When talking about sustainability and climate change, phrases like greenhouse gases and carbon footprint or carbon intensity of a product are used a lot. But what do these phrases mean? A brief explanation of these key terms is given below.
Greenhouse gases (GHGs)
Greenhouse gases (GHGs) are gases in the earth's atmosphere which capture the heat and cause climate heating. The main GHGs are:
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Some fluorinated gases such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3)
Only the first three gases are relevant for livestock production. Each GHG has a different climate heating potential called its global warming potential (GWP). To facilitate comparison, a standardised unit was introduced, namely CO2 equivalents (CO2e) with CO2 as the reference.
Table 1 shows the warming potential for CH4 and N2O relative to CO2. For example, 1 kg of CH4 has 25 times more GWP than 1 kg of CO2, and so methane has a GWP of 25.
Carbon footprint (CFP)
Carbon footprint (CFP) is the total amount of GHGs that have been emitted directly or indirectly during the production and usage of a product or service, or from the activity of a company. For transparent company reporting, a global standard was introduced. Companies need to report their GHG equivalents (GHGe) in three distinct categories. Scope 1 and 2 are the GHGe linked to energy usage of the company, either directly or indirectly. Scope 3 includes the GHGe associated with upstream or downstream activities. To know the total CFP, the company needs to quantify the GHGe for each scope separately and sum them together. Table 2 gives an overview of the different scopes and what is included under each.
Carbon intensity - livestock commodities
Carbon intensity is the amount of GHGe per economical unit. An example is the CO2e per kg of meat or milk produced. For a farm, this is calculated by dividing the total CFP of the farm by the amount of output. The carbon intensity is important to know for food companies further down the value chain.
There are big differences between the various livestock commodities. Figure 1 compares the carbon intensity, in kg CO2 emissions/kg protein for each livestock commodity. These are global figures so might not be exact due to the different production systems used in each country. Nevertheless, the main trends are correct with poultry products having the lowest carbon intensity, followed by pork, and ruminant products having the highest carbon intensity.
Figure 1 also shows that the main drivers for carbon intensity are different for each of the species. For ruminants, CH4 is the main driver, while for poultry it is CO2 linked to feed production. For pigs, CO2 from the feed is similar to the CH4 from the manure.
