The Sahara Desert Hasn’t Always Been a Dry, Desolate Landscape. Some Scientists See Signs It May Be Greening Again

An hour before dawn, in a nameless rock pile in the world’s largest hot desert, Djimet Guemona clambered up a narrow gully. The route was hemmed by high walls, where uncountable centuries of weathering had cinched the sandstone into a rumpled, reptilian skin. From its base, the outcropping had looked like any one of the numerous rock formations, or hoodoos, in the northwest corner of the Ennedi Natural and Cultural Reserve, in eastern Chad. 

But this one, Guemona assured me, contained a special treasure. Though the formation’s interior was labyrinthine, the archaeologist moved swiftly, ignoring the GPS coordinates stored on his phone. He had the location committed to memory.

Rounding a scarp, Guemona stopped in front of a rare expanse of vertical plane where the rock ran smooth. Under torchlight, I could see that hundreds of figures had been carved into its surface. There were ostriches with lollipop heads beside stick-legged giraffes, their necks comically exaggerated. Human forms stood among this crowded bestiary, and beneath them all, in palimpsest, were larger etchings of elephants, older and more deeply inscribed. 

“When I found it, I yelled with excitement,” Guemona told me, casting his headlamp left and right so that the shapes appeared to dance across the rock face. These were prehistoric etchings that hadn’t been mentioned in any of the colonial literature he’d studied. Nor had Guemona received any rumor of their existence from the herders whom he often canvassed for information. Whoever carved them inhabited a deeper past, perhaps 10,000 years ago, when the creatures they depict­ed could still be found throughout North Africa. These images were ghosts from a time when the Sahara was green.

Soon afterward, back at our makeshift camp, I lay on a reed mat in the wide-open. The night sky was giving way to sunrise. After the previous evening’s wind, the land felt deathly still. If you’ve ever spent a night in the Sahara, it is tempting to presume that it has always been this way—dry, desolate, nearly empty of life. The intensity of the silence conjures an impression of stasis that is hard to reconcile with the Sahara’s surprisingly erratic geological history.

The Ennedi reserve, close to the Sudanese border, is the Sahara at its most spectacular. One thousand miles from the nearest coast, it encompasses 19,300 square miles of a vast sandstone plateau, its periphery incised by gorges and ornamented with elaborate rock-forests. From space, it appears as an inverted triangle of textured ochre against the mellow gold of the Saharan sands. There are wastes here, as there are in any stretch of desert: barren tracts of gravel plain flailed by harmattan winds that hit the skin like a hairdryer blowing on full. Animal skeletons lie where they fell, half-covered in sand. Yet Ennedi is also a place of eye-­rubbing beauty and miraculous vitality. Perhaps more than anywhere else in the Sahara, its rare ecology makes it the ideal place to observe the desert’s dynamism in the raw. 

You would have to go back half a billion years to chart the birth of these surreal rock formations, when Ennedi’s central massif emerged from an ancient sea as a mantle of sandstone. It took another 300 million years for Africa to unhitch itself from the Gondwana supercontinent, tens of millions more until the land that would come to be known as Chad crossed the Equator, borne along on Africa’s gradual northward migration.

According to the earth scientist Martin Williams, the author of When the Sahara Was Green, it was toward the end of this long continental journey that the Sahara came into being. Williams traces the desert’s birth to around seven million years ago, when the progressive shrinkage of the Tethys Sea, the primordial ocean that threaded a wide channel between Africa and Eurasia, upended regional hydrological cycles. It was at this point that northern Africa began to desiccate at scale.

In subsequent eons, this arid state didn’t hold. In the mid-19th century, when much of the African interior remained a mystery to the wider world, the German explorer Heinrich Barth returned from a five-year journey from Tripoli to Timbuktu with tales and sketches of prodigious rock-art galleries including depictions of animals that could now only be found 1,000 miles farther south. Similar images would later be identified across northern Africa, from the Atlas Mountains to the Nubian plains. 

It would take many decades, and various empirical advances, before scientists were able to ascertain two critical findings about the region’s environmental story: First, that the Sahara has fluctuated between wet and dry states during the planet’s current geological era, known as the Quaternary, which began about 2.5 million years ago. Second, that this process is cyclical, repeating over long spans of geological time. At intervals dictated by thermodynamic forces far beyond human control, changing atmospheric conditions have dragged the West African rain belt northward, bringing water—­and life—to the desert. Paleoclimatologists have dubbed this phenomenon, when it occurs, a North African Humid Period, or NAHP. It is more commonly known as the “greening of the Sahara.”

