Agricultural greenhouse gases

Table of contents

Summary

  • Human-caused greenhouse gas (GHG) emissions and their build up in the atmosphere are the leading cause of global warming and climate change.
  • The Agricultural Greenhouse Gas Indicator estimates net emissions (emissions minus removals) of carbon dioxide, methane and nitrous oxide from Canada’s farmland and how this is changing over time.
  • In 2021, agriculture accounted for 5% of greenhouse gas emissions across all Canadian economic sectors.
  • Agricultural emissions of all three greenhouse gases increased between 1981 and 2021, however, net emissions have decreased. This is because of a substantial increase in farmland soil carbon storage over time.
  • Further decreasing greenhouse gas emissions is necessary to reduce the impacts of climate change. This can be achieved through improved management of livestock and manure and improvements to annual crop practices.

Agricultural greenhouse gases in Canada: why do they matter?

Human-caused greenhouse gas (GHG) emissions and their build up in the atmosphere are the leading cause of global warming and climate change.

The concentration of greenhouses gases in the atmosphere is higher now than at any point in the past 800,000 years. This means more energy is being trapped in the atmosphere, which is raising air and ocean temperatures and affecting weather patterns. Some changes to the climate are already occurring: more frequent and intense extreme weather (heat, drought, flooding, unseasonable frost, high winds); a longer, warmer growing season; and a change in rain and snow patterns. These changes impact many aspects of life including food production. Agriculture depends on a stable and favourable climate for consistent and profitable yields.

The agriculture sector plays an important role in climate change and can serve as both a source and sink (that is, removal) of greenhouse gas emissions. In 2021, farming and herding accounted for about 5% of Canada’s greenhouse gas emissions.

Agricultural practices that reduce greenhouse gas emissions and improve soil carbon storage can benefit the environment and improve crop productivity and profitability. Building soil carbon reserves can improve soil quality and resiliency. Management practices that improve nutrient-use efficiency can reduce greenhouse gas emissions and may improve profitability to producers by reducing nutrient losses. Producers that can demonstrate that they reduce greenhouse gas emissions by farming sustainably may have a competitive edge when it comes to marketing their products. Many large retailers, wholesalers and food processors favour products and services with reduced climate change impacts. For example, some Canadian companies claim to be carbon neutral. They have accomplished this by reducing emissions from their own operations and by investing in projects and purchasing products from companies that have either reduced their greenhouse gas emissions or are storing carbon.

The Government of Canada also must report on greenhouse gas emissions on farmland. This helps inform Canadians and other countries regarding the contribution that agricultural activities make to the national greenhouse gas emissions, and could be used to provide information regarding management practices that reduce environmental impact.

How does agriculture contribute to greenhouse gas emissions?

Earth's temperature is determined by how much heat energy from the sun is trapped by our atmosphere or emitted back into space. Greenhouse gases perform an essential role in the atmosphere, trapping radiant energy and maintaining the earth at temperatures that can support life. Although these gases are essential for the planet, accumulated human-caused emission of these gases in our atmosphere are likely to bring about major changes in climate – indeed, we are already experiencing impacts from a changing climate. The three main agricultural greenhouse gases are nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2).

The main sources of nitrous oxide are the breakdown of field-applied fertilizers, crop residue decomposition and manure storage. Nitrous oxide can also be released to the atmosphere following the leaching and runoff of nitrogen into waterways and following the deposition of ammonia emitted from fertilizers and manure to the air.

Methane is primarily emitted to the atmosphere through food digestion (enteric digestion) by ruminant animals such as cattle, sheep, goats, and bison. Cattle are the largest source of agricultural methane, contributing approximately 89% of emissions. Methane emissions change from year to year depending on populations of beef and dairy cows. Methane also comes from the decomposition of stored manure.

Carbon dioxide emissions mainly come from plant decomposition, soil amendments, fertilizers and fossil fuel use. Carbon dioxide is released from soil when soil organic matter breaks down. This breakdown can be accelerated by soil disturbance like tillage. Many soil amendments and fertilizers contain carbon, such as limestone (calcium carbonate), dolomite (calcium magnesium carbonate) and urea-based fertilizers. Carbon dioxide is also released during operation of farm machinery that uses fossil fuels as a fuel source, and through the manufacture of some fertilizers and farm equipment.

