Scientists question effectiveness of nature-based CO2 removal using the ocean

Scientists from the University of East Anglia (UEA), the University of Tasmania’s Institute for Marine and Antarctic Studies, Centre National de la Recherche Scientifique, and the Institute for Sustainable Development and International Relations have raised concerns about the ongoing commercialization of marine carbon dioxide removal (CDR) techniques, deeming them “premature and misguided” due to a limited understanding of basic ocean processes.

In a new paper published in the journal Environmental Research Letters, the researchers review the climatic effectiveness of four ‘nature-based’ techniques using marine biological processes: shellfish cultivation, seaweed farming, coastal blue carbon, and increasing whale populations through ‘re-wilding’. While these activities have non-climatic benefits, the authors conclude that they cannot provide a significant contribution to CDR and risk being ‘dead ends’ in terms of meaningful climate mitigation.

The Need for Due Diligence in Ocean-Based CDR

To limit warming to less than 2°C, both emissions reductions and CDR are required, with multiple techniques needing to be developed and up-scaled massively to achieve billion-tonne annual CO2 removal rates within 30-50 years. However, the researchers argue that new methods are being proposed regularly without sufficient checks or balances, particularly in the case of ocean-based CDR.

The ocean-based approaches reviewed are being advocated not only by scientists but also by the private sector, without due diligence on the underpinning fundamental science. “Proponents of these methods have an incomplete or incorrect grasp not only of how the ocean carbon cycle functions, but also the massive up-scaling needed to provide significant climatic benefits,” said co-author Dr Phil Williamson, honorary associate professor at UEA’s School of Environmental Sciences.

Misunderstandings and Knowledge Gaps Affect Credibility

Lead author Prof Philip Boyd, of the University of Tasmania’s Institute for Marine and Antarctic Studies, said: “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.”

The authors highlight that those advocating these approaches have given insufficient attention to basic constraints relating to ecosystem functioning and the ocean carbon cycle, ignoring the many processes returning CO2 to the atmosphere, as well as the challenges of implementation at climatically-significant scale, the (in)security of carbon storage, and the many difficulties in reliable quantification of climatic benefits.

“There is a need for better communication of the basic criteria for CDR viability using marine processes. Safety, durability, verifiability and scalability should be used to prioritise relevant R&D funding by Governments, as well as providing checks and balances for policymakers,” said Dr Williamson.

The authors raise concerns over the ‘opportunity costs’ – the resources directed at these approaches – which they say could be better invested in reducing emissions, as well as other CDR methods, both land and ocean-based, that are more likely to be safe, sustainable, durable, verifiable, and scalable.

“We believe that the use of these four nature-based approaches for carbon offsets is more likely to represent greenwashing, rather than these methods becoming the ‘climate heroes’ that some people are claiming,” added Dr Williamson.

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