Global environmental governance is entering a period of institutional stress. Climate change, biodiversity loss, pollution and ecological degradation are no longer separate technical issues. They are linked to development, finance, trade, technology, energy security and the basic capacity of states to protect people’s livelihoods. Therefore, the question facing the international community is no longer whether environmental governance matters, but whether the existing system can still generate sufficient authority, resources and trust to deal with problems that are growing more complex. The current system has important achievements to its credit. The United Nations has provided the central platform for international environmental cooperation. The 1972 Stockholm Conference, the Rio Earth Summit, the UN Framework Convention on Climate Change, the Convention on Biological Diversity and the 2015 Paris Agreement have gradually built a broad institutional architecture. International organizations, governments, scientific communities, civil society groups and businesses have all become part of this governance process. Yet, this system has its limitations, which are becoming increasingly visible. Environmental governance remains fragmented across institutions, agreements and issue areas. The gap between developed and developing countries persists over responsibility, finance, technology and the pace of transition. In some cases, environmental rules are being reshaped by unilateral pressure,...