{"id":26889,"date":"2025-09-03T09:17:37","date_gmt":"2025-09-03T14:17:37","guid":{"rendered":"https:\/\/blogs.law.columbia.edu\/climatechange\/?p=26889"},"modified":"2025-09-03T09:17:37","modified_gmt":"2025-09-03T14:17:37","slug":"doing-the-utmost-due-diligence-as-the-standard-of-conduct-in-international-climate-law","status":"publish","type":"post","link":"https:\/\/blogs.law.columbia.edu\/climatechange\/2025\/09\/03\/doing-the-utmost-due-diligence-as-the-standard-of-conduct-in-international-climate-law\/","title":{"rendered":"\u201cDoing the utmost\u201d: Due diligence as the standard of conduct in international climate law"},"content":{"rendered":"<div style=\"margin-top: 0px; margin-bottom: 0px;\" class=\"sharethis-inline-share-buttons\" ><\/div><p><span style=\"font-weight: 400\">One of the most profound findings in the International Court of Justice\u2019s (<\/span><a href=\"https:\/\/www.icj-cij.org\/sites\/default\/files\/case-related\/187\/187-20250723-adv-01-00-en.pdf\"><span style=\"font-weight: 400\">ICJ\u2019s) climate change advisory opinion<\/span><\/a><span style=\"font-weight: 400\"> (AO) is that State obligations to mitigate climate change to a level that holds warming to the Paris Agreement\u2019s 1.5<\/span><span style=\"font-weight: 400\">o<\/span><span style=\"font-weight: 400\">C threshold are spread out over the large canvas of international law, including United Nations (UN) climate treaties, particularly the Paris Agreement, UNCLOS, human rights treaties, other environmental treaties, and the <\/span><a href=\"https:\/\/blogs.law.columbia.edu\/climatechange\/2025\/08\/17\/when-custom-binds-all-states-reflections-on-customary-international-law-in-the-icj-climate-advisory-opinion\/\"><span style=\"font-weight: 400\">customary international rule<\/span><\/a><span style=\"font-weight: 400\"> to prevent significant harm to the environment. While most of these treaties, and the customary no-harm rule, do not contain obligations to achieve a particular result, they establish obligations on states to act in a particular manner \u2013 or obligations of conduct \u2013 which are assessed against a standard of due diligence.<\/span><\/p>\n<p><span style=\"font-weight: 400\">The ICJ AO, in interplay with the advisory opinions by the International Tribunal for the Law of the Sea (<\/span><a href=\"https:\/\/itlos.org\/fileadmin\/itlos\/documents\/cases\/31\/Advisory_Opinion\/C31_Adv_Op_21.05.2024_orig.pdf\"><span style=\"font-weight: 400\">ITLOS<\/span><\/a><span style=\"font-weight: 400\">) and the Inter-American Court for Human Rights (<\/span><a href=\"https:\/\/www.corteidh.or.cr\/docs\/opiniones\/seriea_32_en.pdf\"><span style=\"font-weight: 400\">IACtHR<\/span><\/a><span style=\"font-weight: 400\">), clarifies that the due diligence standard of conduct applies in an objective and stringent manner in the context of climate change (see <\/span><a href=\"https:\/\/blogs.law.columbia.edu\/climatechange\/2025\/07\/25\/enhanced-due-diligence-a-new-legal-standard-for-climate-action-in-the-inter-american-system\/\"><span style=\"font-weight: 400\">here<\/span><\/a><span style=\"font-weight: 400\">, <\/span><a href=\"https:\/\/blogs.law.columbia.edu\/climatechange\/2024\/06\/04\/finding-light-in-dark-places-specific-obligations-for-climate-change-and-ocean-acidification-mitigation\/\"><span style=\"font-weight: 400\">here<\/span><\/a><span style=\"font-weight: 400\">, and <\/span><a href=\"https:\/\/blogs.law.columbia.edu\/climatechange\/2024\/05\/29\/itlos-and-the-importance-of-getting-external-rules-right-in-interpreting-unclos\/\"><span style=\"font-weight: 400\">here<\/span><\/a><span style=\"font-weight: 400\">). It also provides a detailed set of factors to determine the content of due diligence.<\/span><\/p>\n<p><span style=\"font-weight: 400\">The ICJ found that some norms, previously thought not binding and falling under the unfettered discretion of States (e.g. the content of NDCs) are in fact binding obligations of conduct based on a due diligence standard, and their breach gives rise to state responsibility.<\/span><\/p>\n<p><span style=\"font-weight: 400\">In this blog post, I address some pertinent issues regarding due diligence as addressed by the ICJ, as well as ITLOS and the IACtHR. In particular, I focus on the relationship between obligations of result and obligations of conduct, the nature of due diligence, factors to determine its content, and the legal consequences of not acting with the required diligence.<\/span><\/p>\n<h2><strong><i>Relationship to obligations of result<\/i><\/strong><\/h2>\n<p><span style=\"font-weight: 400\">The distinction between obligations of conduct and obligations of result is not always clear-cut. However, in general, the fulfillment of obligations of result can be measured against an achieved objective or outcome, while obligations of conduct require a State to act in a particular manner and are usually assessed against a standard of due diligence. The ICJ noted that one type of obligation is not more onerous than the other; the two often coexist and seek to achieve the same objectives through different means\u201d (para. 175). This aligns with the emphasis by ITLOS that an obligation of due diligence does not require a lesser degree of effort to achieve the intended result, but that \u201c[i]In many instances, an obligation of due diligence can be <\/span><i><span style=\"font-weight: 400\">highly demanding<\/span><\/i><span style=\"font-weight: 400\">\u201d (ITLOS, para. 257).