Saharan petroglyphs memorialize the latest of these episodes, the Holocene NAHP, believed to have lasted from 5,500 to 11,000 years ago. We know from lake-ring residues that Lake Chad, on the Chad-Cameroon border, was previously larger than the Caspian Sea, 23 times its current maximum expanse. Studies of images from the Landsat satellite program have identified the shadows of the so-called Sahabi Rivers, which once flowed from “Mega-Chad” all the way to the Mediterranean. Large herbivores thrived in riparian forest. Big cats stalked expansive rangelands.

It was not to last. Around 6,000 years ago, the summer rains sputtered. Once-perennial wetlands turned seasonal, then dried up altogether. Vegetation withered, its life-giving carbon carried off on the trade winds—an age of plenty supplanted by an age of dust. As the ecosystem collapsed, the megafauna, including lions, giraffes, elephants and all manner of ungulates, died off or gravitated south, and the humans who once inscribed their likenesses onto rock shelters withdrew into oases and high refugia, like Chad’s own Tibesti Mountains, or they congregated around the unfaltering waters of the Nile Valley. 

Guemona’s tableau bore testament to one of the most dramatic climate shifts since the last ice age. It is a phenomenon that is believed to have shaped the dispersal of humans out of Africa. Now, according to some researchers, climate change may be causing the Sahara to green again—millennia ahead of schedule, with consequences for ecosystems and human society that are difficult to forecast or comprehend.

My weeklong journey into Ennedi with Guemona,  then the reserve’s chief archaeologist, began in July 2024 in the oasis town of Fada, on the reserve’s western rim. A low-slung compound on the town’s outskirts served as the regional headquarters for African Parks, a South Africa-based conservation nonprofit that has managed the region on behalf of the Chadian government since 2018. We embarked early one morning, setting off in a convoy of three Land Cruisers, two containing expedition members and support crew, the flatbeds stacked high with tents and provisions. A platoon of park rangers trained in first aid, navigation, communication and security brought up the rear

The days were ferociously hot. Chad had endured another drought-stricken year. On the two-day drive northeast from the capital, N’Djamena, sullen livestock herds at the roadside were sacks of bones. After five consecutive years of severe food shortages, the United Nations World Food Program was launching emergency aid operations to stave off the risk of famine in Chad’s hinterlands. But now, near the peak of the boreal summer, annual rains were returning to the southern Sahara. At nightfall, lightning strobed beyond the horizons; by morning, temporary wetlands appeared in topographical depressions. 

Our introduction to Ennedi’s unique geography was the Guelta d’Archei, 25 miles southeast of Fada. Parking at its mouth, we walked into a canyon bound by 300-foot walls. The rock was pocked with deep caves that reeked of bat guano. Standing water pooled along its base. 

Ennedi occupies an unusual ecological niche, midway between sterility and abundance, because of its groundwater. The region sits atop the Nubian Sandstone Aquifer, the largest subterranean water system in the world, which extends from northeast Chad across some 800,000 square miles in Libya, Egypt and Sudan. The Lakes of Ounianga, a constellation of water bodies 100 miles northwest of the Ennedi Plateau, is one of the few places where this colossal repository reaches the surface. Ennedi’s gueltas, small reservoirs concealed within its rock formations, are another.

When we visited Archei, the canyon was deserted aside from a heavyset man and a pair of teenage boys bathing in the murky water. The dromedaries that congregate here during the dry periods between October and June were nowhere to be seen, dispersed, now, by the renewed availability of water elsewhere. But the guelta’s plenitude was still evident in the abundance of scat and footprints covering the sandbanks. Guemona pointed to the clawed prints of the Nile crocodiles that were lurking somewhere unseen.

As we headed east, toward the plateau’s remotest reaches, the desert felt protean. Acacias grew with vigorous, splayed canopies. Chevrons of migrating birds passed overhead, and gazelles scampered over distant ridgelines, kicking up trails of dust. Swifts gorged on insects, and fat toads chorused around ephemeral ponds. In one wadi, we found the tendrils of a newborn river clawing northward, turbid with alluvium, pursued by watering camel herds. In places, across acres of what just one week before was nothing but sand, new grass shoots were germinating by the million.

