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Corn Crop Waste – Part 2

Corn crop waste, Part 2 looks at the impact on our environment

Cool the Climate, Clean the Environment, Improve Public Health, Reduce Rural Poverty with Small-Scale Biochar – Part 2


Why Care that Corn Crop Waste Burns Dirty?

This, the second in a series addressing the climate, environmental and human health consequences of the open field burning of corn crop waste, is about understanding self-interest. Specifically, “Why Care” makes the case that burning corn crop waste pushes climate change enough to worry all global inhabitants and causes such significant public health damage that developing world governments should worry, as well.

Why Burn?

Poor farmers burn of necessity. They have no tractors to turn under stalk. As soon as the harvest is finished, most healthy adults leave to find dry season work in the cities, leaving the infirm, disabled and elderly, all often malnourished, to clear fields for the next crop. The only realistic means is fire.[1]

corn crop waste
Photo credit: Adri Berger, still from film “The Seasons: A Hmong Story”

How Much Corn Crop Waste Is Burned?

In “The Ubiquity of Corn,” I used FAO statistics to show that in 2015 developing world farmers grew 544 million tonnes of corn defined as cob, husk and kernel and therefore grew 1.5 billion tonnes of corn stalk left in their fields as waste. Many authors studying specific areas conclude that farmers burn between 50 and 90 percent of crop waste. I will use more conservative figures: 10 and 25 percent, because in many places poor farmers feed corn stalk to animals or use it in construction, and in others rich farmers with tractors plow their stalk under – and also to avoid being dismissed as a crank. (A 2018 study from North Thailand reports that 41% of corn farmers burned.)

In “Why Care,” I will assume that farmers burn “just” 150 (10%) or 375 (25%) million tonnes of waste annually. (By way of perspective, a major scientific study suggests that in Asia alone 248 million tonnes of crop waste are burned annually.)

What Happens When Corn Crop Waste Burns in the Field?

It is comforting to believe that burning corn stalk is just burning a renewable resource; it simply returns CO2 to the atmosphere that photosynthesis removed earlier. In fact, burning corn waste releases not only “carbon neutral” CO2 but also large quantities of other, long-term greenhouse gases (GHGs) more warming that CO2, dangerous smog precursors and killer PM2.5.

  • Climate change: when burned, each tonne of corn stalk releases 1.585 tonnes of “carbon neutral” CO2. It also releases 1.072 tonnes of eCO2 (CO2 equivalent) as methane (CH4) and NOx, greenhouse gases that are 25 and 298 times as warming as CO2.[2]
  • Smog: Field burning a tonne of corn waste releases 63 kg of CO, 2.72 kg of NH3 (ammonia), 77.1 kg of NMOCs and 3.11 kg of NOx, all important smog precursors.
  • Smoke: Field burning a tonne of corn waste releases 6.26 kg of PM2.5, particles so small that they will pass through the walls of the lungs and into the bloodstream.

What Are the Consequences of Burning 10% or 25% of Developing World Corn Stalk?

effects of corn crop waste burning
Photo credit: https://www.wisegeek.com/
  • Climate consequences: Burning 150 million tonnes of corn waste emits 161 million tonnes of eCO2. Burning 375 million tonnes of corn waste emits 402 million tonnes of eCO2. To put this in perspective, emitting 150 and 375 million tonnes of eCO2 annually is equivalent to the eCO2 emissions of 37 and 93 coal-fired power plants respectively. (Equivalencies courtesy of the EPA.)
  • Environmental consequences: Burning 150 and 375 million tonnes of corn waste emits 30 million and 125 million tonnes of smog precursors respectively. A study of smog over Perth, Australia found annual emissions of NOx in the range of 70,000 tonnes and CO under 300,000 tonnes. The World Health Organization (WHO) estimates that smog kills 3 million people annually. ()
  • Public health consequences: Burning 150 and 375 billion tonnes of corn waste emits 939,000 and 2.3 million tonnes of PM2.5 respectively. WHO ranks PM2.5 the 5th biggest killer in the world today, causing 4.3 million deaths per year, equivalent to TB, HIV, malaria and hepatitis B combined. One kg of PM2.5 is equivalent to the smoke of 71,429 cigarettes; 939,000 tonnes of PM2.5 – 939 million kilograms – is equivalent to the smoke of 67,071,831,000,000 cigarettes. (Author’s calculation based on 14 micrograms of smoke from a standard cigarette.) You understand why developing world farmers suffer high rates of heart attack, kidney failure, lung cancer, respiratory disease, and stroke, all commonly associated with PM2.5 inhalation. ()

Why Care?

Simple self-interest.

Today, developed countries struggle to reduce carbon emissions while maintaining energy intensive lifestyles, not least by making the costly switch from coal-fired power plants to cleaner alternatives. Self-interest suggests that there is reason to care that reducing corn crop waste burning just 10% would cut global eCO2 emissions as much as decommissioning 37 coal-fired power plants – annually.


corn crop waste
Coal fired power plant. Photo credit, Nian Shan, Greenpeace


Today, developing countries struggle with growing demands on unsteady budgets. Self-interest suggests that there is reason to care that reducing corn crop waste burning just 10% would save billions of dollars annually in healthcare costs and lost labor productivity. (The World Bank estimates that the cost of lost labor productivity alone is $225 billion. In East, South and Southeast Asia the resulting cost is as much at a full point loss in GDP. World Bank air pollution impact on labor productivity study.)

Paris v. Carbon Removal

The Paris Agreement of 2015 represents a huge diplomatic achievement – and left the climate change glass half empty. Parties at Paris agreed – sort of – to limiting the addition of still more carbon to a global system that everyone acknowledges is already beyond its holding capacity. The qualifier “sort of” refers to the continued right of “over-emitters” to buy the “unused” “emission rights” of others, therefore simply spreading carbon emissions more evenly around the world, not actually reducing them.

Simply reducing carbon emissions is like tapping on the brakes of a runaway car as you hurtle down a mountain road toward a missing bridge over a deep gorge. It may delay the inevitable ever so slightly, but like Wily Coyote, you are going down, even if you hang suspended for a moment over the abyss.

corn crop waste


The critical issue today is drawing down the carbon overload through cost-effective carbon removal. We need to reverse climate change, not pretend that it is enough to “contain” it.

But how?

For a practical, low-cost, cost-effective, replicable and sustainable solution, please read Part 3 of this series, “Sows’ Ears into Silk Purses.”

corn crop waste


[1] Many argue that burning sterilizes soil and leaves enriching ash. Both claims are false. The fires burn too far above the ground and too fast to kill eggs and spores in the soil. The ash is nutritionally worthless and so light that it blows or washes away without penetrating.

[2] Emission Factors (EFs) from S. Akagi, et al., “Emissions factors for open and domestic biomass burning for use in atmospheric models,” Atmospheric Chemistry and Physics, (2011): 4039-4072. The EF for CH4 is 5.82 kg/tonne and NOx 3.11 kg/tonne. The EPA Global Warming Potentials for CH4 and NOx are 25 and 298. Thus, (5.82 x 25) + (3.11 x 298) = 1,072 kg. I ignore black carbon because of confusion about its GWP. To understand how variable EF figures can be, a recent study of Mae Chaem District, Chiang Mai Province, Thailand where Warm Heart conducts much of its research, used EFs for CH4, NOx and PM2.5 that are much lower (2.4, 0.5 and 6.00 as opposed 5.82, 3.11 and 6.26), but a black carbon EF identical to the one we would have used.


Next Part 3: Biochar Social Enterprise – A Solution?

Download PDF: Cool the Climate (5 Part Series)

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