Nearly two-thirds of all scenarios appear feasible or probably feasible in a world that—hypothetically—refrains from clearing any further forests for agricultural purposes. This result indicates that deforestation is not a precondition for supplying the world with sufficient food in terms of quantity and quality in 2050 and that many options exist based on different strategies. Our analysis reveals that even a global adoption of diets currently prevailing in the Western world would be feasible without deforestation if cropland yields rose massively and cropland expanded strongly into areas that are today used for grazing. Furthermore, high yields17 are no biophysical necessity; the world population can be fed healthily even with low cropland yields and little cropland expansion when diets with a reduced fraction of livestock products are adopted.

According to our analysis, human diets are the strongest determinant of the biophysical option space, stronger than yields or cropland availability. Unsurprisingly, vegan diets and diets with a low share of livestock products (for example, the VEGETARIAN variant) show the largest number of feasible scenarios, in line with other studies19,33,40, representing pathways that also make it possible to avoid the otherwise virulent grazing constraints and significantly reduce the option space. Other factors, such as high yields or intensive livestock systems, do not show such a strong effect on the number of feasible scenarios and do not necessarily reduce cropland demand or grazing intensity because the land-sparing effect can be annihilated by rich diets (Figs 3 and 4 and Supplementary Figs 3–6). These findings underpin the insight of other studies that stress the importance of demand-side measures for sustainability26,27,33,41. A vegan or vegetarian diet is associated with only half the cropland demand, grazing intensity and overall biomass harvest of comparable meat-based human diets. Furthermore, a decreasing share of livestock products in human diets could also be associated with health benefits, particularly in the industrialized regions40,42.

However, it is important to note that livestock provides many services other than food, for example, draught power, nutrient management and risk avoidance. For instance, livestock enables the use of land that cannot be used for cropping due to harsh environmental conditions and thus helps broaden society’s resource base33,34,43. This effect becomes visible in our analysis in scenarios that combine low yields with little cropland expansion. In such contexts, diets relatively high in ruminant products show advantages over the monogastric-based variants. With increased cropland production, however, this advantage of ruminant livestock is lost.

Yields show a smaller effect than human diets on the overall option space, but low yield levels limit the number of feasible scenarios, particularly for diets with meat, which are affected primarily by cropland constraints. In this vein, our results suggest that even in a zero-deforestation world, low-yielding agriculture such as organic farming is a feasible option if paired with a vegetarian or vegan diet, or, to a lesser extent, if based on a massive cropland expansion, adding a nuanced perspective to this controversy23,24,25. In contrast, the expansion of cropland does not critically influence the option space, with the exception of the zero-cropland expansion variants, where approximately half of scenarios are not feasible. Cropland area and grazing intensity are strongly interlinked in our analysis. Under ‘zero deforestation,’ large cropland entails smaller grazing lands and thus higher grazing intensity. The other factors assessed in our analysis do not show such strong overall effects within the entire option space, but they introduce variability within, for example, diet groups (Fig. 4 and Supplementary Fig. 7).

A further substantial contribution to widen the option space could be expected from reducing waste levels8. However, assessing the associated affects was beyond the scope of the paper, due to the intricacies of determining waste levels and discerning avoidable from unavoidable waste flows44. Therefore, we assumed low waste levels to prevail only in the four contract-converge scenarios (Supplementary Table 3). Consequently, the option space might be smaller if these low waste levels could not be reached. Climate-change effects on yields are not taken into account in this study, in line with the projections by the FAO14. Severe effects on the option space can be expected if yields are substantially decreased45. However, the effect of low yields on the option space is reflected in the ORGANIC variant in our assessment.