To Guemona, Ennedi is foremost a museum. We stopped often, usually at the archaeologist’s bidding, and he would lead us into the outcroppings to seek out the rock art he had been documenting for the last three years. He and his genial deputy, Mahamat Ahmat Oumar, often spent whole weeks exploring remote mesas, scouring niches and overhangs for Neolithic artworks, and recording their discoveries on a proprietary database. During our time in the reserve, we lived as they did on these regular forays, sleeping in the open, then waking before sunrise, brushing off the night-blown sand to go again. 

Guemona and Oumar’s list of archaeological sites is already expansive: 1,921 and counting. Deep among these rock-forests, they and their team have uncovered nomadic rock shelters, sprawling necropolises and ancient metallurgical workshops of indeterminate age. But around 60 percent of the finds are petroglyphs, archaic representations of the herding culture that remains the predominant lifestyle throughout the southern Sahara and the Sahel.

The tableau we saw on that first dawn, which Guemona had discovered in June 2022, was of a special order. But there were thousands more scattered across the reserve: paintings of pastoral scenes, horned warriors with shields and spears, etchings of rotund female figures decorated with chevron markings, cryptic geometric patterns. One hoodoo near the outpost of Mourdi had the feel of an art gallery in which every rock exposure was an antique canvas. Among the artworks were several cattle etchings close to full size, and these showed the cows decorated with stippled and dappled motifs, painstakingly engraved with a beveled stone. 

Guemona believes that the sheer diversity of the depictions, which spanned the social transitions from hunting and ­gathering to pastoralism to nomadism, suggest an unbroken chain of human habitation dating back at least nine millennia. “In Chad, this heritage remains virtually unknown,” he told me. “Before we started this work, it was rare to read anything about Ennedi outside specialist scientific journals.” Several times a year, Guemona led field trips for local children, where he would impart the natural and cultural significance of the land they call home. 

After two days, we came across a group of elders gathered in an acacia’s shade. A few younger men in desert fatigues, members of an African Parks community outreach program, were holding forth in front of a flip chart. Since the organization took over the management of Ennedi, its personnel, most of them Chadian nationals, had begun to roll out the conservation strategy that it employs throughout Africa, where it stewards some of the continent’s most precious and embattled biospheres.

The aim is not just to protect but also to restore. Part of this effort has involved reintroducing wild animals that had diminished or disappeared in the face of human encroachment. Several addaxes, critically endangered Saharan antelopes with long, corkscrew horns, had recently been flown in from Abu Dhabi. Outside Fada, a team of biologists was running a breeding program for red-necked ostriches. In Ennedi, as in any living reserve, success depends on the cooperation of the resident population. Today’s conclave was arranged to discuss ways of minimizing contact and grazing competition between domesticated animals and endemic wildlife.

After the meeting, as the crowd dispersed, Idriss Maina Louki, lank and high-cheekboned, in a sky-blue kaptani ensemble and white khadamul turban, lingered behind to talk. Louki, 67, knew about the Sahara’s greener past. According to his folk chronology, the elephants and giraffes memorialized in nearby glyphs existed in the time “before my great-great-grandparents.” But Louki still fondly recalled relic species from his childhood, when he would occasionally glimpse antelopes and cheetahs on his family’s ancestral lands. All that changed with the onset of a multi­year drought in the 1970s, when many of the region’s larger animals died off or were poached for bushmeat. The huge dead trees scattered hereabouts, their trunks splintered and bleached ivory, were the detritus of years of faltering rains. Even as the Saharan climate follows long-term trends, its seasonal rains continue to fluctuate on a more human time frame. In Ennedi, climate catastrophe is not only a living memory but also an ever-present menace. 

The efforts to reintroduce some of Ennedi’s lost phantoms symbolize a welcome sense of regeneration, however fragile, Louki told me. “Most of the younger people only knew these animals from family stories,” he said. His grandchildren were excited to see them return. 

As we continued into the reserve’s western quadrant, the rock formations began to rise in number and scale. Crags that appeared from a distance to be solid monoliths disintegrated on approach, resolving into spires, fungal sculptures, voluminous grottoes—most of them unremarked upon and unnamed. Soon, Ennedi’s rock art receded behind the sheer spectacle of the geography, all of it a testament to what Martin Williams characterized as a “constant tug-of-war between flowing water and windblown sand.”

