At F4CR, we’re often asked, “What are the solutions that can restore the climate?” In the coming months, we will attempt to answer this question (and more!) as they relate to nine categories of carbon dioxide removal (CDR) solutions. In this fifth installment of our Solution Series, we examine the potential of ocean based climate restoration practices to contribute to climate restoration. Our new ocean based CDR white paper looks in greater detail at this solution’s climate restoration potential in terms of durability, financeability, scalability, and equity. This blog post gives a brief overview of some key points.
What is ocean based CDR?
Ocean based CDR solutions seek to increase the ocean’s capacity to absorb CO2, accelerate that absorption, and ensure that the captured CO2 is stored long-term, all while avoiding unintended negative impacts and addressing relevant equity and governance implications. Terrestrial CDR approaches are limited by the quantity of arable land available for carbon removal and storage, so climate scientists and innovators see our oceans as a valuable tool for addressing the climate crisis.
Can ocean based CDR practices restore the climate?
Ocean-based CDR approaches are still novel, and most require more research to understand how to maximize their benefits while minimizing risks. However, given that 30% of anthropogenic emissions have already been absorbed by our oceans, it’s clear that the ocean’s capacity to absorb massive amounts of CO2 is enormous. The questions that remain are:
- How much more CO2 our oceans can safely absorb,
- How to facilitate that absorption safely, effectively, and equitably,
- Which pathways are best suited to climate restoration-scale CDR.
Oceans have three main mechanisms by which they dissolve and store CO2, and there are several approaches to enhancing or accelerating each mechanism.
- The solubility pump moves atmospheric CO2 into the deep ocean as surface water cools. The two main approaches to enhancing oceanic CO2 uptake through the solubility pump are alkalinization and electrochemical ocean capture. Both of these methods allow ocean waters to take up more CO2 without increasing acidity.
- The biological pump converts carbon dioxide into biocarbon and sinks some of that biocarbon into the deep ocean using photosynthesis. Both macroalgal cultivation and carbon sequestration, as well as ocean nutrient fertilization seek to increase ocean primary productivity through the biological pump.
- Lastly, physical transport mimics ocean currents, which transport CO2 throughout the oceans and allow large quantities to be stored for decades to centuries. Artificial upwelling and artificial downwelling are two ways in which physical transport could increase ocean carbon sequestration, but further research on these two methods are necessary to determine whether they are effective CDR strategies.
Estimates for the durability of ocean based CDR vary by solution, and uncertainties still remain about the longevity of carbon storage. Depending on a variety of variables, carbon can be stored for as little as 10 or as many as 10,000+ years through ocean-based solutions.
Ocean based CDR involves a variety of different approaches that enhance oceanic CO2 absorption with varying levels of scalability. Some approaches, like electrochemical ocean capture, could in theory only be limited by the supply of dissolved inorganic carbon in seawater, which is functionally limitless (but has many practical limitations). Macroalgal cultivation and carbon sequestration are limited by the fact that seaweed farms must be millions of hectares in size to have a climatically relevant impact. Other means, such as artificial upwelling, artificial downwelling, and ocean nutrient fertilization require further research to better understand their scalability. Ocean based CDR is a very promising solution in terms of scalability, and further research and funding is necessary to better understand how to maximize these solutions’ scales.
Looking at the financeability of ocean based CDR, ocean nutrient fertilization is the most cost effective ocean based CDR approach, costing less than $25–50 per tons of CO2. However, if profit is the primary incentive, developers are more likely to support the cheapest solution that could accrue fewer benefits — or even burden — an impacted community. Other approaches involve new technology and are more financially demanding, such as electrochemical ocean capture. Although electrochemical ocean capture currently costs anywhere from $150-$2,500 per ton of CO2, this cost could be reduced to less than $100 per ton of CO2 with further R&D.
As with any CDR method, the social implications of ocean based CDR will be influenced by the particulars of deployment and policy. Although none of these approaches are inherently inequitable, equity concerns will emerge with the deployment processes, policies, and actors’ motivations. Historically, the distribution of ocean benefits has been inequitable, and these inequities are mirrored in the modern day. In order to avoid exacerbating existing inequities in the deployment of ocean based CDR, we must understand stakeholders varying needs and concerns while addressing the impacts of existing power dynamics. We must also push leaders to commit to inclusive and robust governance and long-term planning.