Our assessment reveals a particularly intricate trade-off related to food security. According to our scenarios, and in line with19, global dietary patterns that aim for an equal per capita provision of food (contract-converge scenarios) are, in general, terms bound to create trade-offs with targets of national self-sufficiency because they increase the import dependency of many developing regions. In regions with low purchasing power, a decrease in national self-sufficiency (per se neither necessary nor sufficient to guarantee food security at the individual level) may threaten food security46. We find that the reduction in self-sufficiency associated with the MEAT diet cannot, or can only partly, be compensated for by strategies that aim at ubiquitously closing currently prevailing yield gaps on cropland19, a strategy identified as instrumental to warranting food security and to reducing biomass harvest and cropland demand on the global scale8,16,41,47. Massive cropland expansion into grazing land could mitigate this trade-off (Supplementary Table 9). Our analysis reveals that this could reduce import dependencies in some regions, but it would do so at the expense of encroachment of farming into semi-natural or natural land, which is associated with considerable socio-ecological costs48. Note that our results do not assume any trade barriers because they were calculated as the biomass trade flows that would be required to compensate for regional deficits in biomass supply. Socioeconomic barriers or obstacles to biomass trade, which could result from subsidy systems, tariffs or other regulations, could narrow the options space by rendering more scenarios unfeasible. A better understanding of the conditions under which trade influences the development of agricultural productivity49,50 is hence a noteworthy scientific challenge.

Important constraints to the future option space result from limits to grazing intensity. Although cropland availability is a widely discussed planetary boundary3,13,36, many unknowns related to grazing limits prevail. This knowledge limitation is due primarily to the very limited data availability and the huge range of uncertainty related to the extent and intensity of grazing on the global scale2,37. In light of these data gaps, our results have been based on simple assumptions on grazing intensity thresholds and consistent data sets on land use and NPP patterns. There remains a lack of critical knowledge on, for example, the role of management, different livestock species and biomass flows and their geographic location but also on the interrelation between grazing and ecosystem processes and aspects of inter-annual variation (seasonality of grassland production). However, our finding that grazing pressure may become a prohibitive factor in many scenarios calls for concerted research in this area.

The option space analysed here is delineated solely on the basis of a biophysical balance between supply and demand. It is not aimed at exploring probabilities, and it does not support straightforward conclusions regarding the desirability, political practicability or sustainability performance of different scenarios. The approach enables exploration of the biophysical boundary conditions within which developments can unfold. Many more constraints and considerations become decisive when preferred solutions within this option space are to be identified. Assessment tools developed for such purposes need to weigh the full array of the direct and indirect costs51 and benefits of individual pathways to provide problem-shift robust results. A central trade-off relates to the area savings resulting from increased yields. These savings may increase carbon storage52,53, but this effect can potentially be compensated for by emissions from increased energy and resource demand in agriculture or increased biomass use3,7,16,28. The total amount of biomass required for the food system is important. For example, the benefits from increased soil carbon stocks of organic agriculture22 can be annihilated by the larger area demand resulting from lower yields of organic agriculture54. In this regard, the massive green-house gas emission costs associated with the expansion of cropland into grazing land, currently not well documented48,55, will be crucial. Analogous trade-offs can be suspected with topics such as nitrogen leaching, phosphorus depletion or biodiversity loss. In this context, scenarios that rely on smaller cropland areas and lower land use intensity levels could be favourable.

The identification of preferred future options would require additional analyses beyond biophysical analyses and the assessment of fundamental and complex economic, political and social effects associated with envisaged changes, such as the structural change in diet trajectories, farming practices, the replacement of land use systems and economic effects, for example, rising food prices.

Integrated assessment models enable assessment of the cost-benefit structures of future developments, often based on optimization approaches and conducted in detailed, economic sector-specific manner50. Complementary to such approaches, simple, transparent and data-based approaches such as those employed in this article enable scrutiny of the biophysical conditions, constraints and effects of anticipated changes in the land system, for example, by contextualizing results or by providing reality checks56. Fostering both research strands is a prerequisite for advancing our scientific understanding of the trade-offs related to land use and for identifying political strategies that allow developments to stay within the biophysical boundaries the Earth system poses to society.