The Policy Gap: Why Kelp Carbon Isn't Counted (Yet)

Kelp forests grow faster than almost any ecosystem on Earth, and there is good evidence that some of the carbon they fix ends up buried or exported to the deep sea for centuries. So why can't a country count a restored kelp forest in its national climate ledger? Why can't a project developer sell a "kelp carbon credit" with the same institutional standing as a mangrove credit? The short answer: the accounting rulebook that underpins all carbon policy — the IPCC's inventory guidelines — hasn't been written for kelp, and until it is, everything downstream sits in a grey zone. This article explains exactly where the gap sits, why it exists, and what would need to change.

If you're new to the terrain, start with our primer on what blue carbon is and the broader map of blue carbon policy. This piece is about one specific crack in the edifice.

The rulebook everything depends on

Almost every serious carbon claim in the world — national inventories, Paris Agreement accounting, regulated offset schemes, corporate net-zero frameworks — traces back to IPCC methodological guidelines. These guidelines tell governments which carbon pools to measure, how to estimate changes in them, and how to report the results in a way that can be compared and reviewed internationally.

The pivotal document for coastal ecosystems was the IPCC's 2013 Wetlands Supplement, which gave governments inventory-grade methods for three "coastal wetland" systems: mangroves, tidal salt marshes and seagrass meadows. Kelp and other seaweed systems were left out.

That omission wasn't a verdict that kelp does nothing for the climate. It reflected the state of the evidence at the time — and in several respects, the state the evidence remains in today. To see why, you have to understand what an inventory method actually requires.

What it takes to be "countable"

For an ecosystem carbon pool to earn a place in national inventories, scientists and policymakers need, at minimum:

1. A defined, measurable stock. You must be able to say where the carbon is, in what form, and measure its quantity within acceptable uncertainty. Mangroves pass because their carbon is largely in situ: wood, roots and deep sediment that you can sample directly.
2. Demonstrated addition and duration. Carbon fixed by the ecosystem must be shown to remain out of the atmosphere for climatically meaningful timescales — typically a century benchmark in crediting systems.
3. Attribution. A country's actions (protection, restoration) must be linkable to a change in the stock, and the stock must sit within the country's accounting boundary.
4. Cost-effective measurement at scale. Methods have to be feasible for national agencies, not just for research cruises.

Kelp struggles on each count — not fatalistically, but structurally.

The stock problem: kelp carbon mostly isn't where the kelp is

A living kelp forest holds carbon in its fronds, but that standing biomass is modest compared with a mangrove's timber and peat — and it turns over continuously. The climate-relevant claim for kelp is about export: fragments of kelp break off, drift, and some fraction ends up buried in sediments or transported to the deep ocean, where it may be sequestered for long periods. We walk through those routes in detail in our piece on kelp sequestration pathways.

The accounting problem is that the carbon's ultimate fate happens somewhere else — possibly hundreds of kilometres away, possibly outside the accounting country's waters entirely. Quantifying the fraction of kelp production that is truly sequestered, and proving where it went, is an active research problem with wide error bars. Estimates in the scientific literature for the sequestered share of seaweed net primary production span a broad range, and the field has yet to converge on transferable values a government could defend in a reviewed inventory.

The boundary problem: whose carbon is it?

International climate accounting assigns emissions and removals to national territories. If a kelp forest off one country's coast exports carbon to deep water beyond the continental shelf, jurisdiction becomes genuinely awkward: the fixation happened inside one boundary, the sequestration outside it. Until the guidelines specify how to treat transboundary export, inventory compilers have no defensible way to book the removal.

The impact problem: can you prove a project changed anything?

Even at project scale, measuring the sequestration attributable to a specific restoration intervention is demanding. Robust MRV for blue carbon depends on baseline data, counterfactuals and long time-series — all harder in open, dynamic kelp systems than in bounded wetlands.

What this grey zone means in practice

The policy gap has concrete consequences:

• No inventory recognition. Countries that restore kelp forests can't currently report the resulting removals toward Paris targets the way they can with mangroves. That removes a powerful motivator for national-scale programs.
• No mainstream credited pathway. Major voluntary standards have been cautious about seaweed methodologies, reflecting the same evidence gaps. Claims that do get made typically rely on bespoke frameworks or on co-benefits rather than certified kelp-carbon tonnes. Our honest take on the claims landscape is in the seaweed carbon debate.
• Policy attention skews elsewhere. Funding follows accountability. Ecosystems that count in inventories attract national restoration programs; those that don't, rely more on philanthropy and frontier buyers.
• A credibility tax on everyone. Because standards are unsettled, overstated kelp-carbon marketing sometimes fills the vacuum — which then hardens scientific scepticism and slows legitimate progress.

