How Carbon Markets Work | Carbon Pricing, ETS, Carbon Credits and Article 6

A tonne of carbon dioxide can be a molecule, a measurement, a tax liability, a tradable allowance, a carbon credit, an internationally transferred mitigation outcome or a retired environmental claim.

The physical gas does not change when the vocabulary changes. The institution around it does.

Carbon markets are systems that attach economic value, compliance obligations or tradable claims to measured greenhouse-gas emissions reductions, removals or permissions to emit.

The purpose is to turn part of the climate problem into an economic signal: emitting can carry a cost; reducing emissions can create value; scarce emissions allowances can be traded; verified mitigation outcomes can become credits; and international transfers can be recorded under agreed rules.

That sounds simple. It is not.

A market only works as well as the unit being traded. If the tonne is badly measured, non-additional, reversible, double counted or claimed by several parties, the price can be real while the climate value is not.

This is why carbon markets sit on top of carbon accounting. Accounting defines and measures the tonne. Markets decide what economic or compliance role that tonne can play.

Wait, what? A carbon allowance and a carbon credit are not the same thing

This distinction is the first gate.

An allowance normally represents permission to emit a defined amount under a cap-and-trade or emissions-trading system.

A carbon credit generally represents a verified emissions reduction or removal generated by an eligible activity under a crediting methodology.

One originates from a regulated emissions cap. The other originates from a mitigation activity measured against a baseline or removal methodology.

Both can be denominated in tonnes of CO₂e. That does not make them economically or legally interchangeable.

The direct answer

Carbon markets work through several distinct mechanisms:

Carbon tax: government sets the price per tonne; emitters decide how much to reduce.
Emissions trading system: government sets or controls the emissions quantity; the market discovers the allowance price.
Crediting mechanism: verified reductions or removals against a defined methodology generate credits.
Compliance market: regulated entities surrender eligible units to meet legal obligations.
Voluntary market: organisations buy and retire credits for voluntary climate claims under relevant standards and claims rules.
International carbon market: mitigation outcomes can move across national borders under bilateral systems or Paris Agreement Article 6 rules.

The market architecture decides which units exist, who can issue them, who can use them, how they move, how they are retired and what claims they support.

Carbon pricing is broader than carbon credits

Carbon pricing includes several policy instruments that place an explicit price on greenhouse-gas emissions.

The World Bank’s State and Trends of Carbon Pricing 2026 reports 87 carbon-pricing policies globally and just over 29% of global greenhouse-gas emissions covered by direct carbon pricing.

These instruments include carbon taxes and emissions-trading systems. Carbon crediting mechanisms sit alongside them and can feed compliance or voluntary demand depending on jurisdiction and rules.

Carbon markets are therefore not one global exchange. They are a network of policy systems, registries, standards and trading arrangements with different units and eligibility rules.

Carbon tax: price is set first

A carbon tax sets a monetary charge per tonne of covered greenhouse-gas emissions.

A simplified liability is:

taxable emissions × carbon-tax rate = tax liability.

The regulator knows the price. The quantity of emissions reduction emerges from how businesses and consumers respond.

A company will compare the cost of reducing one more tonne against the tax it avoids by reducing that tonne.

If abatement costs less than the tax, reduction becomes economically attractive. If it costs more, the company may pay the tax—unless regulation or other constraints require the reduction anyway.

Marginal abatement cost

Marginal abatement cost is the cost of reducing one additional unit of emissions.

Different actions have different marginal costs:

fixing a steam leak may save money;
installing efficient motors may have modest cost;
electrifying a furnace may require major capital;
capturing the last difficult process emissions may be expensive.

A carbon price changes the order in which these projects become economic.

The market logic is not “every company must use the same technology”. It is “each emitter faces a common carbon cost and chooses among available responses within the rules”.

Emissions trading system: quantity is controlled first

An emissions trading system, or ETS, establishes a regulated emissions quantity and creates allowances that covered entities must surrender for their emissions.