For scientists seeking to establish the contours of that geological tangle, challenges abound. Political volatility has long hindered access for land-based scientific studies. Even today, Chad’s neighbors Niger, Libya and Sudan are each in the grips of civil unrest or violent insurgency. Another part of the problem is morphological. Sandstone is the compressed state of a substance that is otherwise granular and fluid. Even as it solidifies into stone, sand is less likely than other sedimentary rocks such as shale and limestone to preserve the fossils and geological layers that help reveal when past humid periods have occurred. 

In search of a coherent timeline, geologists have had to look farther afield—to archives of dust and vegetation that have blown off the Saharan landmass and accumulated in terrestrial water bodies and on the ocean floor. In the past few decades, a slew of such evidence has indicated that the most recent NAHP, ending roughly 5,500 years ago, was merely the latest in a long-term cycle. One widely cited study that analyzed more than 1,200 sediment samples taken from lakes, wetlands and rivers across North Africa proposed that there have been 230 humid periods over the last eight million years. 

The timing and amplitude of these recurrences is determined by a variety of factors, including ocean current circulation and the onset of polar ice ages. But most researchers agree that the prime driver is orbital precession, one of three cycles that govern the Earth’s rotational orientation as it passes around the sun. Edward Armstrong, a climate scientist at Finland’s University of Helsinki, suggested to me that precession can be visualized as the motion of a spinning top—not its rotation or migration across a surface but the slight axis-­wobble at its apex. Armstrong is part of an international team of researchers engaged in a long-term collaboration between the universities of Helsinki and Bristol, in England, to identify past NAHPs and their influence on human evolution and dispersal. 

Central to the study has been a climate model tuned, or “paleo conditioned,” to reflect various atmospheric parameters over the last 800,000 years, including the Earth’s orbital positioning, its polar ice sheet coverage and the corresponding historic carbon dioxide levels. The resulting simulation, the first to dynamically model the greening cycle, suggests that the phenomenon is triggered by small changes in seasonal solar radiation. This thermal uptick is then reinforced by feedback loops, as burgeoning vegetation suppresses the amount of sunlight reflected back from the Earth’s surface and accelerating rates of evaporation and transpiration increase atmospheric moisture. “It all begins with a slight orbital perturbation and a slight intensification of the monsoon, which then amplifies and amplifies and amplifies,” Armstrong told me.

The next stage of the Bristol-Helsinki study is to illuminate what role humid periods may have played in creating verdant corridors to facilitate the migration of early humans throughout North Africa and beyond. “The Sahara is a gate,” said Miikka Tallavaara, a scholar of hominin environments at the University of Helsinki who leads the multidisciplinary project. “We can be certain that NAHPs were crucial for out-of-Africa range expansions, and the exchange of genes and ideas. But the precise dynamics remain something of a mystery.”

On our penultimate evening in the reserve, we camped by a lone acacia miles from any sign of human habitation. Behind the camp was a dune, and after dinner I walked up to the crest. On the far side, a dust bowl stretched to the horizon. I tried to imagine the scene during the deep greening of the Eemian humid phase, more than 100,000 years ago, with the insects rising in clouds and the birdlife swollen by several degrees of magnitude. In the valley, antelope and other ungulates gathering to drink at year-round waterholes and great elephant herds crashing through stands of broadleaf woodland. And beside me on this ridge, swathed in waist-high grasses, a band of hunter-­gatherers pausing to survey a totally different biome.

Present-day descriptions of Ennedi as a Garden of Eden may be more apt than we know. In 2001, a partial skull was unearthed in the Djurab Desert, 300 miles west of here. The discovery of Sahelanthropus tchadensis, nicknamed “Toumaï” and believed by some to be the oldest known hominin, led to speculation that our distant ancestors have inhabited this region for seven million years. In the face of ongoing academic rancor and dispute, its discoverers have claimed that the Sahara, and not East Africa’s Rift Valley, could be the true cradle of humankind.

Fifty miles south of Fada, under midday sun, Guemona knelt down to pick up a glossy black object from the sand. It was a charred mass of iron, its lumpen residue mixed in with shards of charcoal that had been used to smelt it—evidence, Guemona explained, of a metallurgical site that was perhaps 400 years old. He paused to enter the GPS coordinates in the database on his phone. It went down as the 46th site in the immediate environs. 

