Article 6 and the Ocean: Where Blue Carbon Meets the Paris Agreement

When the Paris Agreement was signed in 2015, one of its most contested provisions was Article 6 — the rulebook for how countries can cooperate on climate targets and trade carbon across borders. It took six years of fraught negotiation before the rulebook was finalised at Glasgow in 2021, and several more before the details gelled. Yet Article 6 is now quietly operational, and it's beginning to touch the ocean. If you've read our broader blue carbon policy explainer, this article goes one level deeper: how Article 6's mechanics actually work for ocean carbon, what's already happened, and what it changes for buyers, projects and coastal nations.

The Core Problem Article 6 Solves

Climate policy has a geographic mismatch: emissions happen everywhere, but the cheapest, highest-impact reduction opportunities aren't evenly distributed. A tonne of CO₂ removed by a mangrove restoration in Southeast Asia delivers the same atmospheric benefit as one reduced by an industrial retrofit in Europe — but the former might cost a tenth as much. Article 6 exists to let money flow to wherever the atmosphere benefits most, without losing integrity along the way.

The integrity problem is simple and ancient: if Country A pays Country B for a removal, both countries might be tempted to count it. Country B wants it in its inventory; Country A wants it toward its own target. One tonne, two claims. Article 6's central mechanism — the corresponding adjustment — exists to make that impossible.

The Two Tracks: 6.2 and 6.4

Article 6.2: Direct deals between countries

Article 6.2 governs cooperative approaches — bilateral or mini-lateral arrangements in which one country buys mitigation outcomes from another. The traded unit is an ITMO (Internationally Transferred Mitigation Outcome), measured in tonnes of CO₂ equivalent.

The mechanics in practice:

1. Authorisation. The selling country formally authorises the transfer, specifying what the ITMOs can be used for — another country's NDC, an international scheme like the airlines' CORSIA, or voluntary corporate claims.
2. Corresponding adjustment. The seller adds the transferred tonnes back to its own emissions ledger; the buyer subtracts them from theirs. The atmosphere sees one tonne; the bookkeeping sees one tonne. No double count.
3. Tracking. Both countries report through UNFCCC infrastructure (an international registry and a central accounting platform), with reviews by technical expert teams.

Early Article 6.2 deals have been modest but real: Switzerland has been a first-mover buyer, signing cooperation agreements with several countries; Ghana, Singapore, Thailand and Japan have all moved into pilot trades. Most early deals involve renewable energy, waste and land use. Ocean trades — blue carbon removals from mangrove or, eventually, seaweed systems — are pending on methodologies, but coastal nations are positioning for them.

Article 6.4: The centralised crediting mechanism

If 6.2 is a farmers' market of bilateral deals, Article 6.4 is the stock exchange. It succeeds the Kyoto-era Clean Development Mechanism, but with tighter integrity rules. A Supervisory Body under the UNFCCC:

• Approves methodologies (the technical rulebooks for measuring and verifying outcomes)
• Registers projects and issues A6.4 emission reductions ("A6.4ERs")
• Oversees a registry where credits retire

Methodologies move slowly but deliberately. Early candidates are landfill gas, cookstoves, and afforestation. Blue carbon methodologies — mangrove first, seaweed later — are in active development. The pace is its own form of rigor: a 6.4 methodology has to survive multilateral scrutiny that a private standard doesn't.

What Article 6 Means for Blue Carbon Specifically

The ocean is late to Article 6 — not because of hostility, but because the measurement infrastructure is younger than the forests'. Still, the physics are compelling:

• Mangroves and saltmarsh are already inventory-grade. Their carbon pools and fluxes are covered by IPCC guidance (the 2013 Wetlands Supplement), which means a country in principle can count them in its inventory and can sell corresponding adjustments across borders. This is why blue carbon advocates have been pushing for mangrove-rich countries to mainstream wetland accounting into NDCs.
• Seagrass is close behind, with measurement methods maturing rapidly.
• Kelp and seaweed systems remain outside the inventory accounting consensus — the carbon cycle is too complex, the permanence too contested (see our honest accounting of where kelp carbon goes), and the deep-sea export pathway too new. If and when methodological confidence firms, Article 6 provides the scaffolding.

The strategic implication for a coastal nation: become as fluent in Article 6 as your natural capital deserves. Countries with extensive mangrove, marsh or seagrass are holding tradeable climate assets. The nations moving first — Indonesia, the Seychelles, several Caribbean states — are building legal and technical capacity so that when demand arrives, they're not starting from paperwork.

