The fair share principle constitutes a core pillar of the 2015 Paris Agreement criteria for the adequacy of a nationally determined contribution to reduce global greenhouse gas emissions and adapt to climate change. For years, courts and national governments considered the principle too ambiguous to be interpretable in a court of law or in legislation. However, this principle is now being interpreted successfully by courts in cases where the adequacy of a national emissions reduction target is in question. Such a shift is important for intra- and intergenerational climate justice by creating a new layer of accountability to ensure that the burdens and responsibilities of addressing climate change are distributed in an equitable and just manner, considering historical inequities in development and emissions and differing national capabilities. This shift was enabled by recent evolutions in international case law and legal scholarship and empirical research from interdisciplinary climate sciences.
The principle of common but differentiated responsibilities and respective capabilities (here on out referred to as “CBDR”) is one of the few requirements assigned to nationally determined contributions (NDCs). The Preamble of the United Nations Framework Convention on Climate Change Paris Agreement lists one of its guiding principles for the pursuit of its objective as being the “principle of equity and common but differentiated responsibilities and respective capabilities, in the light of different national circumstances.” This guiding principle is made operational in stating that the Agreement “will be implemented” in light of these principles (Article 2.2) and that each country’s NDC will reflect this principle (Article 4.3). However, despite this clear mandate, when the Paris Agreement was instated, national governments didn’t have access to tools and frameworks to determine and express their individual capabilities and responsibilities. Governments are asked to provide their own justification in their NDCs for how the CBDR principle factored into their national determination of appropriate action in global effort, however, the wide range of interpretations led to the principle’s ambiguity to grow.
Carlarne & Colavecchio (2019) point to long-standing disagreements between national governments over what fairness and climate equity mean, and the lack of consensus as to whether demands are distributive, relating to now and the future, or also imply a corrective element, relating to past damages. As a result, the terms fairness, equity and justice continue to be contested, and the instances where they are operationalized are highly contextual. In aggregate, they argue that the Paris Agreement signaled an important shift in the international climate change legal framework to define and operationalize concepts of equity, justice, and fairness. They furthermore find that nations align the CBDR principle most closely with the principles of distributive justice (not compensatory) by way of focusing on a fair distribution of the burden of addressing climate change, with the goal of improving conditions for all.
In the absence of a shared definition and measurement of “fair contribution” and CBDR under the Paris Agreement, courts have begun interpreting the fair share principle in deliberations. The Urgenda case (2019) in the Supreme Court of the Netherlands ruled that the Dutch government had a legal obligation to reduce its greenhouse gas emissions by at least 25% by 2020 compared to 1990 levels, based on the country's duty to protect citizens' human rights and fair share of effort under the Paris Agreement (2019, para. 6.3 and 6.5). Similarly, the Neubauer case (2021) in Germany saw the Federal Constitutional Court declare that Germany's climate protection law was insufficient, particularly for the rights of future generations, and ordered a more ambitious carbon reduction target that aligned with the nation’s fair share. The European Court of Human Rights (ECHR), which focuses on whether states’ actions or inactions violate human rights, also raised the fair share principle in making the link between climate change and human rights obligations under European and international law (2020; 2021; Liston, 2020). These cases collectively signify a growing recognition in international and national law of the human rights implications of climate change and demonstrate the role of courts in enforcing climate action obligations outlined in the Paris Agreement. While in some ways contextual to Europe, this growing case law is useful for decision making by courts in other contexts. For example, the Urgenda case could very well offer an administrable framework for US courts to take up similar cases (132 Harv. L. Rev. 2090).
Towards this point, Rajamani et al. (2021) explores how fairness determinations are being made currently by courts (specifically in the cases of Urgenda and Neubauer) and that fair share “ranges” developed in the scholarship based on predetermined indicators can be used in climate litigation where adequacy in question. Rajamani et al. (2021) distills “principled limits” within the wide interpretive range of the narrative justifications that have thus far been provided by nations in their NDCs. These limits build on the evidence base of fairness indicators previously used by nations that was developed in the surveys and reviews (Höhne et al. (2014); Robiou du Pont et al., 2017; Winkler et al., 2018; Holz et al., 2018).
The willingness of courts to take up the fair share principle as an operable aspect of a case reflects the solidification of international norms around fairness and justice in global climate action. This hardening was enabled by breakthroughs in scientific inputs, both in monitoring and modeling, to provide context and expand our thinking through scenarios. Breakthroughs in attribution science, which establishes causation and apportionment of damages to emission sources, is poised to provide increasingly granular and operable evidence for the use of courts (47 Envtl. L. Rep. News & Analysis 10121).
There is still much work to be done to determine what a fair share means in the context of each nation’s capabilities and responsibilities, however, we have enough certainty and precedence that it should factor into a court’s adequacy deliberation for an entity’s climate action plan. Empirical evidence from other disciplines is contributing to the hardening of this goal, as is the positioning of fairness considerations within the procedural aspects of the Paris Agreement. The procedural aspects are more hardened, or binding, for national governments, in comparison to aspirational aspects such as the need to ratchet ambition.Future work to build a shared understanding of fairness would benefit from a focus on the benefits for international cooperation and trust-building for a fairness principle, as research today primarily rests on the nation-specific moral argument. Fairly distributing the burden of climate mitigation is necessary for trust and compliance among national governments, for example between economic rivals such as China and the US.