Farming the ocean – seaweeds as a quick fix for the climate?

Finding ways to keep global warming under 1.5 degrees Celsius is urgent and will need a portfolio of solutions. Seaweeds are marine photosynthetic organisms that humans harvest either from the wild or farm, to be used in many applications and providing various ecosystem services. Large scale farming of seaweeds for absorbing carbon has lately been promoted as a climate “fix”. The major shortcomings of this argument relate to the idea that a carbon sink function should exist through carbon accumulation in seaweed biomass simultaneously as seaweeds are consumed as food by humans, fed to animals, or used in many alternative applications. This carbon instead enters the fast carbon cycle and does not provide any “carbon sink” function. Radical suggestions of intentionally transfer of farmed seaweeds to the deep-sea to accomplish a longer removal are highly questionable from feasibility, economic, ecosystem effects and ethical resource use perspectives. Development of “ocean forests” for carbon capturing through farming should not be compared to forests on land as these provide carbon removal from the atmosphere at sufficiently long time scales to be qualified as carbon sequestration - thus making a difference related to reducing atmospheric greenhouse gas concentrations. Seaweeds can, however, play a role in reducing greenhouse gas emissions from the overall food system through carbon offset - i.e. if replacing food, feed, and/or materials that have larger carbon footprints. The fate/cycling of carbon as particulate and dissolved matter from both farmed and wild seaweeds, are however not fully understood, especially with respect to pathways and time scales relevant for carbon removal/storage. Another potential pathway for their role in decarbonization may be through reducing enteric methane emissions from ruminants and also through bioenergy production. More research is, however, needed for understanding the contributions from such interventions. Presenting seaweed farming as a quick fix for the climate risks facilitating misdirected investments (for carbon abatement solutions) and reducing demand for specific research and technological development that will be needed for increasing our understanding about seaweeds’ contribution to food/feed systems and additional sustainability services and benefits.

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