While decomposition, amendments and management can be a source of carbon dioxide, agricultural lands also have the potential to store significant amounts of carbon. Plants remove carbon dioxide from the air during photosynthesis and convert it to glucose, a carbon containing form of sugar. This is used for growth and development and stored in plant tissues. When plants break down, some carbon accumulates in the soil as soil organic matter. In addition, perennial crops (forages, shrubs, trees) can store and tie up carbon in their roots and above ground structures for years to decades. This can offset some of agriculture’s greenhouse gas emissions.

Agricultural Greenhouse Gas Indicator

The Agricultural Greenhouse Gas Indicator estimates net emissions (emissions minus removals) of carbon dioxide, methane and nitrous oxide from Canada’s crops and livestock. Emissions are estimated using a globally recognized approach recommended by the Intergovernmental Panel on Climate Change (IPCC). This is then adapted to account for specific agricultural conditions encountered in Canada, such as climatic conditions, crop characteristics, as well as livestock production and management.

A number of steps are used to estimate emissions:

  1. Gathering datasets such as long-term climate data, the area of each crop type, recommended nitrogen fertilizer rate for each crop, and the population, reproductive status, weight, feed intake and management practices for livestock and their manure.
  2. Estimating additional information such as the amount of nitrogen in crop residues, nitrogen excretion by livestock, energy intake of cattle, and the rate of change in soil carbon.
  3. Adding together emissions from each greenhouse gas to determine total emissions.

The Agricultural Greenhouse Gas Indicator is calculated annually. The Indicator helps to show how greenhouse gas emissions on farmland has changed over time. And just as importantly, helps to identify where changes to farming practices can reduce or mitigate agricultural impacts on the environment and climate.

Agricultural greenhouse gases in Canada - current state and change over time

Current state

In 2021, agriculture accounted for about 5% of greenhouse gas emissions across all Canadian economic sectors.

The intensity of greenhouse gas emission were generally lower in Western Canada than in Eastern Canada. This occurred for many reasons. In the Prairie provinces, because of the soil types and climate, appropriate land management practices can improve soil carbon storage. In Eastern Canada, wetter conditions lead to greater nitrous oxide emissions, and the warmer and longer growing season means that high yielding, intensively managed and high fertilizer requiring crops (like corn) can be grown. In addition, the size of the dairy herd in Eastern Canada has declined, which has led to a shift from perennial to annual crops which store less soil carbon.

Despite this, some areas of Western Canada have emissions as high as those in Eastern Canada. These areas tend to have large concentrations of beef cattle or swine, or have humid black soils which have high nitrous oxide emissions.

Net GHG emissions (kilograms of CO2 equivalents per hectare), 2021

Change over time

Emissions of all three greenhouse gases increased between 1981 and 2021: nitrous oxide increased by 49%, methane increased by 5% and carbon dioxide increased by more than 150%. However, over the same time, net greenhouse gas emissions have decreased. This is mostly because of the significant increase over time in carbon storage by agricultural soils in the Prairies.

Nitrous oxide emissions increased mostly because of an increase in nitrogen fertilizer application used to boost crop yields. Nitrogen fertilizer use increased by nearly 300% in Western Canada and by 64% in Eastern Canada. Other reasons for the nitrous oxide emissions increase include greater crop residue nitrogen (because of increased crop production) and an increase in manure nitrogen excretion (because of an increased livestock population and an increase in animal size).

Methane emissions were only 5% higher in 2021 than in 1981, but changed considerably over time. Because the majority of agricultural methane emissions are from beef and dairy cattle populations, changes over time were driven by changes in these systems. Dairy cattle populations have decreased steadily since 1981 because of greater milk production per dairy cow – a dairy cow today can produce as much as three times the milk as a dairy cow 50 years ago. Beef cattle populations increased until 2006 and have decreased by about a 25% since then. Population declines have been driven by holdover effects from the bovine spongiform encephalopathy (BSE) crisis, a high Canadian dollar, higher domestic costs and decreasing beef consumption in our diet. However, emission reductions from cattle population declines have partially been offset by increased emissions per animal; in 2021 animals are more productive, and therefore consumed more feed, produced more manure and were larger than in 1981.

