Organic Agriculture: A Solution to Global Warming?

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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.

“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.

Janet V

I doubt you'll ever be able to model, much less implement, an efficient, effective and truly organic farming model that services the excessive meat consumption of the American diet. It's the cows, pigs and chickens, stupid.


"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."

You left something important out, and as a result, this presentation of the numbers may be misleading. What are the overall CO2, CH4, and N20 emissions? If overall CO2 emissions are much greater than overall CH4 or N20 emissions, it is still possible that CO2 from ag sources could still contribute more greatly to global warming in total.

Based on a review of this EIA report (, it appears that despite the greater potency of CH4 and N20, CO2 resultant from agricultural activities contributes more greatly to global warming than either CH4 or N20.

This report does not identify how much C02 comes from agricultural soures, but assuming agricultural production accounts for 7% anthropogenic C02, the total C02 from ag sources would come to 407 million metric tons (0.07*5814MMT). If the 7% number you provided corresponds to all sources of CO2 (not just anthropogenic sources), of course, the contribution would be even higher (MUCH higher).

For CH4 and N20, this report uses "million metric tons - CO2 equivalent" units, and these units basically normalize values to how many tons of C02 it would take to have the same impact on global warming (i.e., these units take potency out of the equation). For CH4, the contribution from ag sources is listed as 225 MMTCO2e, and for N20, the contribution is 218 MMTC02e.

So, assuming the 7% number you provided is accurate, the CO2 from agricultural sources (407 MMT) would still have a greater impact on global warming than either CH4 (225 MMTCO2e) or N20 (218 MMTC02e). And, if the 7% number you provided corresponds to all C02 sources and not just anthropogenic ones, the C02 coming from ag sources would be even greater (MUCH greater).

Perhaps I have gone wrong somewhere with the math above, but it still remains that you should address how much in total (not as a percentage) CO2, CH4, and N20 contribute to global warming. These are the numbers which should be driving your conclusion in this entry.


Per Nelson

The author misses his mark - the release of stored carbon (fuel, chemicals) from both practices vs sequestering carbon is a much better comparison. Then look at the additive effects from both methane and nitrous oxide from both conditions. Then talk about the total GHG change.


You raised and discussed a few good issues, but ignored the strong possibility that with the whole world doing organic farming we wouldn't have enough food to feed all of the world's people - without GM crops....which usually upsets the organic foods community. (see the training nuns at a bordello comment in response 8)...



"I demand inorganic."

As if you'd need to "demand" it. Inorganic food is ubiquitous. Are you sincerely suggesting that our markets are so flooded with organic products that you can't find them? That stores are, what, keeping them from you? That there's a conspiracy against inorganic food? Seriously?

Are you really opposed to organic food, or are you, less candidly, fighting a larger opponent here? After all, sounds as if you're harboring some hostility that goes beyond organic. Sounds, frankly, as if this is a personal battle you're waging that has less to do with facts - though an argument might exist therein - and more to do with some kind of bitter resentment for the "little man."

Also sounds as if industry people, not average consumers, have written many of these comments. I feel as if I'm reading PR from agribusiness, not genuine commentary from free-acting individuals who don't have a financial stake in the game.

Perhaps, in the blog post, there is a valid argument against organics, but, in what follows, do we have commentary or spin?


Mike Italiano

Life cycle assessment (LCA) of bio vs. petroleum fuels shows little environmental difference due to the substantial climate and other pollution caused by resource extraction, manufacturing, and application of pesticides and fertilizers used in agriculture for bio fuels. For example, pesticide manufacturing generates some 30 listed hazardous wastes.

LCA is the scientific method evaluating supply chain environmental impacts over a product's life, including materials extraction, transportation, manufacturing, use, and final disposition.

A transparent, peer reviewed LCA of organic vs. conventional farming is the most accurate way to determine which system is better environmentally. This would take into account that organic agriculture avoids the supply chain pollution loads caused by added pesticides, herbicides, fertilizers, GMOs, hormones, and other additives.

David S (swatter)

I don't claim to know much about farming but my impression that conventional farming was bad for the soil (erosion, low in nutrients, devoid of pest eaters) and organic farming restored it comes from this article I read 30 years ago, and is conveniently available online.