One allowance commonly represents permission to emit one tonne of CO₂e under that system’s rules.

The regulator decides the cap or allowance supply. The market then discovers the price.

This reverses the carbon-tax architecture:

carbon tax: price known, emissions quantity uncertain;
ETS: emissions quantity constrained, allowance price uncertain.

The cap

The cap determines the scarcity of allowances.

If allowance supply is generous relative to emissions, prices can be low.

If the cap tightens while demand remains strong, allowance prices can rise.

The environmental ambition of an ETS therefore depends mainly on the emissions trajectory established by the cap and related rules—not on whether trading exists.

Allowances can be auctioned

Governments can sell allowances through auctions.

Auctioning creates a transparent price-discovery mechanism and can raise public revenue.

Companies bid according to expected compliance needs and abatement opportunities.

Revenue use varies by jurisdiction and can support general budgets, household measures, industry transition, infrastructure or climate programmes.

Allowances can also be allocated for free

Some ETSs allocate part of the allowance supply without auction payment.

Free allocation can be used to manage competitiveness and carbon-leakage concerns for trade-exposed industries.

Allocation design matters. Giving free allowances based purely on historical emissions can reward past pollution. Benchmark-based allocation can instead connect allocation to output and performance standards.

Free allocation does not necessarily remove the opportunity cost of emissions. An allowance used for compliance could otherwise sometimes have been sold or banked, depending on system rules.

Banking

Banking allows participants to save unused allowances for future compliance periods.

Banking can smooth prices and reward early abatement. A company that reduces emissions ahead of schedule can preserve allowances for later use.

But excessive banking can weaken near-term scarcity if too many surplus allowances accumulate.

Borrowing

Borrowing allows future allowances to be used earlier under some systems.

It can improve flexibility but risks shifting compliance forward without delivering early reductions.

For that reason, borrowing is often limited or prohibited.

Price collars, floors and reserves

Pure cap-and-trade can produce volatile prices.

Some systems introduce stabilising mechanisms such as:

auction reserve prices;
cost-containment reserves;
market-stability reserves;
allowance-supply adjustments;
price ceilings or soft ceilings.

These instruments create a hybrid between pure quantity control and pure price control.

Carbon tax versus ETS

Neither mechanism is universally superior.

A tax offers price predictability. An ETS offers direct quantity control under its cap. Both require accurate emissions measurement and enforcement.

The appropriate design depends on policy objectives, sector structure, administrative capacity, market concentration, political institutions and tolerance for price volatility.

This article explains mechanisms rather than ranking political choices.

Crediting mechanism: the unit begins with a baseline

Carbon credits usually emerge from a different architecture.

A project, programme or activity estimates what emissions would have occurred without the intervention. This becomes the baseline or reference scenario under an approved methodology.

The project then measures actual emissions or removals.

A simplified crediting equation is:

baseline emissions − project emissions − required deductions = credited reduction.

For removals, the calculation instead needs to establish net atmospheric CO₂ removed and durably stored under the relevant methodology.

The baseline is the invisible half of every credit

A project’s measured emissions can be real while the credit quantity is still wrong if the baseline is unrealistic.

Suppose a factory emits 60 tonnes after an efficiency project.

If the credible baseline was 100 tonnes, the project reduced 40.

If the baseline was exaggerated to 150 tonnes, the same factory appears to reduce 90.

The physical plant did not change. The claimed credit quantity doubled because the counterfactual changed.

This is why baseline rules are central to market integrity.

Additionality

A carbon credit is intended to represent mitigation that would not have occurred without the incentive or framework that supports the credited activity.

This is additionality.

The Integrity Council for the Voluntary Carbon Market’s Core Carbon Principles describe additionality as requiring credited reductions or removals that would not have occurred without the carbon-credit incentive.

Under the Paris Agreement Crediting Mechanism, UNFCCC also maintains specific methodological requirements and a 2026 standard for demonstrating additionality.

