During the second half of the 19th century, archaeologists unearthed ruins in the desert, some of them substantial, evidence of great cities that appeared before their astonished eyes. It was clear that certain ancient civilisations had existed in regions that today have an arid, sub-arid or desert environment. It was reasonable to deduce that these regions, which are now arid, could not have supported the needs of these ancient societies, and that the climate had changed in historical times. This climate, which has changed so fundamentally over the long history of our planet, was the result of major ice ages during the Quaternary period. During their retreat, around 8,000 years ago, the ice cap was still at the mouth of the Thames. At that time, the Sahara had a temperate climate and the people who lived there created a civilisation. Since then, the ice has slowly retreated northwards in a series of oscillating movements.
At the end of the 19th century, when these ideas were beginning to take root in the minds of scientists, Pierre Kropotkin, a friend of the French geographer Elysée Reclus, discovered in the steppes of Turkestan forests of dried-out, sometimes solidified, trees stretching for hundreds of kilometres. Famous for his work in geography and his anarchist convictions, this Russian not only understood that this was a sudden change, he was the first to deduce historical consequences from this phenomenon. The degradation of the land had caused the nomads to migrate westwards to better pastures. This explains the movement of barbarian hordes towards these regions, in a word, the movement of masses of people towards the green and fertile valleys of our continent.
Silicified tree trunks: Huntington’s discoveries
To confirm these observations, the Carnegie Institute of Washington subsidised a major exploration of Turkestan in 1903, led by the American geographer Raphael Pumpelly. These explorers recognised the importance of the area of parched trees, mostly poplars, and were accompanied by an American scientist who was soon to become famous: Ellsworth Huntington. Huntington was immediately aware of the importance of the changes in climate that had taken place throughout history, a theme to which he devoted the first part of his life. He quickly confirmed Kropotkin’s hypotheses, and began major studies using a variety of investigative methods. This research lasted from his first notes on Turkestan in 1905, to the publication in 1924 of the third edition of his work: Civilisation and Climate, the synthesis of his efforts. Huntington and other specialists convinced by his teachings carried out numerous investigations to verify the variations in water levels in certain Asian lakes, in relation to the location of certain known ruins. These investigations into the water levels used in the construction of the monuments referred to showed great oscillations in the level of the waters, the surface area of which fell or rose depending on the period and the rainfall. The Caspian Sea, a closed sea that bears witness to a vanished Tertiary ocean, was particularly well suited to these investigations, as major civilisations had developed on its shores over the course of time. They also studied changes in facies, both botanical and zoological, in regions that are now desert. Albrecht Penck (1858-1945), one of the founders of glacial geomorphology, observed the movements of vegetation and dunes in the southern Sahara, and confirmed Huntington’s work. Mother Nature’s oscillations of glacial or torrid climatology were manifested according to a succession of geographical frameworks, following each other in a determined order, characterised by precise geobotanical observations. Subpolar vegetation could not suddenly give way to subarid species. A series of interludes had to have existed at each of these extremes, which was of vital importance in reconstructing the landscape of the past.
Other studies have used very curious methods, for example a study in the Syrian desert succeeded, with the help of historical testimonies, in establishing statistics with which to record the number of caravans that crossed this region on their way from Damascus to Chaldea. In this way, it was possible to determine the dates on which the routes changed course, when they became dangerous due to the lack of water and were abandoned. These facts demonstrated oscillations in rainfall and drought activity in these regions, once rich and fertile as ancient texts and archaeology testify.
With these methods, half geographical and half historical, we could only make general statements: the climate had changed since Antiquity. It was certain that a process of drought had been underway since the second century and had subsequently become more intense. It was impossible to determine a precise climatic situation with reference to a region in the past. The only thing left for researchers to do was to infer relationships between the climate crisis and past events. This was not the case with the methods used by Huntington, which had the rigour of mathematical calculations that could be applied to any circumstances of space and time. He soon realised that the double radial impressions that appeared in the cross-sections of large trees that had been cut down, and if averaged over a large number of specimens, determined not only their age but also their dryness or dampness. There is a gigantic tree in California, the Washington Sequoia, which is over 3,500 years old, and specialists believe that it is a veritable meteorological archive. Huntington made a meticulous study of 450 of these trees and used his calculations to draw up accurate and precise graphs. Parallel research on Owens Salt Lake – fed by a river of the same name whose waters lead to Los Angeles – close to Huntington’s redwoods, confirmed Huntington’s data through numerous analyses of the salts present in the lake and river.
