International Environmental Law is a growing field of international law which is eventually getting greater legal and political attention. It is a branch of public international law- a crucial law created by the states themselves for the states to address the problems that occur between the states. Its main objective is to protect the environment with the help of principles, procedures and rules of international law with which it's inclined.

In simple terms, international environmental law embodies those substantive, procedural and institutional rules of international law as its primary goal is protecting the environment. This law covers a wide range of topics such as climate change, ozone depletion, desertification, marine resources and the quality of air, land and water. In today's world, it can be explained as "an intricate system of norms and institutions" which covers modes of regulation that are time and again transnational, informal and voluntary.

Environmental problems have reached their peak, particularly in this century because of human activities. Human activities are classified into two categories firstly, the use of resources at unsustainable levels, secondly the pollution and waste levels have reached beyond the capacity of the environment to absorb them or make them harmless. Such a greater awareness of the need to protect the environment and environmental resources has been accompanied by the adoption of a large number of environmental laws at the international level in the form of international environmental treaties1which embody several principles that are at the core of most environmental protection systems.

Early Development of International Environmental Law

In the mid-twentieth century, international environment law evolved as a subset of international law. Although conservation movements evolved in several nations, these movements did not have much impact because the movements tackled environmental problems only within a particular nation. The conventions focused primarily on particular issues, leading to inadequate impact. Earlier there were some treaties which safeguarded only a few species which were considered valuable resources to humans and protected human health:

• Paris Convention for the Protection of Useful Birds to Agriculture, 1902
• Treaty for the Preservation of Fur Seals, Washington, 1911
• Convention Concerning the Use of White Lead in Painting, Geneva, 1921
• Convention for the Regulation of Whaling, 1931

Three significant principles evolved during the early stage of international environmental law development through the three international arbitrations. First was the 1893 Pacific Fur Seal Arbitration (Great Britain v. United States), and second was the Trail Smelter case (US v. Canada) (1941) in this case the principle of state responsibility for transboundary environmental damage was laid down. The third arbitral award was Lac Lanoux Arbitration Case (France v. Spain) (1957).

Lastly, the evolution of international environmental law by decisions of arbitral tribunals and other international judicial bodies is an exception rather than the rule. Mostly international environmental law has been developed by bilateral and multilateral treaties. During the early development of IEL most of the developed treaties were solely utilitarian; attempts at protecting or conserving particular species were motivated mostly by their usefulness rather than environmental protection per se.[1]

Development of Modern International Environmental Law

The present-day IEL as its form commenced on 5 June 1972, the first United Nations (UN) Conference on the Human Environment in Stockholm (the Stockholm Conference), celebrated as World Environment Day. This conference is viewed as a cornerstone for international attention and action on the significance of the environment in the international system.

According to Ulrich Beyerlin, the Stockholm Conference was characterized by a shift in the interests of states from transboundary environmental matters to international environmental concerns. Simultaneously the states' awareness of the close interdependency of development and the environment improved.[2] This conference resulted in the adoption of the Stockholm Declaration which gives twenty-six principles and an Action Plan containing 109 recommendations. The Stockholm Conference, in its Principle 11 recognized that:

the environmental policies of all states should enhance and not adversely affect the present or future development potential of developing countries, nor should they hamper the attainment of better living conditions for all, and appropriate steps should be taken by states and international organizations with a view to reaching agreement on meeting the possible national and international economic consequences resulting from the application of environmental measure.[3]

The United Nations Conference on Environmental and Development (UNCED) in Rio de Janerio, Brazil held from 3 to 14 June 1992 is another landmark development in the IEL. The objective of this conference was to create sustainable mechanisms which will aid to solve the difficulties the humanity is facing in protecting the environment and still assuring a minimum level of development.[4]

The Rio Conference provided four crucial documents for IEL:

• Rio Declaration on Environment and Development.
• Agenda 21.
• UN Convention on Biological Diversity.
• UN Framework Convention on Climate Change.