Additionality is difficult because the counterfactual world cannot be observed directly.

Common additionality tests

Methodologies can use combinations of:

investment analysis;
regulatory-surplus tests;
common-practice analysis;
barrier analysis;
standardised positive lists;
technology penetration thresholds;
performance benchmarks.

No test is perfect. The aim is to reduce the risk of issuing credits for activity that would have happened anyway.

Over-crediting

Over-crediting occurs when more credits are issued than the real climate benefit justifies.

Possible causes include:

inflated baselines;
weak additionality;
measurement error;
ignored leakage;
unaccounted project emissions;
overestimated permanence;
incorrect activity data.

A market can be liquid and financially active while still over-crediting. Trading volume does not prove environmental quality.

Under-crediting

Crediting systems can also be conservative.

A project might reduce 100 tonnes but receive only 80 credits because the methodology applies uncertainty discounts or conservative parameters.

Conservativeness can protect environmental integrity but may reduce project revenue.

Market design therefore balances measurement confidence against investment incentive.

Leakage

Leakage occurs when an activity reduces emissions inside the project boundary but causes emissions to increase elsewhere.

Examples:

protecting one forest pushes logging to another;
restricting production at one plant shifts production to a dirtier plant elsewhere;
land-use changes displace agriculture into another region.

Crediting methodologies may require leakage deductions or broader system boundaries.

Permanence

Some reductions are effectively permanent once they occur. Others can reverse.

A tonne of fossil CO₂ never emitted is different from a tonne stored temporarily in trees.

Forest carbon can return through fire, disease or harvest. Soil carbon can be lost if management changes. Geological storage has different long-term risks and monitoring systems.

High-integrity crediting systems therefore need explicit reversal-risk rules.

The physical owner remains How Carbon Dioxide Removal Works.

Buffer pools

Some programmes manage reversal risk by withholding a percentage of credits in a pooled buffer.

If a participating project suffers a qualifying reversal, buffer units can be cancelled.

A buffer pool is an insurance-like accounting mechanism. It does not prevent a physical reversal.

MRV

Measurement, reporting and verification are the measurement backbone of carbon markets.

A crediting programme needs to know:

what was measured;
what was estimated;
which methodology applied;
what baseline was used;
what monitoring period applies;
what uncertainty exists;
who checked the claim.

Carbon Accounting owns the general MRV measurement layer. Carbon Markets uses that evidence to decide whether a market unit can be issued.

Validation versus verification

Validation typically assesses whether a project design and methodology application meet programme requirements before or during registration.

Verification typically examines monitored results after implementation to determine whether claimed reductions or removals occurred as reported.

The precise terminology depends on the programme, but the broader principle is consistent: project design and achieved outcome are separate evidentiary questions.

The registry

A carbon registry is the ledger that tracks market units and their status.

A registry can record:

project registration;
methodology;
monitoring period;
verification;
credit issuance;
serial numbers;
account ownership;
transfers;
cancellations;
retirements;
authorisations and labels.

The registry does not create the physical climate benefit. It creates traceability for the claim.

Serialisation

Credits are commonly issued with unique identifiers or serial ranges.

Serialisation helps prevent one unit from being transferred or retired twice inside the same registry system.

Interoperability becomes more complex when several registries and national accounting systems interact.

Issuance

Issuance is the creation of market units after required evidence has been accepted.

Issuance should happen only after the programme is satisfied that the credited quantity meets its methodology and verification rules.

Issuing credits before mitigation occurs is economically different from issuing them after verified performance. Forward contracts can finance projects, but a promise of future credits is not the same as an already issued verified unit.

Transfer

A credit can move from one registry account to another.

Ownership transfer does not necessarily mean the unit has been used for a climate claim.

A trader can buy and resell. A company can hold inventory. A government can acquire units for future compliance.

Retirement

Retirement permanently removes a unit from circulation for a defined use or claim.

A retired credit should not return to the market for another buyer to use again.

