Editor's Note: The following is an excerpt from Mark Hertsgaard's book, Hot: Living Through the Next 50 Years on Earth.

Yacouba Sawadogo was not sure how old he was. With a hatchet slung over his shoulder, he strode through the woods and fields of his farm with an easy grace. But up close his beard was gray, and it turned out he had great-grandchildren, so he had to be at least sixty and perhaps closer to seventy years old. That means he was born well before 1960, the year the country now known as Burkina Faso gained independence from France, which explains why he was never taught to read and write.

Nor did he learn French. He spoke his tribal language, Mòoré, in a deep, unhurried rumble, occasionally punctuating sentences with a brief grunt. Yet despite his illiteracy, Yacouba Sawadogo is a pioneer of the tree-based approach to farming that has transformed the western Sahel over the last twenty years.

"Climate change is a subject I have something to say about," said Sawadogo, who unlike most local farmers had some understanding of the term. Wearing a brown cotton gown, he sat beneath acacia and zizyphus trees that shaded a pen holding guinea fowl. Two cows dozed at his feet; bleats of goats floated through the still late-afternoon air. His farm in northern Burkina Faso was large by local standards—fifty acres—and had been in his family for generations. The rest of his family abandoned it after the terrible droughts of the 1980s, when a 20 percent decline in annual rainfall slashed food production throughout the Sahel, turned vast stretches of savanna into desert, and caused millions of deaths by hunger. For Sawadogo, leaving the farm was unthinkable. "My father is buried here," he said simply. In his mind, the droughts of the 1980s marked the beginning of climate change, and he may be right: scientists are still analyzing when man-made climate change began, some dating its onset to the mid-twentieth century. In any case, Sawadogo said he had been adapting to a hotter, drier climate for twenty years now.

"In the drought years, people found themselves in such a terrible situation they had to think in new ways," said Sawadogo, who prided himself on being an innovator. For example, it was a long-standing practice among local farmers to dig what they called zai—shallow pits that collected and concentrated scarce rainfall onto the roots of crops. Sawadogo increased the size of his zai in hopes of capturing more rainfall. But his most important innovation, he said, was to add manure to the zai during the dry season, a practice his peers derided as wasteful.

Sawadogo's experiments proved out: crop yields duly increased. But the most important result was one he hadn't anticipated: trees began to sprout amid his rows of millet and sorghum, thanks to seeds contained in the manure. As one growing season followed another, it became apparent that the trees—now a few feet high—were further increasing his yields of millet and sorghum while also restoring the degraded soil's vitality. "Since I began this technique of rehabilitating degraded land, my family has enjoyed food security in good years and bad," Sawadogo told me.

Farmers in the western Sahel have achieved a remarkable success by deploying a secret weapon often overlooked in wealthier places: trees. Not planting trees. Growing them. Chris Reij, a Dutch environmental specialist at VU University Amsterdam who has worked on agricultural issues in the Sahel for thirty years, and other scientists who have studied the technique say that mixing trees and crops—a practice they have named "farmer-managed natural regeneration," or FMNR, and that is known generally as agro-forestry—brings a range of benefits. The trees' shade and bulk offer crops relief from the overwhelming heat and gusting winds. "In the past, farmers sometimes had to sow their fields three, four, or five times because wind-blown sand would cover or destroy seedlings," said Reij, a silver-haired Dutchman with the zeal of a missionary. "With trees to buffer the wind and anchor the soil, farmers need sow only once."

Leaves serve other purposes. After they fall to the ground, they act as mulch, boosting soil fertility; they also provide fodder for livestock in a season when little other food is available. In emergencies, people too can eat the leaves to avoid starvation.

The improved planting pits developed by Sawadogo and other simple water-harvesting techniques have enabled more water to infiltrate the soil. Amazingly, underground water tables that plummeted after the droughts of the 1980s had now begun recharging. "In the 1980s, water tables on the Central Plateau of Burkina Faso were falling by an average of one meter a year," Reij said. "Since FMNR and the water-harvesting techniques began to take hold in the late 1980s, water tables in many villages have risen by at least five meters, despite a growing population."

Some analysts attributed the rise in water tables to an increase in rainfall that occurred beginning in 1994, Reij added, "but that doesn't make sense—the water tables began rising well before that." Studies have documented the same phenomenon in some villages in Niger, where extensive water-harvesting measures helped raise water tables by fifteen meters between the early 1990s and 2005.

