The Growing Relevance of the Paris Agreement’s 1.5 °C Temperature Goal in the Light of International Human Rights Law and Climate Change Litigation

[Maria Liana Vodiţă is a legal professional from Germany who has worked as a research assistant and lecturer at the European University Viadrina in Frankfurt (Oder), where she also completed her doctorate in public international law. This contribution was written whilst she was working as a legal clerk (Rechtsreferendarin) at the Ludwig Boltzmann Institute of Fundamental and Human Rights in Vienna, Austria.]

By resolution A/RES/77/276 of 29 March 2023, the General Assembly of the United Nations (UN) requested the International Court of Justice (ICJ) to provide an Advisory Opinion (AO) on “the obligations of States in respect of climate change” under Article 65 para. 1 of the ICJ Statute. More precisely, the ICJ was asked to assess what the “obligations of States under international law [are] to ensure the protection of the climate system and other parts of the environment from anthropogenic emissions of greenhouse gases for States and for present and future generations” as well as what legal consequences these states may face if they – by act and/or omission – fail to comply with these obligations. 

When drafting the AO, the ICJ is expected to have “particular regard to […] the International Covenant on Civil and Political Rights” (ICCPR) in addition to, amongst others, the UN Framework Convention on Climate Change (UNFCCC) and the Paris Agreement (PA). In this context, one of the main focuses of the ICJ’s assessment will lie on the temperature goal(s) mentioned in Article 2 para. 1 lit. a) PA, in which the contracting parties agree to hold “the increase in the global average temperature to well below 2 °C above pre-industrial levels” and to pursue “efforts to limit the temperature increase to 1.5 °C above pre-industrial levels”, as this provision contains a legally binding obligation for the significant number of currently 195 parties to the PA. Furthermore, the AO will likely include an analysis on the interdependence between the states’ obligations under the PA and UNFCCC on the one hand as well as their obligations under international human rights law on the other, as this aspect is gaining significance in the context of climate change litigation (see e.g. the newsworthy decision in favour of young people who had accused state officials in Montana (USA) of violating their constitutional rights by promoting fossil fuels).

The Relevance of the 1.5 °C Temperature Goal under Article 2 para. 1 lit. a) PA 

Since the entry into force of the PA, it has been discussed whether the 1.5 °C temperature goal constitutes a legal obligation for the parties. Considering the wording of Article 2 para. 1 lit. a) PA, the provision indicates an orientation towards the 2 °C mark. At the same time, the parties recognize that a limitation to 1.5 °C above pre-industrial levels “would significantly reduce the risks and impacts of climate change”. This provision hence leaves room for interpretation as to which temperature goal – or range thereof – is legally binding. Considering the analysis and assessment of the latest nationally-determined contributions (NDCs) under Article 4 para. 2 PA, the 1.5 °C goal particularly stands out, as it seems “likely” (probability of outcome: 66%-100%) that global warming will exceed 1.5 °C within the course of the 21^st century (p. 10, A.4).

In this regard, the IPCC Special Report on 1.5 °C from 2018 has shown “robust” differences in climate characteristics between warming levels of 1.5 °C and 2 °C. This corresponds with the newest findings of the IPCC Climate Change Synthesis Report from 2023, which further endorses that the differences in climate change effects differ significantly at 1.5 °C and 2 °C respectively. Risks from droughts and precipitation deficits as well as heavy precipitation events, for example, are projected to be higher at 2 °C compared to 1.5 °C. Furthermore, the increase in global warming will most likely have a significant impact on sea level rise, which poses one of the most significant effects of climate change, as it not only threatens the habitability of certain regions, but the continuity of island states. Moreover, a significantly more extensive decrease in permafrost is predicted at 2 °C, which will most likely trigger climate-related tipping points (p. 21, B.5.2), leading to irreversible consequences with uncertain risks (p. 19).

In the past, it has been discussed that the upper temperature limit should be set at 1.75 °C, i.e. between the two mentioned temperature limits (see German Advisory Council on Environmental Issues (Sachverständigenrat für Umweltfragen) in its Assessment from 2020 and German Federal Constitutional Court (Bundesverfassungsgericht), Decision 1 BvR 2656/18 et al.). It must be kept in mind, however, that the purpose of Article 2 para. 1 PA aims “to strengthen the global response to the threat of climate change” by “enhancing the implementation of the [UNFCCC], including its objective”. This objective is defined in Article 2 UNFCCC and has the purpose to “prevent dangerous anthropogenic interference with the climate system”. In this regard, it had already been concluded inter alia by the UNFCCC Subsidiary Body for Scientific and Technological Advice (SBSTA) in 2015 that the 2 °C temperature goal was not in line with the UNFCCC’s objective and that only a limitation of warming to (well) below 2 °C and in some regions and vulnerable ecosystems to 1.5 °C above pre-industrial levels would suffice (p. 33). It can therefore be concluded that states must abide by a temperature goal that, first, is in line with the wording of Article 2 para. 1 lit. a) PA, but, second, also complies with the UNFCCC’s objective. The exceedance of 1.5 °C could therefore most likely already lead to a failure of states to comply with their obligations, as the predicted consequences would contradict the objectives of both the UNFCCC and – consequently – the PA. 

