HUMANPAST.NET

Environment                  20,000 BC
Africa
Southwest Asia
Egypt
Indus Valley
China
Europe
South America
Mesoamerica
North America
Other

In General

 ...the story begins long before, back at the beginning of the last glacial cycle, 120,000 years ago when the Earth's climate and the level of the seas was about the same as today. From that point in time and for the next 100,000 years waters evaporated from the oceans and, transported by the winds, fell as snow on the near Arctic regions, gradually accreting and compressing into sheets of ice that were in some places up to two miles thick. Twenty thousand years ago at the zenith of this accumulation so much water had been withdrawn from the oceans that sea level was four hundred feet lower than today. Massive glaciers covered the entire northern half of North America, all of Scandinavia and northern Europe, and the northern edge of Eurasia. All the high mountains of Europe, Asia, North America, and South America were sheeted with ice down to their lowermost valleys. (131)

What is now clear is that during the last ice age, and the period that followed it, the climate was much more chaotic than it has been in recent millennia. Generally, the climate was much more variable. Sudden changes occurred from time to time. Collapse of parts of the ice sheets, or release of meltwater lakes that built up behind the ice, led to cataclysmic changes. Armadas of icebergs or floods of icy freshwater swept out into the North Atlantic altering the circulation of the ocean at a stroke and with it the climate of the neighbouring continents. With a flick of the climatic switch, Europe and much of North America could be plunged back into icy conditions, having only just emerged from the abyss of the preceding millennia. Conversely, the stability of the glacial conditions could be interrupted by a re-establishment of the flow of warm water to higher latitudes in the North Atlantic, bringing surprising temporary warmth to the northern continents. (145)

...the isotopic temperature records show some 20 interstadials, ...between 15 and 100 kya. Typically the events start with an abrupt warming of Greenland of some 5 to 10°C over a few decades or less. This warming is followed by a gradual cooling over several hundred years, and occasionally much longer. This cooling phase often ends with an abrupt final reduction of temperature back to cold ('stadial') conditions. (145)

The truly notable feature is the additional emphasis given to the prolonged cold period from 70 to 63 kya, to the cold spell at around 36 kya and to the frequency of extreme cold from 30 to 15 kya. (145)

All the available records confirm that the glacial conditions reached their nadir between 25 and 18 kya: the Last Glacial Maximum (LGM). ...it was a period of unrelenting cold, although short-term fluctuations on the decadal timescale remained substantial. The ice sheets reached their greatest extent around 21 kya. At this time, ice sheets up to 3 km thick covered most of North America, as far south as the Great Lakes, all of Scandinavia and extending to the northern half of the British Isles and the Urals. In the southern hemisphere much of Argentina, Chile and New Zealand were under ice, as were the Snowy Mountains of Australia and the Drakensbergs in South Africa. The total amount of ice locked up in these ice sheets has been estimated to be between 84 and 98 million cubic kilometres as compared to the current figure of about 30 million cubic kilometres. This was sufficient to reduce the average global sea level by about 130 metres. The global average temperature at the height of the last ice age was at least 5 °C lower than current values. Over the ice sheets of the northern hemisphere the cooling was around 12 to 14 degrees C. (145)

Changes in the sea level during the last 100 kyr. (145)

In terms of living conditions, the lower sea levels were a significant benefit for modern humans. Around the world they exposed up to 25 million square kilometres of continental shelf. This had a number of important implications for the migration and survival of the human race. It also has profound consequences for our reading of the archaeological record, as much of the evidence of life during the ice age has either been swept away or lies buried below sediment under the sea. (145)

 

Africa

 





Before the disappearance of its water resources the Sahara, already sand belt and waterless desert in Herodotus' time, is believed to have been part of a "veritable garland" of rich vegetation stretching from the Atlantic to the Indus. The earliest phase of its rock art depicts a multitude of animal species that once inhabited this region: Bubalis antiquus (a now-extinct giant buffalo), Barbary sheep, giraffe, cattle, equid, rhinoceros. Known as the Large Wild Fauna phase, these rock carvings are of unknown age; but as one art historian pointed out, there is no reason to exclude the possibility that they are as old as the painted slabs recently recovered in southwest Africa, which at c. 25/23,000 BC are the earliest recorded examples of African art. (115)