Methane is indeed more potent as a greenhouse gas than carbon dioxide, but it absorbs energy at virtually the same frequencies of radiation as water, which is by far the most significant greenhouse gas. Thus although methane is important in terms of potency, eliminating methane emissions will do little or nothing; water will pick up the slack.


The best way to reduce Global warming is to reduce the human population. 7 billion and counting. More starving people, more poverty. The Green revolution has failed to feed all these teeming masses. Read the report about cancers rising in the third world. While we demand organic food for ourselves, we insist on food produced with heavy doses of poisons for the poorest among us, which leads to more cancer in developing nations, where they have the fewest resources to fight the "war" against cancer.


The answer is multi-fold but the beginning must be fewer people.

In high school for my science project I bred mice in known space. It was an easy experiment and cheap. At first, as long as I made sure that there was enough food available for each living mouse they bred. Soon their population over took the once a week aquarium clean. When that occurred I began to notice that they began to fight more frequently. Mother's ate their kits and other mice would steal kits to eat. Still the population grew as I continued to clean their enclosure once a week and maintain an adequate food supply for the mice living there. I eventually ended the project because the out come was obvious: mice will reproduce no matter what is occurring around them. They will fight, hoard, and kill to hoard. They destroy their environment by reproduction even when disease is rampant. How are we different?


I like how people try to point to using GM crops to "save" poor countries faced with food crises. Why do they have food crises to being with? Ah, yes, massively subsidized Western agribusiness and "free" trade agreements that destroyed indigenous agriculture. Yes, keep the GM crops humming, boys.

Is it too much to ask that, perhaps, that a good portion of our problem here is the amount of land taken up by crops that aren't used to feed people at all, but rather to fatten livestock? Or that reducing portion sizes and consumption of said livestock might have a beneficial effect on the amount of food available (which is already ample) and GHG emissions? Mind you, I'm an omnivore, but the amount of land given over directly and indirectly to livestock production is simply insane.

Jacob H.

I would submit that an organic, vegetarian diet will produce a whole lot less CH4 and NO2 than a non-organic, meat-eating diet.


Interesting discussion, but the studies referenced above are not speaking to each other. Reducing organic agriculture to 'row crops with manure' with all other things being similar to industrial agriculture completely misses the mark. Reductionist thinking like that is a big part of what got us into the mess we are in. There are a myriad of systemic benefits relating to GHG emissions that occur in a transition to local, organic food production. Are they harder to do a controlled study on? Yes, of course. Does that make them less valid? Heck no. You industrial ag folks can have the Gulf, I'll stick to my backyard.

David S (swatter)

for #5 Joel Upchurch:

1) organic farming feeds a lot more people than ex-hippies: there are Whole Foods stores all over this area that do a big business.

2) the idea that opposition to GM crops is the cause of starvation in the world is absurd. Wars and natural disasters have made it extremely difficult for many to feed themselves and extremely difficult logistically to get food to them. When we can distribute food to those in need elsewhere in the world, our methods in the past have been more to "help" our farmers (agroindustries) with a total disregard as to how we destroy their local markets (there is ample economic literature on this). Sometimes, we have also given grain that has rotted from sitting in silos too long because of our price supports for farmers which lead to them producing too much, but I digress.


I may be missing something here, but I do believe that free range animals help push methane back into the ground where less is released into the air. If we are just discussing planting crops, fertilizing, and tilling, then I don't think this article alone does the issue of green house gasses justice. There are so many facets to the discussion... One would think with all the technology we have created, this would be figured out by now. The only thing I do agree with is this issue would be better served w/out all the binary "for or against" ideologies.


Excellent, thoughtful post -- thank you. While I generally eat only organic foods, wear largely organic clothing and work in organic agriculture, I agree that we must always check our assumptions and value good research to help us guide our decisions. We need more investigation of the whole-system input/output balances in organic and other forms of agriculture, addressing all the GHG contributors.

Regarding some of the comments about soil sequestration, I believe the most basic measure of this is soil organic matter (SOM) content. While this varies widely depending on location and soil type, organic systems generally result in much higher SOM. In veg crop systems in California, I have seen from 3 to 8% SOM in sandy to clay loam soils under prolonged organic management, and they have increased over time. Similarly situated conventional soils are generally less than 2%. The result is that more atmospheric carbon is moved into and sequestered long-term in organic soils than conventional, and in significant proportions.

