A number of studies have explored the important interactions between international climate change-related rules and other international norms (particularly trade and human rights). What has been missing is a treatment of the interplay of the climate change regime with other regimes at the governance level. Harro van Asselt’s work fills this void. It is the first full-length monograph on the interactions between climate change governance and other areas. The book constitutes a significant contribution to the debate on how climate change governance should relate to other areas of international governance. Van Asselt’s contribution flows from his successful use of methods and insights from both international relations and international law scholarship, allowing him to cover both international legal, ‘soft law’, and institutional interactions.

The book has two stated objectives. Firstly, it seeks to examine the consequences of the fragmentation of global climate governance and subsequent interactions between different regimes related to climate change (p. 5). Secondly, the book aims to examine strategies for dealing with regime interactions in global climate governance – including both legal methods such as treaty interpretation, and institutional means, which look at the management of interests in terms of effectiveness and feasibility. The author suggests important ways in which participation in one international regime can contribute to the goals of another. The book uses a case study approach to address these questions, examining the interactions between the United Nations (UN) climate change regime and (i) the (now-defunct) Asia Pacific Partnership (APP); (ii) the Convention on Biological Diversity (CBD);Footnote ¹ and (iii) the World Trade Organization (WTO).

Van Asselt’s conceptual framework draws on insights from international law and international relations. Thus, ‘fragmentation’ is defined broadly to include not only overlapping and contradictory international legal rules, but also the increased specialization and diversification of international institutions (p. 35). Van Asselt observes that the concept of ‘fragmentation’ is not value-neutral and immediately gives rise to questions about the extent to which there is, and should be, unity in international lawmaking and institution building (p. 33). He notes that there can be both positives and negatives from fragmentation. On the negative side, fragmentation can impair the authority, unity and coherence of international law, which may allow powerful states to forum shop and prioritize certain fields of international law over others (such as international economic law over environmental law) (p. 41). However, as positive impacts of fragmentation, Van Asselt notes the increased diversity of international law, suiting a wider range of interests and therefore likely to foster stronger compliance, and a global diffusion of ‘best ideas’ (pp. 42–3).

International law scholarship has tended to adopt a narrow approach to fragmentation by focusing on situations where international legal rules are contradictory. Such an approach, however, clearly misses important interactions that are better captured in the international relations literature. Van Asselt takes this broader approach. His book incorporates both the important role of institutional interactions and the role of ‘soft law’. He draws on works by Oran Young and others to set out a conceptual framework which includes what he terms ‘policy interactions’ between different international regimes, broad enough to include not just interactions between international rules (whether binding or soft), but also institutional interactions and behavioural elements (p. 46).

The strength of this approach is well illustrated in the case study dealing with the relationship between minilateral technology forums – epitomized by the APP and the UN climate regime. The APP was created by the United States (US) Bush administration and Australia’s Howard government, with the aim of creating an alternate model for climate law governance outside the frameworks of the UN Framework Convention on Climate Change (UNFCCC)Footnote ² and its Kyoto Protocol,Footnote ³ with a focus on technology development through industry working groups. A narrow focus on regime interaction/fragmentation would not take things very far here, because the APP was a soft law instrument and explicitly stated that it was to be consistent with the UNFCCC. From a strict international law point of view, states could sign up to the APP without conflict with their obligations under the UNFCCC or Kyoto Protocol (where applicable). Van Asselt points out that while APP projects furthered some of the technology transfer aims of the UNFCCC, the APP as a whole involved ‘policy conflict’ owing to it being established on the basis of principles at odds with the UNFCCC/Kyoto approach – namely voluntary commitments rather than Kyoto targets and timetables, and technology-driven approaches, without the UNFCCC/Kyoto principles of common but differentiated responsibilities (CBDR) (p. 101).