African pollen and lake data indicate that the climate during the LGM was some 4 °C colder and drier than present, with the maximum reduction in precipitation occurring in semi-arid regions. (145)

Southwest Asia

 Between about 20,000 and 12,500 BC, glaciers expanded over many areas of American and Eurasia, altering climates around the world. Within this span there were shorter cycles of climate change, periods of several thousand years in which the climates became relatively warmer or cooler, drier or wetter. For most of this period, the sea coasts expanded as ocean levels fell. Forests covered coastal areas around the northern and eastern Mediterranean but many higher areas of southwest Asia were dry steppe or grasslands.(26)

In Israel a detailed lake-level history of the closed Lake Lisan (part of the ancient Dead Sea) indicates that for much of the period from 55 kya to the end of the ice age the level was higher than at present. There were, however, catastrophic droughts associated with the Heinrich events. The impression is that cold-water input to the Mediterranean originating in the collapse of North Atlantic Deep Water formation caused a reduction of evaporation and less precipitation in the Levant. So it is reasonable to conclude that following Heinrich events 6, 5, and 3 much of the Middle East was desert. During these intervals, of which the long cold period from around 67 to 59 kya was the most significant, the region was largely uninhabitable for modern humans. (145)

Across Asia Minor the evidence suggests much less woodland and more steppe and semi-desert steppe than now in the upland areas of Turkey, northern Syria and western Iran. Open woodland or wooded-steppe may have survived over much of western, southern and eastern Turkey. Woodland is thought likely to have been present along the western Levant. ...evidence from the Dead Sea suggests that, at the beginning and end of the LGM, catastrophic droughts in the Eastern Mediterranean coincided with Heinrich events 1 and 2. In this context, it is notable that the settlement at Ohalo II appears to have been abandoned at about the time of the start of event 2. (145)

At low latitudes, perhaps the most important feature of the exposed continental shelf was that it made it easier for people to move about. In particular, in the Persian Gulf, around India, and, most of all, down through southeast Asia and Indonesia the linking of many of the islands (Sundaland) greatly assisted human mobility. (145)

Egypt

 

Indus Valley

 There are a few details that are worth holding on to. The Equilibrium Line Altitude of glaciation in the Himalayas at the LGM was about three-quarters of a kilometre or more lower than it is today. The ice-cap at the LGM was much more extensive than it is today - although there is no agreement over exactly how much more extensive. There have been catastrophic outburst floods from the Karakorams and the Himalayas in the past, floods that reshaped landscapes, floods that carried icebergs full of huge impacted rocks all the way down to the Potwar plateau. Such outbursts continue to occur and even in the much reduced conditions of today's glacial cover they can produce floodwaves 30 metres high capable of smashing whole villages to smithereens and destroying armies. The region is uniquely plagued by the particularly dangerous and rare phenomenon of its main river valleys being dammed by gigantic landslides or by the encroachment of glaciers - a sure recipe for catastrophic outburst flooding. What this would have meant in the Himalayas between 25,500 and 21,500 years ago was 4000 years of deep freeze as the ice tightened its grip on the valleys and the headwaters of the rivers in the mountains. (124)

India seems to have been much drier and more sparsely vegetated at the LGM. In the northwest, there were fairly widespread desert conditions. Salinity in the northern Arabian Sea appears to have been higher than today, indicating decreased input from rivers. This suggests that reduced rainfall and reduced run-off of rivers from the Western Ghats. Southern India was also more arid than at present. With lower sea level, Sri Lanka would have been connected to mainland India and the exposed Palk Strait may have been covered in dry forest or savannah-like vegetation. (145)

