Voluntary Carbon Markets vs Compliance Carbon Markets in Ocean Context

Two systems price carbon, and they are routinely discussed as if they were two versions of the same thing. They are not. One is a market that exists because governments made emitting expensive by law. The other is a market that exists because organisations chose to pay for something no law required. That difference in origin runs through everything: who participates, what a credit is worth, what counts as rigorous, and which projects can get funded at all.

In an ocean context the distinction becomes sharper still, and in a direction most summaries miss. The ocean appears in these two markets in almost opposite roles. In voluntary markets it appears mainly as supply, as mangroves and seagrass and tidal marsh generating credits for sale. In compliance markets it appears mainly as demand, as a shipping industry now legally obliged to buy allowances for the carbon it emits. Money flows into the ocean through one system and out of it through the other, and the two flows are not connected. Here is how the comparison works, row by row.

 

Meaning

 

A voluntary carbon market is one in which organisations buy carbon credits without being legally required to, in order to support climate action or make a claim about their own emissions. A compliance carbon market is one in which covered entities are legally required to hold and surrender allowances or eligible credits against their emissions.

The word voluntary does a lot of work and can mislead. Participation is voluntary, but the buying is increasingly driven by disclosure regimes, investor pressure, supply chain requirements and net zero commitments that are themselves becoming semi-enforceable. Compliance markets, meanwhile, are not uniformly strict. They vary enormously in coverage, price and whether they permit offsets at all. The clean binary of choice versus obligation describes the legal architecture accurately and the commercial reality only roughly.

 

Ocean Relevance

 

Voluntary markets fund blue carbon projects directly. Mangrove restoration, seagrass conservation and coastal wetland protection all generate credits sold almost exclusively into the voluntary market, because that is where buyers who want a conservation story will pay for one.

The compliance side is where the infographic's framing needs qualifying, because compliance revenue rarely reaches ocean projects and in the largest ocean-relevant system it cannot reach them at all. The European Union Emissions Trading System, which now covers shipping, is a cap and trade scheme built on allowances rather than offsets, and it does not accept project credits. A mangrove project cannot sell into the EU ETS under any circumstances. The compliance markets that do admit blue carbon are narrower and national. Australia is the clearest case: its Clean Energy Regulator established a Tidal Restoration of Blue Carbon Ecosystems method under the Australian Carbon Credit Unit scheme in 2022, crediting projects that reintroduce tidal flow to coastal wetlands by removing tidal restriction structures, over a 25-year crediting period, with abatement modelled through the Blue Carbon Accounting Model rather than physical soil sampling. Credits issued under that method are ACCUs, and ACCUs can be surrendered by facilities regulated under Australia's Safeguard Mechanism. That is a genuine bridge from coastal restoration into compliance demand, and it remains close to unique.

 

Main Driver

 

Voluntary demand is driven by corporate climate commitments, sustainability strategy, brand positioning and the perceived need to address emissions a company cannot yet eliminate. Compliance demand is driven by regulation and the price of non-compliance.

The consequence is that the two markets respond to entirely different signals. Voluntary demand is sentiment-sensitive and reputation-sensitive, which is why it contracted sharply after the integrity controversies of 2023 and why recovery has been uneven. A wave of critical journalism can collapse demand for a credit type in months. Compliance demand does not behave that way. A regulated shipping company facing a surrender obligation in April buys allowances regardless of what was published about carbon markets that year, because the alternative is a penalty. Compliance markets are therefore far more stable, far deeper in liquidity, and far less interested in the qualitative merits of any particular project.

 

Participation

 

Voluntary participation is open. Any organisation can buy, any developer can seek certification under a private standard, and no jurisdiction has to approve the transaction. Compliance participation is mandatory for covered entities and closed to everyone else.

Scope definitions therefore carry enormous weight in compliance systems. The EU ETS maritime extension applies to ships above 5,000 gross tonnage calling at EU ports, covering all emissions on voyages within the European Economic Area and half of emissions on voyages into or out of it. That threshold and that geographic split determine which operators face a cost and which do not, and both are the product of negotiation rather than atmospheric physics. Voluntary markets have no equivalent gatekeeping, which is simultaneously their great advantage in flexibility and their great weakness in rigour.

 

Credits and Units

 

Voluntary markets trade project-generated credits verified under private standards such as Verra, Gold Standard and Plan Vivo. Compliance markets trade government-issued allowances, and in some systems a limited quantity of approved compliance credits alongside them.

The distinction between an allowance and a credit is the most important technical point in the whole comparison and the most commonly blurred. An allowance is a permit to emit, created by a regulator, and its total quantity is capped. A credit is a claim that an emission was avoided or a tonne of carbon removed somewhere else, relative to a counterfactual of what would otherwise have happened. Allowances require no counterfactual, so they raise no additionality question. Credits depend entirely on one, which is why almost every integrity dispute in carbon markets concerns credits rather than allowances. Blue carbon sits squarely in the credit category, and inherits every difficulty that comes with it.

 

Ocean Examples

 

The voluntary example is straightforward: a company buys credits from a mangrove restoration project and claims the associated removals against its own footprint.

The compliance example in an ocean context is shipping, and it has moved fast. From 1 January 2026 the EU ETS maritime phase-in reached 100 percent, after 40 percent in 2024 and 70 percent in 2025, meaning shipping companies now surrender allowances for the full extent of their covered emissions. The same date expanded the system's scope beyond carbon dioxide to include methane and nitrous oxide, with the overall allowance cap raised to reflect the addition and the extra allowances auctioned or directed to the Innovation Fund. The methane inclusion matters commercially, because it narrows the advantage of liquefied natural gas as a transitional marine fuel by capturing the methane slip that engines release unburned.