The retirement record is therefore part of claim integrity.

Cancellation

Programmes can cancel units for reasons other than ordinary retirement.

Examples can include buffer-pool compensation, administrative correction or regulatory treatment.

The registry status matters because “issued”, “held”, “retired” and “cancelled” are not interchangeable.

Vintage

Vintage usually identifies the period in which the underlying emissions reduction or removal occurred.

A 2021 credit and a 2026 credit can represent the same nominal tonne but face different eligibility rules, methodologies and market demand.

Newer standards can therefore create price differentiation by vintage.

Compliance carbon markets

Compliance markets exist because law or regulation creates an obligation.

A covered entity may need to surrender allowances, pay a carbon tax, surrender eligible credits or use some combination depending on the jurisdiction.

The regulator determines eligibility.

A credit valuable in one compliance system may be unusable in another.

Voluntary carbon markets

Voluntary carbon markets allow organisations to purchase and retire carbon credits outside a legal surrender obligation.

Demand can come from corporate climate strategies, product claims, internal carbon programmes or other voluntary commitments.

Because government does not necessarily define one universal eligibility standard, voluntary markets depend heavily on programme rules, independent standards, buyer due diligence and claims guidance.

High-integrity carbon credits

Credit quality is multi-dimensional.

The Integrity Council for the Voluntary Carbon Market’s Core Carbon Principles emphasise programme governance, transparency, independent validation and verification, additionality, permanence, robust quantification, no double counting, safeguards and contribution toward a net-zero transition.

A high price does not prove all of these characteristics. A low price does not automatically prove their absence.

Price and integrity are related through buyer demand, but they are not the same variable.

Credit quality is not a single score

Two credits can differ in:

additionality;
baseline conservativeness;
measurement precision;
permanence;
reversal risk;
co-benefits;
host-country authorisation;
claims eligibility;
methodology maturity;
registry transparency.

Buyers should therefore understand the underlying project and methodology rather than treating every tonne as fungible.

Reduction credit versus removal credit

A reduction credit represents emissions reduced or avoided relative to a baseline.

A removal credit represents atmospheric carbon removed and stored under an eligible removal methodology.

The physical climate functions differ.

A company deciding how to counterbalance residual fossil emissions may care especially about storage durability and removal quality, while another buyer may seek emissions-reduction finance in a sector where avoidance remains the relevant intervention.

Nature-based credits

Nature-based projects can involve forest conservation, reforestation, soil carbon, mangroves and other ecosystem pathways.

They can deliver biodiversity and community co-benefits, but may face:

baseline uncertainty;
leakage;
fire and reversal risk;
land-tenure complexity;
measurement uncertainty.

Project design therefore needs safeguards beyond carbon arithmetic.

Engineered removal credits

Engineered removals such as direct air capture with geological storage can be highly measurable and durable but currently expensive and energy-intensive.

Biochar and mineralisation occupy other positions on the cost-durability spectrum.

The physical removal framework belongs to How Carbon Dioxide Removal Works. Carbon markets determine how verified tonnes can become tradable units.

Double issuance

Double issuance occurs when more than one credit is created for the same underlying mitigation outcome.

Strong registries and methodology controls are designed to prevent this.

Double use

Double use occurs when the same unit is used more than once—for example, if a retired unit somehow re-enters circulation.

Registry retirement and account controls address this risk.

Double claiming

Double claiming is more subtle.

A host country can count an emissions reduction toward its national climate target while another country or company also claims that same outcome for a purpose requiring exclusive attribution.

This is one reason Article 6 uses authorisation and corresponding-adjustment concepts for international transfers.

Paris Agreement Article 6

Article 6 creates frameworks for voluntary cooperation among countries in implementing their nationally determined contributions.

Three broad parts matter:

Article 6.2: cooperative approaches involving internationally transferred mitigation outcomes, commonly called ITMOs;
Article 6.4: a UN-supervised crediting mechanism under the Paris Agreement;
Article 6.8: non-market approaches.

