These gases allow light from the sun to enter the atmosphere and warm the Earth but prevent heat from escaping. Without GHGs in the atmosphere, the Earth would be uninhabitably cold. The challenge is that too many GHGs can trap too much heat, causing the average temperature to rise over time.
To reduce greenhouse gas emissions, all industries must work together to minimize the harmful effects of climate change. Agriculture has the ability to reduce its own greenhouse gas emissions, potentially helping offset a significant amount of the emissions from other industries as well by sequestering carbon.
The following sections outline some of the methods that can be used to minimize agriculture’s greenhouse gas emissions.
Enteric methane reduction
Carbon dioxide is the most abundant greenhouse gas (GHG), but it is not the only one, and it is not the most potent one. GHGs include carbon dioxide, methane and nitrous oxide, among others. The warming potential of each greenhouse gas is determined by comparing each gas to carbon dioxide to calculate a number known as the “global warming potential” (GWP). Agriculture, like all large industries, produces a substantial amount of greenhouse gases, including one of the most potent components of GHG: enteric methane.
Enteric methane is produced when ruminant animals (e.g., cows, sheep, goats, oxen) digest plant fibers. The rumen, which is the first chamber in a ruminant’s digestive tract, is essentially a fermentation environment. In this environment, anaerobic bacteria (those that do not require oxygen) break down plant fibers into smaller components that can be consumed as they move through the animal’s gut.
Some of the bacteria in the rumen are methanogens, meaning that they generate methane. This methane is released by ruminants when they belch.
Since methane is a very potent greenhouse gas, it is important to find ways to inhibit methanogens that live in the rumen. This production of methane also represents a loss of energy that could be used by the animal for growth or milk production. Therefore, minimizing enteric methane production will also help animals be more productive (producing more meat and milk).
Researchers are exploring novel feed ingredients and supplements that have shown an ability to inhibit enteric methane production, including seaweed.
Anaerobic digestion is a process in which bacteria break down biomass like manure, sewage sludge, food waste and crop waste in the absence of oxygen. The process takes place inside a sealed vessel called a reactor, which can vary in shape, size and feedstock conditions.
These materials are often considered waste, but when they are used as feedstock for an anaerobic digester (also known as methane digesters or biodigesters), they produce two valuable outputs: biogas and digestate.
Biogas is composed of methane (CH4), carbon dioxide (CO2), hydrogen sulfide (H2S), water vapor and trace amounts of other gases. Biogas can be burned in a generator to produce natural gas that provides heat and generates electricity, or it can be purified to generate renewable natural gas.
Digestate (the solid and liquid residual material left after the process) can be used as fertilizer or bedding material for animals.
Fertilizer from digesters is superior to synthetic commercial fertilizer because it has a much smaller carbon footprint.
Large-scale livestock operations produce large quantities of manure every day, which is often disposed of in piles or lagoons. Poor manure management can lead to higher emissions of greenhouse gases such as methane.
However, manure is not just a waste product — it also contains valuable nutrients, organic matter, solids, fiber and the potential to be used for energy. When properly managed, stored and repurposed, manure can be used as fertilizer and animal bedding, and it can be utilized to produce energy when used as a feedstock for an anaerobic digester (see above section).
Proper manure management can minimize the production of greenhouse gases; however, when applied to fields as a valuable fertilizer, nutrient levels must be carefully managed to avoid over-application of nitrogen and phosphorus, which can cause water pollution and/or soil contamination.
Separating the liquid and solid components of manure by drying the solids and making sure that manure is not stored in anaerobic conditions like lagoons can help decrease methane production. This can also help minimize odors, which is essential for large livestock operations that have nearby neighbors.