Throughout September 2026, the United Nations General Assembly convened for its 81st Session at its New York headquarters.[i] Among the matters at the forefront of international law has been the contention between international environmental commitments and the U.S. government’s own priorities. This most recently appeared when the U.N. General Assembly adopted a May resolution welcoming the International Court of Justice’s 2025 climate advisory opinion, which the U.S. voted against.[ii]
The U.S. explained its vote as rejecting any legal weight for the opinion, while calling for other states to vote against the resolution.[iii] This follows a trend of U.S. withdrawals from climate treaties, including the Paris Agreement in January and the United Nations Framework Convention on Climate Change (UNFCCC) in 2027.[iv] Once both withdrawals take effect, the United States’ principal climate obligations would be customary. The U.S. will likely cite the persistent objector doctrine to avoid them, especially the customary duty to prevent transboundary environmental harm. However, the doctrine cannot be used here, as the rule was settled and accepted by the U.S. long before any U.S. objection.
The International Court of Justice’s 2025 advisory opinion found that even without being parties to climate treaties, states have customary duties, including an obligation of due diligence to prevent significant environmental harm.[v] The U.S. will likely argue it is exempt as a persistent objector under Conclusion 15 of the International Law Commission’s Conclusions on Identification of Customary International Law, which requires that objections be (1) clearly expressed, (2) made known to other states, (3) maintained persistently, and (4) made while the rule is forming.[vi]Crucially, any U.S. argument would fail on the final requirement.
The customary duty to prevent environmental harm has been established for decades. The principle originated in the Trail Smelter case, where the United States secured a ruling against Canada that no state may use or permit the use of its territory in a way that injures another state.[vii] The International Court of Justice recognized the idea as a general obligation for all states in Corfu Channel in 1949.[viii] In 1996, the Court declared that the obligation is “now part of the corpus” of international environmental law,[ix]and in the 2010 Pulp Mills case, it expressly stated that due diligence to prevent environmental harm was a customary rule of international law.[x]
The U.S. record as an objector to this rule is extremely recent and cannot plausibly have begun while the rule was forming. Its first objection appeared only in its 2024 submissions to the Court, which argued that the climate treaties, rather than general custom, governed states’ obligations, and even then conceded that the customary duty exists.[xi] Before then, the U.S. record shows acceptance. In 1992, it endorsed Principle 2 of the Rio Declaration, which restated the responsibility to avoid environmental damage beyond national borders,[xii] and ratified the UNFCCC, whose preamble recalls this responsibility in the context of climate change.[xiii] In 2023, it even allowed the advisory opinion request to pass by consensus.[xiv] A state that endorsed a rule for three decades cannot credibly claim to have objected to it persistently.
The U.S. may respond that it rejects only the duty’s application to greenhouse gas emissions, which are cumulative and global, and that its 2024 argument that the climate treaties displace general custom was a timely objection to that new rule.[xv] This fails for two reasons. First, the UNFCCC preamble shows the U.S. accepted that application in 1992.[xvi] Second, an argument that a treaty displaces custom concerns which rule governs, not whether the customary rule exists, and the Court rejected that argument regardless.[xvii]
When COP31 opens in Antalya on November 9, the U.S. will attend, if at all, as a UNFCCC party for the last time.[xviii] Withdrawal from the climate treaties, however, will not end its customary obligations. Because the U.S. withdrew from the International Court of Justice’s compulsory jurisdiction in 1986, those obligations are unlikely to be tested in The Hague,[xix] but they will shape how other states assess U.S. conduct. The United States helped build the rule that no nation may pollute its neighbors. It cannot now object its way out of it.
Shaunak Kale is a staff member of Fordham International Law Journal Volume L.
[i] See The General Assembly, President of the 81st Session of the U.N. General Assembly, https://www.un.org/pga/81/general-assembly/ (last visited Oct. 2, 2026) (noting that the 81st Session opened on Sept. 8, 2026).
[ii] G.A. Res. 80/263 (May 20, 2026); Press Release, General Assembly, General Assembly Strengthens Fight against Climate Change, Adopting Contentious, Yet Broadly Supported Draft among Several Texts on Myriad Topics, U.N. Press Release GA/12760 (May 20, 2026) (resolution adopted 141-8-28, with the United States voting against).
