Introduction

The report identifies the interconnection between the Earth system stability and human well-being and aims to quantify safe and just Earth system boundaries. To achieve this, the report explores existing scholarship, expert judgement and widely shared norms. It focuses on quantifying safe and just Earth system boundaries for climate, nitrogen, phosphorus and water at global and sub-global scales.

ESB for climate

The report defines the safe ESB for climate by considering the likelihood of triggering significant environmental changes, specifically the crossing of thresholds or tipping points. The report concludes that the safe ESB for climate is around a 1.5°C rise in global temperature. However, more stringent just ESB must be applied to ensure intergenerational and intragenerational justice.

ESB for nitrogen and phosphorus

The Safe and Just Earth System Boundaries report quantifies safe and just Earth system boundaries for nutrient cycles of nitrogen and phosphorus for the land system. The safe ESB for nitrogen and phosphorus are based on extensive literature assessments, expert judgements and widely shared norms. The report endorses an ESB of less than 18% deviation of its mean seasonal variation for nitrogen discharge into surface water bodies. In the case of phosphorus, based on an extensive literature review and expert judgments, the safe ESB for phosphorus cycling should not exceed 10% of the ice-free land surface.

ESB for water

The report proposes safe and just Earth system boundaries (ESBs) for surface water flows, groundwater levels, and quantity and quality. The report proposes that the threshold for surface water quantity should not exceed 20% alteration of monthly flow volumes, while for groundwater, annual drawdown should not exceed the average annual recharge. The authors of the report consider multi-level distribution, water insecurity, and water quality to justify justice criteria for ESB for water.

Sub-global Earth system boundaries

Sub-global Earth system boundaries are the relevant scale for avoiding the loss of Earth system stability and minimising exposure to significant harm for human security. Achieving sub-global ESB requires targeting Earth system domains with a high impact on the biosphere, and enough policy-relevant timescales.

Conclusion

Achieving a just Earth system transformation globally requires a systemic process across energy, urbanisation, food and other sectors. ESBs provide rigorous science-based targets that highlight the levels of environmental changes that lead to significant harm. The report represents a transparent proposal for further debate by scholars and wider society.