In its recent advisory opinion on States’ obligations in relation to climate change, the ICJ addressed several important dimensions of international environmental law. Most notably, it placed significant emphasis on the principle of Common but Differentiated Responsibilities (CBDR). The Court acknowledged that climate change has not been primarily caused by developing countries, but is largely the result of decades, if not centuries, of intensive industrial activity undertaken by developed States. In this context, imposing identical mitigation obligations on developing countries, whose historical contribution to global emissions is minimal and whose developmental needs remain pressing, lacks both equity and logic. Any climate regime that disregards these disparities risks undermining the very principles of fairness and justice that underpin international environmental law. The Common but Differentiated Responsibility (CBDR) is “a well-established concept in the regime of international environmental law because it tries to achieve countries’ equity or certain environmental standards by imposing different obligations to different countries when addressing the global issues.”[1]
Principle 7 of the Rio Declaration (1992) and Article 3(1) of the United Nations Framework Convention on Climate Change (UNFCCC) affirm that States share a common responsibility to protect the climate but possess differentiated obligations based on capacity and contribution. It must be noted that the “principle of common but differentiated responsibilities is not merely a legal construct born of treaty negotiations; rather, they are grounded in scientific findings on climate change.”[2] Moreover, the principle not only takes into account the historical disparities, but also stresses the need “to account for present and future inequities.”[3] It is a duty of the developed countries to take “into full account the legitimate priority needs of developing countries for the achievement of sustained economic growth.”[4] This duty has been ascribed in Judge Yousuf’s Separate Opinion on the ICJ’s Advisory Opinion on Climate Change and must be given due regard as a primary imperative of states. The basis for the duty stems from the disproportionate contribution and the historical responsibility, which is not a “matter of history but a matter of continued contribution, since the historical emissions of industrialized countries continue to have a significant impact on the current climate system.” This also indicates why the carbon budget is calculated from pre-industrial time.[5] Consequently, any climate action framework that disregards differentiated responsibilities risks undermining both climate justice and the effectiveness of international climate governance. The principle of CBDR thus operates not only as a normative guide but as a substantive constraint on the manner in which mitigation burdens are allocated, ensuring that climate obligations do not perpetuate structural inequalities under the guise of environmental protection.
The UNFCCC recognizes that developed countries bear the largest historical and current share of greenhouse gas emissions, while the per capita emissions of developing states remain comparatively low. Judge Yusuf, in his opinion on climate obligations, emphasized that obligations must be proportionate to capacity and contribution, an interpretation consistent with Article 2.2 and Article 4.3 of the Paris Agreement. The Kyoto Protocol, though not in force, also exempts non-Annex I developing countries from binding emission reduction targets, reaffirming differentiated responsibilities. ICJ in its advisory opinion held that, “developing countries have a common but varied responsibility in dealing with the problem of climate change and its adverse effects“.[6] It further noted that “[e]missions from developing countries are growing in order to meet their development requirements and thus, over time, are likely to represent an increasingly significant percentage of global emissions“.[7]
Moreover, the ICJ has emphasised that courts must hold “the balance even between the environmental considerations and the developmental considerations raised by the respective Parties.”[8] In addition to that, the UNFCCC gave Annex I Parties six months from the entry into force of the UNFCCC to submit their reports, while non-Annex I Parties (developing countries) were given three years, and the least developed States were not given a deadline.[9] Furthermore, actions are justified under the necessity doctrine due to essential national interests. Article 25 of the ILC Articles on State Responsibility permits a State to invoke necessity when an act is the only means to safeguard an essential interest against a grave and imminent peril. It must be noted that the necessity “arises where there is an irreconcilable conflict between an essential interest on the one hand and an obligation of the State invoking necessity on the other.”[10]
The principle of common but differentiated responsibility is built upon the principle of equity, as all countries are not held responsible in same degree, but on the basis of their historical contribution to greenhouse gas emissions and economic capacity. Developed countries industrialised before developing countries, which enabled them to form a stronger and more stable economic base, but at the expense of increased emissions. If the principle of equality was applied in this case, developing countries would carry the same degree of responsibility as developed countries. Considering developing countries have contributed to global emissions on a smaller scale when compared to developed countries, placing the same responsibility on them as developed countries would be an unfair burden on them. Hence, the principle of equity is applied instead. All countries share the common goal to conserve the environment, but developed countries have a higher degree of responsibility on the basis of their larger contribution to global emissions and subsequent economic capability to bear the increased responsibility.
[1] Yuli Chen, ‘Reconciling common but differentiated responsibilities principle and no more favourable treatment principle in regulating greenhouse gas emissions from international shipping’ (2021) 123 Marine Policy 104317.
[2] Separate Opinion of Judge Yusuf, Obligations of States in Respect of Climate Change (Advisory Opinion) [2025] ICJ Rep (General List No 187) para 26, p 9.
[3] Ibid para 27.
[4] Ibid.
[5] IPCC, 2023, Climate Change 2023: Synthesis Report, Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Glossary, p. 121.
[6] International Court of Justice, Obligations of States in Respect of Climate Change (Advisory Opinion) 23 July 2025 (General List No 187) para 61, p 31.
[7] Ibid pp 31–32, para 61.
[8] Gabčíkovo-Nagymaros Project (Hungary/Slovakia), Judgment, I.C.J. Reports 1997, separate opinion of Vice-President Weeramantry, p. 88.
[9] United Nations Framework Convention on Climate Change (adopted 9 May 1992, entered into force 21 March 1994) 1771 UNTS 107 (UNFCCC) art 12(5).
[10] International Law Commission, Draft Articles on Responsibility of States for Internationally Wrongful Acts, with Commentaries (2001) Art 25, 80 https://legal.un.org/ilc/texts/instruments/english/commentaries/9_6_2001.pdf accessed 13 February 2025.
