1. Workshop on Hydroflurocarbons (HFCs) Management: Possibilities and opportunities under the Vienna Convention on the Law of Treaties (1969) in enabling the ozone and climate regimes to work in synergy Arancha Hinojal-Oyarbide Paris, 11-12 July 2014

2. 1969 Vienna Convention on the Law of Treaties The 1969 Vienna Convention on the Law of Treaties codifies rules of customary international law relating to the law of treaties. States that are not yet parties to it are bound by the rules of customary international law laid down in the Convention. The Convention’s rules are largely residual. The Convention leaves in the hands of States the decision to agree otherwise. But States’ practice shows that the rules set forth in the Convention are invariably relied upon by States.

3. Modification of treaty obligations Parties to a treaty are free to decide to modify that treaty (or conclude a new treaty on the same subject-matter), so that its norms can be adapted to new circumstances and developments. The new norms express the new will of the parties, and, therefore, they take precedence (lex posterior rule) for those that have consented to be bound by these new norms. When the treaty itself does not provide for its modification or amendment, rules of customary international law apply. The general rule is that a treaty can be amended by agreement of all the parties to that treaty. When a treaty provides for its modification or amendment, as it is the case of the Vienna Convention for the Protection of the Ozone Layer and its Montreal Protocol, the stipulated amendment rules apply. The new norms take precedence for those parties to the treaty that become party to the amendment.

4. Treaty application and conflict of norms A treaty is not something isolated: its provisions are confronted with other treaty norms which can complement each other or may be in conflict with each other. Many conflicts of norms may be resolved by interpretation of treaties. However, to resolve most issues of priority between conflicting norms, treaties should include specific clauses (conflict clauses) regulating the relation of a treaty with earlier or later treaties relating to the same subject-matter. These clauses clarify whether the treaty will take priority over another treaty or treaties or give priority to another treaty or treaties. As in any other legal system, under international law, there are rules aimed at resolving conflict of norms. They apply in the absence of conflict clauses.

5. Application of successive treaties relating to the same subject- matter In the absence of conflict clauses, rules of customary international law regulate which of two treaties must be applied in case of conflict. Such rules are incorporated in article 30 of the 1969 Vienna Convention on the Law of Treaties: 2. When a treaty specifies that it is subject to, or that it is not to be considered as incompatible with [or is without prejudice to or is not inconsistent with], an earlier or later treaty, the provisions of that other treaty [the earlier or later treaty] prevail. 3. When all the parties to the earlier treaty are parties also to the later treaty but the earlier treaty is not terminated or suspended in operation, the earlier treaty applies only to the extent that its provisions are compatible with those of the later treaty [lex posterior derogat priori]. 4. When the parties to the later treaty do not include all the parties to the earlier one: (a) as between States parties to both treaties the same rule applies as in paragraph 3 [lex posterior rule]; (b) as between a State party to both treaties and a State party to only one of the treaties, the treaty to which both States are parties governs their mutual rights and obligations [this rule reflects the principle that the later treaty cannot deprive a State which is not a Party to it of its rights under the earlier treaty].

6. Possible synergies between Ozone and Climate regimes relating to HFCs In the case that the current UNFCCC/KP regime and an eventual VC/MP regime regulating HFCs were complementary (do not exclude each other), no issue of conflict between their norms should arise. States would have to fulfil all the obligations under the treaties/amendment they are party to. If it were deemed that a conflict could arise, in particular in light of those provisions of the KP that explicitly limit their scope to “greenhouse gases not controlled by the Montreal Protocol,” the introduction of a clause in the new amendment to the MP clarifying the effects of the amendment on the relevant provisions of the UNFCCC/KP should resolve conflict problems. If it were deemed that a conflict could arise and no conflict clause were incorporated in the MP amendment, article 30 (4) of the Vienna Convention on the Law of Treaties would apply: – Between States parties to both, the MP amendment and the KP, the MP amendment would prevail (lex posterior rule). – Between a State party to both, the MP amendment and the KP, and a State party to only the KP, the KP (to which both States are parties) would apply.