The planetary boundaries framework is an effort to define a safe operating space for humanity. Its rationale is that sustainable development needs to be achieved in ways that safeguard the stability of the Earth system on which human prosperity relies. However, very few studies explicitly examine the interactions of the Earth system processes that underlie individual boundaries.

My overarching research question is: how can continued anthropogenic climate change affect the geospatially resolvable land and water planetary boundaries, and what are the implications for human livelihood? For most of my analysis, I use the LPJmL dynamic global vegetation model because it contains suitable process representations that provide a dynamic and adaptive Earth system perspective for my investigation of key planetary boundary interactions of the climate, land, water and ecosystem nexus.

Paper I emphasizes the importance of green water dynamics (that is terrestrial precipitation, evapotranspiration and plant-available soil moisture) for ecosystem resilience and human well-being. The underlying analysis suggests that the current status of the proposed planetary boundary for green water is already transgressed. Paper II reveals long-term spatiotemporal dynamics of planetary boundary interactions as breaching the climate change boundary critically affects the world’s major forest biomes. Notably, the most extreme climate change scenarios led to the emergence of a southern boreal dieback in the simulations. Tropical forests further show a shift from evergreen to deciduous rainforest, an important process which is not captured by the definition of the land-system change boundary. Maintaining climate change at the planetary boundary co-stabilizes the land-system change boundary. Paper III extends the biophysical understanding of planetary boundary interactions by discussing their impact on human livelihood and the attainment of the Sustainable Development Goals. Future climate change causes increases in dry anomalies of green water in ~30% of the global land area by the end of the century. As of today (here referring to 2015), nearly a quarter of the world population and ~28% of global harvest would be affected. The dynamic risk space terminology is established to fill the conceptual gap in the analysis of planetary boundary interactions. Paper IV highlights how planetary stability constitutes the non-negotiable fundament for human development and argues why the Sustainable Development Goals have to be aligned with the planetary boundaries framework and which perils might arise from their interactions. Paper V presents the land-system change reallocation tool algorithm which allows for a scenario-driven rearrangement of human land-use to meet varying transgression levels of the land-system change boundary. 

My results of Paper I-V advance the understanding of interactions in the planetary boundaries framework. Moreover, my analysis in a process-based and validated modeling environment gives spatiotemporal detail of the processes at play that exceeds the potential of previously used conceptual models. My work fills a crucial gap in the operationalization of the planetary boundary framework by providing insights into how and where different policy options produce positive or negative outcomes across boundaries. The holistic understanding I present is a prerequisite for any application of the planetary boundaries framework that focuses on future conditions.