No till conventional is somewhat better, but often still lower SOM than tilled organic, I believe. Many people are working on organic no-till systems. Perennial cropping systems, such as the Land Institute is pursuing in KS, will be much better still, especially under organic management.

The larger point about higher impact GHG, like methane and NOx, is critical, though. I think a next set of questions involves broadening the scope of the data -- where are the inputs coming from for the conventional fertilizers (natural gas usually) and pesticides, or for the compost for organic systems? How is material being composted -- hot or cold -- and what off-gassing occurs there? What happens with the crops at harvest (as Ian Kemmish notes) -- are cover crops mulched on the surface for a while or tilled in immediately. We must also be very careful not to speak of compost and manure interchangeably, since they are very different and have very different effects on GHG. More questions remain for a full systems analysis. I look forward to your post on CAFO manure use in compost, James.

A final note for now: large-scale monocropping is in and of itself problematic in many ways, including the input problems noted here (drawing on CAFOs, transporting large quantities of inputs, etc). While many large organic farms exist currently, no large-scale monoculture truly meets the intent of the National Organic Standards. Over time, we must hope that regulation and markets will transform such operations into much more diverse arrays of smaller blocks with longer rotations and increased perennial landscape diversity to support healthy production. That is the intent of the rules, and the result will likely provide many benefits compared to current monocultures, including I believe better GHG management.

For those who believe such systems cannot provide enough food and fiber, many studies have shown that these systems are more productive per acre than larger scale industrial monocultures. The problem is that they don't allow for as much concentration of capital, which means that investors don't back them, thus thwarting their broader adoption and leaving them to marginal markets at the high- and low-end of the wealth spectrum.



What's the carbon footprint of manure that isn't used in organic farming?

It seems unlikely that more animals would be raised in order to produce more manure. So the manure's going to be produced anyway.

Thus we need to subtract the natural carbon footprint of manure from organic farming's carbon footprint.


Long term carbon sequestration is achieved by building up the carbon in the soil, especially top soil.

The other long term sequestration occurs in average standing biomass, which is more difficult to achieve.

More interesting is the possibility of using bio-derived charcoal as a long term soil amendment.

Nothing has been said about the relative amounts of NO released by the conventional application of chemical nitrogen fertilizers. Yes NO is released during manure application, but the excessive application of chemical NO may be more harmful? Can anyone speak to this?

David S (swatter)

Oh, and one more comment on GM foods:

my understanding is that the a) seeds cost more and the product is infertile, meaning that seeds for the next year's planting have to be purchased rather than being derived from the plant itself, and thus b) it is too expensive for farmers in developing countries.

Our highly mechanized methods are also not easily transferrable to countries where labor is cheap and plentiful and machinery, fuel and parts are not.

T.S. in NJ

C'mon Freakonomics Team, there are a couple of big holes in this analysis!

(1) Assuming the manure were not used to enrich soil, wouldn't it still give off methane and NO?

(2) Organic farming is not only about reducing our carbon (or methane or NO) footprint (that is more the focus of the "buy local" movement), but about decreasing our dependence on non-renewable resources by employing renewable resources (that would otherwise go to waste), and about cultivating our food in a manner that does not pollute our planet in other ways. Toxic chemicals from big agriculture build up and persist in the soil, run off into our water ways, infect wildlife, and end up in our bodies. Think about all of the carbon/methane/NO gases that are emitted on a daily basis from the process of remediating toxins in our environment (dredging waterways, capping landfills, administering Superfund sites and related environmental remediation litigation, etc.). Certainly a substantial portion of the production of those gases from those activities are attributable to toxic chemical pollution by big agriculture. Doctors increasingly think many nervous system ailments (for example, ADD) may be caused by toxic chemical exposure, requiring daily medications (produced in carbon-emitting factories), doctor visits and sometimes even death (cancer), so perhaps you should also consider all the carbon/methane/NO emitted in this way as well. My point is that by focusing on carbon/methane/NO so narrowly as applied to organic farming, you're missing the big picture...something that I thought Freakonomics always cautioned against.