This data, which is extremely important for historians because the redwoods and the lake are at the same latitude as the Mediterranean, was confirmed by the work of the Swedish geologist Gerard de Geers, who studied the deposits left by retreating glaciers as a result of higher temperatures. In 1940, he drew up a chronology of the climatic situation over the last few thousand years, and these results, obtained using completely different methods to those used by Huntington, which nevertheless corroborate each other, remove any hesitation. Nowadays, we can study the evolution of the climate in historical times and pinpoint the dates of major atmospheric crises.
The climate has shaped our history
Historians cannot ignore these lessons: important civilisations, such as the one that developed in Mesopotamia, had disappeared corroded by drought. Wind erosion had buried Sumer, Nineveh and the immense Babylon under the sands. On the other hand, other civilisations disappeared because of a reverse phenomenon: the Mayans and the Khmers, who built the magnificent temples at Angkor, and other lesser-known civilisations were smothered under the tropical forest, which suddenly appeared and dismantled their civil and religious buildings, whose ruins can be seen behind thick foliage. So the changes in climate over the course of time, transforming the environment of these ancient societies, was one of the keys to understanding the evolution of universal history.
However, the historian faced a major difficulty: he had to date every change in the landscape, every natural setting, if he did not want to consciously fall into gaudy anachronisms. During the Middle Ages, the Iberian Peninsula had a different climate to that of modern times, and this lack of knowledge was due in part to the mythical nature of Spanish history. So, in order to establish the particular case that interests us in this thesis, i.e. the events of the 18th century, we need to reconstruct the natural environment of the time, which was the consequence of the general evolution of the climate in our hemisphere. Since this was correlated with the atmospheric situation of the Sahara, we reduced this problem by determining the last transformation of this desert, i.e. the date on which it changed from a steppe environment to an arid one. From what we know, it is reasonable to place this transformation during the High Middle Ages, and if this is correct, we must admit the existence of a connection between the mutation of the landscape and the economic and political crisis that had ravaged the Maghreb and most of the Iberian Peninsula at the same time. In other words, the Islamic revolution had a reciprocal effect on the desertification of the Sahara.
Angkor site: putting Saharan desertification into perspective
Most geographers agree on the following principles: today’s deserts are of recent formation. We could debate the climatic mechanisms, but what we do not doubt is that the process of aridity building up to a desert was not simultaneous in all regions. There are ancient deserts and recent deserts. Because of the enormous size of the Sahara, some 5,000 km long from the Red Sea to the Atlantic, and 2,000 km wide from the Atlas mountains to Sudan, almost 10 million square kilometres, the process of aridity could not have been the same in all places. The desert face of its western part is more recent than that of its eastern part.
How can we appreciate this difference? Émile Félix Gauthier, one of the first to study the Sahara, used a very appropriate term. He said that ancient deserts such as Libya were in an “aseptic” state. By this he meant that the geophysical and climatic conditions in these regions were so rigorous that life was virtually non-existent. The fauna and flora had disappeared and caravans did not cross them, as no one dared to do so with ancient means. On the other hand, the more recently formed western desert had major wells, and remnants of vegetation bore witness to a bygone era. There is still a specialised and widespread fauna, and in some places there is enough pasture in winter to feed a few herds of goats and camels, and nomads and caravans still pass through these areas. The geophysical facies also confirms the existence of a divergence in terms of the time at which the soil deteriorated. In the Eastern Sahara, the river systems are filled in and blocked by wind erosion, and the sands hide the reliefs once sculpted by the waters, giving a landscape of grandiose uniformity, but lunar. In a different way, in the western part of the Sahara, a fossil river system remains. Water no longer flows into these great Quaternary valleys, carved out by rivers and streams that have now dried up, but they are easily recognisable. The closer you get to the Atlantic, the more the wadis retain the same geophysical context as European rivers. In the Rio de Oro, for example, you can find the meandering Seguia el Hamra, whose rivers are devoid of vegetation, but whose bed still maintains the sinuous course of a living river. This thesis will only look at the Central and Western Sahara to understand the role played by climate change in the events of the 8th century. But even in these two areas, the processes were not the same; the one in the central region was much more pronounced. There is a tanezrouft or “desert of thirst” that reaches 150 to 300 km in its north-south dimensions. This area is surrounded by highly altered xerophytic steppes, in which the landscape changes towards sub-arid vegetation, and then becomes very arid as you head towards the Mediterranean or Niger. A desertification process always occurs in several stages, where the change in landscape varies successively from steppe to sub-arid, from sub-arid to arid, and modifies the climate of peripheral areas. This law of correlation makes it possible to reconstruct the succession of landscapes that existed in the past. All we need to do is gather enough historical evidence to determine the existence of ancient natural settings, and if possible, establish the chronology of these changes. This task is made easier by the fact that this is a recent process, and we can still recognise the geobotanical and biological evidence.
