No. 102 - Greenhouse Gas Control: Implications for Agriculture (Part 2)

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An enormous 1,440 gigatons of carbon is stored in the soil and detritus on the soil--the remnants of plants and trees. Through photosynthesis, plants and trees convert carbon dioxide into carbon-rich carbohydrates and biomass. After they die, some of this plant biomass is incorporated into the soil as carbon-rich organic matter.

Much of this “organic” carbon eventually cycles back into the atmosphere as CO2 when organic matter is broken down by microorganisms in the soil. However, some is always retained in the soil as organic matter and some may be converted via chemical reactions into stable carbon compounds such as calcium carbonate and magnesium carbonate. Soil carbon can accumulate in carbonates and humus, and the size of the soil “carbon bank” varies with climate and how the land is managed.

How Farming Can Sequester Carbon

Additional atmospheric carbon could be stored in the soil bank by increasing soil organic matter levels through land management and land use changes, a process called carbon sequestration. It is often simply assumed this would be a win-win situation with no new expenses or adverse consequences. The Soil Science Society of America, for example, says in its carbon sequestration policy that, “Increased long term sequestration of carbon in soils, plants, and plant products will benefit the environment and agriculture. Crop, grazing, and forestlands can be managed for both economic productivity and carbon sequestration.”

Traditional farming techniques, such as plowing, reduce soil carbon levels by exposing soil carbon to oxygen in the air, allowing chemical and biochemical oxidation into CO2. Until two or three decades ago, cropland was probably a net emitter of carbon.<26> However, a farming system called conservation tillage, developed in the 1970s, uses chemical weed killers to control weed competition in the fields. Conservation tillers don’t need to control weeds with ‘bare earth’ farming systems such as plowing, hoeing, and fallow. They either use no tillage at all, or perform shallow tillage that exposes less soil to erosion--and less carbon to oxidation losses.

Conservation tillage is one of the most important new farming advances because it reduces soil erosion by 65 to 95 percent, sharply increases the water-holding capacity of the soil, and gradually increases soil carbon levels. Conservation tillage is being used on nearly 200 million acres of cropland in the United States, and on hundreds of millions more acres in Canada, Latin America, Australia, and South Asia.

Encouraging conservation tillage and other practices that increase carbon storage in soil is more complicated than it first appears. Not all soils can increase their carbon load: mineral soils containing relatively low amounts of organic matter (usually less than 20 percent by weight) can, but organic soil (with 20 to 30 percent or more organic matter by weight, depending on clay content) cannot. Since soil can become saturated with carbon, farmers who already use practices that retain carbon in the soil will not be able to increase storage as much as other farmers who do not. Policies intended to reward increased sequestering could have the effect of punishing early adopters of conservation tillage and other practices. Eventual saturation also means soil sequestration is only a short-term solution to the long-term problem of rising carbon dioxide concentrations in the atmosphere.

While corn and soybean producers in the Midwest may be able to adopt techniques to increase carbon sequestration, fruit and vegetable producers may not.<27> Livestock production is a net emitter of methane and other greenhouse gases, so ranchers and dairy farmers may find themselves paying for their emissions with one hand and being paid to sequester emissions with the other. Many dairy farmers and ranchers would have to pay more for emission permits than they would earn through carbon storage activities.

Finally, policies that promote biological carbon sequestration could disrupt other environmentally beneficial practices that farmers do not get paid to use. “At the end of the harvest, California producers flood their land, providing a habitat for ducks and geese,” says John Doggett. “Who’s going to decide what’s more important in cases like this, greenhouse gas reduction or providing a refuge for wild animals?”<28>

Too Little to Matter?

How does the amount of carbon sequestered by farmers compare with U.S. and global greenhouse gas emissions? According to EPA, “land-use change and forestry,” a category that includes changes in agricultural soil carbon stocks, offset 838 million metric tons of carbon dioxide equivalents in 2001, about 12 percent of total U.S. greenhouse gas emissions that year of 6.9 billion metric tons.<29>

Most of the offset was due to forestry, not farming (see Table 1). According to EPA, sequestration in mineral soils in 2001 totaled 59 million metric tons, but was partially offset by emissions from organic soils (35 million metric tons) and emissions from liming (9 million metric tons). Net agricultural sequestration was only 15.2 million metric tons in 2001, a nearly trivial two-tenths of 1 percent of total U.S. greenhouse gas emissions.<30> Agriculture-related emissions (526 million metric tons) were 35 times greater.

Total net carbon sequestration in agricultural soils rose by 14 percent between 1990 and 2001, according to EPA, “largely due to additional acreage of annual cropland converted to permanent pastures and hay reduction, a reduction in the frequency of summer-fallow use in semi-arid areas and some increase in the adoption of conservation tillage (i.e., reduced and no-till) practices.”<31> This small increase was more than offset by a decline in the rate of net carbon accumulation in forest carbon stocks during the same period. As a result, the net CO2 flux from land-use change and forestry decreased by 234.7 million metric tons--more than 16 times agriculture’s entire annual contribution to sequestration.<32>

The U.S. Department of Agriculture, somewhat confusingly, believes farm and grazing land soils currently sequester much more carbon than EPA estimates: approximately 73 million metric tons a year.<33> Even this estimate, hurriedly produced to give treaty negotiators at the U.S. Department of State some ammunition with which to negotiate with other countries, barely exceeds 1 percent of current U.S. greenhouse gas emissions.

Better management of croplands can indeed increase the amount of carbon stored in the soil bank, while reducing erosion and producing other benefits. But the net amount of carbon stored each year is trivial in terms of total U.S. emissions of greenhouse gases.