It is a non-legally binding declaration that provides 27 principles as guiding principles for the state's legislators and policymakers in addressing environmental and sustainability issues. Sources of International Environmental Law

IEL has the same sources as general international law. Article 38(1) of the Statute of the ICJ[5] gives the following sources of international law:

• International conventions, whether general or particular, establishing rules expressly recognized by the contesting states.
• International custom, as evidence of a general practice accepted as law.
• The general principles of law recognized by civilized nations.

Principles of International Environmental Law

The above-discussed conferences stimulated the development of the basic principles of international environmental law, which are reflected in the International Environmental Law Treaties.

• The Principle of Responsibility Not to Cause Transboundary Harm
• The Principle of Precautionary Action
• The Principle of Environmental Impact Assessment
• Polluter Pays Principle
• The Principle of Common But Differentiated Responsibilities
• The Principle of Inter-Generational Equity
• The Principle of Sustainable Development
• The Principle of Prior Informed Consent
• The Principle of International Cooperation
• The Principle of Public Participation
• The Principle of Common Heritage of Humankind
• The Principle of Common Concern of Humankind
• Principle of Access and Benefit Sharing Regarding Natural Resources [6]

The Principle of Responsibility Not to Cause Transboundary Harm

This principle, enshrined in International Environmental law, expresses the idea of prevention. It is sometimes called the Principle of Preventive Action or the No-Harm Principle. The principle places a responsibility on the state to not authorize or tolerate any kind of activities within its jurisdiction which can cause damage to the environment of other states or of areas beyond its national jurisdiction.

This principle however recognizes the sovereignty of each state to utilize its own natural resources but it also emphasises that such right is limited to the reasonable use of resources, as the states have the responsibility not to cause transboundary environmental harm in the territory of another or other states. The principle permits the states to conduct or sanction such activities as they choose within their territorial jurisdiction but within boundaries established by international law and the states also have a corresponding responsibility not to allow such environmental harm to extend to the territories of other states. [7]

The principle essentially needs the activities which do or will cause damage to the environment and violate the standards established under the rules of international law to be prohibited and has been described as being of overriding importance in very effective environmental policy, since it allows action to be taken to protect the environment at an early stage.[8]

Early Case Laws
Trail Smelter Case (the United States v Canada)
This case is the initial step in making the sic utere principle a fundamental rule of modern international environmental law. This Award of 1941 is a landmark decision that highlighted the state's sovereignty to allow its territory to be used for any environmentally significant activities with cross-border impacts. The background of the case was that a privately owned corporation based in Canada started a smelter plant that emits hazardous fumes of sulphur dioxide. This caused damage to forest trees, crop yields, and other agricultural interests in the United States.

Both countries agreed on establishing an arbitral tribunal and the tribunal gave its landmark conclusion concerning future harm and stated: "Under the principles of international law (…) no State has the right to use or permit the use of its territory in such a manner as to cause injury by fumes in or to the territory of another or the properties or persons therein, when the case is of serious consequence and the injury is established by clear and convincing evidence"[9]

The tribunal has denied the states from allowing or engaging in activities that will cause transboundary harm. The arbitration panel in the case introduced the conceptual distinction between the State's liability and responsibility and pointed the Canada's responsibility for causing environmental harm in the US. The breach of obligation under international law has triggered the responsibility of Canada. Canada has to pay damages to the United States because it breached its duty to prevent the harmful activities of the privately owned smelter.

State Responsibility for Transboundary Environmental Harm
When there is a violation of a duty under bilateral or multilateral environmental agreements or rules of general international law by a state, it then entails international responsibility vis-a`-vis the injured state or depending on the specific rule infringed, vis-a`-vis any other State representing a collective legal interest. The State is obliged to make reparations with monetary payment being only one of many means of providing reparation for injury as a legal consequence of the same. The compensation paid is often provided in practice to offset the environmental damages because restitution in kind is not possible. The State has the responsibility for the following:

Responsibility for Public Activities and Omissions
The decision in Trail Smelter carefully noted "no State has the right to use (…) its territory" and hence addressed public activities. In the 2015 Certain Activities and Construction of a Road case, the ICJ had to assess Nicaragua's and Costa Rica's environmental duties linked to Nicaragua's dredging activities and Costa Rica's road construction.[10]

According to Article4(1) ASR: Conduct of Organs of a State
"The conduct of any State organ shall be considered an act of that State under international law, whether the organ exercises legislative, executive, judicial or any other functions, whatever position it holds in the organization of the State, and whatever its character as an organ of the central government or a territorial unit of the State."