Conifer in Tassili: North Africa’s vanishing forests
Snail farms, where snails were prepared for export and consumption, are found in their thousands in southern Tunisia. By analysing the ashes from the pyres, it is possible to locate the ancient forests and classify the most common species. Some of these shellfish beds date back to more modern times, from the Capesian civilisation to the Neolithic cultures of the last millennium, which are now part of history. According to Lionel Balout, some of the deposits are very large: “Under the huge wall of Relilai, 5,000 metres of ash represent some 500,000 m3 of charred wood, and the whole of the Tlidjsene depression, south-west of Tébessa (south of Constantine), has many similar deposits in refuges and caves”.
Although there is enough evidence to suggest recent climatic change in North Africa, we are not aware of any work that would allow us to establish approximate dates for successive changes in vegetation in this area. But we can provide the following information: Mr Picq, a meteorologist who lived in the observatories of the Sahara, has told us that there is a silicification front of plant species that extends into the south of the central Sahara, in the regions north of the Niger. A characteristic flora develops on the banks of the river, but if you head northwards you will find hardwood forests, and then the silicification process begins. Dead, dried-out trees that stand upright are watered by the silica contained in the wind, which penetrates the wood, converting the trunk into a monolith. Further north, they are found blown over by the wind and scattered in the ground in broken pieces in the form of large stones. Further still, they are found in smaller pieces with which the natives make handles for their knives. This is the same phenomenon observed by Kropotkin in Turkestan. This process of silicification, spread out over such a long distance, points to a specific way in which these places dried out at dates not very far in the past, a drying out that was also rapid. The existence of stout species in the Sahara has recently been confirmed by direct observation: there are still conifers in the centre of the desert. An expedition led by the archaeologist Henri Lothe in 1950 to copy rock paintings in the Tassili discovered cypress trees (cupressus dupreziana) in Tamrit “with trunks measuring 6 metres in circumference! The cypresses we saw in front of us were one of the most unusual sights in the desert… We’d never seen this species in the region. The guide explained to me that there are many trees in the surrounding mountains that died a very long time ago. They also come from prehistoric times, and are the rare witnesses of a more humid past….There are about a hundred of them left, but the inventory we made tells us that they were numerous at the top of the Tassili… So, the Hoggar and the Tassili once enjoyed a Mediterranean climate, and so it wouldn’t be surprising if these mountains had been populated.”
Flooding of the Oued Saoura: springs once bathed the Sahara until historic times
It has already been suggested that the Western Sahara is characterised by the presence of a fluvial network of dead rivers, whose morphology can still be clearly distinguished today. Some of these wadis were very important, and once carried large masses of water. The Oued Saoura descends from the Moroccan Atlas mountains and stretches for 500 or 600 km towards the centre of the Sahara. But as the water that flows through it only lasts a few days a year, it is clear that it is not this force that has carved out the bed of this normally dry river. The same is true of another wadi, the Igargar, which is already fossilised and which in the past had impressive dimensions, as described by Emile Félix Gauthier. “Its source was in the tropics and its last basin was near Biskra (in the north-east of Algeria): a thousand kilometres as the crow flies; an intermediate length between the Danube and the Rhine. The Igargar flowed from south to north, from the heart of the desert to its periphery; exactly the opposite of the Wadi Saoura… The consequences of this fact are considerable.”
This can only be explained by the fact that the central regions of the Sahara used to receive a great deal of rainfall, the waters of which fed a large river that carved out valleys and formed an immense fluvial network. In this way, the Igargar followed a direction parallel to that of the Nile, but the former was less wide and its source was in a region that was later gradually converted into desert. In contrast, the two sources of the Nile that feed it are in the heart of the equatorial zone. Two natural reserves of enormous capacity, located in regions that receive extraordinary rainfall at certain times of the year. For this reason, the Nile has remained alive while the Igargar has fossilised.
