Diet for a Cool Planet – Part One

    Long before we discovered that the “rock oil” (now called petroleum) that we had used for centuries to lubricate or illuminate could be burned in internal combustion engines, agriculture was causing global warming. Starting around 10,000 years ago, the first farmers burned forests, liberated soil carbon through tillage, and created methane emitting rice paddies. If not for this, the brief interglacial period we call the Holocene in which human civilization has flourished would probably have ended by now, and we would be back to the Earth’s preferred Ice Age climate.[i] The scars of these endless glaciations are evident to the trained eye halfway down the continental US. This early global warming was a welcome relief from the cold.[ii]

    But all that changed when the Agricultural Revolution gave way to the Industrial Revolution. We found a much more efficient means of heating the planet, by pumping carbon dioxide (CO2) directly into the atmosphere through the smokestack and the tailpipe. And industry came to the farm too; now steel tractors could plow much more land, burning diesel as they went, and more forests were cut to make way for increasing acreages of cropland. Eventually, industrialization led to chemistry, and chemistry to the Haber-Bosch process of using fossil fuels to synthesize nitrogen fertilizer. Now nitrous oxide took its place alongside CO2 and methane in the trio of modern agricultural greenhouse gasses.

    It was too much of a good thing. What was once a pleasant bit of warmth that kept the glaciers at bay, now started cranking up the heat to dangerous levels. How much of this warming can be attributed to farming? Measuring agricultural emissions is trickier than simply counting tons of CO2 coming out an exhaust pipe. Producing and processing food, and getting it to us, is the world’s largest economic activity; 40% of humanity is involved in farming, and more than half the world’s habitable land surface is used for agriculture. There are a myriad of both sources and sinks to calculate. And then there’s the fact that both methane and nitrous oxide trap more of the sun’s heat than CO2 – methane about 28 times, and nitrous oxide about 265 times, over a 100 year period (we deal with this by speaking of CO2 equivalents, or CO2-eq; thus one ton of methane has a CO2-eq of 28 tons).

    Many studies have attempted to estimate the food system’s overall contribution to climate change, and depending on what they count and how they count it, they get widely varying results. A recent study published in the journal Nature Food offers perhaps one of the more definitive answers to this puzzle, and you can guess its conclusion from its title: “Food systems are responsible for a third of global anthropogenic GHG emissions”. Scientific studies are nothing if not to the point. To be precise, 34% of anthropogenic GHG (human caused greenhouse gas) emissions result from the global food system. To break that number down a bit further, 24% of global food emissions come directly from farming and the “land use changes” (deforestation and soil carbon loss) it causes, and the remaining 10% come from supply chain activities (transport, processing, packaging, retail, refrigeration). And Canada, for its part, has the fourth highest per capita agricultural GHG emissions in the world, with total emissions rising 23% between 1990 and 2018.[iii]

    So about those direct agricultural emissions – where exactly are they coming from?

    Some is from the tillage we’ve been practicing for 10,000 years. When soil is plowed, oxygen is introduced, spurring microorganisms to go on a feeding frenzy of soil organic matter. When these microscopic animals digest this organic matter, which is mostly carbon, they exhale it as CO2, just as we do. And a bunch of carbon that was once stably sequestered in the soil is now floating around the atmosphere, trapping solar energy. It is estimated that most agricultural soils have lost between 30% to 75% of their organic matter since the beginning of farming,[iv] and 25% to 40% of the excess CO2 we now observe in the atmosphere came from soils.[v] Yet soils still retain over three times as much carbon as is found in the atmosphere, and over four times as much as is found in all the world’s biomass; they are second only to the oceans as a carbon sink.[vi]

    A rusting plow

    But we can put the carbon genie back into the soil bottle, in much less time than it took us to remove it. This is the focus of regenerative agriculture, which attempts to work with natural processes to help build soil organic matter. The beauty of this approach is that increased organic matter also means increased plant health, nutrition, and drought tolerance, with less reliance on fertilizers and higher net returns for farmers and ranchers.

    The potential is significant. The Earth’s atmosphere currently has 410 ppm of carbon in it. To draw that down to the safe maximum of 350, we would need to remove 60 ppm. Each half percent increase in soil organic matter across the world’s seven billion acres of farmland draws down 15 ppm. So we would just need to increase organic matter by 2% worldwide to bring CO2 concentrations back down to a safe level, or 4.3% to get back to the pre-industrial level of 280 ppm.[vii] I have heard of ranches that have increased their organic matter by 5% in just ten years.[viii]

    How do we do this? The number one way to restore soil organic matter is to till as little as possible. But one of the main reasons farmers till is to control weeds, so if they don’t till, they often turn to increased herbicide use. This is exactly what many no-till or low-till grain farmers in the prairies using seed drills have done. Yet glyphosate, the most widely used herbicide, has been labelled a “probable carcinogen” by the WHO. And pesticides also kill off soil microbes that help sequester carbon in the soil, so the challenge is to develop organic no-till cropping systems.

