Transformation pathways for the land sector in line with the Paris Agreement depend on the assumption of globally implemented greenhouse gas (GHG) emission pricing, and in some cases also on inclusive socio-economic development and sustainable land-use practices. In such pathways, the majority of GHG emission reductions in the land system is expected to come from low- and middle-income countries, which currently account for a large share of emissions from agriculture, forestry and other land use (AFOLU). However, in low- and middle-income countries the economic, financial and institutional barriers for such transformative changes are high. Here, we show that if sustainable development in the land sector remained highly unequal and limited to high-income countries only, global AFOLU emissions would remain substantial throughout the 21st century. Our model-based projections highlight that overcoming global inequality is critical for land-based mitigation in line with the Paris Agreement. While also a scenario purely based on either global GHG emission pricing or on inclusive socio-economic development would achieve the stringent emissions reductions required, only the latter ensures major co-benefits for other Sustainable Development Goals, especially in low- and middle-income regions.

Land conservation and increased carbon uptake on land are fundamental to achieving the ambitious targets of the climate and biodiversity conventions. Yet, it remains largely unknown how such ambitions, along with an increasing demand for agricultural products, could drive landscape-scale changes and affect other key regulating nature’s contributions to people (NCP) that sustain land productivity outside conservation priority areas. By using an integrated, globally consistent modelling approach, we show that ambitious carbon-focused land restoration action and the enlargement of protected areas alone may be insufficient to reverse negative trends in landscape heterogeneity, pollination supply, and soil loss. However, we also find that these actions could be combined with dedicated interventions that support critical NCP and biodiversity conservation outside of protected areas. In particular, our models indicate that conserving at least 20% semi-natural habitat within farmed landscapes could primarily be achieved by spatially relocating cropland outside conservation priority areas, without additional carbon losses from land-use change, primary land conversion or reductions in agricultural productivity.

Ambitious climate change mitigation in all economic sectors is crucial for limiting global warming. Cost-effective mitigation pathways to keep global average temperature increases below 1·5°C by the end of the 21st century often rely on land-based greenhouse gas (GHG) emission reductions, increased land-based carbon uptake and biomass supply to other sectors (eg, energy and transport), and demand-side changes in the food system. To evaluate the broader sustainability of land-based climate change mitigation action, we evaluated synergies and trade-offs of individual and combined supply-side mitigation measures across five planetary boundaries. We also examined the role of a food demand transformation aligned with the dietary recommendations of the updated planetary health diet defined in the forthcoming EAT-Lancet Commission 2.0 report in shaping planetary boundary outcomes. In this modelling study, we used the dynamic land-system modelling framework MAgPIE to assess the consequences of land-based GHG reductions, increased land-based carbon uptake, increased biomass supply to other sectors, and a food-system transformation towards the planetary health diet including food waste reductions on five planetary boundary domains (climate change, nitrogen, land-system change, freshwater use, and biosphere integrity) relative to a reference scenario without land-system mitigation throughout the century. For each planetary boundary control variable, we calculated the level of planetary boundary transgression (ie, the extent to which scenario outcomes exceeded the defined safe operating space) and assessed the contributions of land-based mitigation strategies to reducing planetary boundary transgressions projected for the reference scenario. Our projections show that a food-system transformation together with ambitious land-system and energy-system climate change mitigation can limit global warming to below 1·5°C by 2100, while also reducing planetary boundary transgression (particularly for the climate change, land-system change, biosphere integrity, and nitrogen planetary boundaries). However, a safe operating space was not achieved through these mitigation measures, as most planetary boundaries were still projected to remain transgressed by the end of the 21st century. Increased bioenergy supply alone worsened planetary boundary transgression when only looking at land-system impacts, but combining increased bioenergy supply with GHG pricing in the land system alleviated these trade-offs. Food waste reductions and dietary shifts towards the planetary health diet were projected to ease pressures on the land system and reduce planetary boundary transgression of all assessed planetary boundaries. This research highlights the importance of considering multiple planetary boundaries and the interactions between various mitigation strategies when assessing climate mitigation action in the land system to avoid negative consequences for other aspects of the environment. Following an ambitious climate change mitigation pathway compatible with the Paris Agreement results in a transgression of all assessed five planetary boundaries by 2100. However, the combination of the land-system mitigation measures included in this study produced a substantial shift towards the safe operating space for humanity. EAT-Lancet Commission 2.0.

Achieving sustainable development requires understanding how human behavior and the environment interact across spatial scales. In particular, knowing how to manage tradeoffs between the environment and the economy, or between one spatial scale and another, necessitates a modeling approach that allows these different components to interact. Existing integrated local and global analyses provide key insights, but often fail to capture ‘meso-scale’ phenomena that operate at scales between the local and the global, leading to erroneous predictions and a constrained scope of analysis. Meso-scale phenomena are difficult to model because of their complexity and computational challenges, where adding additional scales can increase model run-time exponentially. These additions, however, are necessary to make models that include sufficient detail for policy-makers to assess tradeoffs. Here, we synthesize research that explicitly includes meso-scale phenomena and assess where further efforts might be fruitful in improving our predictions and expanding the scope of questions that sustainability science can answer. We emphasize five categories of models relevant to sustainability science, including biophysical models, integrated assessment models, land-use change models, earth-economy models and spatial downscaling models. We outline the technical and methodological challenges present in these areas of research and discuss seven directions for future research that will improve coverage of meso-scale effects. Additionally, we provide a specific worked example that shows the challenges present, and possible solutions, for modeling meso-scale phenomena in integrated earth-economy models.