It doesn’t take long to realize how much is at risk when standing waist deep in a mangrove forest in Colombia. The roots cling to one another like fingers, the water is dark, and beneath the sediment are centuries’ worth of stored carbon, silently accomplishing what entire industries are unable to. Apple is relying on this type of location in collaboration with Conservation International. With a projected lifespan of one million metric tons of CO2, their 27,000-acre mangrove project in Colombia is the first fully accounted carbon offset credit for a mangrove ecosystem. It sounds almost too tidy. And it is in a lot of ways.
The term “blue carbon,” which was first used a little more than ten years ago to refer to carbon that is absorbed and stored by coastal vegetated ecosystems such as mangrove forests, tidal marshes, and seagrass beds, has quickly gone from being a fringe scientific idea to a hot topic in boardrooms. Despite making up less than 0.2% of the seafloor, these ecosystems store more than half of the biological carbon in the ocean. Approximately 25% of what humans release into the atmosphere annually is absorbed by the ocean. Blue carbon seems like a clear priority based on the numbers. Unfortunately, the reality is much messier.
To put it simply, the regulatory environment surrounding ocean-based climate solutions is a patchwork held together by ambiguity and goodwill. National jurisdictions oversee coastal and estuarine environments, but these jurisdictions further fragment into networks of subnational regimes, such as port authorities, fisheries boards, conservation organizations, and indigenous land tenure claims, which frequently conflict with one another.
The UN Convention on the Law of the Sea, a consensus-driven framework that operates at the slow pace of diplomacy, is supposedly in charge of offshore environments. Up to 200 nautical miles from their coastlines, individual nations retain resource rights, resulting in a legal framework that makes even seemingly simple tasks like restoring seagrass feel like negotiating treaties.
It’s difficult to ignore how much the enthusiasm is still outpacing the science itself. According to McKinsey’s 2022 blue carbon analysis, seagrass, salt marshes, and mangroves, when fully implemented, could reduce CO2 emissions by 0.4 to 1.2 metric gigatons annually. That amounts to between one and three percent of the current yearly emissions. modest but meaningful. The more intriguing figures, which are closer to three gigatons per year, rely significantly on new approaches like bottom trawling management and large-scale seaweed farming, both of which are still up for debate in science. For example, given the intricate biogeochemical cycles that control the movement of carbon through seawater and ocean currents, it is still unclear exactly how avoided bottom trawling lowers atmospheric CO2.
Perhaps more illuminating than any emissions statistic is what researchers at Global Environmental Change recorded in 2024: ocean carbon sequestration has followed decades-long cycles of excitement, controversy, and disappointment. They contend that neither a scientific advancement nor a decrease in uncertainty caused the current surge of interest. New political alliances and changing perspectives on climate solutions were its main drivers. The ocean has emerged as, in a sense, the new frontier for climate optimism because terrestrial solutions seem to be running out. There is a sense that some of the urgency is genuine and some of it is convenient.
This work is intended to be financed by carbon markets, which are mainly based on terrestrial credits. In comparison to their forest counterparts, blue carbon projects are regarded as subscale, high-risk, and costly. Only a small number of projects have qualified since Verra published the first approved blue carbon conservation methodology in 2020, which was a significant advancement. The Blue Carbon Buyers Alliance is making an effort to aggregate demand, but doing so won’t address supply-side issues like contested land tenure, complicated permitting, community consent requirements, and baseline measurement standards that are still up for debate in science.
This does not imply that blue carbon is a dead end. Even flawed projects are worthwhile due to the co-benefits alone, which include biodiversity, fisheries recovery, and coastal protection. However, as this develops in international policy forums, the real ecological promise of these ecosystems and the rate at which governance frameworks can truly catch up are becoming increasingly at odds. For centuries, the ocean has taken in human emissions without expecting anything in return. It might take a lot longer than the climate can wait to figure out how to credit and safeguard that service.
