New paper highlights vast potential for coastal ecosystems to advance climate goals, and assesses the role of voluntary carbon markets

Mangroves, salt marshes, seagrass meadows and kelp forests—collectively known as blue carbon ecosystems—have gained global attention as powerful natural solutions to climate change. These coastal ecosystems durably capture and store carbon in their biomass and soils at remarkable rates—often faster per unit area than terrestrial forests—while also supporting biodiversity, protecting coastlines, and sustaining human livelihoods.

The study estimates that restoring salt marsh, mangrove, seagrass, and kelp forest ecosystems to their maximum extent could remove around 400 million tons of CO2-equivalents (Mt CO2-eq) annually – more than the annual emissions of roughly 80 million cars. On the other hand, the carbon accumulated and stored over hundreds to thousands of years in coastal sediments can be rapidly re-released back into the atmosphere if disturbed, turning these ecosystems from carbon sinks into sources if their loss continues. Authors estimate that at present loss rates, if sediments are also lost when the ecosystem disappears, 230 Mt CO2-eq could be re-released to the atmosphere each year (excluding kelp forests). This emissions risk underscores the urgency of protecting the ecosystems that remain.

Figure 1: (a) Estimated global blue carbon ecosystem restoration potential (Mha) and the associated estimated annual carbon removal (TgCORG yr-1). (b) Estimated rates of annual ecosystem loss (% yr-1) and associated emissions (TgCORG yr-1).  Values represent means (and 95% CIs). 

Given this tremendous climate change mitigation potential, blue carbon ecosystems are increasingly being integrated into global climate strategies (Fig. 2), fueling much needed attention and financial backing for their recovery. Beyond policy initiatives, the voluntary carbon market (VCM) can serve as a powerful way to support blue carbon ecosystems. The VCM allows proponents of blue carbon restoration or conservation projects to rigorously quantify the project’s carbon impacts, generating credits that can be sold to finance the project, or retired to represent the project’s permanent climate benefits.

Despite its benefits, the current VCM landscape is uneven and faces scientific and market-based barriers. Authors note that nearly 90% of blue carbon VCM projects focus on large stands of mangrove forest, where more established methods and data already exist. Smaller projects, more complex ecosystems (e.g., kelp forests), and novel carbon pools (e.g., dissolved organic carbon), face significant hurdles. 

Figure 2: Key global initiatives that have advanced the conservation and management of blue carbon ecosystems and their inclusion into GHG goals and carbon accounting. 

The review identifies several key constraints that limit the full potential of the VCM to support blue carbon ecosystem recovery:

• High monitoring, reporting, and verification costs, which can make projects financially unviable
• Lack of robust emissions factors, supported by data and growing advances in ecosystem modeling
• Limited seagrass and seaweed ecosystem mapping data and associated rates of ecosystem change
• Growing complexity in carbon accounting, including uncertainties in lateral movement of carbon through coastal systems

For instance, despite an essential need to keep blue carbon project costs low enough to make them possible, authors also note that cost management must not sacrifice project integrity. Adopting a conservative approach—using minimum assurable quantifications where precise estimates are not yet feasible—can help ensure that financial mechanisms remain available while preserving their credibility and equity. Authors also point out existing challenges with habitat connectivity and movement of carbon - how can carbon be best credited when it won’t stay put?

As scientific knowledge gaps are closed and tools are improved, the ability for the VCM to support blue carbon ecosystem management will broaden. Indeed, despite the challenges, the number of blue carbon projects and credits has grown rapidly in recent years, reflecting strong global demand. 

In sum, a long history of blue carbon science and management affirms that recovery of these ecosystems is a powerful natural climate solution. An ongoing commitment to advancing science, policies, and markets will ensure that blue carbon ecosystems can continue to provide climate mitigation, biodiversity protection, and coastal resilience benefits across the globe.

Read the full paper here: Blue Carbon in an Era of Carbon Accounting