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Agriculture, Greenhouse Gases, and Climate Change

By Bill Manci
February 3, 2021
Agriculture, Greenhouse Gases, and Climate Change image

The overwhelming majority of climate science data indicates that climate change, via increased global temperatures, is causing vast changes around the globe—often with devastating impacts. The federal government agency NASA has painstakingly documented the causes and effects of this warming trend. [1]

NASA data clearly show an increase in average global temperature of at least 1.0 degree Celsius since 1930, despite a marked reduction in total solar irradiance since about 1950.

Media attention of the solutions to climate change often focuses on reducing carbon dioxide emissions from the burning of fossil fuels. While these are powerful tools, there are other methods that need to be explored. One of the most significant candidates is modifying how we grow and process the foods we eat, both plant and animal.

How much could changes to farming and ranching practices help alleviate the global warming trend that is taking place? Let’s take a closer look by exploring the relationship between agricultural practices, animal husbandry, and greenhouse gas emissions.

A Review of Greenhouse Gases

The greenhouse effect is a result of the thickening atmospheric blanket (i.e., concentration) of gases that trap and retain heat from the sun. NASA scientists have concluded that four gases are primarily responsible for global warming: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor.

Most people do not associate water vapor with global warming. However, it is the most abundant of the four gases and creates a feedback loop that increases warming—atmospheric water vapor leads to warming, which leads to increased levels of atmospheric water vapor, which leads to more warming.

More than a decade ago, Jane Johnson and her colleagues at the USDA-Agricultural Research Service looked at quantities of greenhouse gases and their sources. [2] Figure 1 shows the relative contributions of the different sources.

Agriculture, Greenhouse Gases, and Climate Change image

Johnson and her team found that 84.6 percent of greenhouse gas emissions were CO2, 7.9 percent were CH4, and 5.5 were N2O.

Interestingly, while the title of their research (“Agricultural opportunities to mitigate greenhouse gas emissions”) suggests there may be opportunities to mitigate overall emission of greenhouse gases, Figure 1 clearly shows the vast majority of these gases originate from the burning of fossil fuels for energy (i.e., power plants and vehicles). Agriculture accounts for only 6.3 percent of greenhouse gas emissions. [2]

Despite the claims by the Johnson team for the low contribution from agriculture, other research groups find contributions in the range of eight to 51 percent—quite a wide range and seemingly in conflict with the Johnson data. [3]

According to Herrero, research teams around the world are in general agreement, with differences attributed to how emissions are allocated to land use and changes in how land use is classified. [3]

So, with such low contributions from agriculture, how could changes to agricultural practices ever hope to overcome the overall rise in greenhouse gas emissions? The answer lies in the details of how contributions are classified, and the physical and chemical characteristics of the various gases—CO2, CH4, and N2O, in particular.

Clarifying Agricultural Contributions

First, if you consider deforestation, burning, the drainage of wetland, and soil tillage in the net equation and calculations, agriculture accounts for about one-third of total net CO2 emissions. [2]

In addition, it’s important to note that not all emitted gases affect global warming equally. Indeed, if we specify the global warming potential of CO2 as 1, the global warming potential of CH4 and N2O are 21-80 and 310 times, respectively, more potent than CO2. [2,4]

This means that small changes in CH4 and N2O emissions can make a big difference, despite the overwhelming contribution of CO2 from energy production.

What about the claim that elevated CO2 levels boost crop yields? (The notion that there could be improved crop quality and increased yields as a result of elevated CO2 concentrations in the atmosphere is partly attributed to former Rep. Lamar Smith (R-TX), who also called climate-change proponents “alarmists.”) [5]

Could this be a silver lining to an otherwise dark cloud hanging over us and our future? In the short term, elevated CO2 does, in fact, enhance crop yields and water-use efficiency. [5] This effect is most pronounced in crops such as wheat and rice, and to a much lesser degree in corn and sugarcane. However, in the long term, positive effects will diminish with higher temperatures and extreme rainfall, which will eliminate previous benefits to yield. [6]

The Contribution of Animal Agriculture

Citing data by the United Nations Food and Agriculture Organization, [7] the watchdog group Climate Nexus [8] claims animal agriculture accounts for:

  • 5 percent of global man-made CO2 emissions
  • 44 percent of man-made CH4 emissions
  • 44 percent of man-made N2O emissions
  • 75-80 percent of total agricultural emissions

This is in addition to water pollution in the forms of soil erosion, and nitrogen and phosphorus fertility to aquatic systems. [8]

It is important to note that, with respect to N2O—as mentioned above, orders of magnitude more potent as a greenhouse gas than CO2—management of soils and other common agricultural activities (e.g., field burning and combustion, manure management, other waste management) represent by far the greatest contributions to N2O emissions—greater than 94 percent. [2]

Curbing Greenhouse Gas Emissions

Research results suggest that the window of opportunity to significantly affect future greenhouse gas emissions is still open, particularly within the agricultural segment. While the energy industries have been the focus of scrutiny relative to CO2 emissions (given their emission dominance), agriculture can play a significant role. Let us examine some of the options.

