*Listen to author Kristin Ohlson on Science Friday on Friday, August 15, to learn more about her thoughts on farming and global warming.
It's tempting to think that the loss of soil carbon is a relatively modern curse, the result of surging populations in poor countries and industrial farming in rich ones. But this is not the case. As soon as humans segued from a hunter-gatherer lifestyle to an agricultural one, they began to alter the natural balance of carbon dioxide in the soil and the atmosphere. Settled agriculture began in the world's great river valleys--those of the Tigris, Euphrates, Indus, and Yangtze rivers--some 10,000 to 13,000 years ago. By around 5000 BC, people began to develop simple tools to plant and harvest. The earliest of these were mere digging sticks, but by 2500 BC, people were using animals to pull plows in the Indus Valley.
Plowing seems so harmless and soothingly bucolic, especially when the plows are pulled by oxen or horses. But as [Rattan] Lal [director of the Ohio State University's Carbon Management and Sequestration Center] pointed out in a speech given in 2000, "nothing in nature repeatedly and regularly turns over the soil to the specified plow depth of 15 to 20 centimeters. Therefore, neither plants nor soil organisms have evolved or adapted to this drastic perturbation." Modern mechanized farming makes the problem even worse: The heavy machinery compacts the soil further, requiring deeper plowing to loosen the soil. As greater volumes of soil are churned up and exposed to the air, the soil carbon--which may have been lying in place under the soil line for hundreds or thousands of years--meets oxygen, combines with it to form CO2, and departs for the upper atmosphere.
Animal husbandry also began upsetting the carbon balance. Before they were domesticated by humans, herds of ruminants roamed the great prairies, nibbling off the tops of the grasses and other plants and graciously dropping off loads of enriching manure in return. Fearful of predators, they clumped together tightly and never grazed in one place for too long. Humans affected a drastic change in the grazing patterns of these herds, though. Instead of continually drifting across the plains, the animals were either restricted to one area by fencing or they grazed freely under the protection of human herders and dogs. In fenced areas, they grazed right down to the bare ground. They often did that in spots under the watchful eye of herders, too—since they had no need to fear predators anymore, they'd loaf around in one place long enough to rip the plants' roots right out of the ground.
But allowing the animals to reduce grassy plains to bare ground halted the great biological process that had created vast underground stores of carbon in the first place: photosynthesis. Plants remove carbon dioxide from the air and, combined with sunlight, convert it to carbon sugars that the plant uses for energy. Not all the carbon is consumed by the plants. Some is stored in the soil as humus—Lal points out that "humus" and "human" share the same root word—a stable network of carbon molecules that can remain in the soil for centuries. There in the soil, the carbon confers many benefits. It makes the soil more fertile. It gives the soil a cakelike texture, structured with tiny air pockets. Soils rich in carbon buffer against both drought and flood: When there is rainfall, the soil absorbs and holds water instead of letting it puddle and run off. Healthy soil is also rich with tiny organisms—an amazing 6 billion in a tablespoon—that can disarm toxins and pollutants that soak into the soil through the rain. Lal believes farmers should be compensated not just for their crops; they should also be compensated for growing healthy soil because of its many environmental benefits.
No other natural process steadily removes such vast amounts of carbon dioxide from the atmosphere as photosynthesis, and no human scheme to remove it can do so on such a vast scale with any guarantee of safety or without great expense. Photosynthesis is the most essential natural process for life on our planet, as it regulates the steady cycling of life-giving carbon into our soil and creates that other gas on which so many of us depend: oxygen.
Lal and his colleagues developed a simple if crude method of estimating the amount of carbon lost from soils in the United States and the world. When I visited him at Plot 87, he gestured at a fringe of dark forest against one side of the test fields. "That forest is my baseline," he said. "When I calculate how much carbon has been lost from the soil in this plot and nearby areas, I compare it against the soil in the forest."
With funding from the EPA, the USDA, and the United States Department of Energy (DOE) and working with students and postdocs around the world, he compared the carbon in forested areas with that in cultivated areas. According to his calculations, Ohio has lost 50 percent of its soil carbon in the last 200 years. But in areas of the world where cultivation has been going on for millennia, soil carbon depletion is much higher—up to 80 percent or more. Altogether, the world's soils have lost up to 80 billion tons of carbon. Not all of it heads skyward—erosion has washed some of it into our waterways—but even now, land misuse accounts for 30 percent of the carbon emissions entering the atmosphere.
