Soil Carbon Credit Markets: Status and Risks

Soil carbon is the most widely marketed and least standardised category in the agricultural carbon market. The underlying idea is straightforward: a practice that adds organic carbon to soil removes carbon dioxide from the atmosphere, and the removal has a value someone will pay for. The difficulty is that the removal is slow, hard to measure, reversible and invisible, which makes the contract that transfers it unusually complicated.

For a grower the practical questions are narrower than the debate suggests. What is being sold, who owns it, for how long, what happens if the practice is abandoned, and what evidence will be required. This article describes how the market is structured, where the frameworks agree and diverge, and which risks sit with the land manager rather than the buyer.

How the market is organised

Most soil carbon credits are issued in voluntary markets rather than under a compliance obligation. A developer registers a project with a standard-setting body, applies an approved methodology, has the result verified by an independent auditor, and receives credits that can be sold to a buyer wishing to offset emissions or claim a removal. Compliance schemes, where a government creates an obligation, operate in parallel in a smaller number of jurisdictions and set rules that voluntary schemes often follow.

The main voluntary standards with agricultural soil methodologies include Verra's Verified Carbon Standard, which hosts the Improved Agricultural Land Management methodology; Gold Standard, which has a soil organic carbon framework methodology; and the Climate Action Reserve, whose Soil Enrichment Protocol is used mainly in North America. In Australia, the Australian Carbon Credit Unit scheme under the Clean Energy Regulator has issued soil carbon credits from approved methods for several years and is the most developed government-run example. In the European Union, the certification framework for carbon removals creates a system for certifying carbon farming, though it is a certification framework rather than a trading obligation. These standards differ in methodology, baseline setting, commitment length, treatment of reversals and what a buyer may claim, so a credit issued under one is not interchangeable with a credit from another even where both describe the same practice.

What a project actually sells

A soil carbon credit represents one tonne of carbon dioxide equivalent removed from the atmosphere and stored, with a set of conditions attached. Those conditions are where the substance lies.

Additionality asks whether the practice would have happened anyway. If a grower was already planning to plant a cover crop for agronomic reasons, the carbon that results is not additional, and a project claiming it sells something that would have occurred regardless. Most methodologies require a regulatory surplus test, a common practice test or a financial test.

Baseline is the counterfactual against which change is measured, usually modelled from historical management, soil and climate data. The choice of model has a large effect on the number of credits generated, which is why baseline setting is the most contested part of every methodology. Permanence is the requirement that the carbon stay in the soil: agricultural carbon is reversible, and a change of management, a drought or a fire can release what was stored. Standards handle this with commitment periods that commonly run from twenty-five to one hundred years, and with buffer pools, where a share of every project's credits is withheld and used to compensate for reversals elsewhere. Leakage is the risk that the practice displaces emissions rather than reducing them, for example if lower yield on the project land is made up by clearing land elsewhere; most methodologies assume it is small, and most reviewers regard that assumption as one of the weaker parts of the framework.

Measurement, reporting and verification

Verification is where the economics become difficult. Measuring soil carbon credibly requires stratified sampling, georeferenced points, bulk density measurement and laboratory analysis, repeated over the life of the project. At field scale the cost of a sampling round can exceed the value of the credits generated in that period, particularly where the expected rate of change is a fraction of a tonne per hectare per year.

The sector's response has been to combine models with sparse measurement: a process model simulates the carbon balance across the project area, and a sample of fields is measured to calibrate and check it. This reduces cost and is the approach used by most large programmes, but it shifts the evidential weight from measurement to the model, and where the model was calibrated on different soils or a different climate the credits may be real in the model and uncertain in the field. Aggregation schemes group many small farms into one project so that a single verification covers a large area, which opens the market to smaller holdings but leaves the grower with little visibility of how the numbers were produced.

Prices and comparability

Soil carbon credits trade across a wide range of prices, and the range reflects differences in what is being sold rather than differences in the cost of the practice. Credits from projects with long commitment periods, independent measurement and a strong additionality story command more than credits from short-term projects verified mainly by model. Buyers increasingly distinguish removal credits, which describe carbon taken out of the atmosphere, from avoidance credits, which describe emissions that did not happen; soil carbon sits in the removal category only where the accounting genuinely demonstrates a stock increase.

Published price series should be treated with caution. Many transactions are bilateral and undisclosed, registry data shows issuances and retirements rather than prices, and credits traded under different standards are not like for like. Anyone comparing a quoted price with a quoted cost per hectare should establish which standard, which vintage, which commitment period, and whether the price is gross or net of developer fees and verification costs.

Risks for growers

The largest risk is the commitment itself. A project typically requires the practice to be maintained for decades, and the contract may register a covenant on the land or oblige a successor owner to continue. For a grower who may sell or lease the land, or who may need to return to tillage after a difficult season, that obligation can cost more than the credits are worth.

The second risk is reversal liability. If the practice is abandoned, or if drought or fire reduces the stock, the project may be required to replace the lost credits. Buffer pools absorb some of this but not all, and the terms differ between standards, so a grower should establish in writing who is liable and what happens if the loss is caused by weather rather than by a decision.

The third is measurement risk: if a future verification finds less carbon than the model predicted, the project may have to cancel credits already sold, and where the contract allows the developer to recover that from future payments, the land manager carries the consequence of an assumption they did not set. The fourth is market risk: credit prices are not guaranteed, and contracts that fix a price for the commitment period protect against a fall but usually pay less.

Questions to ask before signing

• Which standard and methodology version is the project registered under, and is the registration public?
• What is the commitment period, and what happens if I sell the land or need to change practice?
• Who is liable for a reversal, and what proportion of credits is withheld in the buffer?
• How is the baseline set, and what happens to my credits if it is later revised?
• What is the net payment per hectare per year after all fees, and when is it paid?
• What measurement is done on my land, how often, and will I see the results?
• Can I stack the payment with other schemes, or does the contract exclude them?

Common questions

Is soil carbon farming profitable on its own? For most arable farms, no. Credit revenue per hectare is usually small relative to the crop margin, and the practices that generate it have to be justified agronomically first. Payments work best as secondary income on practices that already make sense.

Can I sell credits from practices I already use? Generally not for the carbon already stored, because that change has happened and is not additional. Some methodologies allow a project to start from the current state and credit future change, provided the practice continues beyond the baseline period.

What happens if I have a drought? A drought can reduce the stock and may trigger a reversal. Most standards allow for this through buffer pools or a temporary reduction in credited amounts, but the treatment varies and should be checked in the contract rather than assumed.

Are these credits accepted by regulated markets? In most jurisdictions, no. Soil carbon credits are predominantly a voluntary instrument, and the rules governing compliance markets, including under Article 6 of the Paris Agreement, are still being defined for agricultural removals.

Recommendations depend on local soil, climate and crop conditions. Follow the product label and local regulations, and consult a qualified agronomist for field decisions. Market rules and scheme eligibility change frequently; confirm current requirements with the standard-setting body before entering a contract.