Carbon dioxide emissions more than doubled between 1981 and 2021 because of an increase in the use of carbon-containing fertilizers and soil amendments. When applied to land, these products provide nutrients required for crop growth or reduce soil acidity, but also release carbon dioxide to the atmosphere after field application.

On the other hand, between 1981 and 2021, there was a large increase in the land area on which beneficial management practices were carried out which improved soil carbon storage. These practices include reductions in summer fallow, increased adoption of conservation tillage practices like reduced and no-till and increasing perennial cropping. Furthermore, with the adoption of higher yielding crop varieties and improved fertilization, Canadian crops have become increasingly productive over time. Increased productivity has resulted in a greater amount of residue returned to the soil. Combined, the adoption of beneficial management practices and increased productivity have lead to more carbon being returned to the soil and a slower rate of organic material breaking down, resulting in more carbon accumulating in the soil.

Change in net agricultural GHG emissions (kilograms of CO2 equivalents per hectare), 1981 to 2021

In much of the Prairies, there was no change or a decline in the intensity of net greenhouse gas emissions. This is because crop beneficial management practices were adopted, and greater crop productivity have both promoted greater soil carbon storage. However, in some areas, greenhouse gas emissions increased, primarily because animal populations and fertilizer use increased.

In Eastern Canada, emissions increased in some areas of Ontario, the St. Lawrence River Valley and the St. John River Valley. This was because of an increase in annual cropping (in part because of declining dairy herds) and use of crops with high nitrogen requirements, such as corn.

How can agricultural greenhouse gases be reduced?

For the agriculture sector to continue to meet the growing demand for food, feed, biofuel and other products while reducing emissions, producers will need to innovate, and adopt beneficial management practices that can simultaneously accomplish both goals. Some options include:

  • Livestock
    • Feed management: supplement animal feeds with edible oils or other feed alternatives and additives to reduce methane emissions.
    • Manure management: adopt practices to reduce direct emissions or to capture emissions for bioenergy.
    • Pasture management: implement grazing management practices such as intense, short-duration grazing periods followed by long recovery periods. This can promote soil carbon storage by maximizing grass regrowth and residue return.
  • Annual crops
    • Tillage management: adopt low or zero-till practices.
    • Summer fallow: decrease summer fallow area.
    • Crop rotation: include crops with low nitrogen fertilizer needs in rotation like pulses and other legumes.
    • Perennial cover: increase area of perennial crops to increase carbon storage in agricultural soils.
    • Fertilizer management: optimize nitrogen fertilizer use and reduce nitrous oxide by using a variety of management practices designed to match crop nitrogen demands with supply.
    • Soil cover management: use cover crops and intercropping to maximize the amount of time and area that soil is covered by a living cover. This will increase the amount of plant residues returned to the soil.
  • Multiple land use
    • Silvopasture, (woodlands managed for grazing) can provide additional land for agricultural use while increasing productivity and carbon storage, in the soil and in the woody biomass. Creating silvopastures could also potentially contribute to Canada’s commitment to plant 2 billion trees by 2030.
Description of the image above

An infographic showing an agricultural landscape with crops, a tractor, soil and grazing livestock adjacent to a natural landscape with a watercourse, forest and wild animals. Info boxes are placed to show to which element of the landscape each agricultural sustainability indicator pertains. Arrows connect some of the info boxes to show interrelationships. One info box is present for each of the following indicators: Soil cover, particulate matter, soil organic matter, soil erosion, soil salinization, nitrogen, pesticides, phosphorus, ammonia, greenhouse gases, coliforms and wildlife habitat.

Agriculture and Agri-Food Canada's agri-environmental indicators (AEIs) provide a science-based snapshot of the current state and trend of Canada’s agri-environmental performance in terms of soil quality (soil organic matter, soil erosion, soil salinization), water quality (nitrogen, pesticides, phosphorus, coliforms), air quality (particulate matter, ammonia, greenhouse gas emissions) and farmland management (agricultural land use, soil cover, wildlife habitat). While indicator results are presented individually, agro-ecosystems are complex, so many of the indicators are interrelated. This means that changes in one indicator may be associated with changes in other indicators as well.

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