Variation in the opportunity cost of food production
Animal products generally have substantially greater impacts on species’ extinctions than staple vegetal products (Fig. 1). This is a result of the inherently inefficient nature of these products (Halpern, 2022; Poore, 2018): producing a unit of animal product requires grazing land and/or cropland for feed production, which when combined with the intrinsic feed conversion efficiency of animals leads to high land-use and hence extinction impacts. Ruminant meat, for example, thus has a weighted global median opportunity cost on species extinctions ~ 340 times greater than that of grains. This finding is unsurprising, given that more than three quarters of the human-appropriated land-surface is dedicated to the production of animal products while providing only 17% of global calories (Ritchie, 2019).
In general, staple crops have relatively low impacts on species extinctions; grains (excluding rice), vegetables, roots, oil-crops, and fruits all sit between 10^-10 ∆E/kg and 10^-11 ∆E/kg. Conversely ‘luxury’ crops (those with little to no calorific benefit but generally commanding a high price) such as coffee, cocoa, tea, and spices are all toward the higher end of the impact distribution per-kilogram – although of course these commodities are typically consumed in relatively modest amounts. Sugar beet has an extremely low impact per-kilogram; it is high-yielding compared with most other crops (FAO, 2024), and its production is concentrated in northern and central Europe and northern USA, where the opportunity-cost to biodiversity of agricultural land-use is relatively low.
The extinction impact of one kilogram of production varies within most commodities by nearly an order of magnitude, with some varying significantly more. Exceptions to this general pattern include commodities whose production is dominated by a handful of nations. For example, India and China alone produce around 50% of the world’s rice with relatively similar per-kilogram impacts, hence there is relatively low variation in global impacts of rice. The opposite is true of commodity groups that are produced in many different locations – grains, legumes and pulses and dairy products, for example, are produced in significant quantities on every continent and vary in their per-kilogram impacts by almost two orders of magnitude. Likewise impacts vary widely with provenance for coffee. Coffee produced in South America and Sub-Saharan Africa has an impact approximately 10 times greater than that produced in southeast Asia, explained by lower per-area LIFE opportunity-costs and higher yields of robusta coffee, which dominates Asian production (Bunn, 2015), compared with arabica, which dominates production elsewhere.
Generally, commodities that are produced in tropical or sub-tropical regions have higher per-kilogram impacts than those from temperate regions (evident from the distinction between temperate and tropical fruit and nuts, for example). This is unsurprising, given that tropical regions often house exceptional levels of biodiversity and endemism, greatly increasing the impacts of agriculture on global extinction. In the next section we explore the issue of location in more depth by comparing the extinction impacts of food consumption across six countries with widely differing dietary and sourcing profiles.
Across-country differences in the impacts of food consumption and provenance
We selected six countries as examples for which to compare consumption impacts - the USA, Japan, and the United Kingdom as Global North nations with high, moderate, and low levels of agricultural self-sufficiency, respectively (Beltran-Peña 2020; DEFRA, 2023a); Brazil as a largely self-sufficient, highly productive tropical country which is a globally important producer of many commodities (soy, corn, sugar cane, cattle meat, fruits, and nuts; Valdes, 2022); Uganda as one of several nations in Sub-Saharan Africa that, whilst not reliant on imports, nevertheless faces widespread malnutrition (The Economist, 2022; Development Initiatives, 2018); and India as a largely self-sufficient country and a major exporter of rice, sugarcane, and tea (Beltran-Peña, 2020).
Our results reveal the overwhelming contribution of ruminant meat consumption to the per-capita extinction impact of food consumption in every one of these countries (Fig. 2). The impact profiles of the three nations in the global north are driven almost entirely by their ruminant meat intake, suggesting that even small changes to diet composition would have proportionally large consequences (see next section). In the case of the USA, cattle production is concentrated in southern states, where the extinction impact of a unit area of agricultural land-use is much higher than the north (Eyres, in review). While the UK and Japan consume comparable quantities of ruminant meat per-capita, the UK’s ruminant footprint arises largely from imported cattle and sheep meat from Australia and New Zealand (approximately 25% of consumption) and soy imported from South America. On the other hand, roughly half of all ruminant meat consumed in Japan is imported from high-impact regions (in particular, the USA, Australia and New Zealand, and Mexico) and so on-average the per-kilogram impact of consumption is far greater. Even in India, where approximately one third of the population are lacto-vegetarian and cattle slaughter is banned in many states (Devi 2014), ruminant meats (mainly sheep and goat meat) contribute of 40% of the impact of people’s diets on species extinctions.
