01 — Two different jobs
The popular claim that kelp "sequesters more carbon than trees" sounds like a knockout fact. It isn't — because it quietly mixes up two different things: how fast carbon is captured, and how durably it is stored. Pull those apart and the giant kelp vs trees carbon question gets a far clearer, more honest answer.
Does kelp capture more carbon than trees?
On rate of capture, kelp is hard to beat. Giant kelp (Macrocystis pyrifera) is among the fastest-growing organisms on Earth. In good conditions it can grow on the order of tens of centimetres a day — figures up to roughly 30 to 60 centimetres a day are commonly cited — and can climb from a deep reef all the way to the surface in a single season. A forest of trees, by contrast, takes decades to mature. So per unit area, kelp forests are extraordinarily productive and take up carbon far faster than trees. If the question is purely about carbon capture rate, kelp can genuinely outpace a forest.
That is the real, defensible part of the kelp carbon vs forests story. It is also why kelp is such an exciting tool for rapid ecosystem recovery — a stripped reef can be rebuilt into a living forest within a season or two, not a human lifetime.
Where the comparison breaks down: durable storage
Capturing carbon fast is not the same as locking it away. This is where the popular claim falls apart. Trees build carbon into wood and soils on land, where much of it stays for decades to centuries and can be measured relatively directly. Kelp is a different story: it grows attached to rock, not in soil, and it is not buried where it lives. For kelp carbon to count as durable storage, a meaningful share of it has to be exported and sunk into the deep sea, away from the surface where it would otherwise be eaten, decomposed, or returned to the atmosphere.
And here's the honest catch: exactly how much kelp carbon ends up durably sequestered in the deep ocean — and how reliably that can be measured and verified — is still genuinely debated among scientists. The capture is real and fast; the long-term storage is real but uncertain in scale. Treating the two as the same thing is where "kelp beats trees" becomes a claim the evidence doesn't yet support.
- Speed
- Kelp captures carbon far faster — up to tens of cm of growth a day. Trees take decades to mature.
- Where the carbon goes
- Trees: into wood and soil on land, in place. Kelp: must be exported and sunk to the deep sea to be stored.
- Durability
- Trees lock carbon for decades to centuries, relatively measurable. Kelp's long-term storage is real but its scale is debated.
The honest takeaway
Giant kelp is a remarkable, fast carbon capturer and an extraordinary ecosystem builder. But it is not a proven, like-for-like replacement for the carbon storage that forests provide. The two are complementary, not interchangeable — kelp does the fast, regenerative work in the water; forests do the durable, measurable storage on land. We avoid the tidy headline that kelp definitively sequesters more carbon than trees, because the science simply doesn't back it as a fact yet.
- Capture rate: kelp wins clearly — it grows and takes up carbon far faster than trees.
- Durable storage: trees are the safer bet today, with carbon held in wood and soil that's easier to measure.
- Both matter: the climate needs fast capture and durable storage — and rich ecosystems besides.
Kelp's value also goes well beyond a carbon ledger: it rebuilds biodiversity, supports fisheries and buffers coastlines. Those benefits stand whatever the final word on deep-sea storage turns out to be — which is part of why a healthy kelp coast like the Great Southern Reef is worth restoring.
Where Ocean Greens fits
We restore kelp because of what it does well: rapid regrowth, returning biodiversity, coastal protection and carbon drawdown. We're upfront that the long-term storage side of macroalgae carbon is still being worked out, so we don't sell kelp as a swap for forests or as a finished carbon-offset story. You can read more on our kelp restoration work and on the wider seaweed climate solution.
Common questions
Does giant kelp grow faster than trees?
Yes. Giant kelp (Macrocystis pyrifera) is among the fastest-growing organisms on Earth — on the order of tens of centimetres a day in good conditions, commonly cited up to roughly 30–60 cm/day. It reaches the surface in a single season, while trees take decades. As a rate of carbon capture per area, kelp can far outpace a forest.
Does kelp store more carbon than trees?
Not in a proven, like-for-like way. Capturing carbon fast isn't the same as storing it durably. Trees lock carbon into wood and soil for decades to centuries, where it's relatively measurable. Kelp grows on rock and isn't buried in place, so its durable storage depends on how much carbon is exported to the deep sea — a figure that's genuinely debated.
Why is kelp carbon storage uncertain?
Because kelp isn't buried where it grows. For its carbon to count as durable storage, a meaningful share must sink and stay locked in the deep ocean rather than being eaten, decomposed near the surface, or returned to the atmosphere. How much actually reaches deep-sea storage — and how reliably that can be measured — is still being worked out.
Should we plant kelp instead of trees?
No — it's not an either/or choice. Kelp captures carbon fast and rebuilds rich coastal ecosystems; forests provide durable, measurable storage on land. They're complementary, not interchangeable. Restoring kelp is worthwhile alongside protecting forests, not instead of it.