According to Gauthier: “It is not only its juvenile forms that bear witness to the fact that the waters of the dead valleys of the Igargar flowed at recent dates. Small tropical fish known as chromis have been known for a long time in Biskra, in the oases of the oued Rir, i.e. the last basin of the Quaternary Igargar. These days, they abound in the pools and canals of the palm groves. They have been seen emerging from wells and taking refuge wherever they can in underground springs. Recently, in the same region, a much larger fish was found, the Clarias lazera, a catfish popularly known by the English and French as the “poisson chat”. Formerly a tropical fish that still thrives in Egypt along the Nile, it is now an intruder in the Mediterranean world. In the Algerian Sahara, it can be found all along the Igargar, from the lagoons where it once disappeared to its sources in muddy pools where it lives precariously. In the same region of Biskra, a companion of its much more famous fish dances: Cleopatra’s asp, the snake of charmers, a cobra from Hindustan, which has also emigrated from the tropics. Its presence in southern Algeria remains inexplicable without the involvement of the Quaternary Igargar. The fact becomes even more obvious with the crocodile. It has been found in pools in the Oued Mihero, an artery of the Igargar. It may be the last survivor, and you have to imagine what a biological miracle it is for this animal to survive in such an environment, but it is an undeniable reality. All this takes us back to a time when the Igargar and the Taj asaset wadis joined at their sources, establishing water links between the tropics and the Mediterranean world. This period cannot go very far back in time, because although the rivers died, some of their fauna survived”.
When was this event? We need to establish the terms of the question. Was it a great Saharan river that flowed majestically through its valley, like the Danube today, that managed to carve its bed violently into the rock? This case goes back geological ages. We are more interested here in the last features of the Igargar, when it resembled the rivers of the Mediterranean basin, but did not deserve to be called a wadi. With the data we have on its residual fauna, it is very likely that its long agony lasted until recent times, i.e. historical times.
According to Lothe, in the Tassili, a mountainous region in the centre of the Sahara, there is a small oasis, Iherir, “which is the richest place in the desert in terms of water, a fact inconceivable in other places, lakes follow one another without interruption in the bed of the wadi (perhaps a tributary of the ancient Igargar), some reaching a kilometre in length and 10 or 12 metres in depth”. During the first French expedition to Tassili in 1905, Captain Touchard reported the presence of the last large saurians in the Sahara thanks to the tracks left by these animals. Two years later, one of them was killed by one of Captain Niegen’s subordinates and dissected to decorate the zoology laboratory at Algiers University. The last specimen was killed in 1924 by Lieutenant Bauval. During his expedition in 1950, Henri Lothe was unable to find one despite extensive research. Due to a lack of food, this species had become extinct, and as the country dried out, the fauna gradually disappeared, along with the crocodile, a voracious carnivore. As Lothe rightly points out, “this is a magnificent testimony to the Sahara’s humid past, at a time when a very extensive river network crossed it from north to south, linking the fauna of the salt lagoons (chotts) of Barbarie with those of Niger and Chad”. There is no doubt that the presence of these reptiles confirms that the date of the drying up of the Sahara does not go back very far in time, for the simple reason that this witness could not have lived very long after the disappearance of its natural environmental setting.
These last vestiges of a humid environment survived in the Tassili because of its altitude. But what about the plains of the Sahara? Another fact stands out: under the wadis there are large aquifers. To reach this water, the natives built wells and tunnels. These subterranean galleries have been the subject of considerable work, and are spacious enough for one person to walk through, sometimes reaching a depth of 70 metres. According to Gauthier, in Tamentit, these galleries measure 40 km. This work could not have begun when the water table was at great depth, as would have been the case if the climate and river regime had changed in distant times. Since the natives did not have the technical means to discover them underground, the construction of the wells and galleries began when the water was on the surface. And as the climate worsened, they began to dig into the ground in sync with the drop in water levels, descending as the drought increased. According to some historical accounts, the oases were created during the Christian era, between the 6th and 18th centuries. According to Gauthier, the oldest are those of Gourara: “In Touat, the oriental irrigation procedures, the galleries, i.e. the palm groves as they exist today, date from the third century of the Hegira, our tenth century after Jesus Christ. In the Tidikelt, the oldest palm groves date back no further than the thirteenth century, and the most recent to the eighteenth century.
