошибка цитирования Неверный тег <ref>; для сносок Lecomte2013 не указан текст
  46. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Lewin2017 не указан текст
  47. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Sparavigna2013 не указан текст
  48. ↑ Ошибка цитирования Неверный тег <ref>; для сносок ZakiKing2020 не указан текст
  49. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Zaki2022 не указан текст
  50. ↑ Ошибка цитирования Неверный тег <ref>; для сносок MercuriSadori2014 не указан текст
  51. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Badino2018 не указан текст
  52. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Zhao2021 не указан текст
  53. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Riemer2006 не указан текст
  54. ↑ Ошибка цитирования Неверный тег <ref>; для сносок McDonald2020 не указан текст
  55. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Stojanowski2018 не указан текст
  56. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Scarcelli2019 не указан текст
  57. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Marinova2014 не указан текст
  58. ↑ 58,0 58,1 Ошибка цитирования Неверный тег <ref>; для сносок GrilloMcKeeby2020 не указан текст
  59. ↑ Ошибка цитирования Неверный тег <ref>; для сносок ScerriNiang2021 не указан текст
  60. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Calderón2015 не указан текст
  61. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Chad2016 не указан текст
  62. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Bergmann2022 не указан текст
  63. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Bouchez2019 не указан текст
  64. ↑ Ошибка цитирования Неверный тег <ref>; для сносок GoudieMiddleton2006 не указан текст
  65. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Ribolini2023 не указан текст
  66. ↑ 66,0 66,1 Ошибка цитирования Неверный тег <ref>; для сносок Kohn2011 не указан текст
  67. ↑ 67,0 67,1 Ошибка цитирования Неверный тег <ref>; для сносок Zarriess2010 не указан текст
  68. ↑ 68,0 68,1 Ошибка цитирования Неверный тег <ref>; для сносок Haslett2006 не указан текст
  69. ↑ Ошибка цитирования Неверный тег <ref>; для сносок deCarvalhoFerreira2022 не указан текст
  70. ↑ 70,0 70,1 Ошибка цитирования Неверный тег <ref>; для сносок DammeBenda2018 не указан текст
  71. ↑ Ошибка цитирования Неверный тег <ref>; для сносок EngelRückmann2020 не указан текст
  72. ↑ Ошибка цитирования Неверный тег <ref>; для сносок EhrmannWilson2023 не указан текст
  73. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Guagnin2022 не указан текст
  74. ↑ Ошибка цитирования Неверный тег <ref>; для сносок WagnerWennrich2018 не указан текст
  75. ↑ Ошибка цитирования Неверный тег <ref>; для сносок UllmannNill2020 не указан текст
  76. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Gasse2005 не указан текст
  77. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Graham2017 не указан текст
  78. ↑ Ошибка цитирования Неверный тег <ref>; для сносок NutzSchuster2020 не указан текст
  79. ↑ Ошибка цитирования Неверный тег <ref>; для сносок AwalehBoschetti2020 не указан текст
  80. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Loakes2017 не указан текст
  81. ↑ Ошибка цитирования Неверный тег <ref>; для сносок RiedlMelnick2019 не указан текст
  82. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Fischer2022 не указан текст
  83. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Runge2017 не указан текст
  84. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Dommain2020 не указан текст
  85. ↑ Ошибка цитирования Неверный тег <ref>; для сносок JacksonKelly2020 не указан текст
  86. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Gabrielli2014 не указан текст
  87. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Zech2006 не указан текст
  88. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Kervyn2016 не указан текст
  89. ↑ 89,0 89,1 Ошибка цитирования Неверный тег <ref>; для сносок BastianVigier2019 не указан текст
  90. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Stinchcomb2020 не указан текст
  91. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Müller2011 не указан текст
  92. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Nguetsop2013 не указан текст
  93. ↑ Ошибка цитирования Неверный тег <ref>; для сносок LézineIzumi2019 не указан текст
  94. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Springer2011 не указан текст
  95. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Ifo2017 не указан текст
  96. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Dargie2019 не указан текст
  97. ↑ Ошибка цитирования Неверный тег <ref>; для сносок LaRoche2014 не указан текст
  98. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Rodríguez-Berriguete2019 не указан текст
  99. ↑ Ошибка цитирования Неверный тег <ref>; для сносок MorinhaMilá2020 не указан текст
  100. ↑ Ошибка цитирования Неверный тег <ref>; для сносок ZielhoferFaust2008 не указан текст
  101. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Stoetzel2017 не указан текст
  102. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Zielhofer2019 не указан текст
  103. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Yanes2011 не указан текст
  104. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Censi2010 не указан текст
  105. ↑ 105,0 105,1 Ошибка цитирования Неверный тег <ref>; для сносок Spötl2010 не указан текст
  106. ↑ Ошибка цитирования Неверный тег <ref>; для сносок SegadelliGrazzini2020 не указан текст
  107. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Sbaffi2004 не указан текст
  108. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Incarbona2010 не указан текст
  109. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Jiménez-MorenoAnderson2020 не указан текст