\u00a0 Importantly,\u00a0 an obligation of due diligence, though different in character, is as conducive to the achievement of a particular objective as an obligation of result.<\/span><\/p>\n<h2><i>The legal nature of<\/i><i> <\/i><i>due<\/i><i> diligence: objective, non-discretionary and determinable<\/i><\/h2>\n<p><span style=\"font-weight: 400\">While long considered to be subjective, discretionary, and indeterminate, ICJ, ITLOS and the IACtHR clarified that this is not the case.<\/span><\/p>\n<p><span style=\"font-weight: 400\">ITLOS noted the <\/span><i><span style=\"font-weight: 400\">objective<\/span><\/i><span style=\"font-weight: 400\"> nature of due diligence (ITLOS, para. 257). The ICJ concurred that \u201cwhether or how a relevant element of the obligation to exercise due diligence to protect the environment applies in a particular situation should be determined objectively\u201d (ICJ, para. 300).<\/span><\/p>\n<p><span style=\"font-weight: 400\">It follows, therefore, that \u201can obligation of due diligence should not be understood as an obligation which depends largely on the discretion of a State\u201d\u00a0 (ITLOS, para. 257).\u00a0<\/span><\/p>\n<p><span style=\"font-weight: 400\">Further, due diligence is not indeterminable. One of the most important aspects of the courts\u2019 findings is a comprehensive set of factors to determine due diligence. ITLOS noted that factors to be considered include \u201cscientific and technological information, relevant international rules and standards, the risk of harm and the urgency involved. The standard of due diligence may change over time, given that those factors constantly evolve\u201d (ITLOS, para. 239). Both the IACtHR and ICJ added further factors, as will be shown below. Determination of due diligence is, thus, possible, but it needs to be assessed in a case-specific context; based on what is reasonable under the concrete and specific circumstances of a State. This does not exclude identifying a standard of conduct at a general level, depending on the risk\u2019s overall character (ICJ, para. 137).<\/span><\/p>\n<h2><i><span>Application of due diligence<\/span><\/i><\/h2>\n<p><span style=\"font-weight: 400\">During the proceedings before the courts, particularly before the ICJ, several parties maintained that due diligence is a self-standing norm under international law. This notion was partly enhanced by the <\/span><a href=\"https:\/\/docs.un.org\/en\/A\/RES\/77\/276\"><span style=\"font-weight: 400\">UN General Assembly Resolution 77\/276<\/span><\/a><span style=\"font-weight: 400\">, which requested the opinion from the ICJ. The resolution called upon the Court to have particular regard, <\/span><i><span style=\"font-weight: 400\">inter alia<\/span><\/i><span style=\"font-weight: 400\">, to \u201cthe duty of due diligence\u201d in rendering its answer to the questions put before it.<\/span><\/p>\n<p><span style=\"font-weight: 400\">The ICJ, however, made clear that due diligence does not exist independently. It is not a norm, let alone an obligation, on its own. Rather, it is the standard applying to a State\u2019s expected conduct in fulfilling a (main) obligation \u2013 the obligation of conduct. This can be a customary international obligation (i.e., of cooperation or harm prevention) or a treaty-based obligation (i.e., to prevent, reduce, and control pollution of the marine environment under Art. 194.1 UNCLOS or climate adaptation obligations under Art. 7 of the Paris Agreement), but there must be a (main) obligation to which the due diligence standard applies and in relation to which its compliance is assessed.<\/span><\/p>\n<h2><i><span>The content of due diligence<\/span><\/i><\/h2>\n<p><span style=\"font-weight: 400\">Due diligence is a variable and evolving concept, yet it does not escape determination and concretization. The ICJ, ITLOS, and IACtHR provided a comprehensive set of factors designed to support the determination of due diligence.<\/span><\/p>\n<p><span style=\"font-weight: 400\">a)<\/span> <span style=\"font-weight: 400\">Best efforts<\/span><\/p>\n<p><span style=\"font-weight: 400\">In general, due diligence requires that States undertake their best efforts \u2013 or to do the utmost (ITLOS, paras. 233 and 241; ICJ, paras. 253, 270; IACtHR, para. 232). This is usually defined by what can reasonably be expected of a State in a similar situation (i.e., the employment of best efforts by using all the means at its disposal (ICJ, 229; citing <\/span><a href=\"https:\/\/www.icj-cij.org\/sites\/default\/files\/case-related\/135\/135-20100420-JUD-01-00-EN.pdf\"><i><span style=\"font-weight: 400\">Pulp Mills<\/span><\/i><\/a><span style=\"font-weight: 400\">) or as an obligation to deploy \u201cadequate means, exercise best possible efforts, and do its utmost\u201d <\/span><a href=\"https:\/\/www.itlos.org\/fileadmin\/itlos\/documents\/cases\/case_no_17\/17_adv_op_010211_en.pdf\"><span style=\"font-weight: 400\">(ITLOS <\/span><i><span style=\"font-weight: 400\">Seabed Dispute Chamber<\/span><\/i><\/a><span style=\"font-weight: 400\"> AO)).<\/span><\/p>\n<p><span style=\"font-weight: 400\">b)<\/span> <span style=\"font-weight: 400\">Factors<\/span><\/p>\n<p><span style=\"font-weight: 400\">A comprehensive set of elements or factors for determining due diligence has now emerged. The factors comprise, in a non-exhaustive manner: (i) taking all appropriate measures, (ii) scientific and technological information, (iii) relevant international rules and standards, (iv) different capabilities, (v) the risk of harm and the urgency, (vi) precautionary approach or principle and respective measures, (vii) risk assessment and environmental impact assessment, (viii) notification and consultation (ITLOS, para. 239 and ICJ, paras. 