The Weather of the Future: Heat Waves, Extreme Storms, and Other Scenes from a Climate-Changed Planet - Heidi Cullen (2010)

Part II. The Weather of the Future

Chapter 5. The Sahel, Africa


The word sahel comes from the Arabic sahil, meaning shore, and like so many things about the Sahel region of Africa, it is ironic. This is because the Sahel is a parched shore that both unites and divides the Sahara desert to the north and central Africa’s tropical rain forests to the south. This pairing of opposites is a recurring theme in the Sahel, home to nomads and farmers, Muslims and Christians, Arabs and Africans.

The Sahel is also a place where the past and the future are sharply defined by climate. A semiarid savanna stretching out over 2,400 miles from the Atlantic Ocean in the west to the Red Sea in the east, the Sahel is consistently identified as one of the most vulnerable places in the world to global warming. But the Sahel, perched just on the southern fringe of the Sahara desert, is no stranger to hostile and recurring extremes in climate. You might say the climate history of the Sahel is simply a battle between trees and sand, greens and tans, wet and dry. Climate scientists have tracked this battle over millions of years using evidence left behind on land and in the sea. If you could transport yourself back 10,000 years, you’d see that this was a time when trees, not sand, dominated the landscape of the Sahara. Evidence pulled from the bottom of the ocean indicates that the climate of the Sahara was not dry but overflowing with tropical grasslands and forests and dotted with large permanent lakes—some as large as the United Kingdom, such as Megalake, Chad.1

But eventually green gave way to tan, and trees were once again replaced by sand. Today the Sahara is the world’s largest warm desert. The Sahel has also seen significant change, slipping frequently into periods of drought. A 3,000-year climate record pulled from the mud at the bottom of Lake Bosumtwi in Ghana (see the map) shows evidence of mega-droughts lasting for centuries.2 These shifts in climate have done far more than transform forest into desert; they’ve also altered the course of human history3—which is where this story about the Sahel begins.

Human history starts sometime around 6 million or 7 million years ago, when at least one species of tree-dwelling ape left its forested habitat in Africa and became the first member of the human family, the Hominidae. The species that paleontologists call Sahelanthropus tchadensis, recently discovered in central Chad, is thought to be the “last common ancestor” linking humans to chimps. At some point, an adventurous hominid rose up on two legs, and eventually hominids evolved into an early genus that paleontologists call Australopithecus. More recently, they evolved into our genus, Homo. This matter is still an active debate, but many scientists believe that the need to adapt to open grasslands helped shape the evolution of Australopithecus. Recent evidence suggests that the further evolution of these early hominids can, at least in part, be linked to the steplike shift toward cooler, drier, and more open conditions in the Sahel region.

The evidence for these steplike shifts in climate comes from the ocean floor. Long cores containing mud drilled from the bottom of the Gulf of Aden, off the coast of east Africa, contain almost 10 million years of climate history.4 These cores contain three thick layers of dust, which originated in the Sahel and was picked up and carried by the northeast trade winds and then eventually dumped into the ocean. These thick dust layers represent drier conditions over the Sahel, and they appear at roughly 2.8 million, 1.7 million, and 1 million years ago, which happen to be very important junctures in human history.

The first shift toward colder, drier conditions (roughly 2.8 million years ago) marked a definite transition of the climate of the Sahel from dense woodlands into more open grasslands. As a result, many species saw their forested home replaced by a vast expanse of savanna. Some plant and animal species probably shrank in numbers as a result of this habitat loss, but many other species simply became extinct. The increased competition for food brought about by a changing landscape would have intensified the pressure to adapt.

During this time, at least two new hominid branches emerged. These two new branches in the early human family tree include the genus Homo and the genus Paranthropus. Paleontologists suspect that Homowas more of a jack-of-all-trades, whereas Paranthropus was more of a specialist and retained many common features of Australopithecus. As it turned out, Homo was far more capable of adapting to the changing environment and managed to come up with new strategies to cope with the increased competition for food.

For example, the first evidence of stone tools—crude choppers and scrapers—appears in the fossil record about 2.6 million years ago. The discovery of tool cut marks on mammal bones provides evidence of meat processing and marrow extraction. It is possible that Homo exploited different habitats by exploiting different types of foods. For example, eating meat and marrow would have marked an improvement over a strictly vegetarian diet because, unlike nuts and seeds, meat was available year-round. It is worth noting that the appearance of a bigger, more powerful brain in Homo coincides with the time of drying between 2 and 3 million years ago. Fossil records from the Turkana basin straddling northern Kenya and southern Ethiopia suggest that Homo species were characterized by a more delicate frame and smaller cheek teeth than their Australopithecus ancestors, and indeed had much bigger brains. In time this branch evolved into modern humans.

The other branch of hominids, the genus Paranthropus, with its very large teeth and a specialized chewing apparatus: a saggital crest on top of the skull that supported strong jaw muscles, tried to exploit a fading environmental niche, ate a mostly vegetarian diet and used those strong teeth and jaw muscles to crush nuts and seeds and grind the coarse vegetable matter that could still be found in the denser patches of savanna along rivers. This niche strategy is thought to have left Paranthropus more vulnerable, struggling to adapt to the cooler, more arid landscape, which provided fewer vegetarian options.

