Farms raising cows for milk products or meat are well-known sources for releasing greenhouse gases (GHGs) into our atmosphere. The first of these is carbon dioxide (CO₂), which remains in the atmosphere for hundreds of years and results from deforestation and fossil fuel use, such as growing feed for farmed animals. Another GHG is methane (CH₄): it has a shorter life cycle than CO₂, remaining in the atmosphere for about a decade, and which is released by manure and by cows burping after plants have been broken down in their digestive system – a process known as enteric fermentation. Lastly, there is nitrous oxide (N₂O), which is created by chemical processes when manure or fertilizer are added to soil, for example by a cow grazing. Nitrous oxide is long-lasting, remaining in the atmosphere for around 115 years. Out of the three, it is also the most difficult to measure and stimulate in models.

The first step in quantifying GHGs is to collect real-world data, such as from individual cows wearing portable devices that measure the concentration of gases. Such data can then be used to estimate how many emissions are being generated by individual cows in different scenarios where real-word data is lacking. Once individual estimates are generated, one can model how many emissions are being produced per farm or region.

Even more, such models can then simulate how emissions are affected by changing different policy and economic factors. Since estimations and simulations are a bottom-up procedure, any assumptions about the data are carried over each stage. As a result, some scientists have argued that these emission calculations are inaccurate, especially since emissions calculated from satellites and aircraft technologies differ from those models.

In addition to the difficulties measuring these gases, another challenge is the mainstream media’s misrepresentation of different farming methods. Both media and consumers typically make a distinction between factory-farmed cows and more ‘naturally’-raised cows (e.g., involving pastures and smaller farms). Factory farms are referred to as “industrial” farms in the scientific literature, and they typically involve large-scale and fully enclosed farm buildings. In contrast, farms that seek to increase meat or milk production (e.g., by providing pasture, improving animal health, or using growth-enhancing implants) are known as “intensified” farms. As such, industrialized farms are highly intensified by definition, but intensified farms are not necessarily industrial.

So how do these farms compare when it comes to GHG emissions? One difficulty in answering this is that studies generally combine measures of all three GHGs into a single unit, which typically assumes 100 years as the appropriate time frame. This is problematic because the climate footprint of different farms can change depending on the timescale chosen. For example, non-industrial farms have lower emissions when studied on long timescales, but industrial farms are favorable on shorter timescales.

Moreover, there is a misconception that pasture-based farms have a larger climate footprint than industrial farms, mainly since cows eating fibrous plants emit a lot of methane, but so does the liquid manure of industrial farms. Likewise, industrial farms are the largest contributors of CO₂, but farms that clear forests for grazing also result in high CO₂ emissions. Indeed, converting farms into industrial systems is not recommended because of all the harmful consequences of industrialization, including water pollution and human illnesses. Accordingly, there are many proposed ways to reduce GHGs by intensifying current practices, but such benefits depend on the intensification method used and local contexts.

Overall, researchers disagree when it comes to comparing GHGs from different beef and dairy farms. However, one pattern is clear: plant-based foods have a much smaller climate footprint than animal farming. As such, if you are concerned about the climate effects of farming, you can eat a plant-based diet, which can meet everyone’s nutritional requirements. This study provides advocates with strong evidence that it’s complicated and difficult to improve the environmental impact of cow farming, and that the most prudent environmental approach is to avoid it altogether.