The Paris Agreement adopted on 12 December 2015 by the Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCCC) has been qualified by many as a “historic” moment in the global combat against climate change. The future will tell whether this optimism is justified. Looking at the state of the environment more than 20 years after another “historic” event in the field of global environmental governance – the adoption of the 1992 Rio Declaration on Environment and Development – there are serious reasons to consider the Paris achievement with care. In its 2012 Global Environmental Outlook, the United Nations Environmental Program warned that “The currently observed changes to the Earth System are unprecedented in human history. … As human pressures on the Earth System accelerate, several critical global, regional, and local thresholds are close or have been exceeded. Once these have been passed, abrupt, and possibly irreversible changes to the life-support functions of the planet are likely to occur, with significant adverse implications for human well-being”. Regarding climate change, the Fifth (2014) Assessment Report of the Intergovernmental Panel on Climate Change highlighted that ”Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems”. The alarming state of the environment does not mean that the Rio Declaration (and the UNFCCC, also adopted at the 1992 Rio Earth Summit) remained without impact. It played a significant role in shaping the main principles of international environmental law recognised under international and national law, including an increasing body of jurisprudence in the field of environmental protection. According to Viñuales (p. 2), the Rio Declaration “is perhaps the most representative instrument of the entire body of norms, treaties, domestic laws, and decisions governing our relation with the environment”. Taking into account the failure of environmental law to address nature degradation, it is necessary to study the principles of the Rio Declaration to understand the changes that are needed to reverse the current adverse environmental trends.

The Rio Declaration is examined in the textbooks on international environmental law (e.g. Sands and Peel, Principles of International Environmental Law, CUP, 2012; Birnie, Boyle, and Redgwell, International Law and the Environment, OUP, 2009), but its principles were not, until the publication of the book under review, subject to a stand-alone, systematic, and in-depth commentary. In The Rio Declaration on Environment and Development: A Commentary, Professor Jorge Viñuales brings together analyses by leading scholars in the field offering an up-to-date, critical, comprehensive, and very well researched analysis of the Rio Declaration, and thus of the main principles of international environmental law. Following an introduction into the Declaration's history and philosophy and its significance for international environmental governance, the chapters of the book individually look at the preamble and all 27 principles of the Rio Declaration. The first contextualising chapters explain how the Rio Declaration relates to preceding and subsequent developments in the field of global environmental policy (including the 2012 Rio + 20 Summit). This is particularly useful to help the reader understand the delicate balance between the social, economic, and environmental dimensions that characterise the concept (principle) of sustainable development, as interpreted over time. The historical context is essential to an understanding of the role of and limits to the eco-centric and anthropocentric approaches to environmental governance, in the context of the often difficult interactions between developed and developing countries regarding the distribution of global environmental protection efforts.

All chapters dedicated to the principles of the Rio Declaration are organised around a similar structure. This consistent analytical approach helps the reader to follow the arguments defended by the different authors and grasp the added value of the specific principles. After introducing the negotiation process (based on the travaux préparatoires) and the origins and rationale of the principles, the chapters look at the scope and dimensions (or normative components) of the principles, their legal nature, normative impact, and jurisprudential relevance. Besides the common structure and contextualisation of the analysis, the book under review ensures coherence by introducing at the end of each chapter how the different Rio principles relate to each other. The discussion of the origins and negotiation of the principles provides interesting insights into the difficult task, even for non-binding declarations, of defining concepts of environmental governance that all participating states (developed and developing) can accept. The analysis of the normative components of the principles is most useful to facilitate a sound grasp of the broad range and complexity of issues covered by the succinctly formulated Rio principles. An understanding of the legal nature of the principles is of great interest, particularly given the non-binding nature of the Rio Declaration. This analysis is important to help convey states' obligations under international environmental law (e.g. the duty to avoid harm and to cooperate), independently from commitments under specific environmental treaties. The analysis of the legal nature of principles is also relevant in order to clarify states' rights to enact environmental measures (e.g. as a matter of precaution or to promote the sustainable use of natural resources) – a particularly sensitive issue in the field of international economic (trade and investment) law.

