This article reviews the changes needed to feed more people sustainably with what we have and points to 9 limits we cannot exceed:

  1. acid in our oceans,
  2. ozone depletion,
  3. fresh water,
  4. biodiversity,
  5. nitrogen and phosphorus cycles,
  6. land use,
  7. climate change,
  8. air pollution,
  9. chemical pollution.

Gerten’s team looked at the four boundaries that are relevant to farming: not using too much nitrogen, which causes dead zones in lakes and oceans; not taking too much fresh water from rivers; not cutting down too much forest; and maintaining biodiversity.
Our population is still increasing and we continue to create CO2 beyond our ability to keep an even balance