Authorisation: The Decision That Shapes Everything

A subtle but pivotal feature of Article 6 is that authorisation is a sovereign choice. A country can authorise:

• ITMOs for use toward another country's NDC (with corresponding adjustment — highest integrity, often lower price)
• Units for CORSIA airline compliance
• Units for voluntary corporate use (which may or may not carry a corresponding adjustment; the "no-CA" voluntary unit remains contentious)

This creates a two-tier market reality. A mangrove credit with corresponding adjustment fetches a premium because the buyer can make stronger claims (it's "Paris-aligned"). A no-CA credit is cheaper but can't be used toward national targets and sits less comfortably under net-zero claims. Buyers doing careful due diligence — see our buyer's guide — now routinely ask what the underlying authorisation status is.

What Article 6 Asks of Project Developers

For restoration developers like Tidewright, Article 6 changes the design constraints in concrete ways:

1. Inventory alignment. A project feeding an Article 6 pipeline needs its methodologies consistent with national inventory practice, not just a private standard.
2. Conservative baselines. Corresponding adjustment puts the host country's own NDC on the line, creating strong incentives for conservative crediting — good for integrity, humbling for volume projections.
3. Long-term country relationships. Host governments become quasi-shareholders in outcomes. The transactional "project sells credit, buyer leaves" model gives way to decades-long partnerships with states, councils and traditional owners. Frankly, we think that's healthy: restoration is long work, and Article 6 structurally rewards staying.

Our Canopy Ledger monitoring platform was designed with this in mind: the same satellite, drone and diver-verify data can support a voluntary credit issuance and, if a host country moves into Article 6 cooperation, inventory-consistent reporting. Restoration built to market standard from the start doesn't have to be rebuilt when policy matures.

The Frictions to Watch

Article 6 is not a panacea, and ocean projects should enter it with open eyes:

• Speed. Multilateral method development moves at diplomatic pace. If your project needs carbon revenue this year, the voluntary market is faster — see the trade-offs in our markets explainer.
• Share of proceeds. Article 6.4 levies charges (a percentage of issued credits directed toward adaptation funding in vulnerable countries). That's a feature, not a bug — but it nets against project revenue.
• Methodology gaps. Some blue-carbon-relevant activities (avoided degradation, sediment carbon flux accounting in dynamic coasts) lack approved methods entirely.
• Geopolitics. Corresponding adjustments are politically sensitive — you're literally selling a slice of your NDC headroom. Elections can unravel agreements.

What's Actually Next for Ocean Article 6

Three realistic developments to watch over the next few years:

• First blue-carbon 6.2 trades between mangrove-rich sellers and net-import nations, likely from Southeast Asia and West Africa
• A first Article 6.4 coastal methodology, probably mangrove or general tidal-wetland, after which a wave of projects qualifies
• Seaweed carbon policy movement — the gap we describe in our kelp policy explainer won't close quickly, but research investment (including our own open data contributions) is building the evidence base

Key Takeaways

• Article 6 is the Paris Agreement's carbon trading rulebook: 6.2 enables bilateral deals (ITMOs), 6.4 a centralised UN crediting mechanism.
• The corresponding adjustment is the lynchpin against double counting: when a country sells a removal, it adds it back to its own ledger.
• Mangrove and blue-carbon wetland systems are inventory-grade and tradeable; kelp and seaweed remain outside the consensus for now.
• Authorisation is sovereign. Credits carry different claims depending on whether the host country authorised them with or without a corresponding adjustment.
• For developers, Article 6 shifts the game toward inventory alignment, conservative baselines and long-term country partnerships — a structure we think is genuinely good for ocean restoration.

FAQ

What is the difference between an ITMO and a regular carbon credit?

An ITMO is a mitigation outcome formally authorised by its host country under Article 6, with a corresponding adjustment preventing double counting. Regular voluntary credits are issued by private standards and may or may not carry authorisation. ITMOs command premium value because they carry stronger claims integrity.

Can a private company buy ITMOs directly?

Typically no — ITMOs move at the country level under 6.2. Companies can buy authorised credits under 6.4 or via brokers where host countries have authorised voluntary use. The buying question is always: what was authorised, and does that fit my claim?

Does Article 6 apply to ocean carbon now?

In principle, for mangrove, saltmarsh and (soon) seagrass — the pools are covered by IPCC guidance. For kelp and seaweed systems, the inventory accounting isn't mature enough yet. Policy movement is expected as methods improve.

What is a corresponding adjustment in plain terms?

Bookkeeping honesty for carbon trades. If Ghana sells a tonne of removal to Switzerland, Ghana adds that tonne back to its emissions ledger and Switzerland subtracts it from its own. The atmosphere benefits once; the books balance once.

Will seaweed ever be covered by Article 6?

Plausibly, yes — but on the order of years, requiring better permanence science, standardised measurement, and IPCC-cycle endorsement. We cover the gap and the path in The Policy Gap: Why Kelp Carbon Isn't Counted (Yet).