The normative impact of the principles is examined based on an overview of environmental law treaties that endorse the principles concerned or recognise related concepts. By going beyond the Rio Declaration and looking at a wide range of environmental law treaties, the book under review provides a comprehensive overview of the different sources of international environmental law including, among many others, the UNFCCC. This approach is relevant to an understanding of how the Rio principles can help address more specific environmental challenges (e.g. climate change, biodiversity, resource management) by guiding the determination of more concrete environmental protection obligations. It also helps to identify the limits – and in some cases the counterproductive effect – of some of the principles. The principle of common but differentiated responsibility, for instance, shaped international climate law, and in particular the distribution of the climate change mitigation burden between the developed and developing countries. The differentiation between developed and developing countries under the UNFCCC and the Kyoto Protocol was a determining element in securing the participation of developing countries in these treaties. However, this approach is also largely responsible for the failure of international climate law to stabilise global greenhouse gas emissions. In the absence of emission reduction obligations, China's emissions increased exponentially. Moreover, the US refused to join the Kyoto Protocol, invoking the absence of obligations for developing countries.

Besides its relevance for the definition of substantive environmental law standards (e.g. relating to climate change), the analysis of the recognition of the Rio principles under environmental treaties contributes to the study of the legal nature of these principles. Similarly, the book's careful overview of the use of the Rio principles in judicial practice is an important contribution towards the understanding of both the legal nature of these principles and their practical relevance in addressing specific environmental challenges. The Rio Declaration on Environment and Development discusses the judgments of the International Court of Justice (e.g. in the Pulp Mills on the River Uruguay, Aerial Herbicide Spraying, and Whaling in the Antarctic cases) and inter-state arbitration decisions (e.g. the Indus Waters Kishenganga arbitration and the Iron Rhine arbitration), as well as judgments by the Court of Justice of the European Union, the European Court of Human Rights, the Inter-American Court of Human Rights, and the African Commission on Human and Peoples' Rights. The book also covers investment arbitration practice (e.g. Chevron v Ecuador; Chemtura v Canada; Suez v Argentina; Methanex v USA) and WTO disputes (e.g. the Canada feed-in tariff; China Rare Earth; Brazil Tyres and EU Asbestos cases).

As examined in the book under review, the International Court of Justice, inter-state arbitration, and regional courts have all made an important contribution to the definition of the principles of environmental law. Moreover, investment tribunals and the WTO dispute resolution panels have referred to environmental law principles in their analysis of the legality of state measures that impact on foreign investment and cross-border trade. This is an important step towards the reconciliation of nature protection and economic regulation. The Rio Declaration on Environment and Development helps us to understand the achievements of the Rio Declaration in this process. At the same time, the book makes an important contribution to identifying the limits of the Declaration, and more generally the limits of international environmental law, in achieving sustainable development by effectively addressing global environmental destruction.

The Rio principles recognise the importance of integrating environmental considerations into economic and social decisions, but they provide only limited guidance on how to balance environmental protection with economic and social development in specific cases. The dire state of our environment highlights that, too often, vested short-term economic and social interests prevail. As recognised by the Rio Declaration, it is undeniable that states, in particular developing states, have a right to develop. However, the right to develop should not lead to an uninhabitable planet. Building further on the book's analysis, it seems that, to reverse current environmental trends, a new paradigm of growth is necessary. Taking into account the global scale of environmental challenges, international law has a key role to play in the definition and effective realisation of a new concept of growth. It is necessary but not sufficient to define principles of international environmental law that safeguard states' right to regulate and interfere with the short-term economic interests of polluting firms to the benefit of environmental protection. In addition, economic regulation itself has a crucial role to play in promoting approaches to growth that are compatible with environmental protection, such as by facilitating the trade in green products and stimulating and protecting green investments. To re-orient our economy towards sustainability, principles of environmental law and economic law should not continue to interact as two possibly conflicting fields of law, but should be redefined as equal pillars of a new green economic system.