Assessing global urban CO₂ removal

Here, with the aim of supporting the path to achieving net-zero emissions in cities, we assess the existing literature on carbon dioxide removal (CDR) at the urban scale, seeking to quantify the potential negative emissions contribution of cities globally. Urban CDR options considered here include the storage of carbon in urban vegetation, soils and buildings, and the capture of CO₂ from indoor environments via decentralized direct air capture. Our estimates of carbon storage and capture potentials indicate that deploying CDR options at the urban scale could make a substantial contribution to global mitigation of climate change, alongside supporting the upscaling of climate action from local to regional and national scale. The associated human and environmental well-being effects strengthen the case for cities as carbon sinks. Any upscale of the reviewed technologies is nevertheless constrained by several uncertainties, economic barriers and governance issues that pose substantial challenges to their implementation. From these, we identify key research gaps and recommendations for future research centered around the need for additional field deployments, consideration of the particularities of different urban geographies and socioeconomic contexts, and the establishment of robust cross-sectoral carbon accounting methodologies.