1. A) How and when have successive treaties been used in international law, particularly in international environmental law? Why was a successor treaty chosen as an option over an amendment to the underlying agreement or a new agreement?
B) What type of provision is needed (if any) to indicate that it is a successor treaty? Please include formulations used in other agreements. 

2. Many multilateral agreements have a ‘conference of the parties’ type decision making structure. Are there examples in international law where decisions from such an entity have been referred to in subsequent amendments to the underlying legal instrument, in successor agreements or in a new protocol within the same regime? 

3. Is it possible to reference other legal instruments and the procedures and mechanisms developed by those instruments (to which not all countries may be party) in a new agreement?

Question 1:

Successive treaties are not a specific category of treaties. The term is simply used to identify treaties that are partially or largely overlapping in terms of subject matter and between which incompatibilities may arise. If this is the case, one should first identify whether the treaties contain specific provisions to regulate such situations. If not, their application is governed by the residuary rules of Articles 30 and 59 of the Vienna Convention on the Law of Treaties (these rules can also be regarded as international custom). Incompatibilities must be settled according to the maxims of lex posterior derogate priori (the later norm prevails) and lex specialis derogat generalis (the more specific norm prevails over the more general one).

Examples of specific treaty provisions on this matter are manifold. Article 103 UN Charter, for instance, states that the obligations under the Charter shall prevail over any other international agreement. Article 7 of the NATO Treaty conversely states that the treaty does not affect the rights and obligations under the UN Charter. Article 28 §1 of the European Convention on Extradition finds that this convention shall supersede the provisions of any bilateral treaties or agreements governing extradition between any two Contracting Parties. Article 35(1) of the European Criminal Law Convention on Corruption makes clear that the Convention does not affect the rights and undertakings derived from international multilateral conventions concerning special matters. At the same time, there is no need for any specific provisions to indicate that a certain treaty is a successor treaty. This is a factual matter, to be determined on the basis of possible overlapping.

When the treaties themselves do not contain specific rules, Articles 30 and 59 of the Vienna Convention on the Law of Treaties give rise to three possible scenarios. First, if all the parties to the earlier treaty are also parties to the later treaty, the earlier will be considered terminated if (1) it appears from the text of the later treaty or the intentions of the parties that this should be the case, or (2) if incompatibilities between the two instruments make them incapable of being applied simultaneously. Second, if all the parties to the earlier treaty are also parties to the later treaty, but none of the aforementioned conditions is fulfilled, then the earlier treaty will apply only to the extent that its provisions are compatible with those of the later treaty. Third, if the parties to the later treaty do not include all the parties to the earlier one, a distinction must be made between two relationships: (1) between States Parties to both treaties, the earlier treaty will apply only to the extent that its provisions are compatible with those of the later treaty; (2) 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 will govern their mutual rights and obligations.

When a new instrument would be largely similar in substance to a previous instrument and the majority required for amending the previous instrument (for multilateral treaties this will generally require a 2/3 majority; the Kyoto Protocol, however, refers to a ¾ majority), amendment would appear to be the logical option. It has the benefit of incorporating the existing structures (Conference of the Parties, Secretariat, expert committees, compliance mechanisms,…) into the new treaty, instead of creating new ones.

In addition, this process has the benefit of interpretive clarity: it avoids the problem of needing to identify possible incompatibilities that may arise between successive treaties. At the same time, it must of course be kept in mind that an amended treaty is in principle only binding on those States that have ratified/accepted it. States Parties that have not agreed to the amendment only remain bound by the original document.

An interesting example concerns the different multilateral instruments regarding the use and stock-piling of mines (both anti-personnel and anti-vehicle). A first relevant document here is the Convention on Certain Conventional Weapons of 1980 which established a logistical framework for the negotiation of Protocols containing concrete obligations. On the basis of this Convention, States first concluded a Protocol on Prohibitions or Restrictions on the Use of Mines, Booby-traps and other devices (Protocol II). In 1996, this Protocol was amended to strengthen the legal obligations. States that resisted the amendment, however, remain bound only by the obligations enshrined in the original Protocol. Finally, a considerable number of States found that the amended Protocol II did not go far enough in curtailing the use of anti-personnel mines and for this reason concluded the 1997 Ottawa Convention. Some provisions of the Ottawa Convention actually refer to those of the amended Protocol II (e.g. Article 5(2) on the marking of mined areas), yet it is clear that it can be regarded as a successor treaty to the latter.

