By Sebastián Correa Cruz
A landmark approach to the concept of Sustainable Development was included in the Rio Declaration on Environment and Development of 1992 to denote Sustainable Development as the need to balance environmental and development considerations.
Nonetheless, the Rio Declaration does not make an explicit reference to this concept as a right or obligation of States. Taking the above into account, no easy answer can be given to the question of whether international law requires that all development should be sustainable, or if so, what that would that mean in specific terms.
In that sense, the purpose of this article is to analyze the approach of the legal nature of Sustainable Development as an element of hermeneutical judicial tool or as a primary norm derived from customary international law by studying its core elements found in the Rio Declaration. The analysis will lead to the conclusion that even if Sustainable Development is not just a hermeneutical tool but rather an obligation of means, the general formulation of its elements restricts it to become international customary law.
- Element of Hermeneutical Judicial Tool
A first approach to the legal nature of Sustainable Development claims that the concept cannot be regarded as a primary rule but rather as a meta-principle, pushing and pulling the boundaries of true primary norms when they threaten to overlap or conflict with each other. This position is based on the reasoning that Sustainable Development requires an equitable approach to conflicts between development and environment. In that sense, it would not be possible to identify under the concept of equity a clear primary norm which prescribes the obligations of the States.
Taking the above into account, the concept of Sustainable Development would just constitute a hermeneutical judicial tool, without binding content, which acquires its normativity in the hands of the judge.
- Primary Norm Derived from Customary International Law
In opposition to the approach of sustainable development as a tool for judicial interpretation, authors like Barral claim that there is almost no doubt that Sustainable Development is regarded as an objective for the international community, as stated by the International Court of Justice in the Pulp Mills case, where the Court asserted that the object of Article 27 of the Statute of the River Uruguay (which Argentina claimed Uruguay had breached) was consistent with the objective of Sustainable Development.
Hence, Sustainable Development purports to directly regulate conducts with properly material and direct legal implications as a primary norm of international law. In that regard, Sustainable Development lays down not an absolute but a relative obligation of means to achieve Sustainable Development because the Rule identifies an obligation to take appropriate measures to assure sustainability. In that regard, such obligation of means may be regarded as international customary law under the doctrine of sources of international law because there is enough state practice and the belief of acting under a legal obligation (opinio juris) reflected in over 300 conventions and 112 multilateral treaties, in which references of Sustainable Development are found in the operative part of the conventions which is technically binding on the parties.
- Core Elements of Sustainable Development
- Integration of Environmental Protection and Economic Development
According to Principle 4 of the Rio Declaration, environmental protection shall constitute an integral part of the development process and cannot be considered in isolation from it. In other words, Principle 4 creates the possibility of moving environmental considerations and objectives from the periphery of international relations to the economic core.
This core Principle of Sustainable Development has been included in several subsequent international instruments, such as the Convention on Climate Change, the Convention on Biological Diversity, in the Agenda 21 and in the Convention to Combat Desertification, to mention a few. Nevertheless, it is possible to note that there is ground for an ambiguous approach of the principle in the way that stands as much for the subordination of environmental policies to economic imperatives in the eyes of some, as for the converse to others.
- The Right to Development
The right to development is found in Principle 3 of the Rio Declaration. The inclusion of this right in the Declaration reflects that environmental protection should not outweigh their need for economic development as a counterweight to the described Principle 4 of the Declaration.
Even though this right might have been fully endorsed by the international community in the Declaration, its legal status remains doubtful as it is argued that the right to development is not a right at all due to its uncertain character, as it embraces not just the promotion of economic development by states but also the social and cultural aspects of human development found in the 1966 UN Covenant on Economic, Social and Cultural Rights.
- Intra-generational equity
The definition of sustainable development by the World Commission on Environment and Development of 1987 explains that Sustainable Development is the type of development that meets the needs of the present without compromising the ability of future generations to meet their own needs. This evidences the concept of intra-generational equity as part of Sustainable Development which aims for the redressing of the imbalance in wealth between the developed and developing worlds.
Apart from Principle 5 of the Rio Declaration, the instrument does not refer by name to any concept of intergenerational equity. Furthermore, even though it may be possible to think that intergenerational concerns are now an element in the contemporary development of international environmental law, at present it seems difficult to argue that equity in this form has applicability outside the context of the Rio instruments in which it has been employed. 
- Concluding Remarks
After reviewing the core elements of the concept of Sustainable Development set in the Rio Declaration, it is possible to conclude that nowadays the concept of Sustainable Development under international law is conceived as an objective which is pretended to regulate the conduct of States. In that regard, to perceive Sustainable Development as a hermeneutical tool without binding content would just limit its scope and affect its nature. On the other hand, even if Sustainable Development has enjoyed of collective endorsement by the international community in the Rio Declaration and in other international instruments, the general formulation of its elements may lead to ambiguity, meaning that any chance of evidencing opinio juris and state practice of an obligation of means may be difficult to ascertain or to conclude its customary nature under international law.
