Blue carbon: The science behind the buzzword
The ocean is a major carbon reservoir, with carbon being moved and stored through complicated physical, chemical, and biologically processes.* While research into blue carbon systems is growing, quantification of these systems’ sequestration potential remains challenging. Indeed, factors such as ocean circulation, temperature, nutrients, and light can alter the amount and timescale of blue carbon storage.
These factors all affect the additionality of blue carbon sequestration, a term critical to understanding climate mitigation benefits. “Additionality” refers to measurable carbon sequestration or emissions avoided, in addition to what would have occurred without an intervention. If a marine ecosystem or species demonstrates additionality, that means it can remove carbon from the atmosphere and store it away for timescales relevant to climate change.
While research into blue carbon systems is growing, quantification of these systems’ sequestration potential remains challenging.
The author of this column, working with an international group of marine scientists to review and synthesize the current blue carbon literature, assessed marine ecosystems for their potential to offer this key metric of additionality. Several types of coastal ecosystems—including mangrove forests, salt marshes, and seagrass meadows—are recognized for their proven long-term carbon sequestration potential. Of these, mangroves are the highest, with a productivity comparable to that of primary tropical forests and high soil carbon sequestration rates. Due to the ability to measure, monitor, and manage the carbon stores within these ecosystems, they can be included in parties’ nationally determined contributions (NDCs)—the climate actions that nations put forward to meet their goals under the Paris Agreement.
Other systems and marine organisms, including macroalgae (such as kelp), shelf sediments, zooplankton (including krill), fish, whales, and calcifying organisms (oysters and coral reefs), are gaining attention in blue carbon discussions. For instance, macroalgae and shelf sediments hold promise as blue carbon pathways, but more research is needed to quantify their potential for inclusion in carbon accounting mechanisms and to understand the importance of avoiding emissions.
Most marine organisms—including zooplankton, fish, whales, and calcifying organisms—have limited to no potential as blue carbon pathways, with unproven additionality. They are unsuitable for inclusion in carbon accounting systems because of the complicated factors that influence their role in oceanic carbon storage, as well as threats from unsustainable fishing and climate change. In fact, coral reefs are widely considered as a net source, rather than a sink, for carbon dioxide.
Putting blue carbon into the policy context
The U.S. government is increasingly turning its attention to the ocean-climate nexus. The Infrastructure Investment and Jobs Act—President Joe Biden’s landmark infrastructure package—includes funding for coastal habitat restoration, which can bolster the protection of ecosystems that deliver both climate mitigation and adaptation benefits. Meanwhile, the Our Ocean conference—which recently held its seventh convening in the Republic of Palau—saw countries make 410 ocean commitments valued at $16.35 billion. This included the United States announcing $161.5 million for a national coastal resilience fund and $107.9 million for the development of a NASA instrument to observe coastal ecosystems.
Building on this momentum, President Biden marked Earth Day by signing an Executive Order on Strengthening the Nation’s Forests, Communities, and Local Economies. Along with its significant commitments to the carbon stored in old growth forests, the executive order noted the critical importance of protecting coasts and marine ecosystems, directing agencies to identify opportunities for nature-based solutions within the federal government.
As the ocean-climate nexus gets its due, policymakers need to grasp how to strengthen the climate benefits of marine ecosystems while avoiding the pitfalls that come with monetizing ecosystem services, such as double-counting and greenwashing. Understanding the limiting factors and variability of blue carbon sequestration, the interconnectedness of all marine systems, and the climate and human threats that undermine ecological integrity can help us better support the ability of these systems to deliver critical benefits. Although not all ecosystems and organisms discussed in the blue carbon context deliver mitigation benefits, protection of marine habitats and species is critical to broader climate adaptation and human well-being goals, as well as the preservation of marine biodiversity for its intrinsic worth.
Done right, blue carbon can be a powerful tool in national and international ocean-climate strategies.
Importantly, claiming climate mitigation gains from ecosystems that do not sequester carbon over timescales that affect climate change would only serve to confuse well-meaning policymakers and misdirect vital yet limited research funding.
Enhancing blue carbon at home and abroad
Current U.S. government actions can be strengthened with additional policy interventions that are grounded in blue carbon science:
- Utilize existing offices to assess and explore blue carbon potential: There is an immediate need for comprehensive data curation and visualization of blue carbon systems. In particular, the U.S. Office of Science and Technology Policy (OSTP) can be utilized to assess blue carbon effectiveness. Quantifying and mapping current and potential blue carbon stores can help guide local governments, states, federal agencies, and international entities as they work to manage coastal and marine ecosystems. These efforts would not only enable accurate carbon accounting—which can incentivize and facilitate ecosystem protection—but also highlight current gaps in research.