Some scientists suggest that during the next shift toward colder, drier conditions, about 1.8 to 1.6 million years ago, the branches of both Homo and Paranthropus underwent further splitting and pruning. At this time, the species named Homo habilis became extinct and our direct ancestor, Homo erectus, first appears in the fossil record. Fossil evidence suggests that by the third dry spell, about 1 million years ago, the entire Paranthropus line had become extinct and Homo erectus emerged as the winner, going on to occupy sites in North Africa, Europe, and western Asia—and ultimately evolving into Homo sapiens, modern humans.5 The rest, as they say, is history.

Today, the Sahel is home to more than 60 million people. It is a place that has become synonymous with the word drought. In the past 100 years alone, the region experienced three devastating droughts. The first stretched from 1910 to 1916; the second stretched from 1941 to 1945; and then came the worst of all droughts, a long period of sustained declining rainfall beginning in the late 1960s and known simply as the desiccation.6

Climatologists estimate that from the 1950s through the 1980s, the Sahel saw rainfall decrease by about 40 percent.7 This drought is linked to the deaths of more than 100,000 people, mostly young children; and it set off a wave of migration from north to south, from rural areas to cities, and from inland to the coast.8 As a result, squatter settlements and urban overcrowding, accompanied by rising unemployment, increased. Political instability and unrest intensified across many countries in the Sahel. The dessication is considered by many scientists to be one of the most striking examples of climate variability the world has seen. A looming question now facing climate scientists is: when will another drought of this magnitude occur? Another question is: if and when such a drought recurs, who will emerge as the winner—the people or the sand?

During the 1970s, striking images of this crisis made their way out of Africa and reached television screens and magazine covers all over the world. The pictures of barren landscapes and children with haunting eyes and distended bellies led to coordinated international humanitarian efforts to help reduce the suffering. The crisis also revived a long-standing debate within the scientific community over the fundamental causes of drought. The debate centered on the concept of desertification, a process whereby productive land is transformed into desert as a result of human mismanagement.9

The issue of desertification dates back to the 1930s, during colonial rule in west Africa. There was a growing concern that the Sahara desert might be slowly creeping into the Sahel. The colonial regimes blamed desertification on the African people, specifically on rapid population growth and poor agricultural practices. It was a new twist to an old story. Instead of studying the impact of climate on human history, scientists were studying the impact of human history on climate. Man-made landscape alterations caused by overgrazing, intensive agriculture, and the cutting of trees were offered as a possible cause of the Sahel’s drought.10 At the time, some studies went so far as to suggest that at least one-third of the planet’s deserts were a result of human misuse of the land.

In some respects, framing the problem as man-made allowed it to seem more readily fixable. With upward of 750,000 people in Mali, Niger, and Mauritania totally dependent on food aid and more than 900,000 people in Chad severely affected by the lack of rainfall, the west African countries of Burkina Faso, Cape Verde, Guinea-Bissau, The Gambia, Senegal, Mali, Niger, Mauritania, and Chad became a formal geopolitical entity defined by a shared goal of combating drought. Formed in 1973, the Permanent Interstate Committee for Drought Control has a mandate to invest in research to ensure food security and to reduce the impact of drought and desertification.

Just as they had done in the past, the people of the Sahel were looking for ways to adapt and survive in a changing landscape.

If you look at rainfall records for the 1950s and early 1960s—before the drought began—the weather was actually a little wetter than average. This short-lived boost in rainfall allowed many farmers to grow crops in the northern Sahel, a region that was usually not suitable for agriculture. This type of rainfall-related migration is an age-old adaptation strategy for the people of the Sahel. But when the rains stopped, these crops were the first to go.

During and after the drought of the late 1960s, the only way to survive was to expand cultivated land. To do this, farmers had to cut down trees. By 1975, much of the remaining natural woodland had been converted to farm fields to feed a rapidly growing population. But by clearing native trees and shrubs, farmers were exposing their fields to the fierce Sahara winds; this exposure resulted in plummeting crop yields, and windblown sand buried entire villages. In what would have been an ultimate irony, it was suggested that these attempts to sustain life were actually what led to so many deaths.

Before you can begin to unravel the causes of drought in the Sahel and see how climate change will make those droughts worse, you need to understand why it rains there in the first place.

“That short answer is the African monsoon,” says Alessandra Giannini. Giannini is a climatologist at the International Research Institute for Climate and Society (IRI) at Columbia University and has spent the past several years studying rainfall, or the lack thereof, in the Sahel. “Rainfall in the Sahel results from the collision between two different air masses; the moisture-laden southwesterly winds originating over the Atlantic Ocean and the dry northeasterly trade winds coming off the African continent.”

