Equity has no single uncontested definition in public international law. Some scholars understand it as an expression of broader concepts of justice, whereas others regard it as an independent source of law. This uncertainty has practical consequences in climate governance, where states can invoke fairness to support sharply different interpretations of responsibility. The study notes that equity’s ambiguity has not prevented it from acquiring significance in international law: states incorporate it into treaties and negotiations, and courts have begun to discuss its role directly. In the climate regime, equity is most closely associated with common but differentiated responsibilities and respective capabilities, or CBDR/RC, but the analysis cautions against treating the two concepts as identical.

The 1992 UNFCCC established equity as one of the principles guiding parties’ actions and connected it to CBDR/RC. Its central provision stated that the climate system should be protected for the benefit of present and future generations on the basis of equity, while developed-country parties should take the lead in combating climate change and its adverse effects. This reflected the historical concentration of greenhouse gas emissions in developed countries and the relatively low per-capita emissions of many developing countries at the time. The arrangement strongly expressed distributive and intragenerational justice by assigning different responsibilities according to broad country categories. Its weakness was equally clear: the resulting “development divide” or “binary differentiation” left limited room for differences among developing states, while the Convention’s core obligations offered little mechanism for allocating burdens between present and future generations.

The Kyoto Protocol made the binary approach more explicit. Adopted in 1997 and entering into force in 2005, it required Annex I parties to pursue quantified greenhouse gas emissions reductions while imposing no comparable targets on developing countries. Its emissions trading, joint implementation and clean development mechanisms allowed mitigation units to be generated or transferred across jurisdictions. These arrangements translated historical responsibility into operational legal commitments, but the rigid division between country groups became politically contentious as emissions profiles and economic capacities changed. The United States Senate’s rejection of the protocol in 2001, with President George W. Bush describing it as an unfair means of addressing climate change, demonstrated that equity is context-dependent: the same framework could be portrayed as protecting developing states or as imposing an unjust burden on a major emitter. Although the clean development mechanism offered a route to sustainable development, its procedural shortcomings and limited treatment of future generations exposed gaps in the Kyoto model.

The negotiations that followed exposed a central challenge for climate law: a regime built to correct historical inequality increasingly had to govern countries with widely different and evolving emissions, capacities and vulnerabilities. At the 2011 Durban conference, parties launched a process to develop a universal legal instrument by 2015, intended to enter into force from 2020. The Durban decision deliberately left the legal form open, allowing for a protocol, an amendment, a new annex or another outcome with legal force. It also omitted explicit references to equity and CBDR/RC, even though the negotiations were described as procedurally and substantively equitable. According to the study, that silence was not an accidental oversight. It reflected unresolved disagreement over how differentiated responsibility should operate when a new instrument would apply to all parties. The process nevertheless marked a turning point in which fairness, transparency, inclusion and universal participation became central demands in climate negotiations.

The Paris Agreement substantially loosened the earlier category-based system. Its preamble links equity and CBDR/RC to “different national circumstances,” and Article 2 states that the agreement will be implemented to reflect equity and CBDR/RC in light of those circumstances. The study interprets this wording as a transition from predetermined groups toward differentiation by degree. Historical responsibility and capability remain relevant, but development needs, vulnerability, technological capacity, emissions profiles and other national conditions can affect what constitutes an equitable contribution. Their relative importance may also change over time. Article 4 reinforces this flexible approach by requiring all parties to contribute to global mitigation while recognizing that developing countries will take longer to peak emissions. The study calls this “temporal differentiation”: universal participation remains intact, but identical deadlines and obligations are no longer assumed to be fair in every national setting.

Equity also becomes more concrete in the Paris Agreement’s treatment of loss and damage. Article 8 places the Warsaw International Mechanism for Loss and Damage under the authority of the meeting of the parties and calls for enhanced understanding, action and support. Its work includes improving knowledge of climate impacts, strengthening dialogue and coordination, and facilitating support such as finance, technology and capacity-building for affected countries. This is especially relevant to vulnerable developing states that face severe climate harm despite comparatively small contributions to cumulative emissions. The provision has a corrective dimension because it recognizes the unequal distribution of climate burdens and creates an institutional route for responding to harm. It also has a distributive dimension, raising questions about who should finance responses and who should receive support. Yet the decision accompanying the Agreement states that Article 8 provides no basis for liability or compensation. Loss and damage therefore represents a qualified expression of corrective equity rather than a legal regime assigning responsibility and mandatory compensation.

The global stocktake provides another institutional expression of equity. Article 14 requires periodic assessment of collective progress toward the Agreement’s purpose and long-term goals in light of equity and the best available science. The process is Party-driven and cross-cutting, drawing on nationally determined contributions, biennial reports and submissions from international institutions, regional groups, observers and stakeholders. Its inclusiveness supports procedural equity by allowing governments and non-state actors to explain their circumstances and challenge official accounts of fairness. But broad participation does not automatically produce a consistent substantive test. Without standardized criteria, equity functions less as an independently measurable benchmark for collective progress than as a framework in which competing claims are presented and debated. The study therefore presents the stocktake as both a promising venue for negotiated justice and a persistent source of ambiguity, with considerable discretion remaining in states’ interpretations of equitable contributions.

Intergenerational equity is explicitly named in the Paris Agreement’s preamble but does not appear in the same form in its operative provisions. The study identifies two possible readings: intergenerational equity may operate as a separate interpretive principle, or it may form one dimension of the broader equity concept used in the Agreement. The analysis supports the second, intertemporal interpretation, citing the Agreement’s long-term temperature goals, requirement for progressively greater ambition, five-year submission cycle for nationally determined contributions and instruction to pursue the highest possible ambition. Together, these features permit fairness to be assessed over time rather than solely among states in the present generation. The analysis also notes that recent advisory opinions from the International Court of Justice and the Inter-American Court of Human Rights have moved toward explicitly recognizing the intergenerational dimension of climate equity, including the need to ensure the effective enjoyment of rights by present generations and their transmission to future generations. Overall, the study finds that Paris did not discard differentiation; it made the concept more responsive, multidimensional and temporally aware, while leaving unresolved the practical challenge of turning a flexible legal principle into consistent, measurable action.

Subject of Research: Historical and legal evolution of equity in international climate governance.

Article Title: Tracing equity: a historical inquiry into the international climate change regime

Article References: Manzo, R. (2026). Tracing equity: a historical inquiry into the international climate change regime. Frontiers in Political Science, 8, Article 1824714. https://doi.org/10.3389/fpos.2026.1824714

Image Credits: AI Generated

DOI: 10.3389/fpos.2026.1824714

Keywords: climate equity, Paris Agreement, UNFCCC, Kyoto Protocol, international climate law, CBDR/RC, loss and damage, global stocktake, intergenerational justice, nationally determined contributions, Tracing, equity