Farming versus Forestry

As the numbers presented in the preceding section show, the major payoff in biological carbon sequestration is from having more land planted in trees. For example, a tract of marginal Russian farmland has an average biomass of 8 tons per hectare, while converting the land to forest would achieve an average of 269 tons of biomass per hectare.<34>

Trees are far better for carbon storage than crops, any crops. Unfortunately, humans can’t get much of their food supply from trees, so we have had to clear the trees from nearly half the global land area not covered by deserts and glaciers to produce our food and livestock feed. In the process, we have reduced the levels of carbon storage.<35>

Since 1960, high-yield agriculture has effectively tripled the yields on the world’s best cropland, greatly easing the pressure to clear forests. The Green Revolution strategies (high-yielding seeds, irrigation, chemical fertilizer, and pesticide protection for crops and livestock) permitted human society to feed twice as many people, more adequately (Third World calories have increased by more than one-third) from virtually the same land area as was farmed 50 years ago. The U.N. Food and Agriculture Organization’s Production Yearbooks tell us the world cropland total was about 1.4 billion hectares in the late 1960s, and 1.5 billion hectares in 1999.

Although it may not be their intention, advocates of new carbon sequestration programs could be putting in motion a chain of events that would end this remarkable record of success. A carbon sequestration program for American farmers and foresters could lead to the loss of cropland in favor of forests, leading to a decline in U.S. farm exports, followed by more clearing of forests in such densely populated and still-hungry countries as Indonesia and Bangladesh. Pushing the carbon sequestration agenda too hard could displace U.S. farm exports, while at the same time overstimulating farm output in countries where there are no artificial constraints on farming--but with lower-yielding and more erodable land, harboring far more species diversity.

World farm product demand is expected to increase by at least 250 percent in the next 50 years (especially in densely populated Asian countries with rising incomes).<36> America has the biggest chunk of prime farmland in the world, and about 30 to 40 percent of its farm output is already exported. America currently exports more than 100 million tons of crops and substantial amounts of meat and dairy products to the rest of the world. Policies that encourage the conversion of U.S. cropland into forests would cause Third World countries to clear several times as many acres of forest to replace those exports.

Estimates of the world’s total number of wildlife species range from just 2 million to 100 million, but there is little disagreement that most of the planet’s wildlife species--perhaps three-fourths--are in its tropical forests.<37> Conversely, the high-quality land that now produces most of the world’s crops never had much biodiversity; it had large numbers of a few species, such as the American bison and the Australian kangaroo.

It is for these reasons that Dr. Bruce Babcock of Iowa State University and other experts say any policy intended to increase the use of biofuels or increase soil carbon sequestration should be scored globally rather than locally.<38> The small (relative to the size of emissions) amounts of carbon dioxide that would be sequestered in the U.S. could be entirely or more than offset by other countries encouraged or compelled to clear more tropical forest.

NOTES TO PART 2

1 Joseph Bast is president of The Heartland Institute in Chicago; Dennis T. Avery, an agricultural economist, directs the Center for Global Food Issues at the Hudson Institute in Indianapolis; Alex Avery, a biologist, is Director of Research and Education at the Center for Global Food Issues; James L. Johnston is a senior fellow in regulatory affairs for The Heartland Institute and retired senior economist for Amoco; John Skorburg and Terry Francl are economists at the American Farm Bureau Federation. The authors would like to thank Carlos Stagnaro and David E. Wojick for their comments on early drafts of the manuscript. Any errors that remain are strictly the responsibility of the authors.

26 Don Comis, Hank Becker, and Kathryn Barry Stelljes, "Depositing Carbon in the Bank: The Soil Bank, That Is," Agricultural Research, Vol. 49 #2 (2001), pages 4-7.

27 "Agriculture's role discussed in carbon trading," American Farm Bureau Federation, June 19, 2000, http://www.fb.org.

28 Ibid.

29 U.S. Environmental Protection Agency, U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2001, April 2003, page 151. Note that EPA arrives at its estimates by using the methodology approved by the Intergovernmental Panel on Climate Change. These estimates form the United Nations' official registry of global emissions and sinks.

30 Ibid., page 162.

31 Ibid.

32 Ibid., page 151.

33 Comis, Becker, and Barry Stelljes, supra note 26. The authors report the work of Marlen D. Eve, a soil scientist with USDA's Agricultural Research Service in Fort Collins, Colorado. They report the finding as "20 million metric tons of carbon," which we have converted to carbon dioxide equivalents by multiplying by 44/12.

34 World Resources Institute, forest and land-use change carbon sequestration projects, http://www.wri.org/climate/sequester.html.

35 Areas such as the United States corn belt and the Argentine Pampas were originally grasslands, where the soil carbon penalty for agricultural conversion was much smaller. The world's grazing lands were also mostly grasslands, usually too dry, too fire-prone, or too acidic to sustain forests.

36 Alex McAlla, Agriculture and Food Needs to 2025: Why We Should Be Concerned, Department of Agricultural and Natural Resources, World Bank, Washington, DC, 1994.

37 Paul Ehrlich and E. O. Wilson, 'Biodiversity Studies: Science and Policy," Science, August 16, 1991.

38 Council for Agricultural Science and Technology, Preparing U.S. Agriculture for Global Climate Change, Task Force Report #119, June 1992.

© 2003 The Heartland Institute. Permission is granted to quote from this Heartland Policy Study, provided appropriate credit is given. Nothing in this Heartland Policy Study should be construed as reflecting the views of The Heartland Institute, nor as an attempt to aid or hinder the passage of legislation. Questions? Contact The Heartland Institute, 19 South LaSalle Street #903, Chicago, IL 60603; phone 312/377-4000; fax 312/377-5000; email think@heartland.org; Web http://www.heartland.org.