231-299).<\/span><\/p>\n<p><span style=\"font-weight: 400\">In addition to these factors, <\/span><a href=\"https:\/\/verfassungsblog.de\/enhanced-due-diligence-climate-iacthr\/\"><span style=\"font-weight: 400\">the IACtHR added<\/span><\/a><span style=\"font-weight: 400\"> the following: (ix) integration of the human rights perspective into the formulation, implementation and monitoring of all policies and measures related to climate change to ensure that they do not create new vulnerabilities or exacerbate preexisting ones, (x) permanent and adequate monitoring of the effects and impacts of the adopted measures, (xi) strict compliance with the obligations arising from procedural rights, in particular, access to information, participation, and access to justice; (xii) transparency and accountability in relation to State climate action, (xi) appropriate regulation and supervision of corporate due diligence, and (xiii) enhanced international cooperation, particularly regarding technology transfer, financing, and capacity-building (IACtHR, para. 236).<\/span><\/p>\n<p><span style=\"font-weight: 400\">(i)<\/span><span style=\"font-weight: 400\"> \u00a0 \u00a0 \u00a0 \u00a0 <\/span> <span style=\"font-weight: 400\">All appropriate measures<\/span><\/p>\n<p><span style=\"font-weight: 400\">For the ICJ, taking all appropriate measures \u201cmeans that States must put in place a national system, including legislation, administrative procedures and an enforcement mechanism necessary to regulate the activities in question, and to exercise adequate vigilance to make such a system function efficiently, with a view to achieving the intended objective\u201d (ICJ, paras. 235, 281; ITLOS, para. 235 referring to <\/span><i><span style=\"font-weight: 400\">Pulp Mills<\/span><\/i><span style=\"font-weight: 400\">). This entails not only the adoption of appropriate rules and measures, but also their enforcement and the exercise of administrative control applicable to both public and private operators, such as monitoring the activities undertaken by these operators.<\/span><\/p>\n<p><span style=\"font-weight: 400\">In the view of the ICJ, taking appropriate measures to protect the climate system <\/span><a href=\"https:\/\/verfassungsblog.de\/icj-climate-advisory-opinion-fossil-fuels\/\"><span style=\"font-weight: 400\">also includes<\/span><\/a><span style=\"font-weight: 400\"> addressing \u201cfossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licenses or the provision of fossil fuel subsidies\u201d (ICJ, para. 427).<\/span><\/p>\n<p><span style=\"font-weight: 400\">The ICJ also clarified due diligence requirements for determining the content of Nationally Determined Contributions (NDCs). The ICJ rejected the characterization of NDCs as voluntary and discretionary and confirmed that the content, implementation, and achievement of NDCs are obligations of conduct, based on a stringent due diligence standard (for a discussion, see<\/span><a href=\"https:\/\/voelkerrechtsblog.org\/the-icj-and-the-un-climate-regime\/\"> <span style=\"font-weight: 400\">Voigt, 2025<\/span><\/a><span style=\"font-weight: 400\">).<\/span><\/p>\n<p><span style=\"font-weight: 400\">With respect to the content of NDCs, the ICJ made clear that States do not enjoy unfettered discretion when preparing NDCs (ICJ, para. 270). Rather, their discretion is limited (ICJ, para. 245). As an obligation of conduct, parties are obliged to exercise due diligence when putting forward their NDC and must satisfy certain expectations and standards under the Paris Agreement when doing so, as set out in Art. 4.3 (ICJ, para. 249). This provision is not a voluntary expectation. It is prescriptive in the sense it requires that \u201csuccessive nationally determined contributions will represent a progression\u201d and \u201creflect [a party\u2019s] highest possible ambition\u201d, without prescribing precisely what constitutes a progression, or what reflects a party\u2019s highest possible ambition.\u201d (ICJ, para. 240) These standards require, first, that NDCs represent a progression, which the court interpreted as a legal obligation of due diligence that \u201ca party\u2019s NDCs must become more demanding over time\u201d (ICJ, para. 241).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Second, a party\u2019s NDCs must reflect the highest possible ambition, to which many parties had referred to in their oral statements. The ICJ clarified that each party has a due diligence obligation to do its utmost to ensure that the NDCs it puts forward represent its highest possible ambition in order to realize the objectives of the Agreement. (ICJ, para. 270, 245). It stated that this implies that NDCs must be capable of making an adequate contribution to the achievement of the temperature goal. This provision reveals the necessity for the ambition contained in a party\u2019s NDC to relate to the object and purpose of the Agreement set out in Article 2, i.e. to hold the increase in the global average temperature to below 1.5\u00b0C (ICJ, para. 242). Literature has provided more detail on the contours of \u201chighest possible ambition\u201d in Art. 4.3 (Voigt,<\/span><a href=\"https:\/\/www.qil-qdi.org\/paris-agreement-standard-conduct-parties\/\"> <span style=\"font-weight: 400\">2016<\/span><\/a><span style=\"font-weight: 400\">,<\/span><a href=\"https:\/\/onlinelibrary.wiley.com\/doi\/10.1111\/reel.12514\"> <span style=\"font-weight: 400\">2023<\/span><\/a><span style=\"font-weight: 400\">, Mayer<\/span><a href=\"https:\/\/www.cambridge.org\/core\/journals\/international-and-comparative-law-quarterly\/article\/highest-possible-ambition-on-climate-change-mitigation-as-a-legal-standard\/3AEBF5E43A091E349791B44D5F4FB3E2\"> <span style=\"font-weight: 400\">2024<\/span><\/a><span style=\"font-weight: 400\">).