Ocean-Based Carbon Dioxide Removal (CDR)

Blue Carbon Restoration and Carbon Sequestration

Our planet is being transformed by climate disruption, with some of the worst impacts occurring in the ocean. Currently, most efforts to address climate change are focused on reducing emissions of greenhouse gases. While those efforts remain vital, they’re no longer enough. We must also clean up the “legacy” greenhouse gas pollution already in our atmosphere. 

Ocean Visions believes that we may be able to harness the power of the ocean to restore the climate and the ocean itself. The ocean already holds more carbon than any other part of the biosphere and has the potential to contribute even more. The sheer scale of the ocean means that any ocean-based carbon dioxide removal (CDR) solutions proven to be viable and safe would have the potential to clean up billions of tons of CO2

A number of ocean-based CDR approaches are being explored—including restoring blue carbon.

Restoring Blue Carbon Overview

Coastal vegetated marine ecosystems, including tidal salt marshes, mangrove forests, and seagrasses meadows (all of which are commonly referred to as “blue carbon”), fix CO2 via photosynthesis and can trap organic carbon in their roots and the marine sediments for thousands of years. Disturbance and loss of marine ecosystems leads to rapid release of carbon to the atmosphere. The restoration of degraded systems can protect intact habitats from large-scale carbon release and add carbon sequestration in the restored habitat. 

A significant fraction of the biomass in marine systems is made up of animals, such as fish and whales. Recently, the role of such animals in biogeochemical cycles has gained more attention, with special interest paid to the role that large marine animals may play in ocean carbon cycling and carbon storage. Many of the populations of these organisms, especially the largest predators, have been dramatically reduced as a result of a host of from human activities such as fishing, shipping, introduction of invasive species, and habitat destruction. Intentional actions to recover fishes, whales, and other marine animals have the potential to increase carbon sequestration in the ocean, although considerable uncertainties remain. 

Blue Carbon Restoration and Carbon Sequestration © 2023 by Ocean Visions is licensed under CC BY-NC-ND 4.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-nd/4.0/

Sequestration Potential

Sequestration rates and carbon content of coastal vegetated marine ecosystems vary widely depending on species, geography, hydrological systems, and other factors, but they tend to substantially exceed those of their terrestrial counterparts – temperate and tropical forests. While coastal vegetated marine ecosystems continue to be an important CO2 sink and a critical guardian of millions of tons of soil carbon, they do not currently represent a significant opportunity for additional CO2 removal or avoided emissions. While the rapid loss of these ecosystems in the 1980s and 1990s has slowed considerably, the restoration potential is limited to only a few million hectares globally.

Very little is known about the potential for restoration of marine animal populations to contribute to durable carbon sequestration in the ocean due to our nascent understanding of the role of marine animals in ocean carbon cycling.

Environmental Co-Benefits and Concerns

Restoration and protection of coastal vegetated marine ecosystems is considered a ‘no regrets’ climate mitigation strategy due to its many environmental co-benefits. These ecosystems boost biological diversity, provide critical habitat for many marine and terrestrial species, and benefit local fisheries. Their structural complexity helps protect coastlines from erosion, storms, and sea level rise—providing numerous climate mitigation benefits to society. 

Similarly to coastal vegetated marine ecosystems, restoration of historic populations of marine animals is widely considered to have co-benefits, including biodiversity conservation, restoration of ecological function, and spiritual and aesthetic values. 

Cost Considerations

The restoration of endangered coastal vegetated marine ecosystems and of populations of marine animals require a combination of enabling policies, engagement of user groups (fishers, farmers, developers, supply chain actors) and enforcement. Cost of protection varies widely and depends, among other factors, on local law, tenure rights, population density, and the economic viability of alternative uses (e.g., tourism, aquaculture, shipping). Restoration of coastal and marine ecosystems tends to be cheapest and easiest for mangroves and most expensive for seagrasses. Links to carbon markets are starting to subsidize or even fully finance some of the restoration costs. However, economies of scale have limitations as coastal and marine ecosystems are distributed along hundreds of thousands of miles and project development often requires a “village by village” approach.

Dive Deeper

Join the Ocean-Based CDR Community

Ocean Visions’ CDR Community brings together stakeholders to advance the state of knowledge, build bridges across disciplines, and help the community move towards safe and equitable testing and piloting of the most promising ocean-based CDR approaches.

Explore Ocean-Based CDR Road Maps

Ocean Visions’ ocean-based CDR road maps provide overviews of potential technologies, obstacles they face, and first-order priorities needing attention to advance the field. The road maps are intended to catalyze global collaboration and engagement and will be updated and refined as advances emerge in science, technology, governance, and policy.