This article focuses on the market-related 6.2 and 6.4 layers.

Article 6.2

Article 6.2 provides accounting guidance for countries that cooperate and transfer mitigation outcomes internationally.

These transfers require tracking, reporting and corresponding adjustments under the applicable rules.

The important point is that Article 6.2 is not one central global project standard. Countries can cooperate through bilateral or plurilateral approaches while meeting common Paris accounting requirements.

ITMOs

Internationally transferred mitigation outcomes are mitigation outcomes authorised for international transfer and use under Article 6.2 rules.

They can be measured in tonnes of CO₂e or certain other metrics under the guidance.

Because ITMOs interact with national climate targets, international transfer requires accounting beyond ordinary voluntary-credit retirement.

Corresponding adjustments

A corresponding adjustment prevents the same mitigation outcome from counting simultaneously toward incompatible national claims.

UNFCCC guidance explains the basic logic: the exporting country adjusts its emissions balance to reflect the transferred mitigation outcome, while the acquiring country reflects the acquisition according to the Article 6 rules.

Corresponding adjustments do not rewrite the physical national greenhouse-gas inventory. They adjust the accounting balance used to track NDC implementation and achievement.

This distinction is crucial: the physical tonne remains where it occurred; the international accounting treatment determines who can use the mitigation outcome toward specified goals.

Article 6.4

Article 6.4 establishes the Paris Agreement Crediting Mechanism under UN supervision.

The system includes methodologies, activity registration, validation and verification requirements, a mechanism registry and governance by the Article 6.4 Supervisory Body.

As of September 2026, the UNFCCC Article 6.4 mechanism has approved methodologies and methodological tools, including current work on baseline setting, additionality, leakage and removals. Its mechanism registry procedure was updated in July 2026, with an interim registry user guide updated in September 2026.

This matters because Article 6.4 is moving from rulemaking into increasingly operational infrastructure.

Methodologies are the rulebook behind each tonne

A credit methodology tells a project how to calculate eligible mitigation.

It can define:

project boundary;
baseline;
additionality test;
monitoring equipment;
sampling;
leakage treatment;
uncertainty;
crediting period;
reversal safeguards;
calculation equations.

The credit itself is therefore the end product of a methodology, measurement and verification chain.

Methodology risk

A project can follow a methodology perfectly and still face criticism if the methodology later proves too generous.

Carbon markets therefore need methodology revision processes.

New science, market conditions and technology can change what counts as common practice or a credible baseline.

Crediting period

A crediting period defines how long an activity can generate credits under a particular approval or baseline structure.

Long crediting periods can improve financeability but risk locking in outdated baselines.

Shorter periods allow recalibration but reduce revenue certainty.

Vintage and methodology version can affect value

Buyers increasingly distinguish credits by project type, methodology, vintage, verification, host authorisation and claims eligibility.

This is why carbon credits do not trade like perfectly identical commodities even when every unit is labelled one tonne CO₂e.

Carbon-credit prices vary because the units are not truly identical

The World Bank’s 2026 carbon-pricing review notes variation in credit prices and continuing premiums for certain categories, including some credits eligible for international aviation use and highly rated forest projects.

Price differences can reflect:

integrity perceptions;
compliance eligibility;
project type;
removal versus reduction;
durability;
co-benefits;
vintage;
liquidity;
buyer demand.

A tonne is therefore both a quantified climate unit and a market instrument with attributes.

Spot markets

Spot transactions exchange existing units for near-term delivery.

They provide price discovery for credits or allowances already available.

Forward contracts

A forward contract commits buyer and seller to a future delivery.

This can help finance new projects by providing expected future revenue.

The buyer assumes delivery and methodology risk. The seller gains demand certainty.

Futures and derivatives

Some mature compliance carbon markets support futures, options and other derivatives.

These instruments can help companies hedge future allowance-price risk.

They can also attract financial participants and increase liquidity.