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Parties must, third, be informed by the outcomes of the Global Stocktake in the preparation of their NDCs, according to Arts. 14.3 and 4.9 of the Paris Agreement, and when communicating their NDCs must provide the information necessary for clarity, transparency and understanding, according to Art. 4.8.<\/span><\/p>\n<p><span style=\"font-weight: 400\">Further, the ICJ concluded that the national implementation and achievement of NDCs are obligations of conduct and not voluntary. The obligation that parties \u201cshall pursue domestic mitigation measures\u201d in Art. 4.2(2) is substantive in nature and creates an individual obligation of conduct for each party to the Paris Agreement (ICJ, para. 251).\u00a0<\/span><\/p>\n<p><span style=\"font-weight: 400\">This does not mean that parties are obligated to achieve their NDC targets, but rather that they must make best efforts, based on stringent due diligence (ICJ, para. 254) to obtain such a result. Parties must \u201cpursue domestic mitigation measures\u201d that aim to achieve the objectives of their NDCs which are proactive and reasonably capable of achieving the NDCs set by them, including in relation to activities carried out by private actors (ICJ, para. 252).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Also the fulfillment of adaptation obligations needs to be assessed against the standard of due diligence. The ICJ considers it incumbent upon parties to enact appropriate measures (examples of which are provided in Article 7, paragraph 9) that are capable of \u201cenhancing adaptive capacity, strengthening resilience and reducing vulnerability to climate change\u201d. (ICJ, para. 258)<\/span><\/p>\n<p><span style=\"font-weight: 400\">In sum, with respect to the Paris Agreement, the ICJ concluded that \u201cthe compliance of parties with their obligations of conduct under the Paris Agreement is assessed on the basis of whether the party in question exercised due diligence and employed best efforts by using all the means at its disposal in the performance of that obligation\u201d (ICJ, paras. 229 and 245).<\/span><\/p>\n<p><span style=\"font-weight: 400\">The IACtHR added various components to identifying appropriate measures, such as the need to reflect maximum use of available resources, avoid technologies whose effects have not been fully verified, protect biodiversity and ecosystems, facilitate the continuing participation of Indigenous Peoples in decision-making, stimulate and attract investment in innovation in low-emission activities, as well as to develop new tools and standards for strengthening green finance, review existing trade and investment agreements, and settlement mechanisms for litigation between investors and States (IACtHR, paras. 336-367).\u00a0<\/span><\/p>\n<p><span style=\"font-weight: 400\">The IACtHR also details in particular what due diligence entails in relation to the regulation of private actors (IACtHR, para. 347). Private actors do not fall outside the normative \u201cforce-field\u201d of States\u2019 due diligence. As the activities in question are mostly carried out by private entities, due diligence requires States to regulate their conduct (i.e., \u201cregulatory due diligence\u201d) (ITLOS, para. 236; IACtHR, para. 231; ICJ, para. 428).\u00a0<\/span><\/p>\n<p><span style=\"font-weight: 400\">A State is responsible for its <\/span><i><span style=\"font-weight: 400\">own<\/span><\/i><span style=\"font-weight: 400\"> actions or omissions when failing to exercise regulatory due diligence. In the context of state responsibility, the question of attributing the conduct of private actors to a State therefore does not arise in such circumstances, as a State\u2019s own regulatory performance is at stake. \u201cThus, a State may be responsible where, for example, it has failed to exercise due diligence by not taking the necessary regulatory and legislative measures to limit the quantity of emissions caused by private actors under its jurisdiction.\u201d (ICJ, para. 428; see also IACtHR, para. 345)<\/span><\/p>\n<p><span style=\"font-weight: 400\">A final aspect of due diligence with regard to appropriate measures to be highlighted here is vertical and horizontal policy coherence. The IACtHR observed that \u201c[t]aking into account the standard of enhanced due diligence [\u2026], States have the obligation to ensure coherence between their domestic and international commitments and their obligations concerning the mitigation of climate change. [\u2026] among other measures, States should ensure that public finance and incentives aimed at activities that generate [greenhouse gas (GHG)] emissions are conditioned on strict compliance with national mitigation norms and policies\u201d (IACtHR, para. 344).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Overall, while the respective climate measures of each state will necessarily differ depending on its emission portfolio, drivers, and other national circumstances, the courts have provided comprehensive guidance for states on due diligence for adopting appropriate measures.