Authors: P W Boyd, J-P Gattuso, C L Hurd, and P Williamson Journal: Environmental Research Letters
To limit warming to <2 °C, we need both emissions reductions and carbon dioxide removal (CDR) (IPCC 2022). A diverse range of potential CDR methods have been proposed to achieve billion-tonne (i.e. gigatonne, Gt) annual CO2 removal rates within 30–50 years (IPCC 2022), with multiple approaches needed to be developed and upscaled massively to achieve that goal. The need for robust criteria to assess the viability of candidate CDR mechanisms has long been recognised (Boyd 2008), yet new methods are being proposed regularly with insufficient exploration of such checks or balances. This is particularly true for ocean-based CDR, now attracting greater interest (NASEM 2022) as the constraints on land-based methods become apparent. Here, we focus on four ocean-based CDR methods that, in our opinion, are being advocated, not only by scientists, but also in many cases by the private sector, without due diligence on the underpinning fundamental science. We consider proponents of these methods to have an incomplete or incorrect grasp not only of how the ocean carbon cycle functions, but also the up-scaling needed to provide significant climatic benefits. Such upscaling brings other ocean processes into play that could nullify the effectiveness of the proposed CDR approach. In each case, misunderstanding and knowledge gaps affect the credibility of carbon offset schemes. Our case studies are: calcification-based approaches, expansion of seaweed farming, coastal blue carbon restoration, and 're-wilding' whale populations. We consider that the non-climatic benefits of all these actions have potential to greatly exceed their modest (or non-existent) possible contributions to ocean-based CDR. Click to read the full paper
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