Is there any hierarchy between the laws of the UNFCCC, ICAO and IMO, so that States can comply with the laws of the UNFCCC and, as long as they are in compliance with the laws of the UNFCCC, then States need not comply with the laws of ICAO/IMO?
There is no hierarchy as such between the regimes established under UNFCCC, IMO and ICAO. In international law, the doctrine of peremptory norms is generally recognized, providing that that any treaty provision that conflicts with a “norm” laid down in another treaty or recognized by the international community of states is void. It does not appear that any norms are relevant in this context. Where the doctrine is not applicable, the rules on the application of successive treaties relating to the same subject matter may be relevant. Where parties of one treaty are also party to a later treaty relating to the same subject matter, the rights and obligations are governed by the later treaty.
(1) There is no hierarchy as such between the regimes established under the UNFCCC, ICAO and the IMO. In international law, the hierarchy of jus cogens or ‘peremptory norms’ is generally recognized, including under Article 53 of the Vienna Convention on the Law of Treaties (VCLT) which renders void any provision of a treaty if, at the time of its conclusion, it conflicts with a peremptory norm or jus cogens. Jus cogens are generally recognized as taking precedence over any conflicting norms laid down in treaty law or elsewhere and as including the rule against the use of force and the prohibitions on slavery, genocide and torture. It does not appear that any jus cogens norms are relevant in the present context. Furthermore Article 103 of the UN Charter provides that:
“[i]n the event of a conflict between the obligations of the Members of the United Nations under the present Charter and their obligations under any other international agreement, their obligations under the present Charter shall prevail.”
It does not appear from the query that Article 103 is relevant to the current issue as to whether there is a hierarchy between the three treaties regimes referred to.
(2) In relation to conflicting provisions of treaties which are not jus cogens, the rules on the application of successive treaties relating to the same subject matter may be relevant. These are laid down in Article 30 of the Vienna Convention on the Law of Treaties. In general terms, (and subject to Article 103 of the UN Charter-see above), where all the parties to the earlier treaty are also party to the later treaty, the rights and obligations of state parties to two successive treaties relating to the same subject matter will be governed by the later treaty (to the extent that there is incompatibility), unless there is specific provision to the contrary in one of the treaties. Where the parties to the later treaty do not include all the parties to the earlier one, and where one state is party to two conflicting treaties and the other state is party to only one of those treaties, the treaty to which both are party will govern mutual rights and obligations between those two states.
(3) Parties may choose to create a form of hierarchy between treaties by providing explicitly, for example through means of a ‘savings clause’ in the later treaty, that in the event of a conflict the provisions of the earlier treaty are to prevail (notwithstanding the rules which would otherwise apply under Article 30 of the VCLT).
(4) There appears to be a more fundamental issue underlying the current query however, which is whether the application of the principle of CBDR, as laid down in Principle 7 of the Rio Declaration as well as in Article 3.1 of the UNFCCC, leads to an irreconcilable conflict with the principles of universality and non-discrimination applied under the relevant regimes of the IMO and ICAO by requiring that developing countries be exempt from any levy imposed on international aviation or shipping.
(5) The starting point for resolving this issue is that States which are party to two or more potentially conflicting regimes (whether or not dealing with the ‘same subject matter’ within the meaning of Article 30 VCLT) will generally seek to reconcile any potential conflict by drafting provisions so as to accommodate the requirements of both regimes.
(6) In the absence of any elaboration by any international court or tribunal as to what the principle of CBDR entails in this context, there is a good argument that parties to the UNFCCC retain a degree of flexibility as to the way in which that principle is applied in the context of addressing emissions from aviation and shipping, taking into account the lead responsibility placed on Annex 1 countries to address the issue under the IMO and ICAO.
(7) It is possible to envisage ways in which a levy system might be established so as to meet the requirements of the CBDR principle, whilst also ensuring an effective levy system which is designed to avoid ‘carbon leakage’ for example through the establishment of technical assistance funds or compensatory mechanisms for developing countries to facilitate the transition of their shipping and aviation sectors to a new levy regime.
(8) Further advice on the extent, if any, of any irreconcilable incompatibility between a CBDR approach and the universal/non-discriminatory approach will need to be based on specific textual proposals.
Appendix: Further detail
1. As indicated above, it does not appear that the any peremptory norms/jus cogens are relevant to the potential conflict between the principle of CBDR and the principles of universality and non-discrimination under the IMO or ICAO. Nor does it appear that these issues raise the question of compatibility with the UN Charter, so as to engage Article 103 UNC. Thus the issue of hierarchy depends on specific provision being made under any new agreement, governing the relationship between the various regimes and/or the application of Article 30 VCLT.
2.Were the parties to the UNFCCC to agree binding rules which were inconsistent with those established under the IMO or ICAO the question of the application of Article 30 of the VCLT would arise. It would be necessary to determine whether the relevant regimes dealt with the ‘same subject matter’. If they did, Article 30 would be applicable. If there were express provision addressing the relationship between the earlier and later regimes, the mutual rights and obligations of state parties to both would be governed by that provision. In the absence of a specific provision, the rules of Article 30 paragraphs (3) and (4) would apply, in which case, in general terms, where all the parties to both relevant agreements were the same (unlikely in practice) the earlier treaty would apply only to the extent that its provisions are compatible with the later treaty. Where the parties to the earlier treaty are not all parties to the later treaty (more likely in practice), mutual rights and obligations would be governed by the treaty to which both states are party.