<\/span><\/p>\n<p><span style=\"font-weight: 400\">(ii) Scientific and technological information<\/span><\/p>\n<p><span style=\"font-weight: 400\">The availability of, and the need to acquire and analyse scientific and technological information, are important factors of due diligence, as scientific information may be relevant to assess the probability and seriousness of possible harm (ICJ, 283).<\/span><\/p>\n<p><span style=\"font-weight: 400\">This is not a passive obligation. Due diligence requires States to actively pursue the scientific information. In this regard, reports by the IPCC constitute comprehensive and authoritative restatements of the best available science about climate change at the time of their publication (ICJ, para. 284). The standard of due diligence may also become more demanding in the light of new scientific or technological knowledge (ICJ, para. 284).<\/span><\/p>\n<p><span style=\"font-weight: 400\">(iii) Relevant international rules and standards<\/span><\/p>\n<p><span style=\"font-weight: 400\">In determining the required due diligence, current international rules and standards must be taken into consideration which may arise from binding and non-binding norms (ICJ, para. 287 referencing <\/span><a href=\"https:\/\/www.icj-cij.org\/sites\/default\/files\/case-related\/92\/092-19970925-JUD-01-00-EN.pdf\"><span style=\"font-weight: 400\">Gabcikovo-Nagymaros<\/span><\/a><span style=\"font-weight: 400\">). Such standards may therefore not only be contained in treaties and in customary international law, but \u201cmay also be reflected in certain decisions of the [conferences of the parties (COPs)] to the climate change treaties and in recommended technical norms and practices, as appropriate.\u201d (ICJ, para. 288)<\/span><\/p>\n<p><span style=\"font-weight: 400\">Regarding COP decisions, the ICJ narrowed their application in the context of determining due diligence to those decisions that have acquired the status of customary international law, in so far as they reflect State practice and express an <\/span><i><span style=\"font-weight: 400\">opinio juris<\/span><\/i><span style=\"font-weight: 400\"> and noted that such legal significance can only be determined <\/span><i><span style=\"font-weight: 400\">in concreto<\/span><\/i><span style=\"font-weight: 400\">. It did, however, not indicate when COP decisions \u2013 and which &#8211; may have acquired such status.<\/span><\/p>\n<p><span style=\"font-weight: 400\">The ICJ\u00b4s approach to international rules and standards in the context of due diligence builds on that of ITLOS. For climate change, ITLOS observed that international rules and standards are found in various climate-related treaties and instruments, including the UNFCCC and the Paris Agreement, MARPOL, the Chicago Convention, and the Montreal Protocol, including its Kigali Amendment (ITLOS, paras. 214, 239). ITLOS relied predominantly on the 1.5<\/span><span style=\"font-weight: 400\">o<\/span><span style=\"font-weight: 400\">C global temperature goal and the timeline for emission pathways (i.e. net-zero emissions by 2050) set forth in the Paris Agreement in the interpretation of \u201call necessary measures\u201d under Art. 194.1 of UNCLOS and due diligence (ITLOS, para. 222). In the same vein, the ICJ observes that \u201cthe climate change treaties establish standards that may enable or facilitate the identification and application of the diligence that is due in specific instances\u201d. (ICJ, 313).<\/span><\/p>\n<p><span style=\"font-weight: 400\">The reference to international rules and standards is also important for another reason: to <\/span><a href=\"https:\/\/verfassungsblog.de\/unlocking-unclos\/\"><span style=\"font-weight: 400\">create consistency and harmony in international law<\/span><\/a><span style=\"font-weight: 400\">. By interpreting UNCLOS in the light of the Paris Agreement as the primary legal instrument for addressing climate change (ITLOS, para. 214), ITLOS ensured that the standard applied to states\u00b4 obligations to address climate change under UNCLOS was no different to the one they agreed to when adopting the Paris Agreement. Similarly, the ICJ applies the Paris Agreement standard in the determination of due diligence pertaining to other treaties as well as to customary law. It goes so far to state that \u201cat the present stage, compliance in full and in good faith by a State with the climate change treaties, as interpreted by the Court [\u2026], suggests that this State substantially complies with the general customary duties to prevent significant environmental harm and to co-operate\u201d (ICJ, para. 314). This, according to the ICJ, also applies to States that are not a party to the climate change treaty or treaties. Though it noted that \u201cif a non-party State does not co-operate in such a way, it has the full burden of demonstrating that its policies and practices are in conformity with its customary obligations\u201d. (ICJ, 314)<\/span><\/p>\n<p><span style=\"font-weight: 400\">The ICJ reiterated ITLOS\u00b4 observation that obligations under other treaties (such as under UNCLOS) (ITLOS, 222 and 223) or customary obligations would not be fulfilled simply by States complying with their obligations under the climate change treaties. Treaty law and customary international law are different in character and do not entirely overlap. However, they inform each other. Therefore, the ICJ noted with respect to UNCLOS, that measures under Art. 192 and 194 \u201cmust be adopted in accordance with the obligations incumbent upon States under the UNFCCC and the Paris Agreement, in so far as the States concerned are parties to those instruments\u201c (ICJ, 343).