The Parties to the Paris Agreement have committed to communicate successive ‘nationally determined contributions’ (NDCs) to the global response to climate change. Each NDC is expected to reflect the Party's ‘highest possible ambition’ (HPA) on the mitigation of climate change. This article envisages the possibility of taking HPA seriously: that is, of approaching it as an effective legal standard. It shows that, in some circumstances, the HPA standard can help to assess whether a State has complied with due diligence obligations on climate change mitigation.

Courts and scholars have interpreted open-ended legal norms as imposing due diligence obligations on States and other entities to mitigate climate change. These obligations can be applied in two alternative ways: through holistic decisions, where courts determine the level of mitigation action required of defendants; or through atomistic decisions, where courts identify some of the measures that the defendant must take. This article shows that, whilst most holistic cases fail on jurisdictional grounds, atomistic cases frequently succeed. Overall, it is argued that atomistic litigation strategies provide more realistic and effective ways for plaintiffs to prompt enhanced mitigation action.

Climate change mitigation calls for the limitation and reduction of greenhouse gas (GHG) emissions across all sectors. However, limiting GHG emissions from aviation has proven to be problematic for technical reasons (e.g., lack of low-carbon alternatives) as well as legal reasons (e.g., international aviation does not readily fall within any one state's jurisdiction). Relevant initiatives have followed two streams. At the international level, the International Civil Aviation Organization (ICAO) has adopted technical standards and, more recently, a market-based mechanism to limit emissions from international civil aviation. In parallel, states have adopted their own policies and measures to regulate emissions from both domestic and international aviation, ranging from tax and technical standards to traffic management and infrastructural development. While much of the literature on climate change mitigation in the aviation sector has focused on international efforts, this article reveals the importance of understanding the tensions and complementarities of the two streams.

The Supreme Court of the Netherlands construed the state’s positive human rights obligations as requiring a 25 per cent reduction of its greenhouse gas emissions by 2020 compared with 1990 levels. This article explores how judges can decide the level of state effort required to mitigate climate change. To date, judges have predominantly approached this issue by seeking to identify an elusive benchmark, either by deduction from global objectives or induction from state conduct. This article shows that the judicial assessment of a state’s requisite efforts inevitably relies on equity infra legem. Acknowledging this, judges could learn from the international courts’ experience with establishing clarity in the midst of vague legal rules.

In her response to my case comment in this issue of Transnational Environmental Law, Laura Burgers purports to disagree with my analysis on two points. Firstly, she suggests that we disagree on the method that a court should use to interpret the duty of care of corporations on climate change mitigation. Secondly, she disagrees with each of the four inconsistencies that I identify in the decision by the District Court of The Hague (the Netherlands) in Milieudefensie v. Royal Dutch Shell. In this rejoinder, I respectfully disagree with her characterization of our disagreement.

On 26 May 2021, the District Court of The Hague (The Netherlands) passed an innovative judgment in Milieudefensie v. Royal Dutch Shell. The Court interpreted Shell's duty of care towards the inhabitants of the Netherlands as requiring it to mitigate climate change by reducing the carbon dioxide emissions resulting from its global operations by at least 45% by 2030, compared with 2019. This case comment salutes the identification of a corporate duty of care for climate change mitigation but expresses scepticism regarding the Court's interpretation of this duty. The Court's reading of global climate mitigation objectives and climate science, which form the basis of its determination of Shell's requisite level of mitigation action, is plagued with inconsistencies. It is argued here that, in order to determine the standard of care applicable to Shell, the Court should have relied not only on a ‘descending’ reasoning as to what ought to be done, but also on an ‘ascending’ reasoning accounting for industry practices.