Since the adoption of the Paris Agreement, climate cooperation has increasingly migrated away from the universal, consensus-based forums of the United Nations Framework Convention on Climate Change (UNFCCC) towards smaller, selective groupings of states. Sectoral pledges, trade-based instruments and bilateral financing partnerships now sit alongside and often ahead of the formal multilateral process. This article asks under what conditions such minilateral coalitions strengthen the multilateral climate regime rather than undermine it. Synthesizing regime complexity theory with experimentalist and catalytic- cooperation accounts of institutional design, this article proposes that the decisive variable is not the existence of small-group cooperation itself but whether a coalition remains functionally linked to the multilateral center through reporting, diffusion, and benchmarking mechanisms. Applying this framework illustratively to three prominent coalitions suggests that complementarity is neither automatic nor guaranteed and that the design choices made by coalition architects carry significant consequences for the long-term legitimacy of the UNCCC-centred regime.

climate governance; minilateralism; regime complexity; UNFCCC; institutional fragmentation

The architecture of global climate governance looks markedly different today than it did at the signing of the UNFCCC in 1992. What was once envisioned as a single, universal negotiating process has evolved into a dense and expanding ecosystem of overlapping initiatives. The global Methane Pledge, the European Union’s Carbon Border Adjustment Mechanism (CBAM), the proposed G7 Climate Club and the Just Energy Transition Partnerships (JETPs0 each organize a subset around a specific climate objective, frequently bypassing the slower and more cumbersome consensus procedures of the Conference of the Parties (COP). 

This shift has occurred alongside an intensification of great-power competition over green industrial policy, critical minerals and clean energy technology, all of which have made climate policy increasingly inseparable from questions of economic security and geopolitical rivalry. This proliferation of minilateral arrangements raises a governance question that has not yet been resolved in the literature: does the shift toward smaller, more selective coalitions strengthen the overall climate regime, or does it corrode the authority and legitimacy of the multilateral system built around the UNFCC? Existing scholarship offers two largely separate answers. Regime complexity theorists treat institutional fragmentation as a source of incoherence and strategic opportunity for powerful states, which can select whichever venue best serves their interests (Keohane and Victor 2011). Experimentalist and catalytic-cooperation theorists, by contrast, treat small-group cooperation as a productive and even necessary feature of a bottom-up climate architecture, one capable of generating momentum that eventually feeds back into the wider system (Hale 2020; Sabel and Victor 2017).

This article argues that both accounts are partially correct and that the relevant analytical task is not choosing between them but identifying the conditions under which a coalition behaves according to one logic rather than the other. Drawing on this synthesis, the article proposes an operational test for distinguishing complementary from corrosive fragmentation and applies it illustratively to three prominent coalitions. The purpose is not to offer a definitive verdict on any single initiative, but to demonstrate that the complementarity of minilateral climate governance is a matter of institutional design rather than an........

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