The global counterpart remains unfinished. The IMO Net-Zero Framework, designed to combine a global marine fuel greenhouse gas intensity standard with a pricing mechanism, as binding amendments to MARPOL Annex VI, failed to secure adoption at an extraordinary session in October 2025. Negotiations were adjourned for a year, with talks scheduled to resume in late 2026. Its delay does not suspend anything in Europe. EU ETS and FuelEU Maritime obligations continued unaffected, which is why shipping is currently governed by a regional compliance price rather than a global one.

 

Key Challenge in Ocean Projects

 

For voluntary blue carbon, the challenges are additionality, permanence, leakage and measurement. For compliance participation, the challenge is meeting regulatory eligibility, accounting and verification standards that were largely not written with coastal ecosystems in mind.

The blue carbon difficulties are worth stating concretely rather than abstractly, because the numbers are sobering. Calyx Global found that as of October 2025 only 10 of 81 blue carbon projects worldwide were actively issuing credits, and that a single project, Delta Blue Carbon-1 in Pakistan's Indus Delta, accounted for roughly 73 percent of all blue carbon credits ever issued. The active projects cover around two million hectares and target roughly 20.4 million tonnes of CO2 in removals annually. A market with one dominant supplier and a long tail of projects that have never issued anything is not yet a market in any meaningful sense.

The reasons are structural. Measuring carbon stored metres deep in waterlogged, anoxic coastal soil is technically difficult and expensive, and the monitoring cost often consumes a large share of what the credits are worth. Permanence is genuinely fragile, because coastal ecosystems sit directly in the path of the sea level rise, storm intensification and marine heatwaves the credits are meant to help mitigate. Additionality is contested wherever a mangrove was already under legal protection, and tenure disputes are common because coastal communities usually hold customary rather than documented rights to the land being credited. Compliance eligibility, by contrast, fails for a simpler reason: most compliance systems either exclude offsets entirely or have never written a methodology that a coastal wetland could satisfy.

 

Primary Goal

 

The voluntary market exists to finance climate action beyond an organisation's own operations. The compliance market exists to reduce regulated emissions in line with law.

These goals are less compatible than they sound. Compliance systems are designed to lower emissions inside a defined boundary, and every tonne that leaves that boundary through an offset weakens the cap. This is precisely why the EU excluded international credits from its ETS. Voluntary markets exist to move money outside the boundary, to places where emissions are unregulated and mitigation is cheap. One system is built to contain, the other to redistribute. Blue carbon is a redistribution instrument, and attempts to fit it into containment systems tend to fail for reasons of design rather than quality.

 

The Asymmetry at the Heart of the Comparison

 

Setting the two columns side by side in an ocean context reveals something the row labels do not.

The ocean's largest and fastest-growing involvement in carbon pricing is not as a source of credits. It is as a regulated emitter. Shipping moves roughly 80 percent of world trade by volume and produces close to 3 percent of global greenhouse gas emissions, and it is now paying a compliance carbon price in Europe on the full scope of its covered emissions. That is, by orders of magnitude, the largest sum of money the ocean economy has ever moved through a carbon market. Blue carbon, by contrast, has produced a credit supply dominated by a single Pakistani project.

The money also flows in opposite directions, and almost none of it circulates. EU ETS maritime revenue accrues to member states and the Innovation Fund. It is not earmarked for mangroves, seagrass or coastal communities. A shipping company paying a European carbon bill is not funding ocean restoration, and a mangrove project in Indonesia is not receiving shipping money. The two ocean carbon stories, one about emission and one about sequestration, are financially disconnected despite occupying the same conceptual frame.

The proposed IMO pricing mechanism is the most credible route to changing that, because a global levy on marine fuel emissions would generate a revenue pool and a live argument about where it should go, including claims from climate-vulnerable coastal states. That argument is one of the reasons adoption stalled. Revenue distribution, not emissions targets, is where the hardest disagreement sits.

 

What the Comparison Really Shows

 

The practical conclusion is that anyone planning an ocean carbon project should design for the voluntary market and treat compliance eligibility as a distant option, while anyone operating ships should plan for compliance costs that are now real, rising and no longer regional in ambition.

Blue carbon's defensible case has also shifted, and honestly so. Coastal restoration delivers storm protection, fisheries nursery habitat, water quality improvement and local livelihoods, and those benefits are more reliable and easier to verify than the carbon accounting attached to them. The more sophisticated end of the market has begun pricing blue carbon on that bundle rather than on tonnes alone, which is a better fit for what these ecosystems actually do. Selling a mangrove primarily as a carbon asset means competing on a metric where it is expensive, difficult to measure and vulnerable to the very climate it is meant to address. Selling it as coastal infrastructure that also stores carbon is both more accurate and, on current evidence, more bankable.

 

Note: This article reflects the state of both markets as of September 2026, drawing on sources including the European Commission's EU ETS maritime provisions, International Maritime Organization proceedings on the Net-Zero Framework, Calyx Global research on blue carbon issuance, Verra and Plan Vivo methodology documentation, and the Australian Clean Energy Regulator's ACCU scheme methods. Carbon market conditions change quickly and figures should be checked against primary sources before use in transactions.