Production of pork influences the environment in terms of e.g. global warming, eutrophication and acidification. These impacts are in an LCA term called impact categories. Each impact category is influenced by the emission of several substances such as Carbon dioxide (GWP), nitrogen (AP + EP), phosphorous (EP), ammonia (AP + EP), methane (GWP), laughing gas (GWP), sulphur dioxide (AP) etc.
To calculate the potential on global warming, eutrophication and acidification these are expressed in equivalents, CO2 for GWP, NO3 for EP and SO2 for AP. The GWP for 1 kg pork is 3.6 kg CO2eq. The main contribution on global warming from 1 kg pork arises from laughing gas related to the decomposition of nitrogen, and carbon dioxide related to fossil fuel.
The main contribution in the pork chain to the global warming potential comes from the production of feed, especially grain, which correspond to 2 kg CO2eq.
In an LCA the term 'functional unit' relates to the amount, weight and quality of the specific product investigated, e.g. 1 kg pork.
When more than one product is produced from a process two methods can be used to divide the environmental impact between the product and the co-product. These methods are called 'allocation' and 'system expansion'. 'Allocation' is a division of the environmental impacts according to how much the product costs or weights, whereas in 'system expansion' co-products are considered alternatives to other products on the global market.
Different pig production system affects the environment differently. In pig production system with pigs on range pigs normally have a higher feed consumption per kg pork produced just as N emissions on the fields is of importance.