In other words, if you’re lucky and the conditions are just right, the collision of these two air masses will take place squarely over the Sahel and usher in welcome thunderstorms and much-needed rainfall.11 But as history has shown, the Sahel doesn’t always get lucky. The reason is that the Sahel sits at the northern edge of the African monsoon—and in some years the monsoon simply isn’t strong enough to muscle its way that far north. When this happens, the northern part of the Sahel might as well be the Sahara.

Overall, the northern tier of the Sahel is rarely lucky with respect to rainfall; it averages only about 4 to 8 inches a year. To the south, the situation is a little better, and rainfall averages between 24 and 28 inches a year.12 But even so, there is tremendous variability from year to year. Some climate scientists argue that the concept of average rainfall doesn’t even apply in the Sahel. Also, the rainy season is short and intense—typically centered on August and lasting no more than four months. That means the dry season is very long, in a place where more than 80 percent of the people make their living growing crops and grazing livestock. June through September is known simply as the hunger season—the period when the harvest from the previous year has been exhausted and the next season’s harvest is not yet ripe.

This is exactly why Giannini and her colleagues at the IRI have been working to develop seasonal rainfall forecasts for the Sahel. But Giannini knows all too well that before you can offer a forecast, you need to understand the past. And in the Sahel, that means understanding the causes of the drought.

“Two competing drought mechanisms were being floated around, one local and one remote,” explains Giannini. “The local mechanism involved land use change on the ground in the Sahel. The remote mechanism involved changing the temperature of the oceans. But no one could really demonstrate which was the stronger influence.” The local mechanism pointed the finger at human activity—for example, deforestation and overgrazing. The remote mechanism suggested natural causes. In other words, there were two options: the drought was made either by man or by Mother Nature.

Evidence that local activities can lead to local droughts was first proposed in the 1970s by Jule Charney, an atmospheric scientist at the Massachusetts Institute of Technology. The Charney hypothesis, as it came to be known, suggested that deforestation and overgrazing literally cool the land surface and ultimately decrease clouds and rainfall. Climate models were used to test this idea, and that is when the local mechanism began to unravel. Models looking solely at deforestation were unable to produce the kind of large-scale drought that was actually taking place in the Sahel.13 Furthermore, satellite pictures of the Sahel confirmed that the land surface hadn’t been changed nearly enough to alter rainfall patterns. Strike one for this hypothesis of human causation.

Giannini was interested in testing the other possibility—the remote mechanism. In the 1980s, a group of researchers from the United Kingdom’s Meteorological Office had confirmed that changes in ocean temperature played a big role in generating the Sahel drought.14 It was just a question of how big.

“I wanted to understand a very simple question,” explains Giannini. “I wanted to see how well a climate model could reproduce observed rainfall over the Sahel.” So she used an atmospheric climate model that took only one real-world factor into account: the ocean surface temperature. The model didn’t know anything about the Sahel and its history of deforestation, desertification, and land degradation. As far as Giannini’s climate model was concerned, no one even lived in the Sahel. And as it turned out, that didn’t matter. “I couldn’t believe it. The model reproduced the observed rainfall beautifully,” explains Giannini.15 “We all know these models aren’t perfect, but the connection between ocean surface temperature and drought in the Sahel was very compelling.” So much for blaming the drought on the farmers.

Giannini discovered that ocean temperatures helped regulate the strength of the African monsoon. What was even more fascinating was how each ocean played a specific role. On a year-to-year basis the Pacific Ocean has an effect on the Sahel’s rainfall, thanks to El Niño. During an El Niño event, the Sahel is typically expected to experience a drought, whereas during a La Niña event, when the tropical Pacific is cooler, the African monsoon is expected to strengthen and rainfall is expected to be more abundant. The Atlantic Ocean and the Indian Ocean affect the Sahel’s rainfall over much longer periods, from decade to decade. A warming of the Indian Ocean means a drier Sahel. And in the Atlantic, where the relationship is somewhat trickier, overall, when the southern hemisphere warms more than the northern hemisphere the rain belt across the Sahel is attracted farther south, toward the warmed hemisphere. This effect dries the Sahel.

“Ultimately, we found that you could explain the Sahel drought, as well as its persistence, by looking to the ocean temperatures,” says Giannini.

Understanding this connection to the oceans provides the basis for seasonal rainfall forecasts for the Sahel. In essence, these seasonal forecasts are not attempting to predict how much it will rain on a specific day in the Sahel; rather, they predict when the rainy season might fail altogether or when large-scale flooding is likely. By knowing the present ocean surface temperatures, you can use climate models to forecast how the oceans will probably evolve during the next several months. Climate forecasts are an average of many climate models; similarly, the IRI uses numerous climate models with different conditions in the atmosphere to average seasonal patterns of temperature and rainfall. These averages give the most accurate predictions for the coming season’s climate; indeed, seasonal rainfall forecasts for the Sahel have been issued since 1997, providing significant help in drought planning and food security.

