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Desertification and Civilization

Saudi Aramco World November / December 2007

Three reddish-brown giraffe images watch over Nick Brooks as he struggles, hunched over, to shovel sand from the rock shelter’s floor. Some 150 meters (500') above a sweeping, flat and desolate Western Sahara landscape, the burly environmental scientist is hoping these cliffs of Bou Dheir will reveal just when those animals roamed the plains. Three thousand years ago? Four thousand? Five thousand?

Pinning down dates like these is essential to the study of human response to drastic alterations in climate. While many scientists believe climate change was responsible for the decline of such civilizations as the Mayan, a growing number, including Brooks, believes there’s also evidence that earlier global climate shifts actually spurred the beginnings of the world’s first civilizations.

For all of Earth’s history, the only constant about global climate has been its changes. For those climate-change episodes severe enough (and recent enough) to affect human survival, the response, in most cases, must have been to migrate and continue life in a new place, to adapt to new resources - or perish. But one climatic episode in particular, a massive change during the fourth and early third millennium BC, shifted global rainfall patterns in many subtropical and temperate northern-hemisphere regions and caused severe desertification. Only that change - not any of the earlier ones - was immediately followed by the new human social arrangement we call “civilization.” Was that because the affected humans were larger groups that were forced to share limited resources, since they were boxed into refuges with no other place to go?

“If we define civilization as the emergence of large urban centers, labor specialization, bureaucracy, a high degree of social stratification with centralized authority, monumental architecture and writing - all these emerged as the result of increased competition for resources,” Brooks told me earlier. “What happens is increased territoriality, increased social pressures, technological innovations like irrigation, farming and herding, and concentration of political power.” Beginning around 5500 years ago, Brooks says, humans developed civilizations in Egypt, Mesopotamia, the Indus Valley, north-central China and northern coastal Peru. Like most other scientists, he shuns the idea of “climatic determinism,” but Brooks says the term illustrates that climatic and environmental change of the kind usually associated with the collapse of civilizations also appears to have played a significant role in their emergence.

A research fellow at the Tyndall Centre for Climate Change in Norwich, England, Brooks directs the Western Sahara Project, and he is a special consultant on climate change adaptation for the United Nations Development Program. He has spent considerable time on the topic in Libya, including investigating the role climate change played in the 2500-year-old Garamantes civilization of southwestern Libya, a region known as the Fezzan. At the Sahara’s eastern end, other research is showing how desertification contributed to the emergence of the dynastic civilization of the Nile Valley in present-day Egypt and Sudan. So five years ago Brooks undertook study of the Sahara’s western end, long neglected in part because of politics and funding difficulties.

“The area was pretty much unknown,” says Brooks. “Today the western Sahara is much more vegetated than the same latitudes further east. Certainly there is abundant evidence of water in the past, and, as in the rest of the Sahara, there are plenty of petroglyphs of large, humid-climate fauna.” He says the timing and speed of the Sahara desertification varied from place to place by as much as 1500 years, mediated by geography, topography, hydrogeology and the complexity of regional climatic systems. But most of the process, he says, was essentially complete by or soon after 3000 BC.

In the western Sahara, Brooks has found scads of evidence of human habitation - rock art, burial tumuli, enigmatic stone monuments and thousands of stone tools - but, unlike in the eastern Sahara, there are as yet no findings of civilizations here. The plethora of cultural artifacts spurred Brooks to bring along this year archeologist Anne Pirie of the University of Reading. Focusing on the stone artifacts, she has identified small arrow or spear points similar to some found along the southern edge of the west and central Sahara that have been dated to between 6800 and 6500 BC, as well as much earlier Middle Paleolithic Levallois points that generally date to some 150,000 years ago. There’s much more work to be done, but an exceedingly long human occupation is evident.

The noonday sun turns the desert sprawl below us into a shimmer, and the tender breeze at this relaxing spot tempts us to imagine prehistoric hunters whiling away their hours painting scenes on rock walls as they keep watch for prey in grassy savannah below. On the walls, dramatic scenes of hunters armed with spears, aggressively moving in on herds, excite team member Maria Gaugnin, who’s here researching Saharan rock art for her doctoral degree at the University of Edinburgh. Earlier, while researching in the Fezzan, “we found depictions of hippo and water buffalo,” she says—which could mean the climate was a lot wetter when they were painted. If similar animal images are here, and the art can be dated, she figures it would go a long way toward defining the time of the last wet period. “No one has seriously attempted to match the animals with their environments here in the Sahara,” she says.

Geological dating of the end of the last wet period here falls to another team member, Ann Mather, an earth scientist from the University of Plymouth who specializes in geomorphology and sedimentology. She avidly watches Brooks shoveling out the rock shelter, hoping she’ll be able to sample its lowest layer. All the sand buildup that has reduced the shelter to a crawlspace would have occurred after the dry period began, and so, she reasons, if the lowest layers could be dated, it would help pin down when that drifting started - essentially, when the first wisps of sand blew in.

