What mainstream media doesn’t say about carbon emissions in agriculture

jack dewitt


Greenhouse gas emissions and global warming. Tired of hearing about them? Yeah, me too, but we agriculturists have to stay in the discussion to keep everybody honest.

Consider the conflicting data from these sources. In 2006 the United Nations Food and Agriculture Organization (FAO) stated in their study, “Livestock’s Long Shadow,” that livestock produced 18 percent of the world’s greenhouse gas emissions (GHG). In 2009 the Worldwatch Institute, a Washington, D.C., think tank, morphed that study into 51 percent of GHG emissions from global livestock rearing and processing, declaring livestock farming was destroying the planet.

The 2006 study was later shown to be in error and corrected by the authors, but the mistaken numbers linger on in the press. The error was research bias, perhaps intentional, perhaps not. The FAO analysts considered every factor affecting meat production — land conversion from forest to pasture, production inputs to grow feed, methane and manure emissions, meat processing, etc. That lifecycle assessment was compared to transportation using only emissions from the exhaust pipes, with nothing assigned to road construction, vehicle and parts manufacture, and vehicle and road maintenance.

Today, U.S. agriculture has been assigned 9 percent of GHG emissions by the U.S. Environmental Protection Agency. Transportation — 29 percent: Electricity generation — 28 percent: Industry — 22 percent: Commercial and residential — 12 percent. But a fact little noticed by the press is that the EPA credits agriculture and forestry with offsetting 11 percent of U.S. GHG emissions, sinking CO2 into soil organic matter and plant tissue. A net positive for land use of 2 percent.

I have long bemoaned this omission by the press of agriculture’s global warming positive side. For example, as I outlined in a column last May titled Perspective: Is corn production a villain or a hero in our economy?, corn takes about 1.2 barrels of crude oil to grow an acre, but the growing corn uses photosynthetic energy to capture the carbon-based energy equivalent of over 21.3 barrels of crude oil. About 9.5 of those barrels will be hauled off the field and sold to feed livestock, make ethanol, and manufacture food and industrial items, eventually returning most of the CO2 captured through photosynthesis to the atmosphere. The carbon captured in the fodder and roots, 11.8 barrels worth, will be returned to the soil where it will decay.

A barrel of crude oil, when burned, will produce about 950 pounds (433kg) of CO2. So the 1.2 barrels consumed to produce an acre of corn emitted 1,140 pounds of CO2. The CO2 taken from the atmosphere for plant growth would amount to about 20,235 pounds (21.3 X 950). Most of that CO2, say 90 percent, will be returned to the atmosphere through refuse decay and industrial and food use of the harvested kernels. That would still leave a net atmospheric reduction of CO2 nearly double what was added from fossil fuel.

Why should we worry about CO2 anyway? It makes up such a small percentage of the atmosphere (0.041 percent). Water vapor is by far the most abundant heat absorbing molecule in the atmosphere, for which we are thankful. Without the heat-retaining effect of water vapor, the Earth would be very cold. We are also fortunate that all the heat we receive from the sun is not retained, or we could be another vapor-covered planet like Venus — too hot for life.

When light waves strike the Earth, the waves are lengthened and reradiated in the infrared range, which we cannot see (but can feel as heat). Water vapor in the air, and other gasses, absorb this heat and reradiate it in all directions, some heading back to earth and some, eventually, making it back to space. In this way water vapor serves as a thermostat for the earth.

Water vapor does not absorb all wavelengths in the infrared, which range in length from one nanometer to one millimeter (one billionth of a meter to one thousandth of a meter). So some waves get an unhindered path back to space. This is where CO2 and other minor gasses, such as methane, get involved. CO2 and methane will absorb some of the wavelengths water vapor lets through. (Google Guy Stewart Callendar.)

For an analogy, picture a bucket with holes an inch apart up one side. Pretend water pouring in the bucket is heat and pour it in at a rate that keeps a constant level with half the holes leaking. Then plug the bottom hole and keep pouring. The water level rises to the next hole and an equilibrium is reached. Plug another hole and a new equilibrium is attained, and so on until the bucket runs over. That’s what CO2 does in the atmosphere — it plugs some of the holes water vapor left open for heat to escape. If we get enough CO2 to plug enough holes, eventually we feel the extra heat. (An effect not universally accepted as significant.)

Despite the fact that agriculture and forestry are a net carbon sink, we should all endeavor to use practices that reduce emissions and sink as much carbon back into the Earth as we can. Using the best available modern practices we can both feed the world and help limit planet warming.


Jack DeWitt is a farmer-agronomist with farming experience that spans the decades since the end of horse farming to the age of GPS and precision farming. He recounts all and predicts how we can have a future world with abundant food in his book “World Food Unlimited.” This article was republished from Agri-Times Northwest with permission.

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