  110. ↑ 110,0 110,1 Ошибка цитирования Неверный тег <ref>; для сносок BlanchetTjallingii2021 не указан текст
  111. ↑ Ошибка цитирования Неверный тег <ref>; для сносок GaucheryRovere2021 не указан текст
  112. ↑ 112,0 112,1 Ошибка цитирования Неверный тег <ref>; для сносок Porpoises2016 не указан текст
  113. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Rüggeberg2019 не указан текст
  114. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Kiro2017 не указан текст
  115. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Berger2021 не указан текст
  116. ↑ 116,0 116,1 Ошибка цитирования Неверный тег <ref>; для сносок Sletten2013 не указан текст
  117. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Ramisch2017 не указан текст
  118. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Bäumle2018 не указан текст
  119. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Lubbe2016 не указан текст
  120. ↑ Ошибка цитирования Неверный тег <ref>; для сносок LourencoFitchett2022 не указан текст
  121. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Fitchett2017 не указан текст
  122. ↑ Ошибка цитирования Неверный тег <ref>; для сносок SerratoMarks2021 не указан текст
  123. ↑ 123,0 123,1 Ошибка цитирования Неверный тег <ref>; для сносок CaballeroZawisza2020 не указан текст
  124. ↑ Ошибка цитирования Неверный тег <ref>; для сносок LubellJackes2008 не указан текст
  125. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Garcin2006 не указан текст
  126. ↑ 126,0 126,1 126,2 Ошибка цитирования Неверный тег <ref>; для сносок LiuLepre2021 не указан текст
  127. ↑ Ошибка цитирования Неверный тег <ref>; для сносок LézineIzumi2020 не указан текст
  128. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Nogué2013 не указан текст
  129. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Vaezi2019 не указан текст
  130. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Castilla-BeltránDuarte2020 не указан текст
  131. ↑ Ошибка цитирования Неверный тег <ref>; для сносок MooneyBlack2006 не указан текст
  132. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Wu2019 не указан текст
  133. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Zolitschka2018 не указан текст
  134. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Zerboni2017 не указан текст
  135. ↑ Ошибка цитирования Неверный тег <ref>; для сносок IshiiTamura2021 не указан текст
  136. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Noti2022 не указан текст
  137. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Costas2012 не указан текст
  138. ↑ Ошибка цитирования Неверный тег <ref>; для сносок López-Avilés2022 не указан текст
  139. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Weber2022 не указан текст
  140. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Hipondoka2014 не указан текст
  141. ↑ 141,0 141,1 141,2 Ошибка цитирования Неверный тег <ref>; для сносок MeekerCumming2003 не указан текст
  142. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Fedotov2004 не указан текст
  143. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Marsicek2013 не указан текст
  144. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Aharon2017 не указан текст
  145. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Wahl2014 не указан текст
  146. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Renssen2022 не указан текст
  147. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Rowe2003 не указан текст
  148. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Shuman2017 не указан текст
  149. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Shinker2014 не указан текст
  150. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Andersen2014 не указан текст
  151. ↑ 151,0 151,1 Ошибка цитирования Неверный тег <ref>; для сносок Bar-Matthews2003 не указан текст
  152. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Grillo2022 не указан текст
  153. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Miller2019 не указан текст
  154. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Sawchuk2019 не указан текст
  155. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Smith2016 не указан текст
  156. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Boratyński2018 не указан текст
  157. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Escoriza2017 не указан текст
  158. ↑ Ошибка цитирования Неверный тег <ref>; для сносок BlockSeiter2016 не указан текст
  159. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Rose2023 не указан текст
  160. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Faith2014 не указан текст
  161. ↑ Ошибка цитирования Неверный тег <ref>; для сносок TarekegnKhayatzadeh2021 не указан текст
  162. ↑ Ошибка цитирования Неверный тег <ref>; для сносок CooperDugmore2021 не указан текст
  163. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Vilhelmsen2005 не указан текст
  164. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Hassanin2007 не указан текст
  165. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Holl2020 не указан текст
  166. ↑ Ошибка цитирования Неверный тег <ref>; для сносок LyamDuque-Lazo2020 не указан текст
  167. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Karátson2022 не указан текст
  168. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Djurović2022 не указан текст
  169. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Kunkelova2022 не указан текст
  170. ↑ Ошибка цитирования Неверный тег <ref>; для сносок D'Odorico2006 не указан текст
  171. ↑ 171,0 171,1 Ошибка цитирования Неверный тег <ref>; для сносок IPCCSpecial2018 не указан текст
  172. ↑ Ошибка цитирования Неверный тег <ref>; для сносок ArmstrongMcKay2022 не указан текст
  173. ↑ Ошибка цитирования Неверный тег <ref>; для сносок LuZhang2020 не указан текст
Источник — http://wikihandbk.com/ruwiki/index.php?title=Английская_Википедия:African_humid_period&oldid=12968236