The rise of phase-out as a critical decarbonisation approach: a systematic review

'Phase-out' is increasingly mobilised in research and policymaking as an approach to catalyse the gradual decline of technologies, substances and practices that compromise environmental sustainability objectives. This trend is particularly pronounced in the context of climate change, demonstrated by the accumulation of a vast body of scholarship over multiple decades. Our work provides the first systematic review of the state of this knowledge, mapping out how phase-out is studied and employed as a policy tool for mitigating climate change. We systematically review over 400 publications, spanning three decades (1990-2021) and diverse scientific fields. Our review asks: how has scholarly work discussed phase-out as an approach to mitigate climate change, and how has this changed over time? We tackle this question from five perspectives: (a) elements targeted by phase-outs, (b) policy instruments, (c) affected industries, (d) geographic context, and (e) benefits besides climate change mitigation. Results reveal that phase-out has widely proliferated as a decarbonisation approach, developing into a bridging concept that links diverse communities of contemporary science and practice. This is reflected by engagement with manifold phase-out targets-stretching well beyond the usual suspects related to fossil fuels and end-use technologies-as well as discussion of a growing diversity of industries, policy instruments and geographies in the literature. This global proliferation of phase-outs is propelled by expectations of diverse co-benefits. Aside from gains for the environment, economy, society and health, we find widespread acknowledgment that phase-out can drive innovation and systemic change beyond the mere substitution of problematic technologies and materials. Our study also identifies several underdeveloped and underrepresented directions meriting further study. These notably include phase-out activity beyond Europe, North America and China, hard-to-abate industry sectors and non-fossil fuel targets. We conclude by carving out broader implications for scholars and practitioners to inform future research directions and climate mitigation efforts.