Benefit-cost ratios of carbon dioxide removal strategies

All pathways to achieving the Paris Agreement target of limiting global warming to 1.5 degrees C or 2 degrees C require the large-scale removal of carbon dioxide (CO2) from the atmosphere. Many CO2 removal (CDR) strategies have been proposed, which vary widely in both price per ton of CO2 removed and storage timescale of this removed CO2, as well as mechanism, maturity, scalability, and other factors. However, it has not yet been thoroughly assessed whether the benefits, in terms of climate change-related damages avoided, of CDR deployment exceeds their cost at current reported prices and storage timescales, or what cost is required for CDR strategies with a given storage timescale to provide net benefits and how these depend on socioeconomic assumptions. For CDR strategies that have long storage ( > 500 year) timescales, these questions reduce to whether its price is lower than the social cost of carbon, but here we show for CDR strategies that operate over shorter timescales they also depend on the duration of storage. We demonstrate that for CDR strategies with reported storage timescales of decades to centuries, the benefits of their deployment outweigh their reported costs under middle-of-the-road socioeconomic assumptions, and in some cases their benefits still outweigh their costs under optimistic socioeconomic assumptions. Overall, the benefit-cost ratios of the evaluated CDR strategies vary by more than an order of magnitude, and are strongly influenced by both price and storage timescale. Our results provide a framework that can be used to assess and compare different CDR strategies quantitatively to help guide future research, development, and policy efforts.