Environmentally Harmful Activities of State-Owned Corporations
International environmental laws have flexibility in standards of care, which eventually draws attention to State-owned enterprises (SOEs) and State-controlled entrepreneurial activities. The majority of environmental damage is caused by industrialised states, private producers, and private consumers, but SOEs play a minor role, as there are only a few of them. The government is a major stakeholder in multiple large companies in emerging and post-transition economies and carries out important domestic activities. In this case, the State has the power to influence the activities and decisions taken by the SOE.

According to Article 5 ASR: Conduct of Persons or Entities Exercising Elements of Governmental Authority
"The conduct of a person or entity which is not an organ of the State under article 4 but which is empowered by the law of that State to exercise elements of the governmental authority shall be considered an act of the State under international law, provided the person or entity is acting in that capacity in the particular instance."

According to Article 8 ASR: Conduct Directed or Controlled by a State:
"The conduct of a person or group of persons shall be considered an act of a State under international law if the person or group of persons is in fact acting on the instructions of, or under the direction or control of, that State in carrying out the conduct."

Responsibility of the Home State for Corporate Activities Abroad
The State is responsible for transboundary damages caused by a local public or private actor. Even though the legal conditions of the no-harm rule and the responsibility triggered by its violation are relatively clear-cut as far as the State of origin is concerned, they appear too narrow to effectively address environmental harm caused by transnationally operating companies.

One aspect that appears unaddressed by the no-harm rule is the responsibility of the home State of a transnational corporation (TNC) which has international subsidiaries and operates in other states and causes environmental damage. The transboundary aspect here is not the environmental damage but rather the managerial control of the parent company over its subsidiaries.[11]

State Liability for Transboundary Environmental Damage
The operationalisation of State liability needs a conventional or customary primary rule which is used to put an obligation on the State to pay damages for environmental harm. The customary international law will be a source of primary liability rule in the absence of any general treaty on State liability for environmental liability. Such a rule would not only require the supporting general practice of States, such as domestic jurisprudence, laws or international treaties to this effect, but also States' acceptance that these practices are required under international law (opinio juris).[12]

The Trail Smelter Award of 1941 seems to give a liability rule however it points to Canada's responsibility for transboundary harm rather than Canada's liability. The international law practice does not support the existence of a customary rule of State liability for lawful acts which cause damage. The Convention on International Liability for Damage Caused by Space Objects is the only one among 1414 currently active MEAs that imposes liability on States for damage caused by lawful activities under their jurisdiction or control.

There is a lack of conventional liability that will not be fixed by the general principle of law. The primary rule of State liability for transboundary environmental damage is not supported by the polluter-pay principle. There are two different types of liability State liability and operator liability, only the former is triggered by the occurrence of transboundary environmental damage regardless of the operator to whom the damage is attributable. When it is summed up it shows that the customary international law does not presently give any rule on State liability for transboundary harm due to a lack of meaningful state practice and most importantly opinion juris.[13]

Conclusion
This article has made evident that IEL is an advancing field of international law and consists of substantive, procedural and institutional rules of international law which aim to protect the environment through bilateral and multilateral international agreements. The article established that IEL has gone through two major phases of development first is early development through conventions and the second is the development of modern IEL through international conferences, adoptions, and resolutions by the United Nations General Assembly (UNGA).

The discussion further delved into the details of sources of IEL and noted that in theory, the sources of IEL are the same as those of general international law. It is also brought to light that the most widely recognized sources of international law, and thus IEL are given in Article 38(1) of the Statute of the International Court of Justice.

