International environmental law encompasses the legal norms and processes that address transboundary, regional, or global environmental issues. International environmental concerns generally result from human impacts on the natural environment, such as pollution or resource use related to production or consumption processes. Environmental problems pose at least five distinctive challenges for international law. First, because they typically result from private activities (Nonstate Actors) rather than from government action, international environmental law must either engage these actors directly or, as has been the predominant approach to date, prompt states to regulate private actors under their jurisdictions. Second, because international environmental problems, or scientific understanding of them, tend to evolve rapidly and sometimes unexpectedly, international environmental law often operates under conditions of uncertainty and must be adaptable to changing needs or knowledge. Third, international environmental law must deal with multiple interconnections. International environmental problems, by definition, not only transcend jurisdictional boundaries, but they also implicate social, political, and economic processes, as has come to be expressed through the concept of sustainable development (Sustainable Development). Moreover, because many international environmental problems are intertwined with one another, action or inaction on one issue implicates one or more other issues. Fourth, many international environmental issues, and virtually all global environmental concerns, require cooperation between industrialized and developing countries (History and Evolution), raising complex and highly charged questions of equity and capacity (Common but Differentiated Responsibilities). Finally, international environmental problems frequently require not only the balancing of potentially competing contemporary interests and priorities, but also have significant implications for future generations of humanity (Intergenerational Equity). The evolution of international environmental law has been shaped by these closely intertwined challenges (History and Evolution). Customary or soft law principles (Key Principles) have emerged that reflect the various dimensions sketched above. Perhaps in recognition of the fact that environmental problem-solving requires cooperation rather than confrontation, the primary role of these principles has been to help frame the negotiation and operation of international environmental agreements (Multilateral Environmental Agreements) and the activities of international institutions (International Environmental Institutions). Indeed, the bulk of international environmental lawmaking, implementation, and compliance control (Compliance Mechanisms) occurs today under the auspices of the hundreds of environmental agreements that are now in existence. International courts and tribunals (Courts and Tribunals) have played only a relatively small role in the application of customary or treaty law to environmental issues in the course of dispute settlement. Similarly, the law of state responsibility has found only limited application in the environmental context and states have preferred to negotiate civil liability regimes to address specific risks, such as those posed by oil pollution or nuclear energy production (Responsibility and Liability). This article focuses on the major structural elements and key characteristics of international environmental law rather than on developments in the various substantive issue areas.
Unilateral actions, the case of international environmental problems
