Food systems in a zero-deforestation world: Dietary change is more important than intensification for climate targets in 2050

Global food systems contribute to climate change, the transgression of planetary boundaries and deforestation.
An improved understanding of the environmental impacts of different food system futures is crucial for forging
strategies to sustainably nourish a growing world population.We here quantify the greenhouse gas (GHG) emissions
of global food systemscenarios within a biophysically feasible “option space” in 2050 comprising all scenarios
inwhich biomass supply – calculated as function of agricultural area and yields – is sufficient to cover biomass
demand – derived fromhuman diets and the feed demand of livestock.We assessed the biophysical feasibility of
520 scenarios in a hypothetical no-deforestation world.
For all feasible scenarios, we calculate (in) direct GHG emissions related to agriculture. We also include (possibly
negative) GHG emissions fromland-use change, including changes in soil organic carbon (SOC) and carbon sinks
fromvegetation regrowth on land spared from food production.We identify 313 of 520 scenarios as feasible. Agricultural
GHG emissions (excluding land use change) of feasible scenarios range from 1.7 to 12.5 Gt CO₂e yr⁻¹.
When including changes in SOC and vegetation regrowth on spare land, the range is between−10.7 and 12.5 Gt
CO₂e yr⁻¹. Our results show that diets are the main determinant of GHG emissions, with highest GHG emissions
found for scenarios including high meat demand, especially if focused on ruminant meat and milk, and lowest
emissions for scenarios with vegan diets. Contrary to frequent claims, our results indicate that diets and the composition and quantity of livestock feed, not crop yields, are the strongest determinants of GHG emissions
from food-systems when existing forests are to be protected.