To some extent, Guemona and Oumar’s campaign to catalog Ennedi’s archaeological treasures is a race against time. Occasionally, they sought to show me petroglyphs only to find that, in the months since they had recorded their location, they had disappeared. Perhaps the patinas had collapsed, or perhaps the paint had faded to such an extent as to be undetectable. Guemona couldn’t be sure. Soon after our trip, he hosted a visit from Frédérique Duquesnoy, a French expert in Saharan rock art, who made 3D digital renderings of some of Ennedi’s most notable petroglyphs for posterity.

Still, there was so much left to do. Guemona reckoned that he had reconnoitered around 30 percent of the reserve, but hundreds of square miles remained to survey. Last year, he left African Parks to take a job with Chad’s National Research and Development Center, passing the mantle to Oumar, his protégé. Oumar’s mission is to push further, probing unexplored regions and excavating at sites already known to have “exceptional value.” Oumar told me, “I am convinced that the reserve still holds many secrets that could enrich, and even transform, our understanding of ancient societies in this desert environment.”

The irony, of course, is that Ennedi’s record of the last humid period will endure only until the advent of the next, when it will be vulnerable to the turbulence of a resurgent monsoon. The petroglyphs are at once a flashback and a premonition, for the desert’s current state is only provisional. The ratchet controlling the Sahara’s weather systems is no longer just astronomical but also human.

Already, in fact, Stefan Kröpelin, a renowned geoarchaeologist at the University of Cologne in Germany, has concluded from testimonies of local herders and from his own observations that present warming is strengthening the West African monsoon—and that Ennedi’s relative abundance may be replicated across the Saharan dead zones within a matter of centuries, not millennia. Fluctuating rainfall rates across north and central Africa make forecasting long-term trends difficult. Still, Kröpelin says, regions that were until recently completely lifeless, where “you could not find a single scorpion,” are now showing signs of reanimation. 

Kröpelin has become synonymous with efforts to decode the desert’s climate history. He has spent decades working in some of the Sahara’s most inhospitable environments, and he was instrumental in securing UNESCO World Heritage Site status for both the Lakes of Ounianga and Ennedi, which he describes as “a wonder world.” One of his celebrated studies involved extracting a unique sedimentary core from Lake Yoan, the deepest of the Lakes of Ounianga, where a “chemocline”—a chemical boundary separating fresh water from the anaerobic depths—had allowed organic material to accumulate undisturbed on the lake floor over centuries, providing a pristine record of the Holocene humid period. 

Kröpelin, 74, has officially retired, but he continues to study the desert that has been his life’s obsession. His recent hypothesis that the Sahara’s next greening—a new NAHP—is underway is not uncontroversial, but he insists the signs are there. “Plants don’t care whether there’s more rainfall due to orbital forcing or man-made warming,” Kröpelin told me. If current warming trends continue, increased rainfall will eventually recharge subterranean reservoirs throughout the Sahara, he said. “Once the roots reach the groundwater table, there will be a regreening.” 

Other observers are more skeptical. Francesco S.R. Pausata, a climatologist at the University of Quebec in Montreal, describes Kröpelin’s notion as “a bit of a stretch,” asserting that the claim isn’t supported by the available data. “Projected changes in solar radiation over the coming centuries are far too small to reproduce the strong orbital forcing that triggered the green Sahara in the past,” Pausata told me. The one thing that all “green Sahara” experts share, however, is an intuition that there remain many unknowns, and that here, as everywhere else, weather patterns are bound to become more volatile in the coming decades. Tempting though it may be to conjure visions of a wetter, more habitable future for northern Africa—with more arable land and the return of long-exiled wildlife and the reconstitution of diverse, interconnected ecosystems—the short-term ramifications of such a shift are as likely to be catastrophic.

We were halfway through the return trip south, overnighting in the transit town of Abéché, when the rain caught up with us. The storm came an hour after dusk, announcing its arrival with a sudden gust that sent plastic furniture skittering across the tiled terrace of the hotel where we were staying. Beyond the railings, rain began to fall in billowing sheets, and corrugated iron roofs rattled in a squally wind. Lightning strikes peppered the open space of the airfield nearby. The advent of the monsoon, which one might have expected to fall on a parched land like a benediction, struck instead as something violent and supercharged.

It was the leading edge of a weather event that would only gather in force in the days to come. Within weeks, torrential rains caused flooding throughout Chad, killing more than 500 people and displacing nearly two million more. Similar deluges assailed communities across North Africa, from Morocco to Sudan. In their wake, satellite imagery showed grasslands pressing in from the desert’s margins. On some future day the Sahara will green again. The big question is when.