The development of international environment law in addressing transboundary environmental harm has substantially progressed, given the increased recognition of environmental interdependence and the need for collective action. Early principles like the "no harm rule" established in the Trail Smelter Award 1941 have established the foundation for state responsibility, prohibiting activities that cause environmental harm across borders.

The prospects of international environmental law for dealing with transboundary damage rely on strengthening the existing legal infrastructures and capabilities of international institutions to hold nations and corporations liable. As climate change, biodiversity loss, and pollution continue to transcend borders, it is high time for the global community to reinforce its commitment to a more integrated and effective system of international environmental governance.

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9. Brunnée J (2021) Harm prevention. In: Rajamani L, Peel J (eds) Oxford handbook of international environmental law. Oxford University Press, Oxford, pp 269–285
10. Duvic-Paoli L-AU (2018) Principle of prevention. In: Krämer L, Orlando E (eds) Principles of environmental law. Elgar Encyclopedia of environmental law, vol VI. Edward Elgar Publishing, Cheltenham, pp 161–174
11. Brown Weiss E (1993) International environmental law: contemporary issues and the emergence of a new world order. George Law J 81:675–710
12. Sands P et al (2012) Principles of international environmental law. CUP, Cambridge
13. Boyle A (1991) Making the Polluter Pay: Alternatives to State Responsibility in the Allocation of Transboundary Environmental Costs. In: Francioni F, Scovazzi T (eds) International Responsibility for Environmental Harm. Graham and Trotman, London, pp 363–379
14. Craik N (2020) The Duty to Cooperate in the Customary Law of Environmental Impact Assessment. International & Comparative Law Quarterly 69:239–259
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End Notes:

1. Leary & Pisupati (Note 26) p.4; Bhrat H. Desahi, Institutionalizing International Environmental Law (New York: Transnational Publishers Inc., 2004) p.71.
2. Ulrich Beyerlin, 'Bridging the North-South Divide in International Environmental Law' (2006) 66 ZaöRV, p.260.
3. Beyerlin (Note 39) p.262; Stockholm Declaration, Principle 11.
4. Environmental Law: Introduction to International Environmental Law, p.8 accessed 15 July 2022.
5. Statute of the I.C.J., Oct. 24, 1945, 33 U.N.T.S.993, Article 38(1).
6. Nyekwere, E. H., Okogbule, I. C. S., & Agwor, D. O. N. (2022). Understanding the principles of international environmental law and their reflections in international environmental treaties and non-binding soft law instruments. Journal of Law, Policy and Globalization, 123, 73-84. https://doi.org/10.7176/JLPG/123-08.
7. See 10 Key Principles in International Environmental Law accessed 5 July 2022; See 'No-harm rule' and climate change accessed 5 July 2022; See Gregor Noll, "State Responsibility in relation to Transboundary Environmental Damage" (Master Thesis, Faculty of Law, University of Lund, 2007) pp.17-18.
8. WWF-India & MoEF-India (note 12) p.12.
9. PCA Trail Smelter Case (United States v Canada) (1941) 3 RIAA 1905.
10. ICJ Certain Activities Carried Out by Nicaragua in the Border Area (Costa Rica v Nicaragua) and Construction of a Road in Costa Rica along the San Juan River (Nicaragua v Costa Rica) [2015] ICJ Rep 665, para. 100 and 177.
11. A TNC is characterised by geographically dispersed units whereby its headquarters and subsidiaries are located in different countries, see Sageder and Feldbauer-Durstmüller (2019), pp. 1 et seq.
12. Article 38(1)(b) Statute of the International Court of Justice: "international custom, as evidence of general practice accepted as law".
13. Schmalenbach, K. (2023). States Responsibility and Liability for Transboundary Environmental Harm. In: Gailhofer, P., Krebs, D., Proelss, A., Schmalenbach, K., Verheyen, R. (eds) Corporate Liability for Transboundary Environmental Harm. Springer, Cham. https://doi.org/10.1007/978-3-031-13264-3_3.