But although the climate models rely on ocean surface temperatures to forecast rainfall and temperature, Giannini is quick to add that human activity does still influence the severity of drought in the Sahel. “If you cut down enough trees in the Sahel, there’s no doubt it’s going to get warmer and drier,” Giannini explains. “What people are doing down on the ground can amplify the drought signal.” And it is now well accepted that the combined effects of population growth, deforestation, overgrazing, and lack of coherent environmental policies, along with a significant decrease in rainfall, resulted in the crisis of the 1960s and 1970s, which was unlike any the world had seen before.

Of course, there is another, broader human influence that goes beyond the behavior of the local population. Global warming has already warmed up ocean surface temperature by about 1°F during the past century, and given the already established relationship between ocean temperatures and droughts in the Sahel, this warming trend will almost certainly have a negative impact on the amount of future precipitation there.

Global warming is affecting the region in ways that are not yet fully understood. If anyone can figure it out, Isaac Held would be a good possibility. Held is a senior research scientist at a division of the U.S. National Oceanic and Atmospheric Administration (NOAA): its Geophysical Fluid Dynamics Laboratory (GFDL), a prominent climate modeling center in Princeton, New Jersey. Few people understand the complexity of rainfall in the Sahel better than Held. A member of the Intergovernmental Panel on Climate Change (IPCC), Held served as a lead author of the IPCC’s Fourth Assessment Report chapter on regional climate projections. The IPCC’s regional projections use fourteen state-of-the-art climate models to provide a glimpse into the future. The GFDL climate model is one of the best in the world. And if you believe this model’s projections for the Sahel, you’ll be very worried about the future.

Held knows why the GFDL model behaves as it does; he just doesn’t know if the real world will behave the same way. Remember that today drought in the Sahel is very sensitive to the gradient between ocean temperature in the north and the south. “The models all agree that if you warm the oceans of the southern hemisphere with respect to the ocean of the northern hemisphere, you dry the Sahel,” explains Held. “But if you warm the oceans uniformly, there’s no consensus among the models.”

With regard to total seasonal rainfall in the Sahel, the models actually diverge—some predict more rainfall, and some predict less. Most of the models produce only modest changes out to 2100, but there were two outliers—one projecting a very wet future Sahel and one projecting a very dry future Sahel. The GFDL model was the dry outlier. It projected that summer rainfall in the Sahel would decrease 30 percent or more by the year 2100. Needless to say, a rainfall reduction at that level would be catastrophic. “Our model dries the Sahel in response to uniform warming. And that’s why we dry so strongly into the future. It’s the global warming signal that dominates,” explains Held. “We’re still trying to understand it.” But in the meantime, Held points to model simulations that show a far more robust response.

The models all agree that the Sahel is going to get warmer. The IPCC estimates a warming of roughly 6°F to 10°F by the end of the twenty-first century.16 A recent study looking at future heat extremes shows that heat waves will become longer and more frequent in the Sahel. And by the end of this century, the heat index across all of northern Africa will spike from May through October.17 It is expected that the people in the Sahel region will be the most vulnerable, experiencing up to 160 days per year in the twenty-first century with a significant chance of heatstroke. Today, there are up to 180 days of medium risk in the Sahel and no high-risk days. By the end of the century, the people living in the Sahel are projected to experience the most severe increases in sunstroke in the world.

Regarding rainfall, Held also points to a recent set of experiments by Michela Biasutti and Adam Sobel of Columbia University that show a robust response among all the different IPCC climate models.18 This particular study looked at the timing of the rainfall season rather than at the average amount of rainfall. “They see a delayed onset of the rainy season in almost all the models,” says Held. In other words, the rainy season of the Sahel is projected to start later and become shorter, with storms that will possibly be more intense. This is not good news. (Case in point: on September 1, 2009, Ouagadougou, the capital of Burkina Faso, was hit by an unprecedented storm that brought more than 10 inches of rain in just a few hours. Widespread flooding left nearly 130,000 people homeless; they sought shelter in churches, mosques, and schools.)

Despite these dramatic images, and despite the fears about how global warming may affect the lives of those in the Sahel, Alessandra Giannini tries to remain hopeful.

“Honestly, I don’t like to play this doom and gloom card with respect to the future. As climate scientists, we often spend our lives looking at problems from afar. But in the case of the Sahel, when you look closely at what is happening on the ground, you will be able to see pockets of resilience, pockets of adaptation.” Those pockets of resilience are proof that people working together have the potential to overcome the forces of nature. Just ask Chris Reij, a scientist at the Vrije Universiteit (VU) in Amsterdam who specializes in soil conservation.

Chris Reij spends his life actively looking for ways to promote adaptation that will help the Sahel weather a climate-changed world. “I must admit that I’m doing everything possible to abandon research now. I’ve changed from soil conservation research to development action,” Reij says. “We clearly have enough information to act.”

The reason to act is that the pockets of resilience Giannini mentioned are, in fact, pockets of trees, millions of them.19 Satellite images and tree inventories have found that the Sahel has become greener over the past thirty years.20 Needless to say, the exact cause of this greening is still not perfectly resolved. Some scientists think the Sahel is simply bouncing back from the gradual improvement in rainfall since 1988; others think global warming could actually be helping to boost rainfall totals and spur on vegetation growth.