The team members, myself and three volunteers all arrived in the desert a week earlier on a night flight from Algiers to Tindouf, in southwestern Algeria, where we met with our guides and drivers, Osman and Sidi Ahmed. They are Sahrawi: indigenous Bedouins of Western Sahara. They loaded us into two Toyota Land Cruisers and drove us to the white-walled Rabuni camp, where we provisioned for our two-week foray. Rounding out the local team is our Sahrawi archeologist Hussein Mohammed Ali.

The early morning started us bouncing over desert roads and tracks, using the occasional shortcut across hard-packed sand, all to the lively strings of the Sahrawi tidinit playing on the stereo. First stop was the site of Sluguilla, a previously discovered 26-kilometer (16-mi) stretch of rock engravings on flat stones. Animal images range from giraffes to elephants and rhinos. “This is a place where people would have gathered in the past, exchanged stories, renewed old acquaintances, where the young would meet marriage partners, and so on,” says Brooks.

Sluguilla hasn’t been dated. But clearly this entire area has been tramped by human feet for hundreds of millennia. Stone Age artifacts ranging from Acheulian hand axes - these can go back more than half a million years - to more recent tanged points of chert, the color of dark chocolate, lie scattered wherever we walk.

That evening, after a camel stew simmered on an acacia-wood campfire, Brooks relaxes over sweet green tea and tells us about his recent presentation on climate change, the Sahara and the origins of the earliest civilizations at the British Association Festival of Science. “The Independent, Times, Telegraph, Scotsman and Irish Times were all very keen and prepared articles on it,” he says.

That media interest grew because the idea that climate change could have led to the world’s first civilizations has only recently been considered seriously by academics. The Western Sahara Project members aren’t the only ones. Daniel Sandweiss, professor of anthropology and quaternary and climate studies at the University of Maine, has long been studying the cultural effects of climate changes along the northwestern coast of South America. He too shuns use of the term “environmental determinism,” but he says there is a connection.

“Although environmental factors can move people in particular directions or force people to change in some way, you can’t absolutely predict direct causative links between environmental change and particular human outcomes,” Sandweiss tells me in a later interview. “But you can say that in periods of particularly stressful change, people respond in some way. And archeologically we can look at the outcomes and suggest that, in some cases, there is a link.” Maybe behavior wasn’t determined by the climatic event, since there were many different choices how people might deal with environmental change. “But it appears that part of the response to the changes in the climate is what we see in the culture.”

Clearly not all climate change results in the rise of civilizations, he adds. Conditions have to be right. “If mobile hunter-gatherers living in a region where population density is low have a downturn in their particular territory, they could move somewhere else and continue the same lifestyle. Maybe you exploit different plants and animals in the new location, but you’re still a hunter-gatherer or fisher. And you might some day come back to your original area - you can move around.”

And here is where the difference lies. Sandweiss says that if the new landscape fills up with too many people, the population becomes tied to productive systems - such as irrigation agriculture - that require particular locales and infrastructure investments. “It becomes difficult for people to move around any more,” he says. “At some point there are simply too many people in the group, and too much population surrounding them, to allow them to move, and not enough new places to go.”

Sandweiss has found links with past El Niños (southward currents in the equatorial Pacific Ocean that influence weather and ecology) on the northwestern Peruvian coast. “El Niños may well have been as frequent 9000 years ago as now, but you didn’t get civilization then - because you’re talking about low population densities, hunter-gatherers, fishers who are extremely mobile. The landscape wasn’t filled up, so they moved around.” But he’s found that after a shift in the El Niño system about 5800 years ago that reduced natural sustenance at a time of higher population densities, traces of civilization first appeared. “We’re getting many of the things that most people consider part of civilization,” he says. “Monumental construction, some early evidence for irrigation agriculture, apparently a social hierarchy in which a small number of people had more power and better living conditions than the majority of the people, and they were mobilizing labor to build those mounds. So there’s a significant amount going on, arts of various kinds, and textiles. We’re beginning to get specialization of labor. So many of the things that we see in the standard definition of civilization are coalescing at this time.”

It happened elsewhere, too, around the same time - about 5800 years ago. When the rains failed decade after decade in Mesopotamia, small farming villages were devastated. Dense populations in a landscape with minimal carrying capacity forced the intensification of cropping and food storage - and the first appearance of bureaucracies to enforce equal distribution and protection. Temples, city walls and other public works followed. “The villages had coalesced into cities,” writes Brian Fagan, emeritus professor of anthropology at the University of California and one of the world’s leading archeological writers. “By 3100 BC, the southern cities had become the world’s first civilization. Ur became the hallmark of Mesopotamian civilization.” In his recent book The Long Summer: How Climate Changed Civilization, he tells the story of human adaptation to the demands and challenges of ever-changing climate. “Fagan might be more positive than I am about this innovation, casting it as a creative response to crisis,” says Brooks. “I see it more as a last resort, something that people found themselves doing without ever intending to - not that Fagan would argue that people ever planned to become civilized.”

