Climate law has long been recognized as a field that implicates the notion of legal diversity and, in particular, legal fragmentation. General international law, international environmental law, and numerous functionally determined issue areas may well intersect with one another, in various shifting patterns, leading to the risk of ambiguity over authority propositions pertaining to the climate regime. In The Fragmentation of Global Climate Governance, Harro van Asselt presents a ‘comprehensive study on the consequences of the fragmentation of international climate change law’ (p. 6). It is not the first attempt at this topic, but it is a pioneering book-length study. Highlighting an awareness of the interactions of regimes and their management, van Asselt’s achievements in surveying these many bodies of law, doctrine and scholarship are numerous. This is a fluent, well-structured and ambitious volume, in which the author displays an extremely impressive familiarity with a wide range of the scholarly literature in both law and international relations. The facility of the prose often contrasts with the academic norm and without a cost to the organization of ideas. Above all, now that the paralysis of the United Nations Framework Convention on Climate Change (UNFCCC)^{Footnote 10} has shifted from recurrent to acute to chronic, this very welcome book maps strategies that would minimize the conflicts between different regimes and capture their synergies. What follows gives an outline of the volume, places it in the context of the idea of fragmentation, and presses a number of its arguments and methods.

Most readers will be familiar with the debates over the meaning, import, and novelty surrounding legal fragmentation that have raged since the late 1990s,^{Footnote 11} particularly since the International Law Commission’s (ILC) 2006 report entitled ‘Fragmentation of International Law’.^{Footnote 12} Fragmentation is unarguably one of the key artefacts of contemporary legal scholarship. It is also a deeply practical problem. In 2004, United Nations (UN) Secretary-General Kofi Annan expressed in plain terms some of the challenges of diversity – normative, geographical, functional – with which the fragmentation literature has long grappled, by noting:

Most troubling for lawyers is that with ‘the rise of specialized rules and rule-systems, [a]nswers to legal questions become dependent on whom you ask, what rule system is your focus on’.^{Footnote 14} Van Asselt applies aspects of this literature to the climate governance problematic, aiming to address the arguments more fully than previously attempted.

The structure of the book is straightforward. Part I sets the stage in terms of objectives (that is, to identify and manage regime interaction in the global climate regime), methodology, and case studies. It also provides a brisk overview of global climate governance. The analytical framework of Part II introduces the concept of fragmentation and explores, with tremendous energy and attention to the voluminous scholarly literature, the competing arguments as to its nature. Given the ubiquity of fragmentation in the decentralized and diverse architecture of international law, its presence in international climate law is no surprise. But how does it operate?

Substantive fragmentation is conventionally drawn as operating in three aspects. Functional fragmentation occurs along functionally defined issue areas (or regimes) such as trade, human rights, and environmental law. Geographical fragmentation recognizes that, while significant tranches of international law do apply universally (for example, jus cogens, general principles of international law, and customary international law), many substantive rules of international law do not. Different subjects of international law are governed by different rules of international law. Parallel norm fragmentation highlights the fact that conflicting norms or obligations in the same issue area may apply to the same states or subjects of international law, which raises conflicts between different levels of regulation of the same subject area.^{Footnote 15} Of these varieties, van Asselt’s volume focuses on the first, that is ‘the relationship between different specialized regimes’ (p. 42). The key concern is not the existence of overlapping regimes but ‘how their interrelationships are managed’ (p. 43). As such, two of the three aspects of fragmentation are not considered in the book under review.

While the author’s engagement with the secondary literature in Part II is deeply impressive, the case law is less well served. An example is found in the discussion of the pitfalls of fragmentation, in which the MOX Plant cases^{Footnote 16} are mentioned as an example of a dispute in which multiple legal proceedings were commenced with the result that ‘various specialised rules are created which allow international judicial institutions to come to diverging decisions’ (p. 40). Little else is said about the dispute other than that it was capable of being framed as either a matter for the UN Convention on the Law of the Sea (UNCLOS),^{Footnote 17} European Union (EU) law, or the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR).^{Footnote 18} However, as is well known, the dispute was resolved by the United Kingdom’s (UK) successful invocation of EU law before the International Tribunal for the Law of the Sea (ITLOS), which led the UNCLOS Annex VII Arbitral Tribunal to suspend proceedings pending the determination of competence by the European Court of Justice (ECJ).^{Footnote 19} The relationship between the various tribunals was arguably the decisive aspect of the dispute, but its brief treatment in Van Asselt’s text obscures that. The omission of such discussions risks simplifying and overstating the nature of fragmentation. Indeed, where tensions have arisen between different bodies of law, the prevailing approach has been one of resolution via consideration of extraneous bodies of law. In a related fashion, a minor role is assigned to the courts (in particular the International Court of Justice (ICJ)) in response to the fragmentation of international law and the proliferation of international tribunals. This is largely because van Asselt considers it ‘rather unlikely that cases involving conflicts between the climate, biodiversity and trade regimes would be brought before … regime-independent dispute settlement (e.g., the [ICJ])’ (p. 230). It may be the case that problems of fragmentation are not amenable to resolution through judicial means, but the prospect of advisory opinions being sought from the ICJ still remains.^{Footnote 20}

