Organic Agriculture: A Solution to Global Warming?

Photo: ellenm1

In 2008, the Rodale Institute-an organization dedicated to the promotion of organic agriculture-published a widely noted report entitled “Regenerative Organic Farming: A Solution to Global Warming.” The takeaway was that organic agriculture, due to its reliance on biological rather than chemical methods, could substantially reduce carbon emissions generated by the agricultural sector. Rodale predicted that if the world’s 3.5 billion acres of arable land were placed under organic production, 40 percent of global carbon emissions would be immediately sequestered.
It was an impressive projection and, as far as I can tell, an accurate one. Organic farming’s use of cover crops and composted manure is a remarkably effective way to sequester carbon dioxide. The Rodale report continues to garner widespread attention. As recently as a month ago, Peter Melchett, Policy Director of the U.K.’s Soil Association, championed the assertion that organic agriculture reduces global warming. He spoke as if the claim was conventional wisdom-which, in a way, it is.
But this bit of conventional wisdom is not as simple as it seems.? Yes, organic methods sequester more carbon dioxide than conventional ones. But the ultimate culprit behind agriculture-driven climate change isn’t carbon dioxide. Instead, it’s methane and nitrous oxide-two gasses conspicuously absent from the Rodale study. Agricultural production in the U.S. accounts for only 7 percent of overall carbon dioxide emissions. By contrast, it accounts for 19-25 percent of methane emissions and 70-75 percent of nitrous oxide emissions. Methane, according to the EPA, is 23 times more potent a GHG than carbon dioxide. Nitrous oxide is 310 times as potent.
So the key question, as far as GHG emissions and agriculture goes, is not how much carbon dioxide organic agriculture sequesters. Instead, it’s how much methane and nitrous oxide it sequesters. And this question, like any controversial topic in agriculture, is riddled with caveats and qualifications.? A recent conference in France dedicated to organic agriculture and climate change found that, in some cases, organic systems sometimes had higher GHG emissions and that, in other cases, conventional systems had higher levels of output. “The data,” it judiciously observed, “are very variable according to the situation and the production system.”
Not all assessments of the issue have been so moderate. The most aggressive (and, at the same time, legitimate) answer I could find came from Dr. Steve Savage, a plant pathologist and agricultural consultant based in California. Savage, who dutifully expresses deep admiration for organic production, nonetheless came to the stark conclusion that, regarding GHG emissions and organic agriculture, “gain in soil carbon on an organic farm comes at the substantial carbon cost of methane and nitrous oxide emissions.”
Savage works from two defining premises. The first is that the methods typically used by organic growers to fertilize row crops-namely planting cover crops and applying manure or compost-can, under certain circumstances, create “substantial” levels of nitrous oxide and methane emissions. How substantial?? That brings us to Savage’s other critical premise: 83 percent of the U.S.’s agricultural production today is in row crops (corn, wheat, hay, and soy) grown on a large scale. It is on the basis of these premises that Savage calculates what would happen to GHG emissions if all these staples were produced organically. His answer, which he claims to have checked out with hundreds of scientists, is eye-opening to the extreme: organic methods lead to a “carbon footprint” that’s fourteen times higher than if conventional methods were employed.

The reasons for this vast disparity-which is, of course, just a projection-can be found at the intersection of monoculture and organic fertilizer.? Composted manure-a common fertilizer for organic growers-might not require fossil fuel to manufacture, but it must be stored, shipped and distributed in order to keep pace with the demands of large-scale monocultural crop production. Putting aside for the moment the fact that the vast majority of manure used on big organic farms comes from CAFOs (or concentrated animal feeding operations; I’ll address this issue in a future post), it’s important to note that 2.7 percent of the carbon in composted manure is emitted as methane before the stuff is even spread.? Given that it takes around 4-7 tons of composted manure per acre to grow row crops, the impact of many tons of fermenting manure quickly adds up.
When compost hits the field, it not only continues to release methane, but nitrous oxide as well.? When oxygen levels in the soil are low-when the soil is wet or compacted-about 1-2 percent of the nitrogen in the manure is released in the form of nitrous oxide.? Even if the soil is frozen, nitrous oxide is released-even more so than with conventional methods (as a 2009 study revealed).? Finally, when organic growers till cover crops (such as nitrogenous legumes) back into the soil in the spring, a brief “explosion” of nitrous oxide (remember, it’s 310 times worse than carbon dioxide) occurs (see this and this). According to Savage (and others), conventional farmers are better able to prevent this gas blast by practicing no-till methods. It is the tillage factor that, in part, led an international conference on climate change and organic agriculture to note that, “when calculated per kg of product, in the case of substantially lower yields, organic farming can result in a higher global warming potential.”
What are we to make of the suggestion that organic methods may not be the global warming panacea they’ve been promoted to be?
Criticizing organic agriculture often suggests antipathy for organic agriculture. This shouldn’t be the case. As mentioned, organic agriculture has clear advantages. Most notably, it’s the only codified approach to agriculture that places top priority on soil health.? The fact that methane and nitrous oxide emissions complicate the claim that organic agriculture reduces climate change is no reason to dismiss organic agriculture as a whole. Instead, it provides an opportunity to do something that the intensely polarized agricultural world rarely does: think beyond the organic vs. conventional divide.
Doing so uncovers a world of hidden potential. What would happen, for example, if farmers anaerobically digested methane from fermenting manure and used the energy to produce high grade synthetic fertilizer? What would happen if organic farmers adopted GM crops that led to higher yields and greater nitrogen uptake efficiency? What if conventional growers mixed row crops with specialty crops-crops grown to be fed to people rather than to farm animals or biofuel plants?? What if farmers viewed sustainable farming as an agricultural balancing act, one that drew on the widest variety of possible inputs to achieve the highest yielding and most environmentally sound outputs? These questions only scratch the surface, but they all demand a perspective that transcends the organic/conventional divide.
We can debate the comparative merits and demerits of organic and conventional systems until the cows come home. But until we start substituting pragmatic realism for ideological purism we’re destined to do little more than reap the bitter fruits of a harvest sown with righteousness and extremism.