Reference to Vienna Convention

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Date produced: 01/06/2015

The Geneva negotiating text, in its preambular part, refers to the Vienna Convention on the Law of Treaties: ” (…) [Recalling the Vienna Convention on the Law of Treaties,]”.  If the Vienna Convention is retained as the over-arching framework, what implication does it have for the Paris deal to succeed and what would it mean for countries such as Bangladesh, which has not signed it?

A number of countries are not signatories to the Convention, including Bangladesh, India, South Africa, Thailand, Indonesia, Norway and France. Countries which have signed but not ratified include the USA and Pakistan. If these countries have not signed or ratified the Vienna Convention, can they sign a Climate Treaty which may be under the framework of the Vienna Convention?

If not, will this mean that all the support to be given to developing countries and LDCs such as Bangladesh under the deal (such as Green Climate Fund funding) would be denied to them? Will they then first have to sign and ratify the Vienna Convention?


The Vienna Convention on the Law of Treaties of 1969 (VCLT) is the main international instrument on the international law of treaties. It defines a treaty and relates to how treaties are made, amended, interpreted, how they operate and are terminated under public international law. It directly applies to treaties concluded between States who are parties to the VCLT.

However, many of the provisions contained in the VCLT also reflect customary international law – i.e. international obligations arising from established state practice (as opposed to a written agreement) based on a sense of legal obligation (opinio juris). As a result the rules of VCLT are widely recognized and used as the authoritative guide vis-à-vis the formation and effects of treaties.

Preambular language in an international treaty helps set the context for the operative part of an agreement but has no binding legal value. Thus, reference to the VCLT in the preamble to a new legal instrument on climate change would not result in any new commitments for the parties to the climate change agreement. In particular, it would not result in an obligation to become a party to the VCLT.

Reference to the VCLT does not impede states which are not parties to the VCLT from joining a new agreement adopted in Paris. Such an agreement will not be adopted under the “overarching framework of the VCLT”. Financial support available to parties to the new agreement would not be contingent on acceptance of the VCLT. New commitments, rights and obligations (if any) will derive from the new agreement only.

However, the preamble may be used to guide the interpretation of the following provisions. A reference to the VCLT would, therefore, underline that, with regard to the subsequent application and interpretation of the new agreement, the rules of VCLT apply between parties to the VCLT (unless the climate agreement provides otherwise or contains specific rules). In relation to non-parties to the VCLT, at least those rules of the VCLT that reflect customary law (and would apply anyway) are relevant.

In addition, it may be argued that because of the broad reference to the VCLT other rules of the VCLT that are not yet recognised as customary law should also be taken into account when there is a question of interpretation in relation to a non-Party to the VCLT. If so and to what extent depends on the particular circumstances of the case in question.