But Reij thinks the cause is the farmers. “You could say we’ve come full circle with respect to our ideas about drought and desertification,” explains Reij. “Farmers were not the cause of the drought, but they are a big part of the solution.” Reij has worked in the Sahel since 1978 and has never been one to spread doom and gloom. “I think there are a lot more success stories in the Sahel than we tend to assume,” he says.

One success story involves farmers in Niger. A desperately poor country twice the size of Texas, Niger has seen about 12.4 million acres of trees, shrubs, and crops replace what was once barren ground.21Barren ground is all too common in Niger; four-fifths of the country sits within the Sahara desert. As a result, the vast majority of Niger’s rapidly growing population is concentrated in the southern part of the country, the portion that sits in the Sahel. Niger has one of the highest population growth rates in the world: 3.3 percent, amounting to about 450,000 new mouths to feed every year. Niger’s population has doubled in the last twenty years and each woman bears, on average, about seven children. If this growth rate continues, there will be 56 million people living in Niger by 2050. Experts have already begun to question how a country with a very small band of cultivable land can continue to feed itself, given this population growth and the looming threat of drought.

And yet, because of these conditions, an adaptation strategy is already in the works. In the long battle between trees and sand, the trees have begun to gain some ground—thanks to the help of local farmers.

“The story about the farmers is not a technical story. It’s about a social process. It’s about farmers who broke with tradition and villages that organized themselves,” explains Reij.

The tradition of land “cleaning” and tree removal became com- mon in the 1930s, when the French colonial government pushed Nigerian farmers to grow crops for export. Another by-product of colonialism was the fact that all trees in Niger had been regarded as the property of the state; this gave farmers little incentive to protect them. Government foresters were tasked with managing the trees, but oversight was lax and as a result trees were chopped down for firewood or for construction, without regard for the environmental costs. The loss of tree cover also led to a fuelwood crisis. Poor households were forced to burn animal dung or crop residues instead of using these for compost; that practice reinforced the downward spiral of soil quality and crop yields.

Despite these long-standing habits, in the mid-1980s Reij and his coworkers noticed a new trend among the farmers of Niger; they had begun to cultivate the trees that were on their property.

“When we asked farmers in Niger why they had begun protecting and managing their on-farm trees, the first answer was, ‘because we must fight the Sahara,’ ” explains Reij. “And to them ‘fighting the Sahara’ meant fighting dust storms.” Early in the rainy sea- son the winds from the north tend to pick up. During the drought of the 1960s and 1970s, the winds would bring tremendous amounts of sand with them. As Reij puts it, “The sand acts like a razor. And it was just cutting down their young crops and carrying off the topsoil.”

Roughly 85 percent of the almost 14 million people who live in Niger subsist on rain-fed agriculture, with millet and sorghum making up more than 90 percent of the typical villager’s diet. “The farmers would have to replant three or four times before a crop would eventually succeed,” says Reij. And so, in the mid-1980s, farmers decided to do things differently. Instead of clearing the land of trees, they started to protect their trees, meticulously plowing around them when planting millet, sorghum, peanuts, and beans. “It’s the local farmers who are the real heroes here,” says Reij.

By 2007, somewhere between one-quarter and half of Niger’s farmers were involved in regreening efforts, and it is estimated that at least 4.5 million people had seen the quality of their lives improve significantly.22 Over time, farmers began to regard the trees in their fields as their property. And in recent years, the government has come to recognize the benefits of this strategy and has allowed individual farmers to own trees. Farmers now make money by selling parts of the tree: branches for fuel; leaves; seeds; fruit for food. Over time, those sales generate far more income than simply chopping down the tree for firewood. As a result, the farmers protect this source of income. Crop harvests have also risen. With the trees come better diets, improved nutrition, higher incomes, and an increased capacity to cope with drought. Many rural producers have doubled or tripled their incomes. In some villages, the annual hunger season no longer exists.

Three factors play a role in regreening, or what Reij refers to as farmer-managed natural regeneration (FMNR). “First, despite the deforestation that took place in the 1970s, there was still a rootstock in the subsoil. And that rootstock was still alive,” explains Reij. “So as the rains gradually returned, and the soil and the trees were protected, the trees began regenerating.” The second factor is livestock. “Livestock grazes and digests the seeds. That means when the seeds pass through the intestines of the livestock, they will germinate more easily.” And as it turns out, not all supposedly barren soil is actually barren. “There’s a beautiful word for this,” explains Reij; “it’s called the seed memory of the soil.” Under the right conditions, seeds that have been dormant for more than a decade will suddenly start sprouting again. “And there you have the beginning of your trees,” Reij says, smiling.

When Reij talks about a new green revolution in the Sahel, he means it literally. But it’s not so much about planting trees—an expensive proposition that had been attempted unsuccessfully in the past—as it is about recycling them. In Niger, farmers have protected and managed about 200 million new trees during the past twenty-five years. The number of trees that have actually been planted in that same period is only about 65 million. “But of the 65 million trees that have been replanted, at best 20 percent have survived, leaving only about 12 million planted trees,” explains Reij. “So there is a lesson to be drawn from this; tree planting can help, but protecting and managing natural regeneration is much cheaper and produces quicker and better results.”

