Is blue carbon a ‘red herring’? Problems regarding magnitude, cost-effectiveness and timescale

Avoiding the most catastrophic consequences of climate change will require some amount of carbon dioxide removal, in addition to urgently reducing emissions.  Options for such removal include nature-based solutions, such as “blue carbon” burial in the sediment of vegetated coastal ecosystems (mangroves, salt marshes and seagrass meadows). Very high carbon sequestration rates have been claimed for these blue carbon ecosystems, and many media outlets have uncritically endorsed this message. Unfortunately, there seems to be some over-optimism among researchers, the general public and policy-makers, about the actual climate mitigation potential of coastal blue carbon.

We identify three main reasons why blue carbon ecosystems are unsuitable for directly offsetting fossil fuel emissions. First, the magnitude of the any climate benefit is likely to be much smaller than claimed, due to a range of methodological issues; second, the cost-effectiveness is low, particularly in developed countries; and third, there is a mismatch in timescale between the emission of ancient fossil carbon and the storage of carbon by vegetated ecosystems. Given these limitations, we suggest that blue carbon may be a misleading distraction (i.e. a ‘red herring’) for climate mitigation purposes. Nevertheless, blue carbon ecosystems provide many benefits.  Protection of such habitats and their restoration, where practicable, would protect critical habitat for diverse species, prevent coastal erosion, reduce storm damage, promote food security and provide opportunities for tourism.