In this order of ideas, without a clear understanding of the legal nature of the concept, States will retain substantial discretion in its interpretation, unless specific international action has been agreed. In any case, the role of the Sustainable Development Goals, adopted by consensus in the General Assembly of the United Nations in 2015, will serve as a convenient platform to obtain sufficient State practice that may influence the interpretation of treaties, and the practice of States and international organizations in order to materialize the legal nature of Sustainable Development under international law.
 Rio Declaration on Environment and Development, June 13, 1992, reprinted in 31 ILM 876 (1992).
 Boyle, International Law & The Environment, Oxford University Press, (2009), 115
 Boyle International Law and Sustainable Development, International Law and Policy of Sustainable Development, 65 BYIL (1994), 303.
 Lowe, Sustainable Development and Unsustainable Arguments, in A Boyle and D Freestone (eds.) International Law and Sustainable Development, Oxford University Press, Ch 2. (1999).
 Ídem. However, Lowe claims that the concept of Sustainable Development may reach further to the fact that one day a tribunal might assert on the basis of sustainable development a power to modify not only the application of primary norms of customary law but also obligations.
 ICJ, Case Concerning Pulp Mills on the River Uruguay (Argentina v. Uruguay) judgment of 20 April 2010, pp. 74, para. 177.
 Barral, ‘Sustainable Development in International Law: Nature and Operation of an Evolutive Legal Norm’ (2012) 23 European Journal of International Law, 377
 Boyle, International Law & The Environment, op.cit., 116
 1992 Convention on Climate Change, Article 3(4); 4(1)(f);
 1992 Convention on Biological Diversity, Article 6.
 United Nations Conference on Environment & Development Rio de Janerio, Brazil, 3 to 14 June 1992 AGENDA 21, Ch 8.
 1994 Convention to Combat Desertification Article 4(2)
 Sands, Greening International Law, The New Press, (1994)
 Boyle, International Law & The Environment, op. cit., 119
 Ídem. Critics have argued that this is not a right at all and point to its uncertain character in the ‘Declaration on the Right to Development’ adopted by the General Assembly in 1986, and reiterated in the 1993 Vienna Declaration on Human Rights.
 World Commission on Environment and Development, Our Common Future 43 (Brundtland Report) (1987).
 In its Article 15(7), The Convention on Biological Diversity establishes a framework under which developing countries are entitled to a ‘fair and equitable’ sharing of the benefits arising from the use of genetic resources found in their territory. Boyle, International Law & The Environment, op.cit., 123.
Sebastián Correa Cruz es candidato a Magíster en Derecho Internacional de la Universidad de la Sabana (Colombia), Estudiante del Curso de Formación Diplomática y Consular en la Cancillería (Colombia), Antiguo Pasante en la Misión Permanente de Colombia ante las Naciones Unidas en Nueva York, Abogado con Profundización en Derecho Internacional y Derecho Comercial de la Universidad del Rosario (Colombia); Antiguo Miembro de la Línea de Investigación de Derecho Internacional Penal de la Facultad de Jurisprudencia de la Universidad del Rosario (Colombia), Miembro del Grupo de Investigación de Empresas y Derechos Humanos de la Universidad de la Sabana (Colombia).
- Convention on Biological Diversity of 1992.
- Convention on Climate Change of 1992.
- Convention to Combat Desertification of 1994.
- Rio Declaration on Environment and Development, June 13, 1992, reprinted in 31 ILM 876 (1992).
- United Nations Conference on Environment & Development Rio de Janerio, Brazil, 3 to 14 June 1992, AGENDA 21.
- World Commission on Environment and Development, Our Common Future 43 (Brundtland Report) (1987).
- C.J., Case Concerning Pulp Mills on the River Uruguay (Argentina v. Uruguay), Judgment of 20 April 2010.
- Barral, ‘Sustainable Development in International Law: Nature and Operation of an Evolutive Legal Norm’, European Journal of International Law (2012).
- Boyle, International Law & The Environment, Oxford University Press, (2009).
- Boyle International Law and Sustainable Development, International Law and Policy of Sustainable Development, 65 BYIL (1994).
- Lowe, Sustainable Development and Unsustainable Arguments, in A Boyle and D Freestone (eds.) International Law and Sustainable Development, Oxford University Press, Ch 2.( 1992).
- Sands, Greening International Law, The New Press, (1994).