Strip away the documentation and an afforestation credit is one subtraction. What the project's carbon stocks did, minus what they would have done anyway, minus the emissions the project itself caused, minus what shifted somewhere else. Four terms. Knowing which one dominates tells you where to spend your measurement budget.
The Four Terms
Actual net removals — the change in carbon stocks measured in the project, less greenhouse gas emissions caused by project activities.
Baseline net removals — the change that would have occurred without the project.
Leakage — emissions displaced outside the boundary by the project's existence.
Net anthropogenic removals — what remains, and what gets credited.
| Term | Measured or modelled? | Typical magnitude in ARR |
|---|---|---|
| Actual stock change | Measured | Large |
| Project emissions | Calculated from activity data | Small to moderate |
| Baseline removals | Modelled from land condition | Often near zero on degraded land |
| Leakage | Estimated | Small if land was genuinely unproductive |
Why the Baseline Is Often Small and Why That Matters
On genuinely degraded land with no regeneration trajectory, baseline removals approach zero. This is why ARR on degraded land is attractive: almost the entire measured stock change becomes creditable.
It is also why the evidence that the land was degraded and not regenerating is the single most scrutinised part of an ARR project file. A baseline of zero is a strong claim. If the land was in fact recovering naturally, the project is crediting nature's work.
Historical imagery, ground evidence of the pre-project condition, and a stated reason regeneration was not occurring, such as grazing, fire, compaction, or seed source absence, carry the argument. Assertion alone does not.
Project Emissions Are Not Negligible
The term developers most often underestimate. Site preparation, fertiliser application, fossil fuel use in operations, and biomass burning all sit here.
Nitrogen fertiliser is the one that surprises people: N₂O has roughly 273 times the warming effect of CO₂ per unit mass, so a modest fertiliser programme can offset a meaningful share of early-year sequestration. In a young planting where removals are still small, this term is proportionally largest exactly when it is least expected.
Where the Uncertainty Concentrates
Because errors propagate in quadrature, the largest uncertainty term dominates the total. In most ARR projects that term is the biomass estimate, specifically the allometric model rather than the field measurement.
That has a direct implication for budgets. Adding plots reduces sampling error, which may already be the smaller contributor. Selecting or validating a better-matched allometric equation attacks the larger one. Projects that spend heavily on plot counts while using a generic pan-tropical equation are optimising the wrong term.
The Reporting Discipline
Each term should be traceable to its inputs, and each should be stated with its uncertainty rather than as a bare number. A monitoring report that presents a single net figure without the four components invites the assessor to reconstruct them and reconstruction rarely goes in the project's favour.
Turn climate goals into a verified portfolio
TREEO connects the full carbon cycle, encompassing eligibility, simulation, real time monitoring, and registry ready reporting, thereby combining expert consulting with dMRV technology so the evidence exists before anyone asks for it.
