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Claim check

How much carbon dioxide does a tree absorb in a year?

Misleading

The words are defensible; the impression they create is not.

There is no general figure. Uptake varies by more than tenfold with species, size, age and site, and the numbers in circulation are averages over distributions in which a small minority of large trees accounts for most of the total.

The claim as it circulates

“A mature tree absorbs about 22 kilograms of carbon dioxide a year.”

Where you may have met it: Tree-planting campaign materials and offset calculators; School resources and infographics; Corporate sustainability reporting

Taking it apart

What was claimed
That a single quantity of carbon dioxide per tree per year describes what a tree does, and can be multiplied by a number of trees to give a total.
What was actually observed
Urban forest surveys measured trees on field plots across several cities, estimated their mass from allometric equations, and calculated storage and annual sequestration per tree and per unit of canopy cover. The resulting values ranged over more than an order of magnitude between individuals.
What the evidence supports
That carbon uptake by trees can be estimated well for a stand, a city or a country, with the species mix, size distribution, site conditions and method stated. Population-level figures of this kind are used routinely and are meaningful.
What it does not support
A per-tree constant. Uptake scales strongly with size, so a mean across a size distribution describes almost no individual tree. Stripping away the species, the size, the site and the method does not simplify the underlying work — it produces a claim the work does not make.

The arithmetic is what makes this misleading rather than merely imprecise. Because mass rises steeply with diameter, a survey of trees is dominated by its largest few: in typical urban tree populations, a small minority of large trees holds most of the carbon. An average across such a distribution is a legitimate accounting device for the population and a poor description of any member of it. A young birch in a lawn and a two-hundred-year-old oak on good ground differ by far more than a factor of two, and that difference is the answer to the question rather than noise around it.

  • Size dominates everything else: a large tree can add as much mass in one year as a mid-sized tree contains.
  • Species matters through wood density as well as growth rate.
  • Site matters — water, light, nutrients and competition decide how much of the potential is realised.
  • The year matters: a drought year and a good year are different, and a stressed tree can be a net source.
  • Method matters: mass is estimated from diameter using equations whose error is largest for the biggest trees.

None of this is an argument that trees do not take up carbon, or that the quantity cannot be estimated. It is an argument against the one number, which is doing something no measurement in this literature supports.

The claims underneath

Each one carries its own evidence, scope and caveats. Expand any of them to reach the studies.

There is no such thing as the amount of carbon dioxide a tree absorbs in a year.

Well supported

Good evidence backs this, though some details remain open.

Annual carbon uptake by an individual tree varies by more than an order of magnitude with species, size, age, growing conditions and site, and the widely circulated per-tree figures are means over highly skewed distributions in which a small minority of large trees accounts for most of the uptake.

Who this applies to
Any statement of the form "a tree absorbs X kilograms of carbon dioxide a year", however sourced.
Studied in
Tracheophyta

You may have heard

“A mature tree absorbs about 22 kilograms of carbon dioxide a year.”

Figures of this kind descend from averages over urban tree surveys, where uptake per tree ranged over more than an order of magnitude. Quoted without species, size, age and site, the number is not a simplification of that work — it is a claim the work does not make.

Why we rate it this way, and what the caveats are
Well supportedHigh confidence

Both premises are well established: uptake scales strongly with size, and measured populations of trees are dominated in mass by a small number of large individuals. Together they make a single representative figure impossible in principle rather than merely unavailable.

How far it can be extended

The skew is a property of how tree mass scales with size, which holds wherever trees grow.

Caveats

  • This is not an argument that trees take up little carbon, or that estimation is impossible. Estimates are made routinely and well — with the species, size, site and method attached.
  • Population-level figures for a city or a country are meaningful in a way that a per-tree figure is not.

Last reviewed 2026-08-30

The evidence (2 studies)

Big old trees do not stop absorbing carbon. Most of them speed up.

Well supported

Good evidence backs this, though some details remain open.

In repeat measurements of 673,046 individually tagged trees across 403 species, absolute above-ground mass increment increased continuously with tree size for the large majority of species, even though relative growth rate declined.

Who this applies to
Individual trees across tropical and temperate forests; a statement about trees, not about stands.
Studied in
Tracheophyta

You may have heard

“Old trees stop absorbing carbon, so it is better to cut them and plant new ones.”

The first half is wrong at the level of the tree and the second half ignores the stock. A large tree adds carbon faster than a small one, and felling it releases centuries of accumulated carbon that a replacement takes centuries to rebuild.

Why we rate it this way, and what the caveats are
Well supportedHigh confidence

A very large, global, repeat-measurement dataset with a clear result analysed within species. The main uncertainty is in the allometric conversion from diameter to mass, which is weakest for the very largest trees.

How far it can be extended

The pattern was tested within each of 403 species separately across both tropical and temperate plots, so it is not an artefact of comparing species.

Caveats

  • Relative growth does slow: a large tree adds a smaller fraction of itself each year. The absolute quantity is what matters for carbon.
  • An individual result does not scale automatically to a forest, where mortality and decay run against growth.
  • A minority of species do slow in absolute terms.

Still unanswered

  • How far the acceleration continues in the very largest trees, where the mass equations are least well tested.

Last reviewed 2026-08-30

The evidence (2 studies)

Go deeper

Trees and carbon

Almost every gram of a tree came out of the air. What the soil supplied is roughly one per cent of it.

Related things people ask

Last reviewed 2026-08-30