In international environmental law, there certainly exist various successive treaties, in the sense that there may be considerable overlap in substance. There are numerous treaties on the treatment of hazardous waste or on pollution from shipping. The treatment and protection of a single animal species may simultaneously raise issues under a wide array of instruments, such the Convention on International Trade in Endangered Species, the Convention on Migratory Species, etcetera. At the same time, international environmental law is mostly known for relying largely on framework treaties, which are subsequently developed through Protocols or Annexes (this of course also holds true for the UNFCCC).

The Vienna Convention on the Protection of the Ozone Layer was supplemented by the Montreal Protocol, which in turn was amended on several occasions. Another example is the Convention on Long-Range Transboundary Pollution (re. acid rain). This Convention was supplemented throughout the 1980s and 1990s with a series of protocols inter alia to reduce emissions of sulphur dioxide emissions and nitrogen oxide emissions. In the area of marine pollution, the original MARPOL Convention was later absorbed by the 1978 MARPOL Protocol. This instrument has been subject to numerous amendments. Specific regulations have been worked out in a series of technical annexes.

Question 2:

Multilateral treaties and their protocols often spell out a series of provisions concerning the role and competence of a so-called ‘Conference of the Parties’. At the same time, references in later treaties / protocols to earlier decisions by the Conference of the Parties appear rather rare. Article 3(5) of the Kyoto Protocol contains an example in that it explicitly refers to decisions 9/CP.2 of the Conference of the Parties (another reference can be found in the preamble of the Protocol).

From a law of treaties perspective, there is as such nothing which would prevent States Parties to include an explicit reference to the compliance mechanism elaborated by the Conference of the Parties in an amended version of the Kyoto Protocol (thereby overcoming the obstacle of Article 18 regarding ‘procedures and mechanisms entailing binding consequences’). However, it is a rather exceptional method. If this way is chosen, one should take into account that such referral may become useless if the decision referred to is amended, expires or is withdrawn. Accordingly such referral might become useless if the legal ground on which the decision was taken is amended, expires or is withdrawn.

We understand that negotiators are considering a reference to the compliance mechanism of Decision 27/CMP/1. As discussed, the more logical approach (when looking at past treaty practice), however, would be to incorporate Decision 27/CMP1 in a separate annex to the amended treaty or to the successor treaty (cf. Annex 2 on Dispute Settlement annexed to the WTO agreement). If nevertheless from a practical, negotiating-technical, or tactical perspective the reference-option would be chosen, a more general, abstract, reference is preferable, such as e.g.:

“Commitments or actions undertaken by Parties identified in paragraph 11 above shall be subject to and shall be guided by the compliance procedures developed pursuant to Article 18 of the Kyoto Protocol and as may be applicable from time to time .”

Question 3:

There is in principle nothing which prevents States from referring to existing treaties and their concomitant procedures in a newly negotiated instrument. The consolidated version of the Treaty on the European Union (part of the Lisbon Treaty), for instance, refers in its preamble to the European Social Charter. Article 6 states that the EU shall accede to the European Convention on Human Rights. Many treaties, such as the Vienna Convention on Diplomatic Protection or the UN Convention on Trans-National Crime, provide for possible referrals of inter-State disputes to the International Court of Justice.

References to existing procedures developed by legal instruments to which not all countries may be party could, however, raise compatibility issues depending on the concrete context. In case of a reference to a previously established (quasi-)judicial body, for instance, one would need to verify to what extent the statute/annex establishing this body allows for a broad application of its jurisdiction, restricts access to certain parties, and the like.