Are Organic Farms Really Worse When It Comes to Greenhouse Gases?

A new paper making negative claims has scientists defending organic food.

A farmer harvests organic kale. (Photo: Thomas Barwick/Getty Images)

Jul 24, 2015· 5 MIN READ
Dan Nosowitz is a freelance writer based in Brooklyn. He has written for Popular Science, The Awl, BuzzFeed, Modern Farmer, Gawker, Fast Company, and elsewhere.

Organic farming earned some negative press recently with the publication of a paper that linked it to higher greenhouse emissions, but the truth is a little more complex.

The paper, by University of Oregon Ph.D. student Julius McGee and published in the journal Agriculture and Human Values, found what appears to be a shocking bit of information: “Organic farming,” McGee says, “is correlated positively and not negatively with greenhouse gas emissions.”

The study used data from 49 states collected between 2000 and 2008 (Louisiana is the lone holdout, and data for Alaska was not available for 2000 or 2001) and measured the average levels of greenhouse gases coming from an acre of farmland in the U.S. Though McGee wouldn’t tell me how much those levels have increased, his paper finds that the levels have been on the rise. “The way I’ve set up my model, it’s really hard to see it as the result of anything else,” he says. Given that organic products are on the rise, he figures, isn’t it a disturbing correlation?

Except, not so much. For one thing, McGee’s paper does not compare emissions from conventional farms with emissions from organic farms, which seems to me a strange omission when you’re trying to talk about this subject. What the paper does is look at total emissions over time, consider the rise in organic farming, and connect the two trends with analysis rather than data.

“The model itself doesn’t establish any causation,” McGee acknowledges. “I sort of make that claim with theoretical analysis in which I cite other literature that gives credence to the idea that, hey, maybe this is a causal pattern that’s the result of larger social processes behind organic that’s making it positively correlated with greenhouse gases.”

The paper has been criticized by organic advocacy groups and experts alike.

From a sheer scientific standpoint, not everyone is convinced the study is trustworthy. “I think the conclusions that he came to don’t seem to make a lot of sense with the way he analyzed the data, and the data that he utilized has some issues in it,” says Kris Nichols, chief scientist at the Rodale Institute, a nonprofit that does research relating to organic farming. Nichols also listed, politely, 11 major flaws in the study.

The Organic Center, a nonprofit research institution that works with science concerning sustainable agriculture, wrote in a damning response: “The statistical model used is simplistic and the data insufficient to draw any meaningful conclusions regarding the actual source of GHG emissions.” The Organic Center further notes that McGee’s paper does not account for the massive increase in conventional farmland, much of it to be used for livestock, in the past 15 years. A single acre of new farmland dedicated to conventional cattle would counteract any benefit from dozens of acres of organic farming, which is largely dedicated to fruits and vegetables.

In an op-ed for The Guardian, McGee claims that large organic farms are ruining the reputation of true organics by looking at loopholes, saying that beneficial tactics like crop rotation “are encouraged, but not required” for organic certification. This is wrong, for what it’s worth; crop rotation is required by law (though some would argue the requirements could be more elaborate).

So, McGee’s study has its detractors. But that doesn’t mean examining the impact of organic farming on greenhouse gas emissions isn’t worthwhile. Thats partly because reducing greenhouse gas emissions is not a core tenet of organic farming.

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“I dont think that when the organic standards were created, we were discussing greenhouse gases that much,” says Nichols.

But this is a big deal. According to the EPA, 9 percent of greenhouse gas emissions come from the agricultural sector. Some of that 9 percent is hard to combat; about a third of it comes from methane from cows, and cows are pretty much going to produce methane whether they’re organic or not. But more than half of that 9 percent comes from nitrous oxide emissions from the soil.

Nitrous oxide works like this: Plants need nitrogen to survive and grow. Lots of microbes in the soil, most of which are totally benign or even beneficial by themselves, also love to eat nitrogen. The more a plant absorbs, the better it grows. The United States is the second-largest user of synthetic nitrogen fertilizers, behind China.

But plants are not particularly efficient at absorbing nitrogen fertilizer. They tend to absorb maybe 10 to 15 percent of the fertilizer we lay down, and this fertilizer is so cheap and easy to use that big conventional farms tend to shovel it on far in excess of whats needed. Even worse, conventional farms often just heap on a giant glob of it, enough for an entire growing season, all at once, often in the spring. Partly that’s to avoid the heat of midsummer, which can burn the fertilizer and partly it’s because it’s easier to apply fertilizer when plants are small (or even just seeds).

That leaves an awful lot of pure, synthetic nitrogen sitting around unused by the plants. So those soil microbes are presented with a veritable feast, gorging on the nitrogen and burping out, as an excretion, nitrous oxide. The more synthetic nitrogen-based fertilizer you use, the more nitrous oxide your soil microbes will produce.

Nitrous is the big bad wolf of agricultural greenhouse gases. “Nitrous oxide, as a greenhouse gas, is about 300 times more powerful than carbon dioxide,” says Nichols. But there’s also plenty of carbon dioxide being released. Carbon is an essential element for plants: Ideally, organic farmers want their soil to be a rich store of carbon, delivering the vital nutrient to plants for years and years. In comparison, conventional farms have a tendency to lose carbon over time; this is because synthetic nutrients tend to leach through soil faster, rather than be stored for long periods of time. And the required rotation of crops in organic soil can help replenish the stores of both carbon and nitrogen; legumes and clover are both useful for this.

Another way organic farming is helpful for greenhouse gas emissions comes from the way manure is broken down. You can store and break down manure in two broad ways: aerobically and anaerobically. Aerobically is what we think of as a compost pile: plant and animal material composing out in the open. An anaerobic strategy, which is used more often by conventional farms, buries manure in slurries, tanks, or ponds, where oxygen can’t reach it. Bacteria are going to break down manure no matter what, but without oxygen, they’re going to produce methane, which, according to Nichols, is about 30 times more powerful than the carbon dioxide produced in an aerobic environment.

There are many who hold the opinion that the organic standards aren’t strong enough to properly cope with the problem of greenhouse gases (and many other problems). Criticism of the organic food standards, a legal certification provided by a division of the U.S. Department of Agriculture, is common among some food activists and farmers. For farmers, the complaint is mostly that organic certification is expensive, hence new independent standards such as Certified Naturally Grown, which has similar rules to organic certification but is about a tenth the cost. (The cost is kept down by having other Certified Naturally Grown farmers do the inspecting; to be a member, you have to do at least one inspection.)

Others, like Food Alliance, boast a different set of rules from organic certification. Food Alliance does not ban all synthetic fertilizers and pesticides, the way the USDA does for organic certification; instead, it bans all chemicals rated poorly by the World Health Organization, whether they’re organic or not. It also demands reduced water and energy use and pest management systems that use natural methods, such as ladybugs and decoy plants.

But the interesting thing about the discussion around greenhouse gas emissions and organic farming is not that organic farming does, despite whatever incorrect conclusions are being drawn from McGee’s study, reduce emissions. It’s that organic farming fights emissions accidentally. “I dont think there was a lot of understanding about the potential for organic farming to store more greenhouse gases—sequester carbon—in the soil,” says Nichols. But there could be, and a rejiggering of the organic standards could still nudge the effects of organic farming in that direction.