At low latitudes, perhaps the most important feature of the exposed continental shelf was that it made it easier for people to move about. In particular, in the Persian Gulf, around India, and, most of all, down through southeast Asia and Indonesia the linking of many of the islands (Sundaland) greatly assisted human mobility. (145)

China

 Farther east, the general situation across Siberia was that the climatic zones were pushed to the south. The absence of a polar ice sheet east of the Urals meant that in some respects the consequences of the LGM were less exaggerated here. The evidence suggests that winter temperatures across southern Siberia were about 12°C lower than now being comparable with those in northeastern Siberia at present. Summer temperatures are reckoned as being about 6°C lower throughout Siberia and the central Asian desert region. (145)

Considerable stretches of low-lying land were uncovered around the shores of China, and the Malaysian Peninsula became linked to the islands of Borneo, Java and Sumatra, and to the Philippines. The islands of Japan were linked together into a peninsula owing to the lower sea level, but probably remained separated from the Asian mainland by the Korean channel. The Sea of Japan was almost entirely enclosed as a lake, its only outlet being the Korean channel. So there was the scope for people to move around these regions, but more important, where they lived close to the sea, all evidence of their activities has been lost. (145)

Northern China was much colder and more arid conditions prevailed than at present. The summer monsoon limit was shifted some 700 km to the southeast. The widespread distribution of loess indicates more extensive central Asian desert conditions with low biological activity and a sparse herbaceous vegetation cover. Fossil evidence suggests that the mammoth disappeared during the LGM, whereas they were abundant before and after this period. The upper limits of trees in mountainous areas in both northern and southern China were some 1700m lower than at present. (145)

Farther south in east China and Taiwan, which was connected to the Chinese mainland during the LGM, dry steppe vegetation, with some pine trees in a wooded steppe, covered much of the lowlands. On what are now the highest rainfall areas in the uplands of Taiwan, pollen evidence indicates some forest vegetation persisted. Scattered areas of wooded vegetation covered about a third of the region. In southernmost China the climate was much closer to current conditions, and hence well suited to human habitation. Nevertheless, the subtropical rainforest was replaced by mixed conifer and evergreen broad-leaved forest. Grasslands predominated in lowland areas, with cool temperate forest and open woodlands in upland areas. In the mountainous areas of Northern Yunnan Province of southwest China, there are indications of snowline lowering, indicating a 4-5C depression in temperature and slightly moister conditions than now. In the present subtropical rainforest zone in the uplands of Yunnan Province the climate was nearly as warm as at present, but with much higher precipitation in winter. (145)

Europe

Between about 30,000 and 10,000 years ago, European climates began a long cooling trend with some periods of extreme cold, but for most of the period the summers were cool and the winters relatively mild. The rich European grasslands and mixed forest habitats supported great numbers of herbivores, including reindeer, deer, bison, wild ox, ibex, woolly rhinoceros, and mammoths. France seems to have been densely occupied during this period, particularly near the confluence of the Dordogne and Vezere rivers. This lovely part of the world is a well-watered, heavily forested limestone formation, honeycombed with caves and rock shelters, which offered excellent places to live.(24)

One of the most amply documented Upper Paleolithic cultures in eastern Europe is the Kostenski-Bershevo culture centered in the Don River Valley, about 470 kilometers southeast of Moscow. About 25,000 to 11,000 years ago, the Kostenski-Bershevo area was an open grassland environment, with no rock shelters, caves, or other natural habitations, and with very little wood available for fires. People here left a variety of archeological sites, including base camps, where pit houses were constructed  by digging a pit a meter or so deep, ringing the excavation with mammoth bones or tusks, and then draping hides over these supports. Some excavated pit houses were relatively large, with many hearths, suggesting that several families may have passed the winter together. The people of Kostenski subsisted primarily thrrough big-game hunting, mainly of mammoths or horses, with an occasional wild cow or reindeer. Numerous wolf and fox bones at these sites probably reflect the hunting of these anilmals for their fur for clothing. Like their Upper Paleolithic counterparts elsewhere, the Kostenski people manufactured a variety of decorative items, including "Venus" figurines (representations of women, usually with exaggerated secondary sexual characteristics).(24)

