Advanced Review The European Union: the polycentric climate policy leader? Tim Rayner ∗ and Andrew Jordan The European Union’s (EU) claims to be a leader in international climate policy are well known. Since the early 1990s, a rich and vibrant academic literature has analyzed the internal sources and international consequences of its leadership aspirations, especially in relation to the challenges of mitigation. More recently, attention has turned to adaptation policy. The literature highlights how policy actors have successfully exploited many of the opportunities afforded by the EU’s ‘polycentric’ form, while minimizing its downsides, but that acute challenges lie ahead, particularly if a strong global-level framework remains elusive. It has continually underlined the fact that the EU’s climate policy activities have enormous relevance well beyond European borders. Both in terms of its role as a driver of international policy and a source of transferable policy lessons on how to govern in ‘polycentric’ settings, appreciating the EU’s experience is vital for those seeking to understand the governance of climate change, both within and between states.  2013 John Wiley & Sons, Ltd. How to cite this article: WIREs Clim Change 2013. doi: 10.1002/wcc.205 INTRODUCTION T he European Union (EU) claims, with some justification, to be a global leader in climate policy. Since the early 1990s, a growing literature has explored many different facets of its governing activities. Although in many ways a sui generis system of polycentric or, in EU parlance, multilevel governance, the EU’s experience in handling a range of climate governance dilemmas arguably has a much wider relevance, especially to broadly similar governance systems—including other regional groupings of states, as well as federal and/or quasi- federal states—with which it is often compared. 1–6 As the long-standing commentator on EU climate policy Jørgen Wettestad (p. 26) has put it, ‘both its relative diversity and institutional strength indicate that the EU can be looked upon as a rather benign ‘‘critical case’’: if [it] cannot develop effective climate policies, then the implications for the globe are grim.’ 7 The realpolitik of international climate policy, in which the EU is seeking to build alliances with other major ∗ Correspondence to: tim.rayner@uea.ac.uk School of Environmental Sciences, Tyndall Centre for Climate Change Research, University of East Anglia, Norwich Research Park, Norwich, UK emitters that currently lie outside the Kyoto Protocol, also highlights the need to understand the sources and effects of climate governance in Europe. 8 So whether in terms of its global implications or the academic response it has provoked, the EU’s experience in governing climate policy is hugely important. In her editorial essay on the WIRES climate policy and governance theme, Harriet Bulkeley highlighted a number of important subthemes. 9 Among these are the diverse levels and spaces in which climate governance takes place and policy is enacted, the interaction between policy-making venues at different scales, issues of where power and authority lie, and how these might be researched and understood (p. 312). Another subtheme has to do with sectors, including how responsibilities (and associated costs) are allocated for the twin imperatives of mitigation and adaptation. All of these have been brought vividly to life in the academic literature on EU climate policy, which has grown significantly since the early 1990s. In a world struggling to arrive at binding, multilateral agreements to tackle climate change, the EU’s inherent polycentricity—i.e., its active encouragement of experimental efforts at multiple levels, with active steering of actors at local, regional, and national levels—has become steadily  2013 John Wiley & Sons, Ltd.