Land use is central to addressing sustainability issues, including biodiversity conservation, climate change, food security, poverty alleviation, and sustainable energy. In this paper, we synthesize knowledge accumulated in land system science, the integrated study of terrestrial social-ecological systems, into 10 hard truths that have strong, general, empirical support. These facts help to explain the challenges of achieving sustainability in land use and thus also point toward solutions. The 10 facts are as follows: 1) Meanings and values of land are socially constructed and contested; 2) land systems exhibit complex behaviors with abrupt, hard-to-predict changes; 3) irreversible changes and path dependence are common features of land systems; 4) some land uses have a small footprint but very large impacts; 5) drivers and impacts of land-use change are globally interconnected and spill over to distant locations; 6) humanity lives on a used planet where all land provides benefits to societies; 7) land-use change usually entails trade-offs between different benefits—"win–wins" are thus rare; 8) land tenure and land-use claims are often unclear, overlapping, and contested; 9) the benefits and burdens from land are unequally distributed; and 10) land users have multiple, sometimes conflicting, ideas of what social and environmental justice entails. The facts have implications for governance, but do not provide fixed answers. Instead they constitute a set of core principles which can guide scientists, policy makers, and practitioners toward meeting sustainability challenges in land use.

The disposal of food waste is a large environmental problem. In the United Kingdom (UK), approximately 15 million tonnes of food are wasted each year, mostly disposed of in landfill, via composting, or anaerobic digestion (AD). European Union (EU) guidelines state that food waste should preferentially be used as animal feed though for most food waste this practice is currently illegal, because of disease control concerns. Interest in the potential diversion of food waste for animal feed is however growing, with a number of East Asian states offering working examples of safe food waste recycling – based on tight regulation and rendering food waste safe through heat treatment. This study investigates the potential benefits of diverting food waste for pig feed in the UK. A hybrid, consequential life cycle assessment (LCA) was conducted to compare the environmental and health impacts of four technologies for food waste processing: two technologies of South Korean style-animal feed production (as a wet pig feed and a dry pig feed) were compared with two widespread UK disposal technologies: AD and composting. Results of 14 mid-point impact categories show that the processing of food waste as a wet pig feed and a dry pig feed have the best and second-best scores, respectively, for 13/14 and 12/14 environmental and health impacts. The low impact of food waste feed stems in large part from its substitution of conventional feed, the production of which has substantial environmental and health impacts. While the re-legalisation of the use of food waste as pig feed could offer environmental and public health benefits, this will require support from policy makers, the public, and the pig industry, as well as investment in separated food waste collection which currently occurs in only a minority of regions.

Expansion of land area used for agriculture is a leading cause of biodiversity loss and greenhouse gas emissions, particularly in the tropics. One potential way to reduce these impacts is to increase food production per unit area (yield) on existing farmland, so as to minimize farmland area and to spare land for habitat conservation or restoration. There is now widespread evidence that such a strategy could benefit a large proportion of wild species, provided that spared land is conserved as natural habitat (1). However, the scope for yield growth to spare land by lowering food prices and, hence, incentives for clearance (“passive” land sparing) can be undermined if lower prices stimulate demand and if higher yields raise profits, encouraging agricultural expansion and increasing the opportunity cost of conservation (2, 3). We offer a first description of four categories of “active” land-sparing mechanisms that could overcome these rebound effects by linking yield increases with habitat protection or restoration (table S1). The effectiveness, limitations, and potential for unintended consequences of these mechanisms have yet to be systematically tested, but in each case, we describe real-world interventions that illustrate how intentional links between yield increases and land sparing might be developed.

• Food wastes are banned in animal feed in the EU due to disease control concerns. • Many Asian states operate safe, centralised systems for recycling waste as feed. • Asian-style food waste recycling could reduce the land use of EU pork by one-fifth. • This would reduce environmental impacts without reducing pork quality or profits. • Policy change will require pig industry, consumer, and political support.

Significance: The trade in agricultural commodities is a mainstay of the globalized economy, though the complex nature of commodity supply chains makes it difficult to identify the origin of and impact embedded in products. We brought together detailed data on trade, agriculture, and logistics to produce a subnational map of the origin of Brazil’s exports of beef, offal, and live cattle. Brazil is the world’s largest beef exporter, exporting one-fifth of its total production, and the sector is a major driver of deforestation. We traced cattle from 2,800 municipalities through to 152 importing countries, via thousands of companies handling their export and import. Our work gives an unprecedented insight into the origin of food and impacts embedded in global supply chains.