And the amount of carbon dioxide in the atmosphere has reached a truly staggering level. By 2013, scientists calculated that CO2 had reached 400 parts per million (ppm) in the atmosphere—50 parts per million beyond the level that many experts think can reliably keep the climate stable for human life. Around the world, many clean-energy technologies are being devised and implemented to reduce the amount of CO2 our modern lifestyles emit—from fossil fuels to wind, solar, biomass, and ocean-wave energy, and even, in one wild scheme, supplementing the power grid by salvaging the power of the body heat in crowds. And there are many strategies being used to decrease the amount of energy we consume, including bumping up the fuel efficiency of gas-powered vehicles and building homes and offices that generate more energy than they use.
However, none of these will actually reduce the legacy load of CO2 already in the atmosphere. There are schemes afloat for doing that, but they're expensive--consider the EPA's plan to capture and inject atmospheric carbon into deep wells at a cost of $600 to $800 per ton. Not as sexy to policy makers, but free of cost, is Mother Nature's low-tech approach: photosynthesis and the buildup of carbon in the soil that naturally follows.
And therein lies our great green hope. To be sure, we must continue to cut back on fossil-fuel use and lead less energy-squandering lives. But we also have to extract excess carbon from the atmosphere by working with photosynthesis instead of against it. Farmers, ranchers, land managers, city planners, and even people with backyards have to make sure plants are growing vigorously, without large stretches of bare earth—photosynthesis can't happen on bare earth. We have to take care of the billions of microbes and fungi that interact with the plants' roots and turn carbon sugars into carbon-rich humus. And we have to protect that humus from erosion by wind, rain, unwise development, and other disturbances.
Lal says it can be done. The greatest opportunities are in the parts of the world where carbon has been most depleted by thousands of years of farming, in sub-Saharan Africa, south and central Asia, and Central America.
"The carbon in the soil is like a cup of water," Lal says. "We have drunk more than half of it, but we can put more water back in the cup. With good soil practices, we could reverse global warming."
When good land management practices create a ton of carbon in the soil, that represents slightly more than 3 tons of carbon dioxide removed from the atmosphere. Lal believes that 3 billion tons of carbon can be sequestered annually in the world's soils, reducing the concentration of carbon dioxide in the atmosphere by 3 ppm every year. But others with whom I spoke—especially as I got further and further from academia—are far more optimistic about the potential for change. This is still a new idea, they say, and science has barely nibbled at its edges.
By working with test plots around the world—in Ohio as well as Africa, India, Brazil, Costa Rica, Iceland, and Russia—Lal's center is looking for the perfect combination of land management practices in various climates and soil types that will remove carbon from the air and build it back up in the soil. He and his colleagues have figured out how to rebuild soil carbon in ecosystems across the globe, even in Nigeria, his early nemesis. They employ a variety of approaches, since the world comprises many microclimates and each has a different history of impact, human and otherwise. The one constant around the world is the importance of building political will. For various reasons, it's been hard for us to change.
Lal has written hundreds of papers and several books, including The Potential of U.S. Cropland to Sequester Carbon and Mitigate the Greenhouse Effect, which made its way to president Bill Clinton and to America's delegation to the United Nations' Kyoto Protocol negotiations. Lal has spoken to Congress about the subject six times. In 2011 alone, seven international conferences addressed the connection between soil and climate. Still, Lal's ideas haven't sparked much follow-through among policy makers.
"Soil research is not attractive to politicians," Lal says. "I tell them about 25-year sustainability plans, but they only have a four-year span of attention."
But Lal's ideas and those of other land-use visionaries are sparking plenty of interest and action among those who take the long view. Today, we're experiencing an agrarian renaissance. An interest in wholesome, sustainably raised foods has caused an upsurge in demand, and the number of small farmers in the United States is growing for the first time since the Great Depression: Between 2002 and 2007, the number of small farms increased 4 percent. As these new, often college-educated farmers practice the kind of agriculture and animal husbandry approved of by their customers—reducing or eliminating the use of fertilizers, pesticides, herbicides, hormones, antibiotics, and other chemicals, as well as letting their animals graze on grass instead of stuffing them with food they didn't evolve to eat—many are surprised to find their soil changing. It's becoming blacker and richer with carbon. Some of these farmers don't care a whit about global warming; they're influenced by the industry-connected American Farm Bureau, which claims that 70 percent of farmers don't believe in human-induced climate change. But many other farmers are thrilled to find out that their humus is helping to keep excess carbon dioxide out of the atmosphere. They've become citizen scientists, testing new ways to "grow carbon," as well as entrepreneurs trying to figure out how they can get paid for this new crop.