Importantly, the gap doesn't mean kelp restoration has no climate value. It means the accounting infrastructure hasn't caught up with the ecology. Those are different claims.

What would close the gap

Researchers and policy groups have converged on a fairly clear agenda:

1. Better fate-of-carbon science. The core empirical need is defensible, region-specific estimates of how much kelp-derived carbon reaches long-term storage — and where. That means tracer studies, sediment sampling, eDNA tracking of kelp detritus, and coupling biological measurements to ocean transport models. It's exactly the kind of open, cross-institutional research that benefits from shared monitoring infrastructure; Tidewright's Canopy Ledger platform publishes its monitoring methods openly for this reason, and our impact methodology documents what we measure and what we deliberately do not claim.

2. Conservative interim accounting. Rather than waiting for perfect science, several proposed frameworks suggest booking only the carbon that can be shown to accumulate in the project's own sediments — a small but measurable fraction — while treating deep-sea export as uncounted upside. Conservative defaults, applied consistently, are how mangrove accounting began getting inventory traction.

3. A chain-of-custody framework for export. For exported carbon, some researchers propose "supply-chain" style accounting: the restoring country counts a conservative, modelled fraction of export as a removal, with deduction factors that grow with transport distance and uncertainty. This requires international agreement — precisely why it sits with the IPCC process rather than any single standard.

4. Non-carbon policy levers in the meantime. Biodiversity credits, fisheries enhancement, coastal protection values and water-quality benefits are all countable with existing frameworks, even where carbon isn't. Smart project design stacks what is accountable today while the carbon methodology matures.

Why the wait is worth doing properly

It's tempting to view the policy gap as bureaucratic inertia. It isn't. Inventory guidelines are conservative because double-counted or phantom removals poison the entire system of international climate accounting. The caution around kelp is the same caution that protects the credibility of the mangrove numbers. When kelp methods do arrive — and the trajectory of the science suggests they will, first for sediment-associated pools, later perhaps for export — they will arrive with the durability that only slow institutional process confers.

The practical advice for anyone working in this space mirrors what we tell our own partners: claim what the science supports today, measure as if the stricter standard already existed, and invest in the monitoring that will make the gap closable. That's the posture behind our blue carbon MRV work — and frankly, it's the only posture that survives scrutiny.

Key takeaways

• Kelp carbon sits outside IPCC inventory guidelines and most crediting standards — not because kelp lacks climate value, but because the accounting methods don't exist yet.
• The blockers are structural: the climate-relevant carbon is exported away from the forest, crosses jurisdictions, and is hard to attribute to any single project.
• Closing the gap requires fate-of-carbon science, conservative interim accounting rules, and international frameworks for exported carbon.
• Credible actors today measure more than they claim, use conservative defaults, and stack countable benefits like biodiversity alongside the uncounted carbon.

FAQ

Why aren't seaweeds included in the IPCC Wetlands Supplement?

When the supplement was drafted, the evidence for long-term sequestration of seaweed carbon — particularly the exported fraction — was considered too uncertain and too spatially diffuse to support inventory-grade methods. Reviews since then have noted the science is improving, and researchers continue to argue for inclusion in future updates, but as of now there is no agreed method.

Does that mean kelp restoration isn't worth doing for the climate?

No. The gap is in the accounting, not necessarily in the effect. Kelp restoration also delivers biodiversity, fisheries and coastal benefits that are valuable in their own right. The point is that carbon claims should match what can currently be measured and defended.

Can companies buy "kelp carbon credits" today?

Some project developers sell seaweed-linked credits under proprietary or emerging frameworks, but buyers should treat these very differently from established wetland credits: ask what fraction of the claimed carbon is demonstrably stored, where, and under whose methodology. Our buyer's guide to blue carbon credits lists the questions to put to any seller.

How long until kelp carbon is officially countable?

There is no fixed timetable — it depends on scientific convergence and the pace of IPCC methodology updates, which operate on multi-year cycles. Sediment-based accounting under restored forests is the likeliest first tractable step; full export accounting is a longer-term prospect.

What can project developers do right now?

Measure sediment carbon at their sites, document baselines and counterfactuals, publish methods openly, and frame claims conservatively. When credible standards arrive, projects with years of transparent monitoring will be the first to qualify.