PerspectiveClimate

Rightsizing carbon dioxide removal

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Science  19 May 2017:
Vol. 356, Issue 6339, pp. 706-707
DOI: 10.1126/science.aam9726

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  • Carbon Dioxide Removal: Size Matters
    • Greg H. Rau, Senior Research Scientist, Institute of Marine Sciences, University of California

    “Rightsizing” (1) our expectations of carbon dioxide removal, CDR, must avoid undersizing those expectations given CDR’s anticipated critical role in meeting atmospheric CO2 and climate targets (2). So far CDR discussions have heavily focused on the use of terrestrial biology such as afforestation/reforestation, biochar, soil carbon management, and biomass energy with carbon capture and storage (1-3). Yet the potential capacity of these approaches is limited by available land, water and nutrients and by environmental concerns, raising serious questions as to how large a role such CDR could feasibly play (4,5).
    Field and Mach (1) classify all other forms of CDR as “engineered, nonbiological approaches” like enhanced mineral weathering and direct air capture (DAC), which they characterized as energy intensive, expensive, technically immature, speculative and of questionable potential. This curiously ignores marine photosynthesis representing a gross global CO2 uptake of nearly 200 Gt yr-1 (2), a small fraction of which could be managed or enhanced to effect significant CDR in ways analogous those proposed for terrestrial taxa (6-8). Additionally, mineral weathering together with marine chemistry is the primary way that excess global CO2 is naturally consumed and stored on long timescales (9). Considering global reservoir sizes and annual fluxes (2: Chptr. 6), the mean carbon residence time in the ocean is about 400 years. This is about 16X longer than the mean...

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    Competing Interests: None declared.