Exploring pathways for world development within planetary boundaries.

The pressures humanity has been placing on the environment have put Earth's stability at risk. The planetary boundaries framework serves as a method to define a 'safe operating space for humanity' and has so far been applied mostly to highlight the currently prevailing unsustainable environmental conditions. The ability to evaluate trends over time, however, can help us explore the consequences of alternative policy decisions and identify pathways for living within planetary boundaries. Here we use the Integrated Model to Assess the Global Environment to project control variables for eight out of nine planetary boundaries under alternative scenarios to 2050, both with and without strong environmental policy measures. The results show that, with current trends and policies, the situation is projected to worsen to 2050 for all planetary boundaries, except for ozone depletion. Targeted interventions, such as implementing the Paris climate agreement, a shift to a healthier diet, improved food, and water- and nutrient-use efficiency, can effectively reduce the degree of transgression of the planetary boundaries, steering humanity towards a more sustainable trajectory (that is, if they can be implemented based on social and institutional feasibility considerations). However, even in this scenario, several planetary boundaries, including climate change, biogeochemical flows and biodiversity, will remain transgressed in 2050, partly as result of inertia. This means that more-effective policy measures will be needed to ensure we are living well within the planetary boundaries.