Twenty thousand years ago the great glacial meltdown began. Torrents of frigid waters raced to the sea, which slowly began to rise. Gradually the huge icy burden was removed from the land. In northern Russia rivers choked with meltwater flowed southward across the steppes and eventually spilled into the Black Sea's Ice Age lake. The icewater filled this lake to a level where it entered the Sakarya River, formed an estuary and advanced into the interior of Anatolia. Fifty miles in from the coast, this narrow and winding arm of the expanding lake found an outlet to the Sea of Marmara, having intercepted a cleft in the bedrock wrenched open through the grinding action of the North Anatolian fault... Exploiting the crushed and permeable rock in this crack, the meltwater passed through to the Mediterranean Sea. In the process, the Ice Age lake freshened and became potable for humans and animals. (131)

The true LGM falls in between the Heinrich events 2 and 1 at around 23 kya and 16.5 kya. Its impact was particularly severe on northwestern Europe. The massive extent of the Fennoscandian ice sheet reduced much of the region north of the Alps and the Pyrenees to a polar desert. Permafrost extended down to southern France, just north of Bordeaux, and into the uplands of northern Provence. The areas just to the south of the main ice sheets had little or no vegetation. Dune activity during the LGM seems to have been quite widespread in England, northern France and the Low Countries, and eastwards across Germany and Poland. In effect, for humans these areas were uninhabitable. Only in the Dordogne region of southwest France and the foothills of the Pyrenees, where modern humans had lived for many millennia before the LGM, is there widespread evidence of their having stuck it out during the LGM. Even in the Mediterranean region, there appears to have been little thick woody vegetation. Here the predominant picture was of an arid semi-desert. The occasional small pockets of open woodland where local soil moisture levels permitted would have broken this desolate landscape. The refugia for deciduous and needle-leaved species were mainly on the western side of the mountains of Greece. (145)

In central and eastern Europe it might be assumed that the conditions were even less hospitable for humans, but not so. The landscape was desolate with a few cold-tolerant trees (pine, birch and spruce, for example) in isolated pockets. Further east, in the Russian steppes, woodland seems to have survived along river valleys. Elsewhere, it was predominantly open steppe or steppe-tundra. In many places, where there was inadequate vegetation, windblown dust formed dunes. Precipitation, now around 600 mm, may have been only about 60-120mm per year. In spite of all this, humans do seem to have been present in some places for much of the LGM. A number of well-dated encampment sites have been found along the valleys of both the Danube and the Don. Furthermore, some refuge areas of woodland may have existed immediately to the southwest of the Carpathians. (145)

Along the eastern shores of the Black Sea and the high ranges of the Caucuses, pollen evidence indicates that there were scattered pine and birch forests but broad-leaved trees were probably localised in distribution. Only small areas of dense temperate forest appear to have survived in the lowlands of the southern Caucasus. These are thought to have been a glacial refuge for many temperate trees, although there is little direct evidence of these trees surviving there during the LGM. The Black Sea was shallower and smaller than today, while the Caspian Sea was somewhat deeper and more extensive. There may have been a thin band of deciduous forest along the southern shores of both these seas. (145)

Farther east, the general situation across Siberia was that the climatic zones were pushed to the south. The absence of a polar ice sheet east of the Urals meant that in some respects the consequences of the LGM were less exaggerated here. The evidence suggests that winter temperatures across southern Siberia were about 12C lower than now being comparable with those in northeastern Siberia at present. Summer temperatures are reckoned as being about 6C lower throughout Siberia and the central Asian desert region. (145)

The other feature was that to the south, it seems, there was not a large ice sheet over the Himalayan Plateau, but rather a scattering of glaciers and small ice caps. Permafrost desert conditions appear to have existed in the unglaciated parts of the mountains. A consequence of this lack of ice cover and the general aridity is that it may have made parts of southern Siberia to the east of Lake Baikal more congenial than might have been expected. For instance, to the west of Lake Baikal at Mal'ta around 23 kya the vegetation was steppe merging into tundra with lakes, small streams and rivers that were crisscrossed by reindeer migratory routes and rich with waterfowl. The relatively less extreme climate is probably the reason why this part of the world seems to have remained habitable throughout the LGM. (145)