[iii] U.S. Mission to the United Nations, Explanation of Vote on a UN General Assembly Resolution Entitled “Advisory Opinion of the International Court of Justice on the Obligations of States in Respect of Climate Change” (May 20, 2026), https://usun.usmission.gov/explanation-of-vote-on-a-un-general-assembly-resolution-entitled-advisory-opinion-of-the-international-court-of-justice-on-the-obligations-of-states-in-respect-of-climate-change/.
[iv] Paris Agreement: United States of America: Withdrawal, U.N. Doc. C.N.71.2025.TREATIES-XXVII.7.d (Jan. 27, 2025) (depositary notification) (withdrawal effective Jan. 27, 2026); United Nations Framework Convention on Climate Change: United States of America: Withdrawal, U.N. Doc. C.N.102.2026.TREATIES-XXVII.7 (Feb. 27, 2026) (depositary notification) (withdrawal effective Feb. 27, 2027, under UNFCCC art. 25).
[v] Obligations of States in respect of Climate Change, Advisory Opinion, ¶¶ 271–315 (July 23, 2025), https://www.icj-cij.org/case/187.
[vi] Rep. of the Int’l L. Comm’n, 70th Sess., Apr. 30–June 1, July 2–Aug. 10, 2018, U.N. Doc. A/73/10, at 121 (2018) (Conclusion 15 and commentary).
[vii] Trail Smelter (U.S. v. Can.), 3 R.I.A.A. 1905, 1965 (Trail Smelter Arb. Trib. 1941).
[viii] Corfu Channel (U.K. v. Alb.), Judgment, 1949 I.C.J. 4, 22 (Apr. 9) (recognizing “every State’s obligation not to allow knowingly its territory to be used for acts contrary to the rights of other States”).
[ix] Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, 1996 I.C.J. 226, ¶ 29 (July 8) (“The existence of the general obligation of States to ensure that activities within their jurisdiction and control respect the environment of other States or of areas beyond national control is now part of the corpus of international law relating to the environment.”); see also Gabčíkovo-Nagymaros Project (Hung./Slovk.), Judgment, 1997 I.C.J. 7, ¶ 53 (Sept. 25) (reaffirming same).
[x] Pulp Mills on the River Uruguay (Arg. v. Uru.), Judgment, 2010 I.C.J. 14, ¶ 101 (Apr. 20) (“[T]he principle of prevention, as a customary rule, has its origins in the due diligence that is required of a State in its territory.”).
[xi] Written Statement of the United States of America, Obligations of States in respect of Climate Change (Request for Advisory Opinion), ¶¶ 1.3, 4.1, 4.5 (Mar. 22, 2024).
[xii] U.N. Conference on Environment and Development, Rio Declaration on Environment and Development, princ. 2, U.N. Doc. A/CONF.151/26/Rev.1 (Vol. I), annex I (Aug. 12, 1992).
[xiii] United Nations Framework Convention on Climate Change, pmbl., May 9, 1992, S. Treaty Doc. No. 102-38, 1771 U.N.T.S. 107 [hereinafter UNFCCC] (“Recalling also that States have, in accordance with the Charter of the United Nations and the principles of international law, . . . the responsibility to ensure that activities within their jurisdiction or control do not cause damage to the environment of other States or of areas beyond the limits of national jurisdiction . . . .”).
[xiv] G.A. Res. 77/276, U.N. Doc. A/RES/77/276 (Mar. 29, 2023); Obligations of States in respect of Climate Change, supra note v, ¶ 47 (noting that the resolution “was adopted without a vote”).
[xv] Verbatim Record, Obligations of States in respect of Climate Change, I.C.J. Doc. CR 2024/40, at 70 (Dec. 4, 2024) (statement of the United States); see also Written Statement of the United States of America, supra note xi, ¶¶ 4.2, 4.15–4.21.
[xvi] UNFCCC, supra note xiii, pmbl.
[xvii] Obligations of States in respect of Climate Change, supra note v, ¶¶ 162–171.
[xviii] Information for COP 31 Participants, U.N. Framework Convention on Climate Change, https://unfccc.int/cop31/ifp (last visited Oct. 2, 2026) (COP31 to be held Nov. 9–20, 2026, in Antalya, Türkiye); see C.N.102.2026.TREATIES-XXVII.7, supra note iv.
[xix] Letter from George P. Shultz, U.S. Sec’y of State, to Javier Pérez de Cuéllar, U.N. Sec’y-Gen. (Oct. 7, 1985), reprinted in 24 I.L.M. 1742 (1985).
This is a student blog post and in no way represents the views of the Fordham International Law Journal.