Part III consists of three case studies of potential regime conflict, namely, between the UNFCCC and ‘minilateral’ clean technology agreements, the UNFCCC and the Convention on Biological Diversity (CBD),^{Footnote 21} and the UNFCCC and the World Trade Organization (WTO). The first of these serves to show that institutional coordination between the climate regime and clean technology agreements can promote the respective strengths of each regime, thereby supporting the goal of complementarity and avoiding harmful competition. Van Asselt notes, however, that the legal techniques for regime interaction are relatively limited (p. 108), to the point of non-existence (p. 117), and so much of the coordination takes place at the managerial and institutional plane, drawing on comparative institutional comparisons. As such, while of consistent general interest, this is of greatest relevance to international relations scholars (whose literature is well mined) and institutional economists (whose literature is not).

The trade and climate regime relationship is a frequently cited interaction in the climate law field and is explored in the longest chapter (8) of this book. As with the other case studies, the discussion commences with a series of brief introductions (how international trade affects climate change; the WTO and its attitude to the environment in general and climate change in particular) followed by the primary consequences of the interaction. This section is particularly interesting and details the range of trade issues that may arise, including in relation to the Kyoto flexibility mechanisms, trade related policies and measures under the Kyoto Protocol,^{Footnote 22} the transfer of climate-friendly goods and services, and preferential trade measures. Each of these discussions is tantalizingly short, but each is well referenced and convincing as far as it goes. The main event is the analysis of border adjustment measures, invoking as they do concerns of competitiveness, leakage, and ‘eco-imperialism’. The views of other scholars are well surveyed but, again, engagement with the case law is rather slight. While the landmark cases are referred to, the analysis could have been more involved. Too often a familiar ratio is provided without a reference to competing arguments or analyses. Where more extended arguments are given (for example, at pp. 183–90), the author deploys the arguments of others. Given his mastery of the literature, it would be welcome to hear his own voice more clearly.

In general terms, the book can occasionally be guilty of ‘climate change utopianism’, in which generous interpretation sits awkwardly with the known world. For example, we are told that the UNFCCC’s dense negotiating environment creates a ‘momentum [which] ensures that all countries have moved forward … towards a common goal of avoiding dangerous climate change’ (p. 18). No evidence is proffered for this, presumably because it does not exist. The treaty itself may have established that goal, but over two decades of meetings, practices, processes, and rules have yet to move all countries in this direction, as much as we might wish otherwise. Similarly, it is allegedly ‘undeniable that [the Clean Development Mechanism (CDM)] has helped to scale up low carbon investment in developing countries’ (p. 20). But many do deny this.^{Footnote 23} It has long been argued that the CDM’s additional contribution in this realm has been slight. These are, however, minor criticisms, at the margins of the book’s argument.

More substantively, there is sometimes the sense that problems are overstated. Consider the remark that ‘claims that the UNFCCC is the main show in town should be critically examined in the light of climate action emerging at various levels and jurisdictions and undertaken by a variety of public and private actors’ (p. 23). The suggestion is that action at levels other than that of public international law creates a problem of fragmentation that the UNFCCC is ill-equipped to deal with. There is no doubting the complex of climate action going on (by international organizations, clubs such as the Group of Eight, multi-stakeholder partnerships, and civil society bodies, etc – as enumerated at pp. 24–6), but is this a problem of legal fragmentation properly? Do they call into question the authority propositions of extant bodies of law or cause ambiguity over what the law is? The presence of regime complexity is not a functional equivalent of fragmentation. Moreover, the fact of the UNFCCC being merely a part of this complex should not be seen as problematic ipso facto, not least as the UNFCCC explicitly advocates such developments. Its Preamble recognizes ‘the need for … strategies at the global, national and … regional levels’, and a wide range of national actions, policies and measures are promoted in Articles 3(4), 4(1), 4(2), 5 and 6. At the institutional level, Article 7(6) allows for competent national agencies to act as observers at the Conferences of the Parties (COPs). In this light, complexity is not a synonym for fragmentation but a recognition by the treaty system of its own limitations and the sometimes superior or complementary capacities of actors at different levels.

The Fragmentation of Global Climate Governance is a very welcome, often enlightening account of a topic that has long yearned for a comprehensive treatment. While there may be an irony in seeking succour from regimes like the constipated WTO to ease the UNFCCC’s own blockages, the inter-institutional cooperation urged by van Asselt is never less than well informed and practical. Nor is there any absence of familiarity with the existing scholarship. What is lacking, perhaps, is a belief that international tribunals, including the ICJ, have a serious role to play in cutting across the challenges of fragmentation. Just as no one specialized institution can address all the problems it raises for climate governance, and carries its own biases, each can provide its own partial solutions, leading to the possibility of revision and mutual learning.