In Greenland the difference between the coldest parts of the last ice age and current conditions was some 20C. Effectively the interdecadal variance and its impact were some tenfold greater. These wild swings must have been immeasurably more demanding than our present climate. They would have required an extraordinarily adaptable, flexible and migratory lifestyle to adjust to changing environmental conditions. At the simplest level, it is probably true to say that even now such a climate would make any form of agriculture, as we currently know it, virtually impossible...(145)

 

South America

 Ironically, the site with perhaps the best claim to a pre-12,000 BP date date in the Americas is among the farthest south, Monte Verde, in south central Chile. Here Tom Dillehay and his crew have excavated a camp site that has been radiocarbon-dated to about 13,000 years ago, and below the levels of that age are layers of tools and debris that may be much older, perhaps up to 33,000 years old.(26)

The Monte Verde dates have recieved some support in the form of radiocarbon dates of hearths from sites near Pedra Furada, in eastern Brazil, where numerous stone tools and animal bones were found with charcoal in stratified layers that yielded a consistent series of twelve dates from about 32,000 to 17,000 years ago.(26)

We have two areas lying at similar distances from their respective poles. In one, the northern, we have many evidences of heavy glaciation, extending over a period of perhaps 40,000 years, but ending about 14,000 years ago, to give way to the present climate about 10,000 years ago. In Chile and Argentina, on the other hand, in the same relative latitude just as close, presumably, to a pole, we have no glaciation until after the climate has become normal for the present temperate zone in the north. It appears that in Argentina a cool period set in just as the hipsithermal phase with higher temperatures set in all over the northern hemisphere! Clearly, then, there was no similarity in climatic trends, but rather the opposite. (132)

Mesoamerica

 

North America

 Today, Eskimos using skin boats easily cross the ninety kilometers of open sea separating Siberia and America, and recently an American woman slathered herself with grease and actually swam from Alaska to Siberia. But such a sea crossing would not have been necessary during much of the Pleistocene. During periods of glacial advance within the last million years, enourmous quantities of water were converted to ice, lowering the sea level sufficiently to expose a 1500- to 3000-kilometer-wide expanse of the floor of the Bering Sea. This land bridge--usually referred to as Beringia--was probably available at least four times in the last 60,000 years.(25)

Prior to 10,000 years ago, species of deer, bison,camels, bears, foxes, mammoths, moose, caribou,and even rodents crossed from Siberia into the New World. Going in the other way--from America to Asia--were foxes, woodchucks, and, during the early Pliestocene, the ancestors of modern forms of horses, wolves, and other animals.(25)

Interior Alaska and Canada were relatively rich environments in the mid-Wisconsin interglacial, and at times humans may have had a narrow but clear ice-free run all the way to South America during this period. Pollen cores from easternmost Beringia suggest that from 30,000 to 14,000 years ago, the time when most archeologists think the first Americans arrived, the "landscape of Beringia consisted of relatively bare polar desert or fell-field tundra, a rocky terrain sparsely vegetated by herbs and dwarf shrubs. This suggests that the late Wisconsin environment in this part of Beringia was as harsh as the modern high Arctic.(25)

Several lines of solid evidence suggest that during the last ice age the North Pole was located in or near Hudson Bay. ...the best guess for the site of the pole seems to be approximately 60 degrees North Latitude and 83 degrees West Longitude. The first line of evidence that the last North American ice cap was a polar ice cap is based on the shape, size, and peculiar geographical location of the ice sheet. (132)

