The environmental costs and benefits of high-yield farming
How we manage farming and food systems to meet rising demand is pivotal to the future of biodiversity. Extensive field data suggest that impacts on wild populations would be greatly reduced through boosting yields on existing farmland so as to spare remaining natural habitats. High-yield farming raises other concerns because expressed per unit area it can generate high levels of externalities such as greenhouse gas emissions and nutrient losses. However, such metrics underestimate the overall impacts of lower-yield systems. Here we develop a framework that instead compares externality and land costs per unit production. We apply this framework to diverse data sets that describe the externalities of four major farm sectors and reveal that, rather than involving trade-offs, the externality and land costs of alternative production systems can covary positively: per unit production, land-efficient systems often produce lower externalities. For greenhouse gas emissions, these associations become more strongly positive once forgone sequestration is included. Our conclusions are limited: remarkably few studies report externalities alongside yields; many important externalities and farming systems are inadequately measured; and realizing the environmental benefits of high-yield systems typically requires additional measures to limit farmland expansion. Nevertheless, our results suggest that trade-offs among key cost metrics are not as ubiquitous as sometimes perceived.
Agriculture already covers around 40% of Earth’s ice- and desert-free land and is responsible for around two-thirds of freshwater withdrawals1. Its immense scale means that it is already the largest source of threat to other species2, so how we cope with very marked increases in demand for farm products3,4 will have profound consequences for the future of global biodiversity2,5. On the demand side, cutting food waste and excessive consumption of animal products is essential1,5,6,7,8. In terms of supply, farming at high yields (production per unit area) has considerable potential to restrict humanity’s impacts on biodiversity. Detailed field data from five continents and almost 1,800 species from birds to daisies9,10,11,12,13,14 reveal that so many depend on native vegetation that for most the impacts of agriculture on their populations would be best limited by farming at high yields (production per unit area) alongside sparing large tracts of intact habitat. Provided it can be coupled with setting aside (or restoring) natural habitats15, lowering the land cost of agriculture thus appears central to addressing the extinction crisis2.
However, a key counterargument against this land-sparing approach is that there are many other environmental costs of agriculture besides the biodiversity displaced by the land it requires, such as greenhouse gas (GHG) and ammonia emissions, soil erosion, eutrophication, dispersal of harmful pesticides and freshwater depletion5,7,16,17,18. Measured per unit area of farmland, the production of such externalities is sometimes greater in high- than lower-yield farming systems17,18, potentially weakening the case for land sparing. However, while expressing externalities per unit area can help identify local-scale impacts19, it systematically underestimates the overall impact of lower-yield systems that occupy more land for the same level of production20. To be robust, assessments of externalities also need to include the off-site effects of management practices, such as crop production for supplementary feeding of livestock, or off-farm grazing for manure inputs to organic systems20,21,22.