Ethical choices behind quantifications of fair contributions under the Paris Agreement

Contributions to mitigate climate change should be equitable under the Paris Agreement, yet researchers take sharply diverging approaches to assessing national effort. This Perspective evaluates the literature and presents guidelines for policy-relevant-and ethically explicit-research on equity. The Parties to the UNFCCC and Paris Agreement agreed to act on the basis of equity to protect the climate system. Equitable effort sharing is an irreducibly normative matter, yet some influential studies have sought to create quantitative indicators of equitable effort that claim to be value-neutral (despite evident biases). Many of these studies fail to clarify the ethical principles underlying their indicators, some mislabel approaches that favour wealthy nations as 'equity approaches' and some combine contradictory indicators into composites we call derivative benchmarks. This Perspective reviews influential climate effort-sharing assessments and presents guidelines for developing and adjudicating policy-relevant (but not ethically neutral) equity research.