Feeding 10 billion people and achieving negative emissions within Planetary Boundaries – insights from global modelling

This talk will present key results from a suite of comprehensive simulations performed with a configuration of the LPJmL biosphere model able to represent the dynamic and spatially detailed status of terrestrial Planetary Boundaries (PBs, i.e. guardrails describing maximum tolerable levels of land-system change, biosphere degradation, freshwater use and nitrogen leaching to avoid Earth system destabilisation).

An application of the PB simulator addresses the question how much food could be supplied globally while respecting these multiple PBs, and to what degree this supply could be increased through transformative actions towards more sustainable food production and consumption patterns. A further application demonstrates the potential to achieve ‘negative emissions’ through dedicated biomass plantations (as a measure to limit transgression of the climate change PB) within these PBs. A main finding is that almost half of current food production is environmentally unsustainable in that it depends on PB transgressions. Subsequent simulations show that the same amount of food presently produced under these unsustainable conditions, and even up to about 50% more, could be provided without violating the PB constraints in any place. This would be sufficient to feed around 10 billion people. The required underlying transformations of the food system are rather radical though: ambitious prerequisites are more efficient use of freshwater and nitrogen fertiliser in many places, reallocation of rainfed and irrigated cropland to areas where that would still be acceptable from a PB point of view, halving of food losses, dietary shifts towards lower shares of animal-based products, and (importantly) combinations thereof.

While this poses grand challenges regarding transformation of world agriculture and optimisation of resource use, currently debated methods to achieve ‘negative emissions’ via large-scale deployment of biomass plantations are likely to require large areas as well as freshwater and nutrients on their own. We will show that the option space for such measures is therefore actually very limited, if the terrestrial PBs were to be maintained. In addition, PB interactions such as ongoing and aggravating climate change including more frequent and intense droughts may seriously affect both the food production and negative emissions potentials. A conclusion is that quantitative robust understanding of these major tradeoffs and dilemmas requires even more comprehensive and integrated nexus studies bringing together the relevant aspects in a consistent PB modelling framework, not least also accounting for the social dynamics underlying the required transformations in the real world.