Thus we are able to say that warm conditions in the Arctic Archipelago of Canada persisted for the entire duration of the Wisconsin glaciation, from 40,000 years ago down to the establishment of modern conditions. Yes, if the pole were in Hudson Bay, the Arctic should be warm. And the Arctic was warm. However, there is much more evidence. ...the Arctic Ocean was warm during most of the ice age, particularly from about 32,000 to about 18,000 years ago.
Temperate conditions had evidently prevailed in Antarctica in the not distant past. The sediment indicated that no fewer than three times during the Pleistocene Epoch a temperate climate had prevailed in the Ross Sea.(132)

We have two areas lying at similar distances from their respective poles. In one, the northern, we have many evidences of heavy glaciation, extending over a period of perhaps 40,000 years, but ending about 14,000 years ago, to give way to the present climate about 10,000 years ago. In Chile and Argentina, on the other hand, in the same relative latitude just as close, presumably, to a pole, we have no glaciation until after the climate has become normal for the present temperate zone in the north. It appears that in Argentina a cool period set in just as the hipsithermal phase with higher temperatures set in all over the northern hemisphere! Clearly, then, there was no similarity in climatic trends, but rather the opposite. (132)

Even more interesting is the question of whether Beringia effectively represented a refuge during the LGM. Analysis of beetle assemblages provides interesting insights into the climate during the ice age. At times temperatures in the region were relatively high. The Stage Three evidence suggested that at times northeast Siberia and Alaska were surprisingly mild. During the interstadials of Stage Three the region had temperatures that appear to have been comparable with modern times. Even as late as 30 to 25 kya parts of northeastern Siberia experienced summertime temperatures close to modern values. This relative warmth appears to have continued into the LGM. At the time, unlike the North Atlantic, the northern Pacific and the Gulf of Alaska were largely free of sea ice. This would have led to maritime cloud cover spreading over the extensive plains between what is now Chukotka and Alaska. The climate would have been colder than now in summer but relatively mild in winter. Combined with the extensive megafauna of the region, this may have made parts of the region habitable during the LGM. (145)

Other

 Considerable stretches of low-lying land were uncovered around the shores of China, and the Malaysian Peninsula became linked to the islands of Borneo, Java and Sumatra, and to the Philippines. The islands of Japan were linked together into a peninsula owing to the lower sea level, but probably remained separated from the Asian mainland by the Korean channel. The Sea of Japan was almost entirely enclosed as a lake, its only outlet being the Korean channel. So there was the scope for people to move around these regions, but more important, where they lived close to the sea, all evidence of their activities has been lost. (145)

In Japan, where lower sea level provided land links between the four major islands and the Asian mainland, there is evidence of modern human occupation from around 30 kya. Here, there was a southwards shift of the vegetation zones. Permanent ice seems to have covered the uplands of what is now Hokkaido, with a belt of tundra and open boreal woodland in the lowlands. Farther south the lowland grassland with scattered stands of alder, ash and willow. Forests of a rather open character with oak and pine seem to have been widespread in the mid-altitude uplands. Open woodland, consisting mainly of pine and birch, covered much of Japan's uplands, from about the middle of the main island to the south of the linked chain of islands. Here, trees that prefer warmer temperate conditions, such as the cryptomeria, persisted only locally in the lowlands of southern Japan. Mean annual temperature here seems to have been about 7-9C lower and precipitation was probably less than a third of present values. (145)

There is little information from Indo-China and Malaysia. There are indications of pine forest occurring in the present rainforest areas of Thailand and Malaysia. In Sumatra and west Java the climate appears to have been drier. There also seems to have been a lowering of the mean annual temperature by about 4-7C. In the highlands of these islands and New Guinea, where modern humans have lived since 40 kya, it was 2-3C cooler, but not drier. In what is at present an extremely wet rainforest climate (3200-5000 mm annual rainfall) in lowland western Borneo (Kalimantan), there is evidence of savannah development. In the present rainforest region of Sarawak and Sabah (northern Borneo), the rainforest persisted through the LGM. Other evidence suggests that there would have been an arid climate and sparser vegetation over most of the exposed the exposed continental shelf between the islands of Indonesia that is often termed 'Sundaland'. (145)