<\/span><\/p>\n<p><span style=\"font-weight: 400\">What can be drawn from this is that the Paris Agreement permeates other international obligations of states, both under treaty and customary law, and informs their interpretation and the exercise of due diligence. Thus, the standards and norms included in the Paris Agreement become the benchmark against which, to a large extent, the performance of states in respect to climate change is assessed under other international treaties and under customary law (See Voigt,<\/span><a href=\"https:\/\/onlinelibrary.wiley.com\/doi\/10.1111\/reel.12514\"> <span style=\"font-weight: 400\">2023<\/span><\/a><span style=\"font-weight: 400\">). Such an approach ensures that states are consistently held to the 1.5<\/span><span style=\"font-weight: 400\">o<\/span><span style=\"font-weight: 400\">C temperature threshold and to acting with the necessary due diligence in this regard, also in fulfilling their <\/span><i><span style=\"font-weight: 400\">other<\/span><\/i><span style=\"font-weight: 400\"> obligations under international law.<\/span><\/p>\n<p><span style=\"font-weight: 400\">iv)<\/span><span style=\"font-weight: 400\"> \u00a0 \u00a0 \u00a0 <\/span> <span style=\"font-weight: 400\">Differentiation<\/span><\/p>\n<p><span style=\"font-weight: 400\">The need to act with due diligence applies to all states. However, consistent with the principle of common but differentiated responsibilities and respective capabilities (CBDR), the standard varies (ICJ, para. 247). The ICJ noted that CBDR reflects the need to equitably distribute the burdens of the obligations in respect of climate change.<\/span><\/p>\n<p><span style=\"font-weight: 400\">The ICJ observed that CBDR does not categorically place different burdens on a state based on whether is a developed or developing country. Rather, in its view, the principle calls for taking into account the circumstances of the state in question, such as historical <\/span><i><span style=\"font-weight: 400\">and current <\/span><\/i><span style=\"font-weight: 400\">contributions to cumulative GHG emissions, and their different current capabilities and national circumstances, including their economic and social level of development and other national circumstances of the party in question (ICJ, para. 148). The court also observed that the inclusion of the phrase, \u201cin the light of different national circumstances\u201d in the Paris Agreement, adds nuance to the principle by recognizing that the status of a State as developed or developing is <\/span><i><span style=\"font-weight: 400\">not static<\/span><\/i><span style=\"font-weight: 400\"> (ICJ, 226) (see, on the nuanced and dynamic nature of CBDR, Voigt and Ferreira,<\/span><a href=\"https:\/\/papers.ssrn.com\/sol3\/papers.cfm?abstract_id=2827633\"> <span style=\"font-weight: 400\">2016<\/span><\/a><span style=\"font-weight: 400\">)<\/span><\/p>\n<p><span style=\"font-weight: 400\">Importantly,\u00a0 the ICJ notes that in between the most developed and least developed states \u201care States that have progressed considerably in their development since the conclusion of the UNFCCC in 1992 [&#8230;] and some of which now contribute significantly to global GHG emissions and possess the capacity to engage in meaningful mitigation and adaptation efforts, as well as other States with significant resources and technical capabilities to contribute to addressing global climate change\u201d (ICJ, para. 150).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Moreover, in referring to the ITLOS climate change advisory opinion, the ICJ noted that CBDR \u201crequires a State with greater capabilities and sufficient resources to do more than a State not so well placed,\u201d but that, based on CBDR, \u201cimplementing the obligation of due diligence requires even the latter State to take all the means at its disposal to protect the climate system in accordance with its capabilities and available resources&#8221; (ICJ, para. 291). It stated:<\/span><\/p>\n<p><span style=\"font-weight: 400\">\u201cThe difference between the respective capabilities of States, as one of the factors which determines the diligence required, cannot therefore merely result from a distinction between developed and developing countries, but must also depend on their respective national circumstances. The multifactorial and evolutive character of the due diligence standard entails that, as States develop economically and their capacity increases, so too are the requirements of diligence heightened. Finally, the reference to available means and capabilities cannot justify undue delay or a general exemption from the obligation to exercise due diligence\u201d (ICJ, para 150).<\/span><\/p>\n<p><span style=\"font-weight: 400\">v)<\/span><span style=\"font-weight: 400\"> \u00a0 \u00a0 \u00a0 \u00a0 <\/span> <span style=\"font-weight: 400\">Precautionary approach or principle and respective measures<\/span><\/p>\n<p><span style=\"font-weight: 400\">Due diligence is also informed by the risk at stake and the urgency to act. In general, \u201c[t]he standard of due diligence has to be more severe for the riskier activities\u201d (<\/span><a href=\"https:\/\/www.itlos.org\/fileadmin\/itlos\/documents\/cases\/case_no_17\/17_adv_op_010211_en.pdf\"><span style=\"font-weight: 400\">Seabed AO<\/span><\/a><span style=\"font-weight: 400\">). The notion of risk in this regard should be appreciated in terms of both the probability or foreseeability of the occurrence of harm and its severity or magnitude. With respect to climate change, the risks are exceptionally high as it poses a \u201cquintessentially universal risk to all States\u201d which is \u201cof a general and urgent character\u201d (ICJ, para. 138) and \u201can existential problem of planetary proportions that imperils all forms of life and the very health of our planet\u201d (ICJ, para. 456). States are therefore required to take all appropriate measures to prevent significant harm where reliable scientific evidence of a risk of significant harm exists (ICJ, para. 293).