3.5 Which food products have the highest overall impacts?
3.5.1 Relative GHGs of different food products.
Relative GHGs of different food products
Ripple et al. (2014)
This study shows the difference in GHG per kg of produce from different food types.
Per kg of products, all ruminants (cattle and sheep mainly, but also goats) have higher GHGs than other foods, primarily due to methane production. These data do not take into account any assumptions about the potential for grazing livestock to contribute to soil carbon sequestration (see earlier in this chapter for more on this).
Monogastric (single stomach) livestock such as pigs and poultry have lower GHGs due in the main to the lack of methane produced by enteric fermentation and other efficiencies such as feed conversion rates.
While GHG contributions from livestock vary by type, there are very important non-GHG issues to consider when making comparisons.
Seafood GHGs can vary, but are still lower than ruminants.
Fruits, vegetables and grains have the lowest GHGs. This study focuses on protein-rich foods, but many fruits, vegetables and grains have similar GHGs to pulses shown here (unless airfreighted, grown in greenhouses etc., in which case the GHG per kg of product may be increased considerably as discussed earlier in this Chapter).
One consideration to bear in mind is how different functional units can influence relative GHGs (see Chapter 2 for more on functional units). For example, if we measure GHG emissions per 100g of protein, rather than per kg of product, then the relative difference between meats and vegetables can decrease. This is important when seeking to define what healthy and sustainable eating patterns look like (see Chapter 7 and Chapter 9 for more on this).
3.5.2 Animal products dominate contributions from western diets – the UK as an example.
WWF UK’s Livewell report in 2011 showed the relative GHGs from food, based on an average diet.
Meat and dairy contribute the most GHGs in typical western diets
Relative contribution of different food groups to diet related GHG emissions. WWF-UK (2011). Livewell Report, UK
It shows that, from a dietary perspective, meats, fish, eggs and non-dairy protein sources contributed over half of the GHGs arising from a typical British diet.
Dairy contributed the next highest (14%), and a third was GHGs from fruit and vegetables. Fruit and vegetables in general have a lower per kg GHG than animal products, but can have higher GHGs than sugary processed foods. If people consumed more fruits and vegetables, in line with health recommendations, clearly the impacts of this category would increase and other categories could decline.
3.5.3 GHG hotspots in production and supply chain vary by food type.
Emissions from agriculture dominate the carbon footprint of most foods – methane emissions from ruminants; nitrous oxide from soils; CH₄ and N₂O from manure; and CO₂ from energy use on the farm (tractor fuel and fuel for heating) and for the production of mineral fertilisers.
This is always the case for animal products but for plant based foods there are some exceptions:
- Transport will dominate if produce is air-freighted or when fruits and roots are transported very long distances
- Packaging: contributes significantly to GHG emissions of bottled drinks
- Preparation/cooking: this can be significant for lower impact foods, e.g. a baked potato
- Storage – frozen peas, or see frozen carrots example here
These are just examples, and many of the topic areas have been discussed in more detail already. A great deal depends on the energy source that is used: for example if peas are frozen using renewable energy then the relative impact of the freezing and storage process will be lower than if fossil-fuel based energy is used. The same would apply for preparation and storage.
All the post harvest impacts very much depend on the energy source used. Using packaging as an example, the contribution of this step to a product’s carbon footprint is influenced by the recycling rate of packaging materials (for example glass bottle, jars and metal tins). Higher recycling rates would in theory reduce the relative GHG emissions for producing 1 bottle of beer for example, because the bottle would not need to be made from scratch every time, although breakage rates and the distance to the recycling plant will influence the conclusion.