Over time, Sawadogo grew more and more enamored of trees, until now his land looked less like a farm than a forest, albeit a forest composed of trees that, to my California eyes, often looked rather thin and patchy. Trees can be harvested—their branches pruned and sold—and then they grow back, and their benefits for the soil make it easier for additional trees to grow. "The more trees you have, the more you get," Sawadogo explained. Wood is the main energy source in rural Africa, and as his tree cover expanded, Sawadogo sold wood for cooking, furniture making, and construction, thus increasing and diversifying his income—a key adaptation tactic. Trees, he says, are also a source of natural medicines, no small advantage in an area where modern health care is scarce and expensive.

"I think trees are at least a partial answer to climate change, and I've tried to share this information with others," Sawadogo added. "My conviction, based on personal experience, is that trees are like lungs. If we do not protect them, and increase their numbers, it will be the end of the world."

The largest environmental transformation in Africa

Sawadogo was not an anomaly. In Mali, the practice of growing trees amid rows of cropland seemed to be everywhere. A bone-jarring three hour drive from the Burkina Faso border brought us to the village of Sokoura. By global standards, Sokoura was very poor. Houses were made of sticks covered by mud. There was no electricity or running water.

Children wore dirty, torn clothes, and more than a few were naked, their distended bellies hinting at insufficient diets. When one of our team let an empty plastic bottle fall to the ground, kids wrestled for it as if it were gold. Yet to hear locals tell it, life was improving in Sokoura.

It was a five-minute walk from the village to the land of Omar Guindo. Missing a front tooth and wearing a black smock over green slacks, Guindo said that ten years ago he began taking advice from Sahel Eco, a Malian NGO that promotes agro-forestry. Now, Guindo's land was dotted with trees, one every five meters or so. Most were young, with such spindly branches that they resembled bushes more than trees, but there were also a few specimens with trunks the width of fire hydrants. We sat beneath a large tree known as the "Apple of the Sahel," whose twigs sported inch-long thorns. The soil was sandy in both color and consistency—not a farmer's ideal—but water availability and crop yields had increased substantially. "Before, this fi eld couldn't fill even one granary," he said. "Now, it fills one granary and half of another"—roughly a 50 percent increase in production.

Back in the village, we examined the granaries, which were built by layering mud over stick frames. Oblong in shape, the structures had sides that were six feet wide and fifteen feet tall. A notched tree trunk served as a ladder to an opening near the top. Reij was the first to climb, serenaded by jovial laughter from the crowd below; it was not often these villagers got to see a white man make a spectacle of himself. Reij played to the crowd, joking about being too clumsy to manage such a steep ladder and asking one of the grannies to help him. After inspecting all four granaries, the Dutchman descended, turned to me, and exclaimed, "This is thrilling." Pointing to the closest granary, he said, "This one still has a little millet in it. The next one is more than half full, the third is totally full, and the last is a third full. What that means is, this farmer has tremendous food security. It is now May. Harvest will be in November. So he has plenty to last his family until then and even some in reserve."

As word of such successes travels, FMNR has spread throughout the region, according to Salif Ali, a neighboring farmer. "Twenty years ago, after the drought, our situation here was quite desperate, but now we live much better," he said. "Before, most families had only one granary each. Now, they have three or four, though the land they cultivate has not increased. And we have more livestock as well." After extolling the many benefits trees have provided—shade, livestock fodder, drought protection, firewood, even the return of hares and other small wildlife—Salif was asked by one member of our group, almost in disbelief, "Can we find anyone around here who doesn't practice this type of agro-forestry?"

"Good luck," he replied. "Nowadays, everyone does it this way."

These farmers were not planting these trees, as Nobel Prize–winning activist Wangari Maathai has promoted in Kenya. Planting trees is much too expensive and risky for poor farmers, Reij said, adding, "Studies in the western Sahel have found that 80 percent of planted trees die within a year or two." By contrast, trees that sprout naturally are native species and more resilient. And, of course, such trees cost the farmers nothing.

Even naturally sprouting trees were off-limits to farmers until laws were changed to recognize their property rights. Tree management was traditionally part of normal agricultural practice here, Salif explained; it was encouraged by the Barahogon, a voluntary association of farmers to which both Salif and his father belonged. But the practice was largely abandoned after first colonial and later African governments declared that all trees belonged to the state, a policy that gave officials the opportunity to sell timber rights to business people. Under this system, farmers were punished if they were caught cutting trees, so to avoid hassles they often uprooted seedlings as soon as they sprouted. In the early 1990s, a new Malian government, mindful that forestry agency officials had been killed in some villages by farmers furious about illegal burning of trees by forestry agents, passed a law giving farmers legal ownership of trees on their land (though farmers did not hear about the law until NGOs mounted a campaign to inform them via radio and word of mouth). Since then, FMNR has spread rapidly. Recently, farmers even shared their knowledge with officials visiting from Burkina Faso—twenty mayors and provincial directors of agricultural and environmental agencies. "They seemed astonished to hear our story and see the evidence," Salif recalled. "They asked, 'Is this really possible?'"