    There are a number of recent books written by farmers having success with this growing vegetables on smaller scales: Bryan O’Hara of Tobacco Road Farm in Connecticut (No-Till Intensive Vegetable Culture: Pesticide-Free Methods for Restoring Soil and Growing Nutrient-Rich, High-Yielding Crops), Maine farmer and former Jonny’s Seed researcher Andrew Mefferd (The Organic No-Till Farming Revolution: High-Production Methods for Small Scale Farmers), and Jesse Frost of Rough Draft Farmstead in Kentucky and the No-Till Grower’s podcast (The Living Soil Handbook: The No-Till Grower’s Guide to Ecological Market Gardening). The Rodale Institute has also developed a system using an implement they invented called a “roller crimper”. But more work is needed to scale these efforts up and diversify beyond vegetables.

    Another reason for tilling is to loosen and aerate the soil, making planting easier and providing a burst of nutrients as oxygen invigorates soil microbes – while also, as previously mentioned, burning off soil carbon. But nature has worked out ways to keep soil aerated without humans needing to plow it. Left undisturbed, soil becomes a mindbogglingly complex community of bacteria, protozoa, fungi, nematodes, arthropods, and earthworms, all living within a medium of minerals and organic matter, and interacting symbiotically with plant roots. All this life works in concert to create conditions that will be friendly to more life, and that means making it easier for air and water to penetrate into the earth. So fungi, for example, produce a substance call glomalin, which causes soil particles to aggregate into small crumbs, leaving air spaces in between; earthworms likewise leave tunnels in their wake.

    Yet tillage smashes this delicate community to pieces, particularly the crucial fungal hyphae. Deprived of its natural processes of aeration, the soil becomes dependent on regular tillage, as an increasingly deadened soil collapses soon after each pass with the plow or disc, in need of another mechanical hit. The solution is to allow these microscopic underground cities to flourish, and watch the above ground plant biomass grow strong on the nutritional dynamism at play in its rhizosphere.

    Another way to avoid tillage is to simply grow perennials, which are planted once, then live for years without further soil disturbance. Temperate climate examples include nuts, most fruit, some greens and herbs, wild plants like fiddleheads, nettle and ramps, maple syrup, and of course asparagus and rhubarb. But it’s the tropics where perennials really shine: bananas and plantains, coconut, avocado, olive, date and oil palms, cacao, coffee, sugarcane, and the overlooked but prolific breadfruit, which can produce over a thousand pounds of potato-like fruit from a single tree.[ix]


    Yet annual grains currently make up over 70% of our global caloric intake, which is why the Kansas-based Land Institute has been working for several decades to breed perennial grains, oilseeds, and legumes. They currently have a cousin of wheat in the early stages of commercialization.

    Yet another approach is being taken by Wisconsin farmer Mark Sheppard on his New Forest Farm, as well as Philip Rutter at the Badgersett Research Farm in Minnesota. Both are breeding and trialing hazelnuts and chestnuts as potential perennial replacements for soybeans and corn (hazelnuts have a similar protein content to soybeans, and chestnuts a similar carbohydrate profile to corn). These are visionary projects that could completely transform large-scale agriculture, moving it to a system that doesn’t require annual tillage, and allowing more carbon to be stored safely underground, as well as in the woody biomass of the crops themselves.

    To be clear, all these efforts at soil carbon sequestration would not grant us a free pass to keep burning hydrocarbons. At a certain point, soils become saturated with organic matter and you can’t easily add more. But this could be a temporary stop-gap, buying us some much needed time to keep global temperatures at safe levels while we rapidly transition off of fossil fuels over the next 30 years.

    Fertilizing climate change

    Adding fuel to the fire, so to speak, is not just tillage, but the use of artificial fertilizers. The Haber-Bosch process that gave us the Green Revolution also produces all three greenhouse gasses: nitrous oxide (seeping from soils doused in nitrogen fertilizer), CO2 (in production), and methane (from its feedstock, natural gas). The UNCTAD has written that synthetic nitrogen fertilizer is “the biggest contribution of agriculture to climate change”, a perspective echoed by the National Farmers Union in Canada.[x] And Canada has doubled its artificial nitrogen fertilization since 1993.

    As if that’s not enough, nitrous oxide also destroys the ozone layer. According to the European Nitrogen Assessment, “the total costs of nitrogen pollution of water, the atmosphere, and other impacts on ecosystems and climate change…is more than twice the monetary benefits of nitrogen in agriculture.” It’s a textbook example of economic externalities at work.