Reij says, “The point is, you can solve the problem of climate change and the problem of poverty in parallel. That’s the nice thing.” In essence, the trees set off a chain reaction that improves the local economy as well as the environment. “With more tree species in the system, you increase biodiversity. And at the same time, it means you produce more fodder, which means you can sustain more livestock,” explains Reij. Perhaps the biggest benefit has come to many of the poorest members of Nigerian society—women and young men. “It’s a lot easier for women, because they can prune those trees and they have the firewood immediately at hand,” explains Reij. And as for the young men, the annual exodus to search for higher-paying jobs in urban areas has slowed, thanks to new opportunities to earn income in an expanded and diversified rural economy. “So you have all kinds of positive spin-offs,” says Reij. He points to some recent economic research, which suggests that increasing agricultural production by 10 percent can reduce rural poverty by somewhere between 6 and 9 percent.

The trees also act like a buffer during worst-case scenarios, and such scenarios may happen more frequently in a climate-changed future. In 2005, a year when the western Sahel saw flooding, the rains failed yet again in Niger. Reij visited villages with trees and villages without trees. He found that famine was much less of a problem in villages with many trees than in villages with few trees. Likewise, villages with many trees did not suffer any drought-related infant mortality. “People told us that because they had more trees, they could cut and prune trees and sell firewood on the market. They could then use that money to buy cereal to feed their children,” says Reij. “No doubt it was a brutal situation, but at least the children made it through.” Reij knows this is not what perfection looks like, but for right now, it’s close enough.

Ultimately, evidence from Niger demonstrates how relatively small changes in human behavior can transform the regional ecology, restore biodiversity, and increase agricultural productivity. Reij thinks such behavioral changes may even help bring rain back to the Sahel. “If you put a thermometer into barren, sandy soil you immediately get 120°F. But just 1 meter away, where you have some surface cover, the temperature immediately drops to 109°F,” says Reij. “And with a bit of luck, if you have vast areas of regreening, the question is: might that begin to have positive impacts on local rainfall as well?” For Reij, this might just be the perfect answer.

In June 2009, Reij helped launch the Sahel Regreening Initiative in Burkina Faso and Mali. He says, “We thought: why not start an initiative which tries to build upon and scale up the existing successes in Niger? When we talk about adaptation to climate change, I am convinced that reforestation is a fairly effective answer. You improve the environment, you improve agricultural production, and you reduce poverty. There is every reason to be hopeful. We have the wind at our back.”

The question is whether that will be enough. This is a matter of which forcing the Sahel will be most sensitive to in the coming decades—the oceans, the land surface, or global warming. The oceans have probably dominated the climate of the Sahel for all of human history. But as Reij has shown, the land surface is also clearly very important, especially in the Sahel, where it has the ability to outfit the landscape and help offset some of the changes that climate change will bring.

Unfortunately for the Sahel, Niger’s tree experiment is an isolated event. Some recent climate model simulations propose that until 2025, the impacts of land degradation and vegetation loss over sub-Saharan Africa may be even more important than global warming for understanding climate change.23 Until 2025, these models show that a drier, warmer climate goes with decreased agricultural production, on the order of 5 to 20 percent. Peanuts, beans, maize, rice, and sorghum will be likely to have the biggest drops in yield.24 A recent study focused on Mali found a 17 percent reduction in crop yields out to 2040. Scientists consider these studies red flags. They recommend immediate action to develop more heat-resistant crops for the Sahel. In Benin, for example, a shift to yams and manioc is suggested as one adaptation strategy. And then, of course, there are the trees.

Reij points again to those pockets of resilience. “These predictions for 2050 and beyond, a 5°F increase in temp, a 20 percent decrease in crop yields—in the context of a doubling population, that’s quite dramatic. That’s why I look for villages where farmers were able to depress temperatures by 5°F using trees, and villages where the use of simple conservation techniques helped increase crop yields by 40 or 50 percent or even more. You have to be able to find examples that show it’s possible to counterbalance what lies ahead.” The people of the Sahel have a lot riding on this battle between trees and sand.

As scientists continue to search for perfect answers, red flags are clear on the horizon. Held has been watching as more red flags appear with each passing year and each new research experiment. And as he settles in to prepare the next round of IPCC simulations for the Sahel, he has one big concern of his own. “My biggest concern is that the GFDL model turns out to be right,” says Held. If that happens, then sand may have finally won the battle in the Sahel once and for all. Unless, of course, like Reij, we abandon the search for perfect answers and simply begin to fight back. That might be the biggest Sahelian irony of all.

Africa and the Sahel: The Forty-Year Forecast—Famine, Crop Loss, and Water Resources


Forecast July 2015

There are few secrets in this parched, hostile landscape, especially about climate. As the models projected, the African climate was changing—becoming hotter and drier.