Brooks says in Western Sahara there isn’t yet enough information to develop a narrative equivalent to that of Mesopotamia, but he wants to test the hypothesis that the social changes indicated by the arrival of cattle herding and the building of monuments paralleled, and were in large part a response to, changes in climate, especially desertification. “In particular, we want to know whether these developments postdated those in the rest of the Sahara,” he says. “And if so, whether there is any evidence that western Sahara acted as a refuge for those feeling aridity in parts of the Sahara to the east, where desertification was more advanced.”

After a night under a canopy of a million stars, we break camp and split into two groups - one will look for archeological sites and the other, with Mather, for alluvial fans and other datable geological formations. To most reliably date events like ancient climate change, several indicators are best, to cross-check one against another. Mather’s passion is the alluvial fans, which happen when water flows erode hillsides into flat valleys and the transported sediment forms large, delta-like structures. If these can be dated, they could indicate when the region last experienced regular heavy rainfalls. Before coming here, she pored over satellite photos to pinpoint fans that looked promising.

We bounce over rocks and soft sand with our GPS units at arm’s length out the window, looking for Mather’s fans. She looks at escarpment after escarpment. “Don’t know if these are alluvial,” she says. “They all look colluvial to me.” (Colluvial means they were built up through rockfall.) “We really need a place where there is some catchment area.”

When she finds the right one, it will be a prize. “The newest sediments end up on the bottom of the fan and the oldest near the top,” she says. She wants to date the newest, because that’s the last time great volumes of water flowed here. But she says she needs fans with well-defined layers deep enough to yield a sample that she could date by optically-stimulated luminescence (OSL). OSL is expensive—around a thousand dollars per sample - but it provides a pretty accurate measure of when the soil was last exposed to sunlight.

Alas, things often look different from a satellite. None of the fans proves datable, so Mather turns to Plan B. She says she can also date the end of the last wet period using sediments from a massive, dried-up lake bottom she spotted on her satellite map. Off we bound, crossing the lake’s ancient shoreline, zigging and zagging over the cracked mud surface. We pass two parallel rows of stones, but they are not ancient: They are used for camel racing. At the old lake’s center, Mather declares, “Let’s dig a hole and see what’s under here.” We dig down about half a meter. “I would love to have a [natural] channel here,” says Mather, “so I could see the layers and tell how far we have to go down.” But we find no layers; neither the fans nor the lakes pan out.

In the late afternoon we rejoin the others, who have been exploring rock shelters eroded over thousands of millennia out of sandstone and mudstone seafloors. Many are rich with rock art. Gaugnin has found some indications of climate characteristics: white rhino images. She points to one, explaining, “See here? It has a longer head and a slight hump on the shoulder and a wider mouth.” It’s the wide mouth that’s the clue: It means it’s more of a grazing animal than the black rhino, and grazing means it lived in a wetter climate than the black rhino likes.

We all pitch in, searching more walls for pictographs. Excitement abounds when new images are spotted. “Maria, I have what might be a hippo here,” Brooks calls out. “Not much of its head, but the body....” Gaugnin extricates herself from a tight cave corner and bounds over. “No, the legs are far too long,” she sighs. “It looks more like a gazelle with a fat rump.”

Next to the shelter with the white rhino image, Gaugnin has spotted a collapsed rock shelter with more rock paintings. That gives her an idea: If the approximate date of the collapse could be determined, it would provide at least an end date - a date after which the painting must have been made. Mather concurs. “Let’s take a sample from the broken edge,” she says. “Here, this one follows the bedding plane.” Clink, clink goes the hammer as a fist-sized chunk of sandstone and pyroxene falls loose. “We’ll use cosmogenic dating on this one,” she says, marking today’s date and GPS coordinates on the sample with a felt pen.

Such are the trials and perils of dating western Saharan climate change. It’s not as easy as picking up soil or rock samples and sending them off to the lab and waiting for the answer. It’s fraught with approximations, relative dates, post hoc dates, cross-checks and correlations.

Like the alluvial fans and lake bottoms, the Bou Dheir cave bottom doesn’t yield a good, datable sample either. But on the way back to Rabuni, Mather spots something on the roadside she hadn’t expected: a tufa, or carbonate, outcropping. That usually indicates the remains of a freshwater lake. She motions to driver Sidi Ahmed to stop, bounds out of the Toyota with her geologist’s hammer and pecks away at the chalk-like protrusion. She points to one good sign. “It’s quite filamentous,” she says, “so it’s likely not just formed by groundwater.” She takes a sample for dating, probably by way of the uranium-thorium method - similar in principle to carbon-14 dating.

Samples packed away, we bounce back across the arid result of Earth’s last great climate change. What might happen this time around? The 130-country Intergovernmental Panel on Climate Change - co-winner of the Nobel Peace Prize - has mentioned that future responses to global warming could include the “migration of hundreds of millions of people from equatorial regions.”

Brooks isn’t surprised. Our desert trip done, freshly shaved and sipping a café au lait in a splash of morning sun on the hotel patio in Algiers, he voices his hope that the latest climate change might be the dawn of a new, more responsible model of civilization. Speaking of the old model, he says, “We’ve done our early development period, and our period of adolescent rebellion and irresponsibility. We’re now into post-adolescence.”

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