Core Legal Answer & Context: Yes, there has been a discernible and increased reliance on non-binding international instruments in environmental governance since the 1972 Stockholm Declaration. This trend is primarily driven by several pragmatic considerations. Firstly, the urgency and complexity of global environmental challenges often necessitate rapid responses, which are difficult to achieve through the lengthy and often contentious negotiation processes required for binding treaties. Non-binding instruments, often referred to as 'soft law,' allow states to express political commitment, articulate shared principles, and establish common goals more quickly and with broader participation, as they do not immediately impose strict legal obligations. Secondly, soft law offers greater flexibility, enabling states with diverse economic development levels and environmental priorities to find common ground without committing to rigid, potentially costly, or politically sensitive legal obligations. This flexibility fosters consensus-building and allows for an incremental approach to international environmental law development, where principles initially articulated in soft law can gradually harden into customary international law or be incorporated into subsequent binding treaties.

Regarding whether these instruments have been 'more useful' than treaties, it is more accurate to view them as complementary rather than superior. Treaties provide legal certainty, enforceability, and a robust framework for compliance and dispute resolution, which soft law inherently lacks. However, soft law instruments are invaluable for setting agendas, raising awareness, developing norms, and paving the way for future binding agreements. They can influence state practice and 'opinio juris' (a sense of legal obligation), thereby contributing to the formation of customary international law. Their utility lies in their ability to facilitate dialogue, build trust, and establish a common understanding of environmental problems and potential solutions, often serving as the crucial first step before states are ready to undertake legally binding commitments.

Relevant Statutes and Sections:

• Stockholm Declaration on the Human Environment (1972): A foundational non-binding instrument that articulated 26 principles for environmental protection and sustainable development, establishing the basis for international environmental law. It emphasized the right to a healthy environment and state responsibility for transboundary harm.
• Rio Declaration on Environment and Development (1992): Reaffirmed and built upon the Stockholm principles, introducing key concepts such as sustainable development, the precautionary principle, the polluter pays principle, and common but differentiated responsibilities.
• Agenda 21 (1992): A comprehensive, non-binding action plan for sustainable development adopted at the Earth Summit, outlining specific actions for governments, international organizations, and major groups.
• Forest Principles (1992): A non-legally binding authoritative statement of principles for a global consensus on the management, conservation, and sustainable development of all types of forests.
• For contrast (binding treaties): The Montreal Protocol on Substances that Deplete the Ozone Layer (1987), the Convention on Biological Diversity (1992), and the UN Framework Convention on Climate Change (1992) and its protocols (e.g., Kyoto Protocol, Paris Agreement) demonstrate the role of binding instruments in specific environmental regimes.

Important Landmark Cases: While soft law instruments do not directly generate 'cases' in the same way treaties do, their principles often inform judicial decisions and the development of customary international law. The Trail Smelter Arbitration (United States v. Canada, 1941) is a landmark case that established the principle of state responsibility for transboundary environmental harm, a concept later enshrined and elaborated in non-binding instruments like the Stockholm and Rio Declarations. This demonstrates how early legal principles can inform the development of soft law, which then further solidifies and disseminates these norms. The subsequent widespread adoption of principles like the precautionary principle and polluter pays principle, initially found in soft law, into national legislation and international treaties, illustrates their profound influence and utility in shaping environmental jurisprudence and policy globally.

Clear Conclusion: The increased reliance on non-binding international environmental instruments is a pragmatic and effective development in international law. These instruments are not 'more useful' than treaties but serve a distinct and crucial role. They provide flexibility, facilitate consensus-building, and allow for the rapid articulation of norms in a complex and evolving field. By setting aspirational goals and establishing common principles, soft law instruments often pave the way for future binding agreements, thereby fostering a dynamic and adaptive framework for global environmental governance that complements the legal certainty provided by treaties.