The economic details belong to Finance. Here the important energy-system function is risk management around future carbon cost.

Liquidity

A liquid market has enough buyers and sellers that units can trade without every transaction causing large price movements.

Liquidity improves price discovery.

But liquidity alone says nothing about environmental integrity. A low-quality unit can trade actively.

Market fragmentation

Carbon markets are fragmented because different systems use different:

eligibility rules;
methodologies;
vintages;
claims frameworks;
registries;
national authorisations;
compliance obligations.

Fragmentation can reduce liquidity but preserve policy autonomy.

Interoperability can improve efficiency but requires trust in each other’s measurement and integrity rules.

Carbon border measures and embedded emissions

As carbon pricing expands, trade increasingly interacts with carbon-accounting data.

A border mechanism can depend on the embedded emissions of imported products and the carbon price already faced in the exporting jurisdiction.

This makes product-level carbon accounting economically material.

Carbon Accounting owns the measurement. Carbon Markets owns the price signal and tradable instruments built on top of that measurement.

Internal carbon pricing

Companies can use an internal carbon price even when no external tax or allowance obligation applies.

Common forms include:

a shadow price used in investment analysis;
an internal fee charged to business units;
an internal trading system;
a target cost used for scenario planning.

Internal carbon pricing is not a public carbon market. It is a management tool that imports carbon value into internal decisions.

The carbon-price signal reaches technology choices

A carbon price can alter the economics of:

energy efficiency;
renewable electricity;
electrification;
hydrogen;
carbon capture;
low-carbon materials;
fuel switching;
industrial process redesign.

But the response depends on the alternatives available.

A high carbon price cannot instantly create a technology that does not yet exist at scale. A low carbon price can still influence low-cost efficiency measures.

Carbon price and carbon intensity interact

If two products face the same carbon price but one has half the emissions intensity, the lower-carbon product has a smaller carbon-cost burden per unit.

This is how carbon accounting becomes a competitive variable.

For example, low-carbon steel can carry a lower embedded-carbon liability than conventional steel under some policy designs.

Carbon markets can finance mitigation—but only if revenue reaches the activity

A carbon-credit price can help a project become financially viable.

But the value chain can include:

project developer;
local landowner or community;
methodology costs;
validation and verification;
registry fees;
brokers;
exchanges;
financiers;
taxes;
buyer.

Gross credit price and net project revenue can therefore differ materially.

Transaction costs

Small projects can struggle because measurement and verification costs do not scale down perfectly.

Programme aggregation, digital MRV and standardised methodologies can reduce transaction cost.

But automation should not weaken evidence quality merely to make issuance cheaper.

Digital MRV

Sensors, satellite data, smart meters, remote sensing and digital registries can shorten the path from physical measurement to verified market unit.

Digital systems can improve audit trails and reduce manual error.

They do not eliminate methodological judgement. A satellite image still needs a model translating observed land cover into carbon stocks.

Singapore as a carbon-market case

Singapore combines a domestic carbon tax with a limited pathway for eligible international carbon credits.

According to Singapore’s National Environment Agency, the carbon tax applies to covered industrial facilities emitting at least 25,000 tonnes CO₂e annually. The rate is S$45 per tonne for emissions years 2026 and 2027.

Eligible taxable facilities can use qualifying international carbon credits for up to 5% of taxable emissions under the International Carbon Credit Framework, subject to eligibility rules.

This creates a layered mechanism:

facility emissions are measured under the Carbon Pricing Act MRV framework;
tax liability is calculated;
domestic abatement remains the primary route for most emissions;
a limited portion can be met with eligible international credits;
eligible credits must satisfy Singapore’s integrity and Article 6-related requirements.

The case demonstrates how carbon tax, carbon accounting and international credit markets can coexist without being the same instrument.

Singapore’s Article 6 connection

Singapore’s International Carbon Credit Framework requires eligible international credits to meet criteria linked to environmental integrity and Article 6 cooperation.