3. A central issue, is whether the three regimes in question, or instruments adopted under them which constitute treaties can be said to be dealing with the ‘same subject matter’ so as to fall within the scope of Article 30 VCLT. As a leading commentator has pointed out, the approach to take in interpreting this aspect of Article 30 is ‘not yet settled’ with some commentators taking a broad view, requiring only that two treaties are broadly concerned with, for example the environment, while others take a much narrower view requiring much closer proximity in the aims and objectives of the regimes in question. Others argue that it is sufficient that certain provisions cover the same subject matter for Article 30 to apply. It is not possible to advise on this issue in this context with a high degree of certainty as to how a tribunal might determine the issue or in advance of seeing what form an agreement under the UNFCCC might take. It can only be stated that the greater the degree of overlap between such an agreement on bunker fuels and the concerns addressed by the IMO/ICAO regimes, the greater the chance that Article 30 VCLT applies. The existence of Article 2(2) KP might be said to point to a degree of overlap, although the underlying objectives of the two regimes and the UNFCCC clearly remain different.
4.The underlying question here however appears to be whether there is an inevitable and irreconcilable conflict between the principle of CBDR and the principles of universality and non-discrimination as applied under the IMO/ICAO.
5. The principle of CBDR is expressed in the Rio Declaration as follows:
“States shall cooperate in a spirit of global partnership to conserve, protect and restore the health and integrity of the Earth’s ecosystem. In view of the different contributions to global environmental degradation, States have common but differentiated responsibilities. The developed countries acknowledge the responsibility that they bear in the international pursuit to sustainable development in view of the pressures their societies place on the global environment and of the technologies and financial resources they command. “
6. Article 3.1 of the UNFCCC provides:
“The Parties should protect the climate system for the benefit of present and future generations of humankind, on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities. Accordingly, the developed country Parties should take the lead in combating climate change and the adverse effects thereof.”
Article 3.2 of the UNFCCC provides:
“The specific needs and special circumstances of developing country Parties, especially those that are particularly vulnerable to the adverse effects of climate change, and of those Parties, especially developing country Parties, that would have to bear a disproportionate or abnormal burden under the Convention, should be given full consideration.”
7. Article 2(2) of the Kyoto Protocol provides:
“The Parties included in Annex I shall pursue limitation or reduction of emissions of greenhouse gases not controlled by the Montreal Protocol from aviation and marine bunker fuels, working through the International Civil Aviation Organization and the International Maritime Organization, respectively.”
8. Article 2(2) KP can therefore be said to reflect the principle of CBDR in that it places the responsibility for pursuing limitation or reduction of emissions of GHG through ICAO and the IMO on Annex I Parties. Article 2(2) does not however specify the form of such rules under those regimes (I have not been referred to any subsequent decisions of the parties to any of the three regimes on the interpretation of Article 2(2) in this context).
9. I have not been referred to any detailed analysis of how the principle of CBDR might influence or inform the introduction of a levy on international shipping or aviation under those regimes or under the UNFCCC/KP. Assuming a starting position of seeking to reconcile any new rules with the requirements of the UNFCCC, the IMO and ICAO, so as to maximize the chances of obtaining widespread agreement on new rules, the implications of applying the principle of CBDR need to be examined. It is possible to envisage a regime which applies the principle of CBDR alongside a universal and non-discriminatory levy regime, with a view to assisting developing countries in meeting their obligations and facilitating the transition to such a regime, whilst also preventing the carbon leakage which could arise if the vessels or aircraft of developing countries are exempt from the new levy.
10. In my view, and in the absence of any detailed examination of decisions taken by the Parties under either the UNFCCC or the IMO/OCAO on this issue, there does not appear to be any legal reason in principle why the principle of CBDR may not be reflected in ways other than by excluding developing countries from an international levy. It is possible for example to envisage a regime which takes account of CBDR by establishing mechanisms to assist developing countries in meeting their obligations under a new levy regime.
11. It has been argued that exemptions for developing country vessels and aircraft will result in carbon leakage as operators reflag their vessels to states which are exempt from the levies. In such circumstances it appears to be open to Parties to the UNFCCC to adopt a levy regime which is designed to prevent such carbon leakage by incorporating universal and non-discriminatory rules on application, whilst at the same time making provision for specific assistance to be given to developing countries to facilitate their transition to a levy system and/or to compensate developing countries for the negative impacts that a levy system/ ETS could have on them.
 For the purposes of the VCLT, a peremptory norm of general international law is ‘a norm accepted and recognised by the international community of States as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent norm of general international law having the same character’ (Article 53 VCLT)
 See Case Concerning Military and Paramilitary Activities in and against Nicaragua ICJ rep (1986) 14 para 189.
 Armed Activities on the Territory of the Congo (New Application (2002) (Democratic Republic of the Congo v. Rwanda), ICJ rep 2006, judgment 3 February 2006, para 64.
 There is continued debate as to which norms are included within the scope of jus cogens, see the discussion in “Normative Hierarchy in International Law” Dinah Shelton AJIL Vol. 100, No. 2 (Apr., 2006), pp. 291-323Published 2006
 “Conflicts in International Envrionmental Law” Springer 2003, Wolfrum and Mazt see pages 148-151.