A Comparative Review of terrestrial and marine carbon dioxide removal (CDR) methods

• CDR methods are categorized by terrestrial vs. marine and biological vs. nonbiological. • OAE, EW, BECCS and biochar sequestration are well-rounded CDR methods in terms of cost, scale and CO 2 storage. • Biological CDR approaches occupy much more space than nonbiological CDR approaches. • The costs of moving air and seawater for direct air capture (DAC) and direct ocean capture (DOC) are high. Carbon dioxide removal (CDR) methods that remove CO 2 gas from the air and ocean are an essential long-term strategy to complement point source carbon capture. Many CDR methods have been proposed in recent years, and this review organizes and assesses these methods to aid researchers and decision-makers in accelerating development and deployment of CDR. This review organizes CDR methods into four categories: 1) marine/biological, 2) marine/nonbiological, 3) terrestrial/biological, and 4) terrestrial/nonbiological. For each of these categories, the fundamental mechanisms governing CO 2 separation are explained, and key CDR methods within each category are discussed. This review also provides a comparison of the four categorical CDR methods based on cost, scalability and carbon storage duration. The infrastructure needs of each CDR category are then covered, and a quantitative study is performed to estimate the costs of moving seawater vs. air to remove CO 2 . Finally, the operational footprints of various CDR approaches are compared on a 1 Mt/y capture scale. Overall, this review examines the pros and cons of each CDR method to aid decision-makers in selecting the CDR approach that works best within their given constraints.