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Where scientific uncertainty exists, States should not refrain from or delay taking precautionary actions of prevention in the face of risk. According to Principle 15 of the Rio Declaration, precaution requires that where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation (see also Article 3, paragraph 3, of the UNFCCC).<\/span><\/p>\n<p><span style=\"font-weight: 400\">The obligation of due diligence is closely linked with precaution. As ITLOS already confirmed (ITLOS, paras 213 and 242), it is \u201can integral part of the general obligation of due diligence\u201d (<\/span><a href=\"https:\/\/www.itlos.org\/fileadmin\/itlos\/documents\/cases\/case_no_17\/17_adv_op_010211_en.pdf\"><span style=\"font-weight: 400\">Seabed AO<\/span><\/a><span style=\"font-weight: 400\">). The ICJ agreed with this conclusion that \u201cwhere there are plausible indications of potential risks,\u201d a State \u201cwould not meet its obligation of due diligence if it disregarded those risks\u201d and, in that sense, the \u201cprecautionary approach is also an integral part of the general obligation of due diligence\u201d under the duty to prevent significant harm to the environment\u201d (ICJ, para. 294).<\/span><\/p>\n<p><span style=\"font-weight: 400\">(vi)<\/span><span style=\"font-weight: 400\"> \u00a0 \u00a0 \u00a0 <\/span> <span style=\"font-weight: 400\">Risk assessment and environmental impact assessment<\/span><\/p>\n<p><span style=\"font-weight: 400\">Due diligence also requires States to take certain procedural measures, which are distinct from substantive measures, to prevent risks (ICJ, para. 295), However, as ITLOS noted, \u201cprocedural obligations, such as the requirement to conduct an environmental impact assessment [EIA], may, indeed, be of equal or even greater importance than the substantive standards existing in international law\u201d. (ITLOS, para. 345<\/span> <a href=\"https:\/\/pca-cpa.org\/en\/cases\/11\/\"><span style=\"font-weight: 400\">with reference to Chagos Award<\/span><\/a><span style=\"font-weight: 400\">)<\/span><\/p>\n<p><span style=\"font-weight: 400\">In this context, the ICJ pointed to the need to undertake an EIA, which it considered a rule of customary international law (with reference to <\/span><a href=\"https:\/\/www.icj-cij.org\/case\/150\"><span style=\"font-weight: 400\">Certain Activities<\/span><\/a><span style=\"font-weight: 400\"> and <\/span><a href=\"https:\/\/www.icj-cij.org\/sites\/default\/files\/case-related\/135\/135-20100420-JUD-01-00-EN.pdf\"><span style=\"font-weight: 400\">Pulp Mills<\/span><\/a><span style=\"font-weight: 400\">). This aligns with the confirmation by the IACtHR that, \u201cin compliance with the standard of enhanced due diligence, States must conduct a meticulous assessment of activities that could result in significant harm to the climate system before granting approval\u201d (IACtHR, para. 363).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Since customary international law does not specify the scope and content of an EIA, the specific character of the respective risk and the specific circumstances of each case need to be taken into account (ICJ, paras. 296, 298). Such specific assessment could also \u201cidentify previously unknown information about possibilities for reducing the quantity of GHG emissions by relevant proposed individual activities\u201d (ICJ, para. 298).<\/span><\/p>\n<p><span style=\"font-weight: 400\">The obligation to conduct an EIA concerns <\/span><i><span style=\"font-weight: 400\">planned<\/span><\/i><span style=\"font-weight: 400\"> activities and must be carried out on the basis of the best available science. It must be conducted prior to the implementation of a project and applies to both those planned by private entities and by States (ITLOS, 358). Moreover, it should include not only the specific effects of the planned activities concerned but also the socio-economic impacts and <\/span><i><span style=\"font-weight: 400\">cumulative<\/span><\/i><span style=\"font-weight: 400\"> impacts of these and other activities (ITLOS, para. 365). Planned activities may not be environmentally significant if considered in isolation, whereas they may produce significant effects if evaluated in interaction with other activities (ITLOS, para. 365).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Ultimately, \u201cit is for each State to determine in its domestic legislation or in the authorization process for the project, the specific content of the environmental impact assessment required in each case, having regard to the nature and magnitude of the proposed development and its likely adverse impact on the environment as well as to the need to exercise due diligence in conducting such an assessment\u2019\u201d. (ICJ, para. 298)<\/span><\/p>\n<p><span style=\"font-weight: 400\">(vii)<\/span><span style=\"font-weight: 400\"> \u00a0 \u00a0 <\/span> <span style=\"font-weight: 400\">Notification and consultation<\/span><\/p>\n<p><span style=\"font-weight: 400\">Due diligence also contains an obligation of States to notify and consult in good faith with other States where planned activities within the jurisdiction or control of a State create a risk of significant harm, and notification and consultation is necessary to determine the appropriate measures to prevent that risk. (ICJ,<\/span><span style=\"font-weight: 400\"> para. 299 with reference to <\/span><a href=\"https:\/\/www.icj-cij.org\/case\/150\"><span style=\"font-weight: 400\">Certain Activities<\/span><\/a><span style=\"font-weight: 400\">)<\/span><\/p>\n<p><span style=\"font-weight: 400\">This applies in particular \u201cwhere an activity significantly affects collective efforts to address harm to the climate system\u201d (ICJ, para. 299). This can be understood as notification and consultation to be especially warranted when planning fossil fuel extraction or combustion projects, which may affect other states\u00b4 fossil fuel phase-out policies or their transition to renewable energies.<\/span><\/p>\n<p><span style=\"font-weight: 400\">c)<\/span> <span style=\"font-weight: 400\">Qualifier: Stringent\/Enhanced Due Diligence<\/span><\/p>\n<p><span style=\"font-weight: 400\">As explained above, the catalogue of factors to assess whether the obligation to act with due diligence has been met is detailed and specific, and allows for the determination of lawful \u2013 or unlawful \u2013 state behavior in relation to their obligations to address climate change. This constitutes a significant hardening and concretization of international climate law and circumscribes the conduct to be exercised in the compliance with international legal obligations.<\/span><\/p>\n<p><span style=\"font-weight: 400\">The courts also qualified the level of due diligence. ITLOS observed that, given the high risks of serious and irreversible harm to the marine environment from GHG emissions, the standard of due diligence under UNCLOS should be set high and considered it to be <\/span><i><span style=\"font-weight: 400\">stringent<\/span><\/i><span style=\"font-weight: 400\"> (ITLOS, para. 243). With respect to transboundary pollution affecting the environment of other States, the standard is even more stringent (ITLOS, paras. 248, 256, 258).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Similarly, the ICJ confirmed that the standard of due diligence is stringent because of the seriousness of the threat posed by climate change (ICJ, paras. 138, 246, 399) and on account of best available science indicating that the \u201c[r]isks and projected adverse impacts and related losses and damages from climate change escalate with every increment of global warming\u201d (ICJ, para. 254).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Given the \u201cextreme gravity of climate impacts\u201d and \u201cthe urgency of effective measures to avoid irreparable harm to the individual,\u201d the IACtHR found that States must act with enhanced due diligence to comply with the obligation of prevention arising from the obligation to guarantee the rights protected by the American Convention in the context of the climate emergency (IACtHR, paras. 233-236).<\/span><\/p>\n<p><span style=\"font-weight: 400\">Accordingly, states must do their utmost in addressing climate change (ICJ, para. 246). Due diligence takes on a particular quality in the context of climate change, requiring a heightened degree of vigilance and prevention. This includes the exercise of regulatory due diligence in taking all necessary regulatory and legislative measures to limit the quantity of emissions caused by private actors under a state\u00b4s jurisdiction and control. There is now a legal imperative \u2013 alongside a moral one &#8211; to address this \u201cexistential problem of planetary proportions that imperils all forms of life and the very health of our planet\u201d which not only is daunting, but also self-inflicted (ICJ, para. 456). <\/span><\/p>\n<h2><i><span>Conclusion<\/span><\/i><\/h2>\n<p><span style=\"font-weight: 400\">The Advisory Opinions issued by the ICJ, ITLOS, and IACtHR make clear that nothing short of the utmost effort by each individual State would satisfy the duty of States. Due diligence \u2013 once believed to be soft and weak \u2013 has now emerged as a potent and powerful standard, against which to assess compliance of international obligations. There is no hiding behind discretion and sovereign entitlements anymore. States must act with stringent due diligence and do the utmost in addressing climate change or they will incur the consequences of international responsibility: restoration, in the form of restitution, satisfaction, and \u2013 importantly \u2013 compensation for climate harms.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"<p>One of the most profound findings in the International Court of Justice\u2019s (ICJ\u2019s) climate change advisory opinion (AO) is that State obligations to mitigate climate change to a level that holds warming to the Paris Agreement\u2019s 1.5oC threshold are spread out over the large canvas of international law, including United Nations (UN) climate treaties, particularly [&hellip;]<\/p>\n","protected":false},"author":2336,"featured_media":26308,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[69613,5673,69207],"tags":[69255,177],"class_list":{"0":"post-26889","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-blog-series","8":"category-litigation","9":"category-cross-cutting-issues","10":"tag-advisory-opinion","11":"tag-icj","12":"czr-hentry"},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.3 - 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