The Ministry of Sustainability and the Environment explains that eligible credits used under the framework require host-country authorisation for corresponding adjustment, helping prevent double counting against national climate targets.

By May 2026, Singapore reported 11 implementation agreements and project application calls in several partner countries, while noting that eligible credit supply takes time to develop.

This is what an international carbon market looks like in practice: treaties and accounting rules become project pipelines, registries, authorisations and compliance options.

Worked example 1: carbon tax decision

A factory faces a carbon tax of $45 per tonne and is considering an efficiency project.

The project costs the equivalent of $18 per tonne avoided over its life.

If the accounting boundary and operating assumptions are sound, the project can reduce both fuel expenditure and carbon-tax liability.

The carbon price changes the investment case without specifying which efficiency technology the factory must choose.

Worked example 2: ETS allowance choice

Two factories face the same ETS.

Factory A can reduce emissions for $20 per tonne.

Factory B’s next reduction costs $90 per tonne.

If allowances trade at $50, Factory A has an incentive to reduce more and potentially sell or bank surplus allowances, while Factory B may prefer to buy allowances for its expensive residual emissions.

Trading moves abatement toward the lower-cost opportunity while the cap controls total allowance supply.

Worked example 3: forest credit baseline

A forest project claims that without carbon finance, 10,000 hectares would be cleared.

Independent evidence later suggests only 4,000 hectares faced credible deforestation risk.

The project may still protect real forest, but the original baseline can overstate credited climate benefit.

The lesson: credit integrity depends on the counterfactual, not only what happened inside the project boundary.

Worked example 4: direct-air-capture removal

A DACCS project removes and geologically stores 10,000 tonnes of atmospheric CO₂.

After deducting lifecycle emissions, 8,800 tonnes qualify under the applicable methodology.

The programme verifies the monitoring period and issues 8,800 removal credits.

The registry gives each unit a unique identity. A buyer purchases 1,000 and retires them.

The project created the physical removal. The market converted verified removal into finance and a traceable claim.

Worked example 5: Article 6 transfer

Country A authorises a mitigation outcome for transfer to Country B under an Article 6 cooperative approach.

The outcome is tracked as an internationally transferred mitigation outcome under the relevant rules.

Country A applies the required corresponding adjustment when accounting for its NDC. Country B accounts for the acquisition under the applicable Article 6 framework.

The purpose is to prevent both countries from using the same mitigation outcome toward incompatible national claims.

Worked example 6: Singapore tax plus ICC

A Singapore taxable facility emits 100,000 tonnes CO₂e.

Under the normal 5% ICC limit, up to 5,000 eligible international credits can potentially be used for the relevant tax obligation, subject to the detailed rules and any applicable rollover treatment.

The remaining taxable emissions continue to face the domestic carbon-tax framework.

The policy design therefore makes international credits a limited compliance option rather than a complete substitute for domestic decarbonisation.

Failure mode: allowance mistaken for credit

A company describes an ETS allowance as though it represented a verified project reduction.

Repair: distinguish permission-to-emit units from credited mitigation units.

Failure mode: baseline inflation

A project exaggerates what would have happened without the project.

Repair: use conservative baselines, current data and independent review.

Failure mode: non-additional project

A profitable project that was already fully committed receives credits for activity that would have occurred without carbon revenue.

Repair: apply the methodology’s additionality requirements honestly and update common-practice tests as markets change.

Failure mode: reversal ignored

A forest project issues long-lived climate claims but has no credible response if carbon later burns.

Repair: use permanence requirements, monitoring, buffers or other approved reversal mechanisms.

Failure mode: one tonne claimed twice

A host country counts a reduction toward its NDC while a buyer uses the same outcome for a claim requiring exclusive international attribution.

Repair: use the relevant authorisation, corresponding-adjustment and claims rules.

Failure mode: registry entry treated as proof of quality

A buyer assumes any serialised credit is automatically high integrity.

Repair: examine methodology, baseline, additionality, verification, permanence, safeguards and claims eligibility—not merely registry existence.

