Greenhouse gases in agriculture

Agriculture is the third largest source of greenhouse gases in Quebec. What GHGs does it emit, what activities produce them and how can they be reduced?

Discussions about greenhouse gas (GHG) emissions in agriculture often remain rather vague. How much GHGs do farms really produce? Is methane really as bad as it’s made out to be? What about carbon dioxide (CO₂)? Should farms be concerned about it or not?

Our article untangles these questions by presenting the most common agricultural GHGs, their sources, their characteristics, and the best strategies for reducing them.

What is a GHG?

Let’s start by clarifying that GHGs are gases that naturally occur in the atmosphere and are essential to life. Without them, it would be too cold on Earth to sustain human life. Their molecular structure allows them to let the Sun’s rays pass through while preventing the heat radiated by the Earth from escaping back into space.

GHGs have several natural sources, including volcanoes, forest fires, decaying vegetation and… water vapor. The problem is not that they exist, but that they are increasingly abundant. It is their uncontrolled increase that is causing the current global warming and disrupting the fragile environmental balances.

The beginning of this phenomenon dates to the 1760s. As Europeans launched the first Industrial Revolution, American colonists started clearing forests to create fields. This work released carbon trapped in the soil into the atmosphere and contributed significantly to the GHG emissions of the time. Later, in the 1950s, farms discovered the Green Revolution, its chemical fertilizers and its motorized equipement, which further increased their emissions.

Today, it is urgent to reverse this trend. Thankfully, it is possible to do so!

Different GHGs produce different effects

In Quebec, 96% of emissions are composed of three GHGs: carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O).

All three warm the atmosphere, but each one has a unique molecular structure and therefore produces specific effects. In concrete terms, each has a different warming potential, which is the ability to trap more or less heat over a given period. The molecular structure of each GHG also determines its lifespan: once emitted, some remain in the atmosphere for as little as ten years and others, for several centuries!

Despite these differences, we can convert all GHGs into CO₂ equivalent (the most common GHG). This allows them to be placed on an equal footing so that their effects can be measured globally.

Agricultural GHGs on the rise

Today, agriculture accounts for 10% of Quebec’s emissions, according to the inventory of Quebec GHGs in 2022 and their evolution since 1990, published by the Quebec Ministry of Environment, Fight Against Climate Change, Wildlife and Parks (ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs). This makes agriculture the third largest source of GHGs in the province, after transportation (43%) and industry (31%).

With transportation, agriculture is also the only sector where GHG emissions have increased over the past 23 years. In fact, Quebec’s barns and fields emitted 12% more GHGs in 2022 than in 1999, although there has been a slight decrease (-2%) since 2018.

This rise in emissions is mainly due to an increase in pig manure and the nitrogen fertilizers. Conversely, GHG emissions from ruminant digestion have decreased since 1999, thanks mainly to a reduction in livestock numbers.

In short, we must continue to take action against GHGs in agriculture. But which ones should we target, and how?

Methane (CH₄)

Where does it come from?

Methane holds a special place in this whole issue. Although it accounts for only 13% of the province’s total emissions, 47% of them come from agriculture. More specifically, agricultural methane results from enteric fermentation in ruminants (the famous cow burps and farts) and manure management. The second largest source of methane in Quebec is compostable waste sent to landfills (40%).

Farms therefore have a key role to play in reducing this GHG, especially since it accounts for… 60% of agricultural emissions!

Why should we be concerned?

Methane is not only the most important GHG on farms, it also has a very high global warming potential.The moment it is emitted, it traps 80 times more heat than CO₂. That being said, after a few decades, this warming potential disappears. In short, although methane is a very powerful GHG, it persists a relatively short time. Reducing these emissions therefore has the potential to bring about rapid positive effects on the climate.

What are the possible solutions in agriculture?

Since methane from farms is linked to the number of raised ruminants, reducing their livestock numbers is certainely the best way for them to reduce this GHG. The good news is that this can be achieved without sacrificing their business volume or income. The solution lies in increasing the productivity of each animal through healthier feed, better welfare, and tighter management of herd replacements.