Unpacking the issue of provenance further, Fig. 3 shows the proportion of the impact of consuming one kilogram of a commodity that arises from imported food. The extinction impacts of food consumption within the United Kingdom and Japan are both driven almost entirely by imports. Although these countries produce 60% and 38% of their food domestically (DEFRA, 2023a; MAFF 2023), 95% and 98% of their impacts respectively come from imported commodities. In terms of species extinctions, for both nations almost all of the impacts of food they consume are accrued in other nations. Given their size and population densities, some reliance on imported food is inevitable, but this result suggests that sustainably intensifying domestic production and investment into less damaging production overseas should be key policy concerns for these countries. Conversely, current trends in both countries towards promoting low-yielding domestic agriculture (DEFRA, 2023b; USDA, 2021) – which may increase reliance on imports from higher-impact regions – are a cause for concern. In addition, for the UK, the effects of post-Brexit trade deals on the extent to which they increase imports of ruminant products from Australia and New Zealand should also be carefully scrutinised (Roberts, 2024; Bateman, 2023; Fuchs, 2020).
In contrast, the extinction impact of food consumed in Brazil, Uganda, and India arises very largely from domestic production, with the impact of imports being just 2%, 9%, and 4% respectively. We suggest reducing the impacts of the food people need in these countries will often best be addressed by sustainably increasing yields and thus increasing production to meet rising demand without clearing remaining areas of natural habitat (Bateman, 2023; Balmford, 2021). The USA also has a low proportion of import-driven impacts (~ 10%) - it produces the bulk of its food domestically, although it is nevertheless reliant on imports of commodities such as coffee and bananas – however, yields in the USA are already relatively high (at least, for vegetal products), so conservation policies may be more effective if directed at dietary shifts (Williams, 2021), as we explore in the next section.
Dietary shift in the USA
Last, turning from consumption and provenance, we illustrate for the USA how our approach can be used to investigate the potential impact of various broad changes in people’s diets. We constructed simple scenarios which modify the relative consumption of food groups based on vegetarian and plant-based Eatwell guides (PBHP.UK, 2023; NHS, 2022a, 2022b; Sustain, 2018), and a no-ruminant scenario in which poultry and pig meat replace ruminant calories (Table 1). The total calorific contribution of the modified groups was scaled to meet the calorific value of the products that are replaced such. In reality, vegetarian and plant-based consumers are likely to have lower total calorific intakes, so we probably underestimate the mitigation effects of shifting to such diets (Scarborough, 2023). Stimulants and spices do not meaningfully contribute to calorific intake, so we elected to set them as constant.
Table 1
Contributions to total calories of different food groups in the basic dietary scenarios. Each scenario has the same overall calorific intake as the baseline.
|
Fruit and vegetables
|
Legumes, beans, nuts
|
Grains, roots, starchy carbohydrates
|
Dairy
|
Eggs
|
Ruminant meat
|
Poultry and pig meat
|
No-ruminant
|
Baseline
|
Baseline
|
Baseline
|
Baseline
|
Baseline
|
None
|
Replaces ruminant
|
Vegetarian
(Eatwell)
|
40%
|
10%
|
35%
|
10%
|
5%
|
None
|
None
|
ePlant-based (Eatwell)
|
40%
|
25%
|
35%
|
None
|
None
|
None
|
None
|
Our results underscore the greatly disproportionate extinction impacts of eating animal products, especially ruminant meat. Replacing ruminant calories like-for-like with poultry and pig meat leads to a dramatic decrease of 90% in overall extinction impact of people’s diets. The vegetarian and plant-based diets have impacts slightly higher than the no-ruminant scenario (50% and 10% respectively) due to the approximately 4-fold increase in the intake of fruits and vegetables in those scenarios compared to the baseline. Clearly, there is significant scope for reducing the harm to nature by changing consumption patterns given the prominence of ruminant meat impacts in the USA, but mitigating impacts in a healthy way beyond reducing ruminant consumption is likely to be more complex, and subject to location and sourcing.
It is important to note that due to economic and other non-linear effects which will be discussed in the next section, these results are not reflective of a scenario in which everyone in the USA changes diet at once. We also conducted this analysis for the United Kingdom (see supplementary materials), finding that replacing animal-derived calories with entirely plant-based calories leads to just over 50% reduction in impact – notably a similar finding to that of Scarborough (2023), assuming that baseline consumption is comparable with the medium meat-eater group in that study.