Agriculture is the largest driver of land use change, water consumption, erosion, and biodiversity losses. The most recent IPCC report warns of worsening food shortages as climate change further exacerbates already declining crop yields. An emerging bioenergy industry has also increased land demand. Collectively, this has led to sharp debate and an increased need to better understand how competing land demands can be met by current and future land supply. To estimate demand, we collected a range of published values for global food and bioenergy land requirements. For supply, although frequently assumed to be unsuitable for crop production, we examined the extent global pasture could meet land demand. We determined the amount of pasture suitable for crops using two separate geographically distributed models: ERWATR and CROSUR. ERWATR is based on erosion, crop water needs, and vapor pressure deficit; CROSUR considers a larger range of factors and is grounded in FAO crop suitability indexes (CROSUR). Using pasture to supply future demand could avoid triggering land use change and forest clearing—but may displace livestock. Potentially displaced livestock was estimated using geospatial data on cattle, goat and sheep density.
Results/Conclusions
Future land demand for food ranges from 130 – 385 million hectares (Mha) and bioenergy ranges from 52 to 650 Mha. For bioenergy, we take a central estimate of 200 – 300 Mha. For supply we estimate ~278-473 Mha of occupied pasture was suitable for crops using ERWATR, and ~632 – 787 Mha using CROSUR. Thus, 12.1% - 33% of global pasture is suitable for row crops—the equivalent of 22.5% - 59.6% of current cropland. Optimistically, if 130 Mha are required for food then ~148 – 657 Mha are available for carbon mitigation using bioenergy or afforestation. Pessimistically, if 385 Mha are required for food then ERWATR shows a deficit of 107 Mha or a slight surplus of 88 Mha, while CROSUR estimates 247 – 402 Mha would remain for carbon mitigation. Although a large fraction of pasture could support row crops, just 1.7% to 4.2% of the global livestock herds are associated with these lands. The low displacement of meat and dairy production could be offset by row crop production, or through modest changes in diet or livestock productivity. Results give reason for cautious optimism that existing agricultural land can sustainably feed the world and help mitigate climate change.