Clarias Lazera: The toponymy of the Sahara bears witness to a recently inhabited region
As Emile Félix Gauthier might say, the Central Sahara is still not “aseptic”. This region no longer has the life of yesteryear, but still retains the memory of it; and all its explorers agree on the following fact: these areas of the desert were once inhabited, right up to the dreaded Tanezrouft. Evidence of ancient populations can be found scattered all over the land, and in certain privileged places, evidence of troglodyte life, where engravings and cave paintings abound. These works show not only the demographic density of these now desert regions, but also the fauna and flora that have disappeared. Right in the Erg, in the Ténéré, the driest region of the Sahara today, Lhote found the remains of fishermen’s camps and several mounds of fish bones “that could fill several carts”. Scattered across the ground, both in the Tanezrouft and in the Rio de Oro, are rollers or large mortars carved from a single piece of stone. There is no doubt that they were used to flatten grain and reduce it to flour. These tools are similar to those still used in Sudan, but they are always found in places where there is no vegetation whatsoever.
The current toponymy of the Central Sahara shows that these places were inhabited by people, and abandoned at recent dates. In a truly “aseptic” desert, so to speak an ancient desert, there are no place names. As no one has passed through these places for hundreds of years, if not thousands, the ancient geographical names, if they existed at all, have been forgotten. Because of this, the explorers of these areas were obliged to baptise the highest points of the relief with their knowledge and understanding. This did not happen in the Central and Western Sahara; on the contrary, the traveller is surprised by the abundance of names mentioned in the guidebooks. How can we explain this wealth of place names in places so far from any urban concentration? We have to admit that at other times, a large population had given a name to the various high points, and that its disappearance is recent because the toponymy has remained in memory, and has come to us through the caravans.
It was in the guides’ interest to keep these names in mind in order to find their way around, and this tradition has been handed down from father to son. It can’t be very old. As the adverse conditions of the Sahara increased, caravan traffic declined. We know, for example, that in modern times, during the 16th century, they crossed the central desert assiduously, from southern Tunisia to Timbuktu, and sometimes consisted of several thousand camels. It is not only maritime trade that has reduced this traffic, but also the ever-increasing risks caused by the climate, which has diminished its importance. The fact is that when Europeans began to explore the Sahara, the number of caravans was already at a minimum. In other words, if the Europeans had not intervened with their technical means, the toponymy of the Central Sahara would also have eventually disappeared. But the existence of this toponymy confirms this recent depopulation, the consequence of a climatic crisis.
A brief chronological reconstruction of the historical deterioration of the Central Sahara
The historical sources demonstrating that the climate in North Africa was different from that of today have already been presented in “When North Africa was not yet entirely desert”.
With the dendrochronological and geographical elements, the zoological and biological elements, and the historical and archaeological evidence mentioned, we can draw up a short chronology of the climate of the Central Sahara:
11th century BC: The central regions of the Western Sahara had a green appearance, typical of a grassland environment. If this is indeed the case, this region received 800 millilitres of rainfall a year.
6th century BC: During Herodotus’ time, some areas of the Central Sahara retained their former character, while others were beginning to deteriorate. Water was perhaps falling at the rate of 600 millilitres a year, which was already unevenly distributed during the summer.
1st century BC: During Strabo’s time, the drought process was much more advanced. An arid facies had already been reached, with perhaps parts of the Central Sahara still sub-arid. Precautions had to be taken when crossing these regions on horseback.
3rd century AD: North African fauna changes rapidly. Most of the central Sahara has a sub-arid facies with rainfall of around 250 millilitres of water per year.
6th to 8th centuries: The xerophilous steppe, the antechamber to the desert, appeared throughout the Central Sahara.
11th century: The sub-arid facies reached the confines of the Mauritanian Atlantic.
The drying out of the Sahara due to its enormous size and the excessive nature of its radiation, the work of correlation laws that unify the most diverse geographical settings, coincided with climatic troubles in the environmental framework of the Iberian Peninsula.
This also makes it possible to understand and correctly interpret the rare and laconic texts that have come down to us. As we shall see, when we analyse the revolutionary crisis that took place in Spain at the beginning of the 18th century, one author tells us that hunger had wiped out half the population, and we are not prepared to regard this proportion as the fruit of the hyperbolic genius of the ancients. We are not prepared to regard this proportion as the result of the hyperbolic genius of the ancients, but we can square it with a more far-reaching phenomenon: the transformation of the landscape had ruined the country’s traditional agriculture.
On the other hand, there is an observation to be made: there was a notable convergence between the development of powerful ideas and the modification of the environmental framework, which was probably not the only one in our history; the accentuation of drought from Asia to Africa during the High Middle Ages was a parallel phenomenon with a divergence in monotheistic ideas that simultaneously manifested itself in these regions. It was the fruit of a long previous evolution, and rapidly reached considerable proportions and dimensions: The fable of Islam, and Arab civilisation.
When fable becomes history, part 1
When fable becomes history, part 2
When fable becomes history, part 3
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