The environmental community is also taking heed of the soil's potential to address climate change. Worldwatch Institute issued a 40-page report about the connection between soil and climate in 2010. The National Wildlife Federation has targeted global warming as the single greatest threat to wildlife and issued a report in 2011 on "future-friendly farming" that can mitigate climate change. The environmental community has been leery of embracing land-use management to combat global warming, worried that doing so might soften pressure on the energy and manufacturing sectors to reduce emissions. But the growing understanding of the link between global warming and soil carbon is revolutionizing the environmental movement.
It's revolutionizing me and the way I think about soil. I'm the granddaughter of farmers and the daughter of avid gardeners. I grew up against the aural backdrop of their discussions about their own and other people's gardens. There was never a car trip that didn't involve pulling to the curb to admire someone's bougainvillea or bottle brush. There was never a trip from one part of the state to another that didn't include several side trips to their favorite fruit stands (Patty's Perfect Peaches, are you still there?). No matter where they lived, my parents were never without well-tended flower beds, a large vegetable patch, and a compost pile. Even when she was in her early nineties, I saw my mother struggle up from her chair with dismay when a guest threw a tea bag in the trash. "We do it this way," she said, even though there wasn't really a "we" anymore, as my father had been dead for several years. She pulled away the tea bag string and pried out the staple, then put the tea bag in a white ceramic jug that she kept under the sink. She was still making compost for the 3-square-foot plot she kept in her senior apartment complex. When she was on her deathbed, silent for days, none of the family's attempts at engaging her in conversation worked, until my brother Dave exclaimed, "Mom, I just planted my tomatoes!" She raised up on her elbows and muttered, "Black cherry tomatoes?" It was a variety she'd become fascinated with after I'd brought a basket home from a farmers' market. That was the last thing she said. She died a few hours later.
So I was raised to appreciate soil and the people who work with it. I first heard about Lal from a farmer named Abe Collins, who'd taken Lal's ideas and those of other scientists to transform his land and then became an evangelist for soil carbon. When I talk to Collins on the phone, he always sounds as if he can barely catch his breath. Part of this is purely physical; he's usually just run in from moving his cattle from one field to another or working on his fences. But part of it is excitement at the idea that he and others have stumbled upon something that really matters to the world, and that they'd better hurry up and get everyone to listen.
I would love to doubt global warming—or, more accurately, global climate change, because earth's atmospheric temperature has indeed risen 0.8°C since the industrial revolution, but that doesn't mean it's warmer everywhere. Instead, the weather is wackier everywhere, with a higher incidence of extreme weather events like downpours and droughts, floods and fires. I pine to be what's called a "climate denier," but the science won't let me. Scientists began tracking the buildup of carbon dioxide in the atmosphere decades ago. The measurements ticked steadily upward, but other, even more ominous data followed as the weather got warmer and weirder around the world. As environmentalist and author Bill McKibben wrote in a sobering 2012 article for Rolling Stone magazine, May of 2012 was "the warmest May on record for the Northern Hemisphere—the 327th consecutive month in which the temperature of the entire globe exceeded the 20th-century average, the odds of which occurring by simple chance were 3.7 x 1099—a number considerably larger than the number of stars in the universe."
Still, it's a miserable conviction. I cringe when I read about polar bears drowning because their icy landscape has given way, or when I hear meteorologists predict seasons of increased hurricanes and pronounce each succeeding year the hottest since people began recording such things. I take no pleasure in an unseasonably warm winter day or an unseasonably cold spring, feeling as if the progression of the seasons has been shattered. I groan when global warming turns up as a story in my favorite magazines or a plot thread in a novel or movie. Because why think about it when huge policy changes are needed and policy makers seem incapable of making brave decisions? The actions of an ordinary person seem so paltry.
But for the first time since I read about global warming some 25 years ago, I feel hopeful. The soil will save us. I really believe that.
Reprinted from The Soil Will Save Us
by Kristin Ohlson. Copyright (c) 2014 by Kristin Ohlson. By permission of Rodale Books. Available wherever books are sold.
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