Livestock and global change: emerging issues for sustainable food systems.

The global food system is experiencing profound changes as a result of anthropogenic pressures. The ever-increasing human population (more than 9 billion by 2050), together with changes in consumption patterns (i.e., increasing demand for livestock products) caused by urbanization, increasing incomes, and nutritional and environmental concerns, is shaping what we eat, who eats, and how much, more than ever. The double burdens of nutrition (overconsumption and undernutrition), together with the need to reduce the impacts of climate change, are defining research agendas, affecting policies, and modifying conceptions about food in different ways around the world (1, 2) and have been the topic of other recent Special Features in PNAS (3, 4). Against this background, the global food system that will have to improve its resource use efficiency and environmental performance significantly to ensure the sustainability of global food production and consumption. Livestock, the largest land use sector on Earth, is an important part of this puzzle. Many solutions to the challenges of feeding the world sustainably lie in how we manage this sector. The demand for livestock products is projected to grow substantially in the coming decades (5). This growth will be driven by increasing populations, economic growth, and rapid urbanization in many parts of the developing world. The main conclusions from such projections is that a shift to diets with more animal products and fats is likely to happen, mostly in the developing world, as a result of increased incomes and urbanization (6). Although the consumption per capita of cereals is likely to stabilize, population growth will increase the total quantities of both meat (almost doubling) and cereals (50%) needed to feed the world in 2050. The supply response of the global agriculture and livestock sectors, if current trends continue, is likely to be able to accommodate these demand increases (5). Most recent projections have important common features: