Beyond Normative Consensus: The Enforcement Mechanics and Causation Challenges of Upstream Fossil Fuel Regulation Post-2025

Abstract

In the Advisory Opinion of the International Court of Justice (ICJ) on the Obligations of States in Respect of Climate Change of July 23, 2025, the key moment was explicitly enshrined when the Court made state obligation to regulate the emissions of greenhouse gases a part of customary international law[1]. While the obligation of states to take steps in regulating upstream activity including the granting of licenses, exploration, and subsidy of fossil fuels was recognized by the ICJ to be a breach of international law, the question of the actual enforcement mechanism remained unanswered. This article attempts to discuss the issue of enforcement after the 2025 Advisory Opinion with an emphasis on the problem of attribution, “clear and direct causal link,” and the concept of due diligence in a transnational context.

I. Introduction & Theoretical Context

The process of global climate governance for decades has taken place within treaty-based consensus mechanisms, such as the UN Framework Convention on Climate Change (UNFCCC) and the Paris Agreement, that rely upon the nationally self-defined targets[2]. The ICJ’s groundbreaking advisory opinion of 2025 brought about a change to the established model by asserting that climate protection falls under the umbrella of general public international law, including no-harm rule.

 It is important to note that the decision of the Court has gone beyond just tailpipe emissions at the point of use and has actually indicated that the lack of proper diligence in controlling the fossil fuels’ extraction and production process by a state, through issuing extraction licenses and corporate approval as well as state subsidies could very well be an internationally wrongful act according to state responsibility principles[3].

Nevertheless, turning such definitive and normative principle into actual and contentious judgment in international courts is quite difficult. While there is the recognition of the duty to prevent the environmental harm under the general international law as an obligation erga omnes and erga omnes partes under international treaties, any state claiming for reparations or cessation will have to meet quite heavy evidentiary burden. The crux of the problem is in establishing the direct legal causal link between administrative acts of the sovereign state upstream and the environmental impact downstream.

II. Statutory & Customary Framework: The Standard of Due Diligence

To analyze enforcement, one must first deconstruct the legal standard articulated by the Court: due diligence as an obligation of conduct, not of result.

Under traditional rules of State Responsibility (codified in the ILC Draft Articles on Responsibility of States for Internationally Wrongful Acts, or ARSIWA), a state incurs responsibility if:

1. An act or omission is attributable to the state under international law; and
2. That act or omission constitutes a breach of an international obligation.

   The operational mechanics of this responsibility across the supply chain can be mapped as follows :

Stage in Causal Chain	Action / Trigger	Legal Framework & Obstacle
1. Upstream Sovereign Act	Subsidies, permits, & licensing regimes	Breach of Due Diligence: Failure of the state to adequately regulate or restrict high-emitting projects
2. Corporate Exploitation	Private fossil fuel extraction & commercialization	Attribution Barrier: Intervening private action making it difficult to attribute corporate conduct to the state.
3.Downstream Global Harm	Cumulative transboundary climate impact	Causation Assessment: Proving a direct legal connection between state licensing and specific environmental harm.

1. The Variable Due Diligence Standard

Due diligence is not static. The ICJ confirmed that the required degree of care is contingent upon:

• The scientific knowledge available (with IPCC reports accepted as authoritative factual baselines)[4].
• The degree of risk involved in the permitted activity.
• The state’s capacity and economic development (aligning with Common But Differentiated Responsibilities and Respective Capabilities – CBDR-RC).

2. Upstream Conduct as a Duty Breach

Because climate science now unequivocally links ongoing fossil fuel expansion to breaching the 1.5°C threshold, the threshold for what constitutes “diligent state behavior” has heightened dramatically. A state that actively subsidizes carbon-intensive sectors or issues new exploration permits without adequate climate impact assessments (EIAs) fails to meet its obligation of conduct under customary international law.

III. Critical Analysis: The Evidentiary Friction Points of Causation

Whereas proving a breach of due diligence has become relatively easy as a result of the Advisory Opinion issued in 2025, the main difficulty in climate change cases lies in proving legal causation in order to get remedies under Article 31 of ARSIWA[5].

Barrier	Core Legal Obstacle	Primary Evidentiary Challenge
1. Plurality of Causes (Multiple Emitters)	Damage is caused by collective global emissions rather than a single state’s actions.	Attributing legal responsibility when no single state is the sole or primary cause of harm.
2. Reasonable Proximity (Direct Causal Link)	Traditional doctrine requires a clear, unbroken causal chain from act to injury.	Bridging the gap between upstream licensing/subsidies and  downstream transboundary harm.
3. Proximity & Intervals (Cumulative Impact)	GHG damage accrues over decades of historical and continuous atmospheric accumulation.	Proving temporal causation for cumulative, long-term environmental degradation.

1.    The “Clear and Direct Causal Link” vs. Probabilistic Attribution

Historically, international courts (such as in Corfu Channel, Trail Smelter, and Certain Activities Carried Out by Nicaragua) required a direct, unbroken causal link between the wrongful state act and the specific injury suffered[6]. Regarding international disputes over climate change, it is the accumulation of greenhouse gases in the atmosphere over a period of more than a century and involving several countries that causes harm.

• Scientific Attribution: Probabilistic event attribution science can now determine, with high statistical confidence, how much human-induced climate change increased the likelihood or intensity of a specific extreme weather event.
• Legal Attribution: International jurisprudence struggles to convert probabilistic risk increase into legal proximate cause. If State A grants a license to an oil company, which extracts petroleum, which is refined and burned in State B, contributing 0.5% to global emissions, can an injured State C establish that State A’s licensing decision was a “direct cause” of a specific cyclone.

2. Plurality of Responsible States and Joint Liability

Under Article 47 of ARSIWA, where several states are responsible for the same internationally wrongful act, the responsibility of each state may be invoked[7]. The principle of no exemption from liability even when several states are responsible was supported by the International Court of Justice in its Advisory Opinion of 2025.

However, translating this principle into contentious proceedings introduces complex procedural barriers:

• Market-Share / Contribution-Based Allocation: Tribunals must decide whether compensation should be apportioned based on a state’s historical cumulative emissions, its current production output, or its level of financial subsidies.
• The “But-For” Test Inadequacy: If a respondent state argues that its upstream licensing contributed only a fraction of global emissions, and that the damage would have occurred regardless (“but-for” test), traditional legal doctrine risks exonerating all major emitters individually. Courts must instead adopt a substantive contribution to cumulative risk standard.

3. State Inaction vs. Corporate Intervention

Upstream licensing acts as an indirect trigger: the state permits, but private corporate entities extract and commercialize fossil fuels. Respondent states frequently argue that the intervening acts of private corporations break the legal chain of causation. To overcome this defense, claimant states must prove that the state’s failure to regulate or restrict corporate activity was itself the primary due diligence breach that enabled the emissions trajectory.

IV. Practical & Jurisdictional Implications for International Disputes

The ICJ’s clarification of state responsibility creates immediate strategic consequences for future contentious litigation across international forums:

Forum / Domain	Primary Legal Mechanism	Practical Impact Post-2025 Advisory Opinion
International Tribunal for the Law of the Sea (ITLOS)	UNCLOS Part XII (Protection of Marine Environment)[8]	Strengthens claims against states granting offshore drilling licenses by equating marine pollution with GHG-induced ocean warming/acidification.
Regional Human Rights Courts (ECtHR, IACtHR)	Human Rights & Environmental Degradation Interlinkages	Provides a legal standard to hold states accountable for domestic fossil fuel subsidies that violate systemic human rights (Life, Health, Property).
Domestic Law & Public Law Challenges	Administrative Judicial Reviews	Litigants can use the ICJ’s customary due diligence standard to challenge executive decisions approving fossil fuel projects as arbitrary or inconsistent with international obligations.

Furthermore, the legal consequences affirmed by the ICJ specifically the obligation of cessation mean that states found in breach of their customary due diligence may not merely be required to pay damages; they may be legally obligated to withdraw existing fossil fuel subsidies and phase out non-compliant extraction licenses[9].

V. Conclusion

The 2025 Advisory Opinion of the ICJ has laid to rest the normative debate concerning the obligations of states under general international law with regard to climate change. The new battleground for climate change jurisprudence lies in the procedures of enforcement and the science of causation.

For the customary rule of due diligence to be made effective in adversarial litigation, the tribunals must develop rigid causation tests to fit the new science of cumulative atmosphere. In doing so, they will come to understand the fact that failure by a state in its legislative and administrative duties (e.g. subsidies and licensing) is indeed a direct contribution to the global climate threat.

VI. References

[1] Obligations of States in Respect of Climate Change (Advisory Opinion) [2025] ICJ Rep 1

[2] United Nations Framework Convention on Climate Change (adopted 9 May 1992, entered into force 21 March 1994) 1771 UNTS 107 (UNFCCC); Paris Agreement (adopted 12 December 2015, entered into force 4 November 2016) 3156 UNTS 79.

[3] International Law Commission, Draft Articles on Responsibility of States for Internationally Wrongful Acts (2001) UN Doc A/56/10 (ARSIWA), art 2.

[4] Intergovernmental Panel on Climate Change, Climate Change 2023: Synthesis Report (Sixth Assessment Report, IPCC 2023).

[5] ARSIWA (n 3) art 31

[6] Corfu Channel Case (UK v Albania) (Merits) [1949] ICJ Rep 4; Trail Smelter Arbitration (United States v Canada) (1938 and 1941) 3 RIAA 1905; Certain Activities Carried Out by Nicaragua in the Border Area (Nicaragua v Costa Rica) (Compensation) [2018] ICJ Rep 15.

[7] ARSIWA (n 3) art 47.

[8] United Nations Convention on the Law of the Sea (adopted 10 December 1982, entered into force 16 November 1994) 1833 UNTS 396 (UNCLOS) pt XII.

[9] Obligations of States in Respect of Climate Change (n 1) paras 180–185 (discussing legal consequences and duty of cessation)