Recognizing farmers' property rights was equally crucial in Niger, according to Tony Rinaudo, an Australian missionary and development worker who was one of the original champions of FMNR. "The great thing about FMNR is that it's free for farmers," Rinaudo told me. "They stop seeing trees as weeds and start seeing them as assets." But only if they're not penalized for doing so. In Niger, said Rinaudo, FMNR had a hard time gaining traction until he and others convinced government officials to suspend enforcement of the regulations against cutting trees. "Once farmers felt they owned the trees in their fields, FMNR took off,"

Rinaudo recalled.

The pattern has been the same throughout the western Sahel: FMNR has spread largely by itself, from farmer to farmer and village to village, as people see the results with their own eyes and move to adopt the practice. Not until Gray Tappan of the U.S. Geological Survey compared aerial photos from 1975 with satellite images of the same region in 2005 was it apparent just how widespread FMNR had become: one could discern the border between Niger and Nigeria from outer space.

On the Niger side, where farmers were allowed to own trees and FMNR was commonplace, there was abundant tree cover; but in Nigeria, the land was barren. Reij, Rinaudo, and other FMNR advocates were surprised by the satellite evidence; they had had no idea so many farmers in so many places had grown so many trees.

"This is probably the largest positive environmental transformation in the Sahel and perhaps in all of Africa," said Reij. Combining the satellite evidence with ground surveys and anecdotal evidence, Reij estimated that in Niger alone farmers had grown 200 million trees and rehabilitated 12.5 million acres of land. "Many people believe the Sahel is nothing but doom and gloom, and I could tell lots of doom-and-gloom stories myself," he said. "But many farmers in the Sahel are better off now than they were thirty years ago because of the agro-forestry innovations they have made."

What makes FMNR so empowering—and sustainable—Reij added, is that Africans themselves own the technology, which is simply the knowledge that nurturing trees alongside one's crops brings many benefits. "Before this trip, I always thought about what external inputs were required to increase food production," Gabriel Coulibaly said at a debriefing session after our fact-finding expedition. Coulibaly, a Malian who worked as a consultant to the European Union and other international organizations, added, "But now I see that farmers can create solutions themselves, and that is what will make those solutions sustainable. Farmers manage this technology, so no one can take it away from them." After a string of similar comments from other activists—"The farmers understand why they are doing this, so they will defend it," one said—Reij leaned over and, his eyes shining, whispered, "They have been transformed into FMNR champions."

And FMNR's success does not depend on large donations from foreign governments or humanitarian groups—donations that often do not materialize or can be withdrawn when money gets tight. This is one reason Reij sees FMNR as superior to the Millennium Villages model promoted by Jeffrey Sachs, the economist who directs Columbia University's Earth Institute. The Millennium Villages program focuses on twelve villages in various parts of Africa, providing them free of charge with what are said to be the building blocks of development: modern seeds and fertilizer, boreholes for clean water, health clinics. "If you read their website, tears come to your eyes," said Reij. "It's beautiful, their vision of ending hunger in Africa. The problem is, it can only work temporarily for a small number of selected villages. Millennium Villages require continuing external inputs—not just fertilizer and other technology, but the money to pay for them—and that is not a sustainable solution. It's hard to imagine the outside world providing free or subsidized fertilizer and boreholes to every African village that needs them."

Outsiders do have a role to play, however. Overseas governments and NGOs can encourage the necessary policy changes by African governments, such as granting farmers ownership of trees. And they can fund, at very low cost, the grassroots information sharing that has spread FMNR so effectively in the western Sahel. Although farmers have done the most to alert peers to FMNR's benefits, crucial assistance has come from a handful of activists like Reij and Rinaudo and NGOs such as Sahel- Eco and World Vision Australia. These advocates now hope to encourage the adoption of FMNR in other African countries through an initiative called "Re-greening the Sahel," said Reij.

If humanity is to avoid the unmanageable and manage the unavoidable of climate change, we must pursue the best options available. FMNR certainly seems to be one of them, at least for the poorest members of the human family. "Let's look at what's already been achieved in Africa and build on that," urged Reij. "In the end, what happens in Africa will depend on what Africans do, so they must own the process. For our part, we must realize that farmers in Africa know a lot, so there are things we can learn from them as well."

Reprinted by arrangement with Houghton Mifflin Harcourt from Hot: Living Through the Next 50 Years on Earth by Mark Hertsgaard. Copyright © 2011 by Mark Hertsgaard.