The baseline is the carbon trajectory that would have occurred without the project. It cannot be measured, but only argued, and because credits are the difference between baseline and measured project carbon, the baseline determines revenue as directly as the measurement does.
Four Ways to Construct One
| Approach | Basis | Strength | Weakness |
|---|---|---|---|
| Historical extrapolation | Past loss rates in a reference region | Simple, data-available | Reference region choice drives the answer |
| Modelled projection | Drivers of change projected forward | Handles changing conditions | Model assumptions carry the argument |
| Jurisdictional allocation | Landscape risk allocated centrally | Consistent, hard to game | Little project discretion |
| Matched control areas | Comparable unprotected areas tracked live | Empirically grounded | Finding true matches is difficult |
The direction of travel across standards is from the first toward the third. The reason is straightforward: project-selected reference regions produced defensible-but-divergent baselines for neighbouring projects, which is indefensible when viewed from outside.
The Conservativeness Requirement
Standards require baselines to be conservative, meaning where uncertainty exists, the assumption should understate rather than overstate the project's benefit.
This is not merely ethical framing. A baseline that an assessor finds optimistic attracts discounting, and the discount is applied to the whole crediting stream rather than to the disputed portion. Conservative baselines cost credits upfront; optimistic ones cost more later.
Why Baseline Choice Interacts With Sampling
Credits are a subtraction, so uncertainty compounds across both terms.
If the baseline is externally set and the project's own estimate is imprecise, the entire uncertainty burden sits on the project side, and the conservative deduction takes its share from the only number the project controls.
That is the practical reason methodological rigour on the project side has become more valuable as baselines have moved outside project control, not less.
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