Another option: limit emissions due to manure. To achieve this, manure pits can be covered or emptied more often. Farms can also separate manure into solid and liquid fractions or use it in biogas production.

Nitrous oxide (N₂O)

Where does it come from?

In Quebec, nitrous oxide accounts for only 5% of provincial emissions, but 75% of them come from the agricultural sector. This is mainly due to the use of nitrogen fertilizers.

This situation is intimately linked to modern agriculture. Naturally, plants grow by drawing the nitrogen they need from the soil (except for legumes, which draw it from the air). When they die, these plants return their nutrients to the soil, including nitrogen.

Today’s agricultural reality is very different. First, the sharp decline in organic matter in the soil reduces the potential sources of nitrogen. In addition, crops that require a lot of nitrogen do not meet their needs through the addition of legumes such as soybeans in crop rotation. This is why farms spread additional nitrogen fertilizers… and allow some of it to escape into the atmosphere as nitrous oxide.

Why should we be concerned?

First, nitrous oxide accounts for more than a third of GHG emissions from the agricultural sector. Second, its warming power is 275 times that of CO₂, and it remains in the atmosphere for over 100 years. In short, although it accounts for only 5% of Quebec’s emissions, it causes a lot of damage to our climate.

What are the possible solutions in agriculture?

There are two main options for farms that want to reduce their N₂O emissions.

The first, which is fairly well known, is to apply fertilizer using the 4R technique. First, you choose the right fertilizer for each crop, then you apply it at the right rate and at the right time in the crop’s growth cycle, and finally in the right place, i.e., where the roots will absorb it most easily.

The other option for reducing nitrous oxide emissions on farms is to diversify crops and increase the amount of biomass returned to the soil. To do this, farms can add cover crops or green manure composed of legumes to their rotation. As they decompose, these plants will make all the nutrients they contain available for the next crop, including nitrogen.

Carbon dioxide (CO₂)

Where does it come from?

Carbon dioxide is the main GHG emitted by Quebec: it accounts for 80% of provincial emissions! On farms, it’s the opposite: this GHG is barely present, accounting for less than 5% of total emissions.

In the province, transportation is the primary source of carbon dioxide. On farms, it is rather nutrients such as lime and urea, the application of which releases carbon. Historically, another major source of CO₂ was land use change (e.g., clearing woodland to create fields). However, this is less true today, at least in North America. As for emissions from tractors and other motorized equipment, they are negligible.

Why should we be concerned?

Farms should be concerned about carbon dioxide even if they produce very little of it.

Indeed, it is not only the most abundant GHG in Quebec, it also persists for several hundred years in the atmosphere. So, even if the Earth stopped emitting it tomorrow, it would still take us a few hundrer years to get rid of it. Therefore, the sooner we stop producing it, the sooner we can get out of this mess. Finally, there is so much carbon dioxide in the atmosphere that every effort to reduce it counts.

What are the possible solutions in agriculture?

Producing less carbon dioxide in agriculture can be achieved by reducing the use of lime and urea. But it makes even more sense to focus on a technique that is still relatively unused: planting more plants, both in summer and winter, to sequester more carbon.

Indeed, the carbon that plants feed on is the one making up carbon dioxide. Through photosynthesis, plants capture this GHG to break it down: they release its oxygen into the atmosphere and convert its carbon into stems, leaves, and roots.

This plant-based carbon is then transferred to the soil through manure and crop residues. Once stored beneath our feet, carbon performs several beneficial functions: it contributes to organic matter (an important element in soil health and stability) as well as water retention and biological activity.

To sum up, there are several ways in which the agricultural sector can reduce its GHG emissions. The good news is that this often involves making better use of resources without threatening farm income.

What is sure is that farms have an important role to play in the fight against climate change and can contribute to significantly reducing GHGs. Indeed, many agricultural businesses have already begun the transition. They know that, even though GHGs are essential to life on Earth, they now threaten our climate and everything that depends on it, including… agriculture.