The forestry carbon offset market is built on a straightforward premise: plant trees, measure how much carbon they sequester, issue credits representing that sequestration, and sell those credits to companies offsetting their emissions.

In principle, it’s elegant. In practice, the measurement challenge is enormous, and the precision implied by carbon credit certificates is often illusory.

I’ve worked with forestry projects across Victoria and New South Wales. The gap between the marketed certainty of carbon accounting and the actual uncertainty of forest carbon measurement is substantial. Here’s why.

The Basic Challenge

Carbon stored in forests exists in multiple pools: above-ground biomass (trunks, branches, leaves), below-ground biomass (roots), soil organic carbon, and dead organic matter (litter and deadwood). Measuring each pool accurately across large forest areas is technically difficult and expensive.

Most forestry carbon projects use allometric equations — mathematical models that estimate biomass based on tree measurements like diameter at breast height and tree height. You measure a sample of trees, apply the equations, and extrapolate to the entire forest stand.

This works reasonably well for plantation forests with uniform species and age. It’s much less accurate for mixed-species native forests with variable structure, age, and composition.

The Uncertainty Margins

Published research on forest carbon measurement uncertainty typically reports error margins of 10-30% for above-ground biomass estimates in well-studied forest types. For less-studied ecosystems or forests with high structural diversity, uncertainty can exceed 50%.

A 2024 study in the journal Environmental Research Letters compared carbon stock estimates from different methodologies applied to the same forest plots. The estimates varied by up to 40% depending on the allometric equations used, the sampling strategy, and the assumptions about wood density and carbon content.

That level of uncertainty is rarely reflected in the carbon credits issued. A project might issue 10,000 tonnes of credits with an implied precision to the tonne, when the actual measurement uncertainty could easily be ±2,000 tonnes.

Baseline and Additionality Problems

Carbon credits are supposed to represent emissions reductions that wouldn’t have happened otherwise — the concept of additionality. For forestry projects, this means comparing the carbon stored in the project scenario against a baseline scenario representing what would have happened without the project.

Constructing defensible baselines is fraught with assumptions. What would have happened to the land without the carbon project? Would it have been cleared? Left to regenerate naturally? Used for agriculture? The answer affects the credit calculation by orders of magnitude.

Conservative baseline assumptions reduce the number of credits but increase confidence that they represent genuine additionality. Optimistic assumptions boost credit volumes but risk issuing credits for carbon storage that would have happened anyway.

The incentives favour optimistic baselines. Project developers get paid per credit, and purchasers want more credits per dollar. Independent verification is supposed to catch inflated baselines, but verifiers work for the project proponents, creating a structural conflict of interest.

Permanence and Leakage

Forest carbon is impermanent. Bushfires, disease, illegal logging, or policy changes can release stored carbon back to the atmosphere. Carbon credit standards attempt to address this through buffer pools (a percentage of credits withheld to cover unexpected losses) and permanence obligations (legal commitments to maintain the forest).

But the risks are difficult to quantify. What’s the probability of a catastrophic bushfire over a 100-year permanence period? Climate change is increasing fire frequency and intensity in Australian forests. How do you price that risk into today’s credit issuance?

Leakage is another challenge. If a carbon project prevents logging in one area, does that logging simply shift to another area, resulting in no net emissions reduction? Accounting for leakage requires system-level analysis that’s rarely done rigorously.

The Verification Problem

Third-party verification is supposed to ensure that carbon projects meet the requirements of the relevant standard (Verified Carbon Standard, Gold Standard, Australian Carbon Credit Units scheme). Verifiers audit project documentation, check measurements, and assess whether credits have been correctly calculated.

But verification is a sampling process. Verifiers don’t measure every tree or check every calculation. They review a subset of data, assess the methodology, and certify compliance based on that sample.

I’ve seen verification reports that flag methodological issues or data gaps but still certify the project because the issues don’t exceed the threshold for non-compliance. The credits get issued, but the underlying uncertainties remain.

Real-World Example: Blue Gum Plantations

Blue gum (Eucalyptus globulus) plantations in southwestern Australia are a common carbon offset project type. The growth rates are well-understood, the allometric equations are robust for this species, and plantation management is straightforward.

Even here, actual carbon accumulation varies significantly based on site quality, rainfall, pests, and management. A plantation established in 2020 might project 200 tonnes of CO2 sequestered by 2030, but actual performance could range from 150 to 250 tonnes depending on conditions.

Credits are typically issued annually based on growth projections and periodic measurements. If actual growth underperforms projections, are credits clawed back? Some standards require this; others don’t. The result can be an overestimation of net sequestration.

The Policy Context

Australia’s carbon credit market operates under the Emissions Reduction Fund and the Safeguard Mechanism, both administered by the Clean Energy Regulator. The framework has evolved significantly since its introduction, generally in the direction of tighter requirements and more conservative crediting.

But political and economic pressures push in the opposite direction. Land holders want carbon projects to be financially attractive. Companies buying offsets want abundant supply to keep prices low. Project developers want streamlined approval and generous credit calculations.

These pressures don’t invalidate carbon forestry, but they do create risks that measurement standards get loosened to accommodate market demand rather than tightened to reflect genuine uncertainty.

What Should Be Done

Wider confidence intervals. Carbon credits should explicitly incorporate measurement uncertainty. Instead of issuing 10,000 credits, issue 8,000 credits that reflect a conservative estimate with higher confidence. The current system implies false precision.

Better baseline standards. Default baseline assumptions should be conservative and regularly updated to reflect actual land use trends, not hypothetical worst-case scenarios that maximize credit issuance.

Larger buffer pools. The percentage of credits withheld to cover permanence risks should be higher, especially for projects in fire-prone landscapes or politically unstable regions.

Independent verification funding. Verifiers should be paid by the credit purchasers or a central fund, not by project developers. This removes the conflict of interest inherent in developer-funded verification.

Post-issuance monitoring. Credits should be subject to retrospective adjustment if subsequent monitoring shows that projected sequestration didn’t occur. This creates accountability for optimistic projections.

The Bottom Line

Forestry carbon projects can deliver genuine climate benefits. Trees do sequester carbon. Reforestation and avoided deforestation are essential components of climate mitigation.

But the current carbon offset market often treats these projects with a level of certainty that the underlying science doesn’t support. The measurement uncertainties are real, the permanence risks are real, and the verification gaps are real.

Companies buying forestry carbon offsets should understand that they’re buying something more uncertain than the certificates suggest. A tonne of forest carbon is not equivalent to avoiding a tonne of fossil fuel emissions — it’s probabilistic, it’s impermanent, and it’s less precisely measured than marketed.

For those evaluating whether and how to participate in carbon markets, the message is: proceed with caution, favour conservative methodologies, and don’t treat carbon credits as a perfect substitute for actual emissions reductions.

The forest carbon is real. The accounting is approximate. Keep that distinction in mind.