The trees were waging an all-out war against the brutality of the sun, and they seemed to be winning. Tens of millions of acres of Sahelian farmland had been planted with trees, and every leaf was viewed as a symbol of hope for the future. Agricultural productivity had increased, and there was actually a surplus of fuelwood. In the drier regions of Niger and Burkina Faso, people had begun reclaiming abandoned fields and getting new grain harvests by investing in simple water-harvesting technologies. Farmers were doing everything in their power to adapt to climate change, and the trees were their shield against the increasingly harsh climate. Through support from the Bill and Melinda Gates Foundation and OXFAM America, the regreening initiative had spread across the Sahel.

November 2022

But there was only so much the trees could do. Without significant infrastructure investment, farmers across the Sahel were alone in their battle against the climate. Across the Sahel, yields of peanuts, beans, maize, rice, and sorghum were beginning to fall. Those farmers able to obtain heat-resistant seeds from international aid groups fared better. And those who shifted to more drought-resistant crops, such as yams and manioc, actually managed to put some food on the table. But ultimately, without rainfall, it was no secret that the farmers, who had lovingly planted and tended these trees as if they were their children, would be forced to watch as they eventually fell victim to the inevitability that was climate change. Climate change was leaving more and more people with less and less.

This basic realization led to a growing resentment across the African continent, because it was also no secret that the rich had caused the problem while the poor of the world bore the brunt of the impact. The experts said it would only get worse, and their advice was simple—adopt aggressive emission reduction goals and take steps to help victims of climate change adapt. They said it was a matter of national security.

To return to 2010: As it turns out, half of all CO2 emissions come from only about 10 percent of the world’s population. And that 10 percent includes Saudi Arabian oil moguls and Chinese investment bankers, not just rich Americans—the operative word isn’t American; it’s rich. The atmosphere doesn’t care whether you drive a Ferrari in Dubai or Shanghai or New York. All it sees is the CO2. As a result, several experts have come up with ideas on how to even the CO2 playing field—spread the CO2 wealth, so to speak. One group of scientists recently suggested a Robin Hood idea that essentially takes emissions (by means of a cap and tax) from the rich and distributes them among the poor. These scientists see their plan as a way to help lift people out of poverty.25

After all, CO2 is just another term for energy. The World Bank estimated that if people in the United States swapped their SUVs (about 40 million, total) for fuel-efficient compact cars, the change would free up space in the atmosphere for about 142 million tons of CO2. If you could magically convert that CO2 back into energy and give it to the poor, it would provide basic electricity to about 1.6 billion people. In essence, everyone in Africa could have lights and running water.26 To repeat, it seemed like a good way to even the playing field—and to decrease resentment. But in the end, no one really wanted to give anything up for the sake of strangers.

In 2015, this basic inequity between rich and poor remained a serious problem. And climate change, described by national security experts as a threat multiplier,27 was turning up the heat, literally. Conflict was spreading across the African continent like wildfire. You needed only look at the past few years for evidence. The instability in the Sahel—especially Darfur—showed how quickly disputes over access to water and food during times of drought became politicized. The climate problem magnified preexisting threats stemming from ethnic and religious conflicts. The former UN secretary-general, Ban Ki Moon, had made that very point in the Washington Post more than 15 years earlier:

Almost invariably, we discuss Darfur in a convenient military and political shorthand—an ethnic conflict pitting Arab militias against black rebels and farmers. Look to its roots, though, and you discover a more complex dynamic. Amid the diverse social and political causes, the Darfur conflict began as an ecological crisis, arising at least in part from climate change.

Two decades ago, the rains in southern Sudan began to fail. According to U.N. statistics, average precipitation has declined some 40 percent since the early 1980s. Scientists at first considered this to be an unfortunate quirk of nature. But subsequent investigation found that it coincided with a rise in temperatures of the Indian Ocean, disrupting seasonal monsoons. This suggests that the drying of sub-Saharan Africa derives, to some degree, from man-made global warming.28

Experts were warning that attempts by the United States to build a “hearts and minds” coalition against Islamist extremism were being undermined by climate. They listened carefully to the latest tape from Osama bin Laden, on which he railed once again about the inequities of global warming and CO2 emissions.29 Jobs for young men in North Africa, to take just one example, had been further reduced by warmer temperatures and declining rainfall, intensifying resentment and unrest.

Scientists had even modeled the connection between conflict and temperature, to prove the point.30 The data were painfully clear: conflict increased in lockstep with temperature. And when you looked at conflict combined with climate model forecasts of future temperature trends, there was a roughly 50 percent increase in armed conflict—almost 400,000 additional battle deaths—by 2030. The need to reform the policies of African governments and foreign aid donors to deal with rising temperatures had become urgent.

