Towards a green water planetary boundary


Green water - soil moisture, evaporation, and precipitation over land - is fundamental to safeguard Earth system functioning. Nonlinear green-water driven changes in climate, ecosystems, biogeochemistry, and hydrology are becoming increasingly evident and widespread.

Yet, considerations of continental to planetary scale green-water dynamics are yet to be assessed and incorporated in management and governance. Here, we propose a green water planetary boundary (PB) - as part of the planetary boundary framework that demarcates a global safe-operating space for humanity - for assessing green-water related changes that can affect the capacity of the Earth system to remain in Holocene-like conditions.

We consider green-water related processes associated with all scales: spatially distributed units, regions or biomes, and the Earth system as a whole. The proposed green water PB variable is selected through expert elicitation based on a set of transparent evaluation criteria that consider both scientific and governability aspects.

Finally, we clarify the appropriate use of a green water PB, outline remaining challenges, and propose a research agenda for future navigation and quantitative assessments of the biophysical Earth system scale boundaries of green water changes.</p>


Publication info: Wang-Erlandsson, L., van der Ent, R., Staal, A., Porkka, M., Tobian, A., te Wierik, S., Fetzer, I., Singh, C., Jaramillo, F., Greve, P., Gerten, D., Keys, P., Dahlmann, H., Gleeson, T., Steffen, W., Cornell, S., and Rockström, J. 2021. Towards a green water planetary boundary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13583,, 2021.