Additionally, the Ocean Research Advisory Panel (ORAP) within the Ocean Policy Committee should facilitate ongoing conversations between both theoretical and applied international scientists, policymakers, and technical staff—conversations that would feed directly into ORAP recommendations. As the body of blue carbon research grows alongside the need to take climate action, creating the space for experts to have ongoing dialogues with policymakers can help maximize intervention success, more efficiently direct limited research dollars to promising new avenues of study, and avoid the pitfalls described above that can be magnified when research results are not accurately centered in a policy context.
- Expand international assistance for ocean-climate policies: The need to protect and restore blue carbon ecosystems does not stop at the U.S. border; yet the difficulty of creating blue carbon inventories and implementing ongoing monitoring, management, and reporting programs is a barrier to many countries seeking to unlock the potential of blue carbon ecosystems within their NDCs. As the United States has included blue carbon in its national greenhouse gas emissions (GHG) inventory, it is well placed to aid other nations in following suit.
Specifically, the National Oceanic and Atmospheric Administration’s (NOAA) Blue Carbon Inventory Project, part of a larger U.S. government initiative to build capacity abroad to develop GHG inventories, supports countries in undertaking the inclusion of wetlands in their own inventories. This program is a critical tool to enhance coastal ecosystem protection in biodiverse regions and ensure the broader suite of co-benefits these ecosystems provide. Yet it should be expanded in terms of its country and ecosystem scope as well as duration.
An additional barrier for many blue carbon-rich countries is overcoming existing institutional arrangements that silo climate action from coastal ecosystem management. Tailoring U.S. recommendations to country-specific institutional arrangements can help overcome these silos and eliminate the bureaucratic barriers to blue carbon gains.
- Elevate adaptation: If properly managed, blue carbon ecosystems can provide numerous adaptation co-benefits while conferring additional ecosystem services—such as clean water, food security, and livelihood support—on local communities. In fact, this November’s UNFCCC COP27 in Sharm el-Sheik, Egypt, has been dubbed the “Adaptation COP,” as its regional focus on climate risks in Africa signals the importance of adaptation to many developing nations and emerging economies.
To this end, adaptation goals—along with the behavioral science data that support them—need to be elevated within the office of the special presidential envoy for climate, the U.S. State Department, NOAA, and OSTP, with clear points of contact for community engagement. These goals should also prioritize addressing adaptation needs in historically disadvantaged communities—both at home and abroad—and recognizing differentiated needs of marginalized individuals and groups within those communities.
- Establish protections for polar regions and the high seas: Blue carbon is likely increasing in polar regions due to climate change-driven sea ice, ice shelf, and glacial loss. Unfortunately, there is growing interest in exploiting polar regions for fishing—and for drilling and shipping in the Arctic.
The Biden administration should continue to uphold the United States’ long-standing leadership in the Antarctic through sustained levels of research funding and taking a strong stance in favor of Southern Ocean protections within the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), particularly against nations such as Russia, China, and Norway that want to limit spatial protections and increase ecologically detrimental fishing pressures on krill—the keystone species in the Southern Ocean that is increasingly at risk of climate change impacts. In the Arctic, the Biden administration should not approve any new offshore oil and gas leases—which disturb carbon stored in ocean sediments—and the United States should work through the Arctic Council to limit emissions from shipping.
Additionally, the United States must be much more strident in its support of a U.N. high seas, or “BBNJ,” treaty. Much of the high seas is unexplored and understudied, and taking a precautionary approach to its management could help avoid emissions associated with bottom trawling, deep-sea mining, and industrialized fishing vessels, in addition to the biodiversity benefits of protection.
- Create an Ocean Climate Action Plan: Ocean systems are complex, and the policy underpinning the U.S. approach to ocean use, management, planning, and protection—both within domestic and international waters—is spread across several agencies and departments. Creating a U.S. “Ocean Climate Action Plan” that incorporates blue carbon management and research could help the United States streamline and reach its ocean-climate goals.
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Done right, blue carbon can be a powerful tool in national and international ocean-climate strategies. But despite the mitigation and adaptation benefits of blue carbon ecosystems, any nature-based solution is ultimately limited by the continuing rise in global temperatures—a reality that underscores the continued need to make rapid cuts to greenhouse gas emissions and deployment of renewable energy and energy efficiency technologies.
Alongside these actions, the U.S. government must continue to follow the science and lead on blue carbon interventions in order to help U.S. and global communities grappling with the climate crisis.
*Author’s note: The ocean stores carbon in four primary pools: 1) dissolved inorganic carbon, 2) organic carbon, 3) marine biota, and 4) the sediment floor.