Carbon (CO2) Sequestration

Retaining carbon in the soil (i.e., sequestering carbon) is a function of retaining organic matter. This can be accomplished through reduced tillage or by eliminating tilling. As a result, there will be reductions in soil erosion. Quite simply, targeted harvesting of a plant’s seeds (e.g., wheat, corn, soybeans), rather than removal of the entire plant, helps to retain captured CO2 within the soil. Applying manures as replacements for conventional chemical fertilizers closes an additional nutrient cycle and short-circuits what would otherwise be carbon released to the atmosphere. [2]

Organic Agriculture

Organic approaches include, by default, several carbon sequestering techniques: low- and no-till, minimal harvest, cover-cropping to reduce soil erosion, and rotational cropping to naturally replenish and retain soil nutrients such as carbon and nitrogen, and prevent emissions such as CO2, CH4, and N2O. [2] Of course, organic agriculture includes a prohibition on the use of pesticides, which removes chemical roadblocks to natural and beneficial biochemical and microbiological nutrient recycling that may occur.

Minimizing Nitrogen Fertilizers and Wastes

As previously mentioned, N2O is more than 300 times more potent as a greenhouse gas than CO2. Anything farmers can do to minimize the use of nitrogen fertilizers can make a huge difference. Additionally, cattle manure contains high amounts of nitrogen, which over time is converted to N2O through the nitrification and denitrification chemical processes. Appropriate sub-surface manure applications to fields can help to sequester carbon and nitrogen before they have an opportunity to release as CO2 and N2O. [2]

Move to More Efficient Livestock—Fish and Aquaculture

Cattle and swine are some of the least efficient converters of what they eat (feed) into things we can eat. Scientists have a term for this—feed conversion ratios (FCR). Swine and cattle have some of the highest ratios on the planet—in the range of six to nine (or more) pounds of feed per pound of production. Chickens are more efficient at about three to one. Fish are the conversion champs, displaying ratios of 1.5 to 1 or better. [9] In short, fish as a food source comprise more edible product and much less waste to contribute to greenhouse gas emissions.

In an approach reminiscent of low-till and no-till farming, aquaculturists also use a sustainability technique called integrated multi-trophic aquaculture, or IMTA. [10] With this approach, for example, floating net pens used to produce salmon are surrounded by production systems for shellfish such as clams, mussels, or oysters.

These filter-feeding bivalves collect solid wastes from the salmon net pens and utilize them as a food source. A third system to produce aquatic macroalgae surrounds both the salmon and the bivalves. These macroalgae absorb dissolved nutrients from the salmon and sequester carbon and nitrogen into usable food or organic fertilizer. Specific designs for IMTA are limited only by a producer’s imagination and creativity.

Aquaponic systems (those that produce fish indoors and direct their wastes to the production of plants in greenhouses) are classified under the IMTA moniker as well. The overall goal of IMTA systems is to close cycles and direct fish nutrients to secondary and tertiary production of plants and other valuable crops and products (e.g., vermiculture, organic compost, and fish-emulsion fertilizers).

Avoid the Production of Livestock

Many argue that people should move away from the production and consumption of livestock completely. If humans were to move to a vegetarian culture, Climate Nexus claims cropland usage would decrease by 90 percent, greenhouse gas emissions would fall by 96 percent, and nitrogen fertilizer use would plummet by 94 percent. [8]

Of course, there are many reasons why a move toward universal vegetarianism will never happen. That said, reducing meat consumption could play a role. However, from a nutritional perspective, issues that are likely to result from the elimination of animal meats from the diet include certain essential amino acid and some vitamin deficiencies. [11]

Regardless of the approaches we adopt to limit emissions of greenhouse gases, scientists agree that it must occur. Agriculture, working in tandem with energy production industries that move from the use of fossil fuels to renewable energy sources, can dramatically limit emissions, achieve sustainability, and secure our environment for future generations.

Sustainable Eating for Sustainable Health
By Nell Stephenson


  1. Anonymous. National Aeronautics and Space Administration (NASA) web site.
  2. Johnson, J.M.-F. et al. 2007. Agricultural opportunities to mitigate greenhouse gas emissions. Environmental Pollution 150:107-124. doi:10.1016/j.envpol.2007.06.030
  3. Herrero, M. et al. 2011. Livestock and greenhouse gas emissions: the importance of getting the numbers right. Animal Feed Science and Technology 166-167:779-782.
  4. Fountain, H. 2020. Belching cows and endless feedlots: fixing cattle’s climate issues. New York Times, 21 October 2020.
  5. Schipani, V. 2017. CO2: friend or foe to agriculture?
  6. Anonymous. 2014. Assessment report 5. The Intergovernmental Panel on Climate Change.
  7. United Nations Food and Agriculture Organization. 2020. Key facts and findings—by the numbers: GHG emissions by livestock.
  8. Anonymous. 2020. Animal agriculture’s impact on climate change. Climate Nexus.
  9. Anonymous. 2020. Feed conversion ratio. Wikipedia.
  10. Anonymous. 2019. Integrated multi-trophic aquaculture. Wikipedia.
  11. Cordain, L. 2011. The Paleo Diet. John Wiley and Son, Hoboken, New Jersey, 266pp.

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