Greenhouse gases emissions: methane, nitrous oxide and carbon dioxide

On almost every occasion, when I have told people about my decision to stop eating beef, people have, of course, asked why. When I say that it is because of the impacts of cattle on the environment, people are often clueless as to how cows can have such a negative effect on the environment, climate in particular. Many people I have spoken to about this do seem to know that cows produce methane and they understand that this is a gas that contributes to climate change. However, people do not seem to know about the other ways in which cattle affect the environment, more specifically the other greenhouse gases (GHG) that cattle are accountable for. Approximately 18% of global GHG emissions are as a result of livestock production (Stehfest et al., 2009) and cattle represent approximately 65% of these emissions. Therefore I have decided to centre this blog post around the ways in which cattle-rearing emits three major GHGs - methane (CH₄), nitrous oxide (N₂O) and carbon dioxide (CO₂).

Methane (CH₄)

The livestock supply chains emit...

44% of anthropogenic CH₄ emissions

CH₄ has a large impact on global warming as it is the second largest contributor to radiative forcing. CH₄ is produced when organic materials decompose as a result of the enteric fermentation digestion process in livestock, in particular ruminants (cattle, sheep and goats) (Carlsson-Kanyama and Gonzalez, 2009). In addition, cattle do not convert feed particularly efficiently, when compared with other animals such as pigs. This means that emissions of CH₄ per unit in cattle are higher which demonstrates that cattle-rearing is inefficient and a significant contributor to total GHG emissions. 

Nitrous oxide (N₂O)

The livestock supply chains emit...

53% of anthropogenic N₂O emissions

According to the Food and Agricultural Organisation of the United Nations (FAO) State of Food and Agriculture 2016 report, N₂O is the most significant cause of ozone depletion in the stratosphere. In order for cattle to survive they must be fed (obviously). Commonly, nitrogen fertilizers are utilised to grow the crops that cattle eat. Nitrogen fertilizers produce N₂O indirectly after the fertilizer has been applied to the cropland. In addition, N₂O is produced through the microbial transformation of nitrogen in soils and manures (Carlsson-Kanyama et al., 2009).

This table below compares the emissions of both N₂O and CH₄ from cattle and pigs in the production of beef and pork. As you can see, in order to produce beef, much greater levels of non-carbon dioxide emissions are emitted from cattle compared with from pigs. This significantly highlights the extent to which producing beef, and so consuming beef, is contributing to climatic change.

Figure 1 | Table showing the differences between N₂O and CH₄ emissions from both cattle and pigs. 

(After  Carlsson-Kanyama and Gonzalez, 2009)

Carbon dioxide (CO₂)

The livestock supply chains emit...

5% of anthropogenic CO₂ emissions

The FAO State of Food and Agriculture 2016 report states that deforestation and land degradation have direct impacts on the release of CO₂ into the atmosphere through their effects on the global carbon cycle.

Figure 2 | Global carbon cycle to show the exchange of carbon between the atmosphere, the ocean, the terrestrial biosphere and the lithosphere. 

(source: global-greenhouse-warming.com)

Plants remove CO₂ from the atmosphere for photosynthesis. In order to create pastureland, deforestation occurs. This demonstrates how grazing cattle has a direct impact on GHG emissions by removing trees, a key carbon sink and element of the global carbon cycle. Land degradation affects the global carbon cycle through reducing the soils ability to sequester carbon through the removal of the organic-rich top layer of soil as cattle walk over it. Overgrazing therefore has significant effects. As grazing land for ruminants covers more than 25% of the global land surface (Stehfest et al., 2009), cattle have an extreme effect on the global carbon cycle and so the climate.

I am hoping this post has provided a good background on how cattle are key contributors to climate change through the various GHGs they emit. Please comment below for any further questions!