[1] NBS-SA report reference for definition.

[2] Rockström, J., Steffen, W. L., Noone, K., Persson, Å., Chapin III, F. S., Lamb-in, E., ... & Foley, J. (2009). Planetary boundaries: exploring the safe operating space for humanity.

[3] Raworth, K. (2012). A safe and just space for humanity: can we live within the doughnut. Oxfam Policy and Practice: Climate Change and Resilience, 8(1), 1-26.