Even though the APP is now defunct, van Asselt is right to point out the importance of this precedent as a possible model for global climate governance (p. 108). Indeed, the 2015 Paris AgreementFootnote ⁴ in many ways represents the triumph of the voluntary, technology-driven approach of the APP, with its inclusion of voluntary ‘nationally determined contributions’ (NDCs), rather than economy-wide targets and timetables, and a move away from differentiation in mitigation obligations. Van Asselt states that it is too early to tell whether a minilateral approach to climate change (for example, involving major emitters) is likely to be effective (p. 213). This, in my view, underplays the significance of the APP as an embodiment of a neoliberal, voluntaristic ideology that is inherently incapable of effectively addressing climate change.Footnote ⁵ The embodiment of this ideology in the Paris Agreement, with its purely voluntary mitigation commitments, raises serious concerns about its likely effectiveness.Footnote ⁶

The Fragmentation of Global Climate Governance includes a wide-ranging discussion of possible strategies for improving coherence in climate change law and governance, including through treaty interpretation, drafting techniques, and institutional methods, such as better coordination of decision-making bodies and bureaucracies (for example, joint meetings of Secretariats or Conferences of the Parties). Van Asselt argues that the effectiveness of each of these management coherence strategies should be measured by the extent to which it ‘(1) fosters a shared understanding of the regime interactions and their consequences; (2) that it leads, or may lead, to efficiency gains that reduce the burden of simultaneous implementation of both regimes; and/or (3) that a normative conflict has been avoided or resolved’ (pp. 79–80). He rejects the inclusion of criteria related to regime effectiveness because, for him, this is too subjective or ‘in the eye of the beholder’. Further, van Asselt argues that regime effectiveness is ‘an empty vessel’ because a regime such as the UNFCCC represents ‘different aims based on countervailing interests’ (p. 56).

I have two difficulties with this. Firstly, the UNFCCC, and now the Paris Agreement, do have reasonably clear objectives. Secondly, the criteria van Asselt utilizes arguably imply normative judgements themselves. Turning to the first issue, the UNFCCC has the stated objective of ‘avoiding dangerous anthropogenic climate change’. Determining what constitutes ‘dangerous’ involves a value judgement, but the international community has accepted 2 degrees Celsius (2°C) as constituting a ‘dangerous’ threshold,Footnote ⁷ and the Paris Agreement has a stated goal of ‘[h]olding the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels’.Footnote ⁸

Turning to the second issue, van Asselt’s very criteria for successful interaction management necessarily imply normative evaluations. For example, it remains unclear why ‘avoiding normative conflict or resolving it’ should, in itself, be of value. To illustrate, van Asselt explains that, to date, a normative conflict between the WTO agreements and possible unilateral climate change-related measures (particularly in the form of border adjustment measures) has not occurred. Nevertheless, he argues that a ‘policy conflict’ is involved in relation to the two regimes because of their diverging objectives and, in particular, the chilling effect of the WTO in relation to both possible domestic climate change-related implementation measures (such as border adjustment measures) and the possible inclusion of trade-related measures in the climate change regime (pp. 163, 190). Van Asselt makes a convincing argument that synergies between the two regimes could best be promoted by a dialogue between countries considering such measures and developing countries concerned about their possible protectionist impact, which includes a discussion of finance issues (pp. 197–8).

Yet, this sensible proposal implicitly involves a normative judgement that it is valuable to prioritize measures necessary for an effective global climate regime vis-à-vis the WTO regime. Moreover, to the extent that the WTO has a chilling effect on states pursuing more aggressive climate change measures, surely avoidance of conflict in itself is not particularly helpful. In fact, overt conflict could be positive in terms of policy development, as it could trigger required changes in WTO rules to the extent that these act as a brake on required climate change-related mitigation measures. While van Asselt is right in saying that it can be difficult to obtain agreement on normative benchmarks (dismissing sustainable development as too vague and of uncertain status (p. 229)), the answer I would suggest is not to embed normative assumptions within effectiveness criteria, but rather to make these transparent and seek to justify them.

In the post-Paris phase of development of global climate governance, the interaction between the UN climate regime and other regimes will continue to be of enormous importance. Van Asselt’s well written and thoroughly researched contribution constitutes essential scholarship in this area. In concluding, van Asselt acknowledges that there is much work still to be done in understanding the deeper causes of institutional complexities and interactions in relation to global climate change governance (p. 268). This is true, but van Asselt has done much to advance this research agenda.