    And yet the air we breathe is 78% nitrogen. Nitrogen-fixing bacteria exist in the soil, often in association with legumes, to take that atmospheric nitrogen and turn it into a form that plants can use. Biological solutions exist that would provide our crops with all the nitrogen they need, without all the negative externalities associated with synthetic nitrogen. We just need to reorient our mindset away from an industrial/control-of-nature one to an ecological/partner-with-nature one.

    Reducing our dependence on synthetic nitrogen was one of five GHG mitigating policies that Farmers for Climate Solutions, a coalition of Canadian farming groups, asked the Canadian federal government to fund in their spring 2021 budget (the government said yes to all of them). The other four were increased cover cropping (soils covered with plants sequester more carbon than bare soils), normalizing rotational grazing of livestock (I’ll discuss this in Part Two), protecting wetlands and trees on farms (both of which are carbon sinks), and powering farms with clean energy (think solar panels and electric tractors). The UNCTAD was thinking along similar lines when they wrote that carbon sequestration in farmland could offset all agricultural emissions through a combination of organic fertilization, low tillage, and planting legumes in rotations.[xi]

    Beyond the farm gate

    “Food miles” is a concept that has been popularized, yet its impact is often overstated. According to the Nature Food study referenced above, transportation only accounts for 4.8% of food system emissions, with “the majority of emissions arising from local to regional transport via road (81%) or rail (15%), rather than navigation [boats] (3.6%) or aviation (0.4%).” In other words, how you get to the grocery store or farmers market and back probably matters a lot more than where in the world your food came from, at least from a carbon footprint perspective. (But don’t get me wrong, I love local food for a whole host of other reasons).

    How you prepare a food can also have a huge impact; one study found that up to 60% of the carbon footprint of a cup of coffee came from the automatic coffee machine, with only 2% from transport.[xii]

    Packaging is slightly more important than transport, at 5.4% of food emissions. Add to this the crisis of plastic pollution in our environment, and it’s one more reason to seek out food with as little packaging as possible.

    Food waste matters even more than these two factors, with the FAO estimating that one-third of all food grown gets wasted globally. About 8% of our total GHG emissions worldwide can be attributed to food waste. In low-income countries, this tends to happen at the farm, where a lack of refrigeration and efficient transportation leads to food spoiling before it can reach the market. In a high-income country like Canada, wastage happens more on the consumer end, with us buying too much food and then letting it spoil in our refrigerators, or refusing to buy “ugly fruit”. Throwing it into a landfill just amplifies the problem, as that anaerobically rotting food then emits methane.[xiii]

    So we’ve looked at the CO2 and nitrous oxide emissions from our food system, but what about the third major greenhouse gas, methane? We can’t talk about methane without talking about meat, and that’s such a contentious and complex subject, it’s going to need a whole Part Two to itself.

    At the end of Part Two, you’ll find my list of recommendations on how to eat your cake and have a cool planet too.


    [ii] This trend reversed temporarily when the human population suffered repeated devastations, first from Mongol invasions, then the Black Death, and finally from diseases brought by Europeans to the Americas. Each of these population collapses brought decreased agricultural activity and the regrowth of forests, sucking tons of carbon out of the atmosphere. Thus from about 1300 to 1850 we have The Little Ice Age, when villages in the Swiss alps were destroyed by advancing glaciers, and the Baltic Sea froze over twice.

    [iii] Wake Up Before It Is Too Late: Make Agriculture Truly Sustainable Now for Food Security in a Changing Climate, UNCTAD

    [iv] Regenerative Organic Farming: A Solution to Global Warming, Rodale Institute

    [v] Wake Up Before It Is Too Late: Make Agriculture Truly Sustainable Now for Food Security in a Changing Climate, UNCTAD

    [vi] ibid

    [vii] Course by Dan Kittredge, Bionutrient Food Association,

    [viii] Workshop by Glenn Alzinga, Alderspring Ranch,

    [ix] The Carbon Farming Solution: A Global Toolkit of Perennial Crops and Regenerative Agriculture Practices for Climate Change Mitigation and Food Security, Eric Toensmeier

    [x] Wake Up Before It Is Too Late: Make Agriculture Truly Sustainable Now for Food Security in a Changing Climate, UNCTAD, and Tackling GHG Emissions from Livestock Production, NFU

    [xi] Wake Up Before It Is Too Late: Make Agriculture Truly Sustainable Now for Food Security in a Changing Climate, UNCTAD

    [xii] ibid

    [xiii] Food Wastage Footprint and Climate Change, FAO

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