A new taxonomy to map evidence on carbon dioxide removal side effects

Beyond rapid emission reductions, carbon dioxide removal (CDR) is critical to ambitious climate change mitigation strategies, yet the environmental, socio-political, and economic implications of its deployment remain insufficiently understood. Recent exponential growth in literature is rapidly filling this gap but makes synthesizing the evidence on CDR side effects increasingly challenging. We address this issue by mapping this literature and proposing a taxonomy to synthesize and compare evidence on CDR side effects for six widely discussed CDR options. The expansive evidence warrants the use of machine learning to systematically select relevant research and provide an inventory of nearly 400 side effects and challenges. Side effect profiles per CDR option and amounts of evidence per region vary considerably, with very rich evidence in Europe and comparatively little information for Africa, South America, and Oceania – geographies where large-scale CDR deployment is nevertheless projected. Across all evaluated regions, there is a predominance of articles discussing evidence for negative effects compared to positive ones. Starting from the limitations of our analysis and gaps in the literature, we provide guidance for future studies that can build on the newly developed taxonomy of side effects as an entry point for more comprehensive and detailed side effect descriptions and quantifications.