A development towards the 2 °C limit would, however, not only affect the legal obligations of states following provisions of the PA and UNFCCC, but also general principles such as the precautionary principle, which the European Court of Human Rights (ECtHR) acknowledged to be a legally binding principle (concerning this aspect see ICJ, Case concerning Pulp Mills on the River Uruguay (Argentina v. Uruguay), Judgement of 20 April 2010, § 164) under international environmental law (see ECthR, Tătar v. Romania (Judgement of 27 January 2009, no 67021/01, § 70)). The precautionary principle entails taking preventive action in the face of uncertainty in order to preclude causing irreversible harm, whereas the exceedance of the 1.5 °C temperature goal is expected to lead to such irreversible-negative impacts as mentioned above. Consequently, the relevance for the concretization of the legally binding temperature limit results inter alia from the necessity for States to recognize and consequently abide by their obligations under international law. Furthermore, recent developments in climate change litigation (as shown below) are reinforcing this significance of the 1.5 °C temperature goal.

Interdependence Between the States’ Obligations under the PA/UNFCCC and Under International Human Rights Law

As of June 2023, there have been 2,341 climate-related cases filed worldwide, compared to 1,550 cases in 2020 and 884 cases in 2017. In this regard, applicants inter alia claimed alleged violations of human rights, including the right to life, physical integrity and health, the right to family and home as well as the right to a healthy environment (where applicable), prompting states to take into consideration the effects of climate change in the context of their human rights obligations, especially considering the right to life. To this effect, the heat-humidity risks to human health due to the exposure to hyperthermic conditions that pose a risk of mortality from surface air temperature and humidity conditions are estimated to become particularly severe in scenarios of global warming levels over 1.7 °C above pre-industrial levels (p. 16).

Following the COP26 in Glasgow in 2021 and the adoption of the Glasgow Climate Pact, where the 1.5 °C goal was “cemented […] as the primary global temperature ceiling, shifting emphasis from ‘well below 2 °C’, […] with the more severe impacts of 2 °C warming emphasized”, there has been a recognizable shift towards the 1.5 °C goal in the context of climate litigation cases, a trend that can also be observed within the most recent cases before the ECtHR. Currently, there are several cases pending before the ECtHR which could lead to the court not only determining a human rights violation under the Convention for the Protection of Human Rights and Fundamental Freedoms (ECHR), but also specifying the obligations of states in regards to taking measures in order to prevent a global temperature increase of more than 1.5 °C. This especially concerns the case Duarte Agostinho et al. v. Portugal et al., which was referred to the Grand Chamber. In this case, the applicants claim a violation of Articles 2 (right to life) and 8 (right to respect for private and family life in the context of the state’s obligation to taking the necessary precautions for the purpose of protecting health and environment as well as delivering the necessary information) of the ECHR in the light of the states’ obligations under the PA and specifically the temperature goal mentioned in Article 2 PA. In its communication, the ECtHR has asked the parties to elaborate on whether the applicants suffer the consequences of the alleged insufficient action of the respondent states to achieve the 1.5 °C target, without further mentioning the 2 °C goal. Furthermore, the ECtHR inquired whether the respondent states fulfilled their obligations under the ECHR in the light of relevant provisions and principles of international environmental law, such as the precautionary principle (specifically referring to ECthR, Tătar v. Romania, no 67021/01, §§ 109 and 120). The Court is hence contextualizing the States’ obligation under Art. 2 PA in regards to the 1.5 °C temperature goal and will have the opportunity to specify these obligations within its judgement, as other courts have already done. It remains to be seen whether the ECtHR concretizes human rights obligations under the ECHR in general and in particular towards the 1.5 °C aim or leaves the determination mostly within the margin of appreciation of the parties.

Summary and Outlook

It is becoming increasingly clear that states must understand their obligations under international human rights law in the light of the treaties and principles of international environmental law and vice versa. This also seems coherent with the PA’s Preamble, where it is stipulated that “Parties should, when taking action to address climate change, respect, promote and consider their respective obligations on human rights” (para. 11 of the Preamble) and which must be taken into consideration for the purpose of the interpretation of the treaty according to Article 31 para. 2 of the Vienna Convention on the Law of Treaties. Considering that potential human rights violations are being discussed inter alia by the ECtHR under the scenario of the global temperature rising to more than 1.5 °C above pre-industrial levels, the upcoming judgements in climate litigation cases under human rights law have the potential of acting as a concretization of the states’ obligations under the UNFCCC and PA, although the latter strictly do not concern their jurisdiction.

The benchmark regarding the temperature goal in Article 2 para. 1 lit. a) PA will nevertheless most likely concretize in the direction of the 1.5 °C goal as the lowest possible threshold and the most optimistic scenario according to the IPCC (p. 10, Box SPM.1, Table 1, Category C1) in order to prevent a dangerous-anthropogenic interference with the climate system as mentioned in Article 2 UNFCCC. According to the most recent NDC Synthesis Report presented to the COP27 in November 2022, however, the implementation of current NDCs until 2030 would lead to a peak temperature rise in the range of 2.1-2.9 °C until the year 2100, so that states are urged to promptly improve their efforts to protect the climate system by any means.