March 2030

By 2030, piracy had become an epidemic on the order of HIV-AIDS. The piracy industry popped up after Somalia’s central government collapsed in 1991. With no patrols along the shoreline, commercial fishing fleets from around the world came to plunder Somalia’s tuna-rich waters. Initially, the pirates stepped in as a vigilante response to that illegal commercial fishing. Armed Somali fishermen confronted the crews of illegal fishing boats and demanded that they pay a tax. These were acts of desperation by local fishermen who had lost their livelihood. The entire country was, in fact, on the brink of starvation. It was not uncommon for pirates to smile when they were picked up by navy ships—they knew that they would at least get three square meals a day. But over time, these desperate bands of fishermen grew into something bigger, more organized, and much more sinister.

As rising ocean temperatures, pollution, and overfishing gradually erased their livelihood, more and more fishermen traded in their nets for machine guns and were hijacking any vessel they could catch: a sailboat, a yacht, an oil tanker, or a food ship chartered by the United Nations. Desperate times, they said, called for desperate measures. They said they had no other choice.

Because of all the hijackings, the waters off Somalia’s coast were now considered the most dangerous shipping lanes in the world. The United Nations agreed to put a maritime peacekeeping force in place to patrol the waters, but there was only so much it could do. The main victims of the pirates were the Somali people. Nearly three out of every four Somalis had come to depend on food donations in order to survive. But the pirates were routinely overtaking the UN peacekeeping vessels, and the attacks made it very hard for the United Nations to keep sending provisions. Somali people were starving because the boats couldn’t get through.

As of March 2030, no food ships had set sail from Mombasa to Mogadishu in months—the voyage was simply too dangerous. Despite the efforts of the international aid community and peacekeeping troops, conflict across Africa had increased along with the temperature. It looked more and more as though Africa was heading toward the status of a failed continent.

January 2050

After years of conflict, drought, and food shortages, Africa was finally able to capitalize on something it has in abundance—sunshine. The Desertec project had been on the table for years, but two key elements were always missing: European funding and the support of African countries. When increasing demand from China and India sent oil and gas prices into the stratosphere, the Germans were eventually able to pull the money together, on the promise that Desertec would offset Germany’s dependence on Russian gas supplies. The Desertec consortium, brought together by Munich Re, the world’s biggest reinsurer, consisted of some of Germany’s biggest and most powerful companies, including Siemens and Deutsche Bank. The plant symbolized a way to solve the problems of climate change and energy security simultaneously—and if everything went according to plan, it might help Africans as well.

North African governments sold their desert in return for water. Let us use your desert to generate power, the Desertec consortium argued, and you can use our energy to desalinate seawater so as to irrigate crops that will help feed your growing populations. North Africa’s demand for water had, in fact, increased by two-thirds—an amount that was far beyond the available supply. For Africa, energy security was far less of a concern than water security. The deal was straightforward—Desertec would generate electricity for export in return for desalinating seawater for Africa—and it was a deal that was very hard to pass up. So with little to lose, the North African countries signed on, making one request—the plant was to be renamed Desertec-Africa.

The science was there. Every year, each square yard of the Sahara desert receives more heat from the sun than would be obtained by burning two barrels of oil. The calculations showed that all of Europe’s electricity could be made in an area just 150 miles across. The Desertec-Africa plant used a technology known as concentrated solar power (CSP). The sun’s rays would be concentrated by the use of mirrors, to create heat. The heat would then be used to produce steam to drive steam turbines and electricity generators. The advantage a CSP plant like Desertec-Africa had over standard solar photovoltaic panels, which convert sunlight directly to electricity, was that it had heat storage tanks. The tanks were able to store heat during the day and then power steam turbines during overcast periods, bad weather, at night, or when there was a spike in demand.

The cost overruns were substantial, and sandstorms and warring factions in North Africa made construction of the Desertec-Africa project an ordeal. But thanks to an important innovation that allowed the plant to use less water, construction was kicked into high gear. Like a standard coal- or oil-fired power plant, a solar thermal station requires large amounts of cooling water—something that is nearly impossible to come by in the Sahara desert. The water condenses the steam after it goes through the generator’s turbines. But the innovation allowed the Desertec-Africa plant to be fitted with an air-cooling system that cut water demand by up to 90 percent—a huge break for investors. While many still argued that Desertec-Africa would make Europe’s energy supply a hostage to a politically unstable region and that Europe was unfairly exploiting Africa for its sunlight, the project went ahead.

By 2050, Desertec-Africa was producing about half of Europe’s electricity, with a peak output of 400 gigawatts—roughly equivalent to the output of 400 coal-fired power stations. The electricity generated by Desertec-Africa reached Europe via high-voltage power lines and trans-Mediterranean links that went from Morocco to Spain across the Strait of Gibraltar; from Tunisia to Italy; from Libya to Greece; from Egypt to Turkey, via Cyprus; and from Algeria to France, via the Balearic Islands. Part of a wider European super-grid that conveyed power generated from wind turbines in the North Sea, hydroelectric dams in Scandinavia, geothermal activity in Iceland, and biofuels in eastern Europe, Desertec-Africa had helped reduce European emissions of CO2 by about 80 percent. The consortium had hopes of expanding. After all, a patch less than 450 miles across the Sahara could meet the entire world’s electricity needs.