Failure mode: high price treated as proof of quality

A premium credit is assumed to be environmentally superior solely because it costs more.

Repair: price is a market signal, not an integrity audit.

Failure mode: cheap credits replace easy internal reductions

A company buys credits while ignoring efficiency upgrades that are cheaper and within its direct control.

Repair: separate internal abatement strategy from external credit use and follow the claims framework or compliance rules that apply.

Failure mode: voluntary credit subtracted from inventory without accounting basis

A company reports Scope 1–3 emissions, buys credits, then silently rewrites the inventory total downward.

Repair: keep the greenhouse-gas inventory and credit-retirement claim distinct unless the applicable standard explicitly permits a particular accounting treatment.

Failure mode: methodology never updates

A renewable project remains credited as additional long after the technology becomes ordinary business practice.

Repair: revise baselines, additionality rules and methodology eligibility as markets mature.

Failure mode: market liquidity mistaken for climate effectiveness

A heavily traded credit category is assumed to deliver strong mitigation because transaction volume is high.

Repair: evaluate environmental performance independently of trading activity.

Common misconceptions

Carbon tax and emissions trading are different pricing architectures.
An allowance is not the same as a carbon credit.
A carbon credit is only as strong as its baseline, additionality, quantification, permanence and MRV.
A registry records units; it does not prove their physical quality by itself.
Retirement is different from ownership transfer.
Vintage can affect eligibility and value.
Compliance and voluntary markets use different obligations and eligibility rules.
A reduction credit and a removal credit perform different climate functions.
High credit price does not automatically prove high integrity.
Corresponding adjustments affect international accounting balances rather than rewriting the physical national GHG inventory.
Article 6.2 and Article 6.4 are different cooperation architectures.
Carbon credits should not be casually netted against corporate inventories without an applicable accounting basis.
Market liquidity is not the same as environmental integrity.
A carbon price influences technology economics but does not guarantee that every sector has an immediate low-cost substitute.

A universal carbon-market audit

Identify the instrument: tax, ETS allowance, credit, ITMO or other unit.
Identify the legal or voluntary framework.
Define the tonne or metric precisely.
Check the underlying greenhouse-gas accounting standard.
For ETS units, inspect cap trajectory and allowance supply.
Check auction and free-allocation rules.
Check banking, borrowing and market-stability rules.
For credits, identify methodology and version.
Test baseline quality.
Test additionality.
Measure project emissions and leakage.
Assess permanence and reversal controls.
Review validation and verification.
Check registry issuance.
Check serial numbers and ownership.
Check vintage.
Check compliance or claims eligibility.
Check host-country authorisation where relevant.
Check corresponding-adjustment treatment where relevant.
Check for double issuance, double use and double claiming.
Verify retirement before making a retirement-based claim.
Separate credit price from integrity assessment.
Separate corporate inventory accounting from external credit use.
Review community and environmental safeguards where relevant.
Reassess methodology and market rules as standards evolve.

The deepest carbon-market principle

Carbon markets do not create climate benefit by trading pieces of data.

The climate benefit happens in the physical world:

a tonne is not emitted;
a factory changes process;
methane is destroyed;
a forest remains standing because the intervention genuinely changed behaviour;
carbon dioxide is removed from air and stored durably.

The market exists to attach economic value and traceable ownership to that physical change.

If the physical change is weak, the market cannot repair it.

If the physical change is strong but the registry and accounting are weak, the market can misallocate the claim.

The deepest rule is therefore: a carbon unit must be economically tradable only after it is environmentally definable, measurable and uniquely claimable.

How Carbon Markets fits the Energy series

How Carbon Accounting Works owns inventories, CO₂e, Scope 1–3, lifecycle emissions, carbon intensity and MRV. How Carbon Dioxide Removal Works owns physical atmospheric removal and durability. How Carbon Capture Works, How Carbon Dioxide Transport Works and How Geological Carbon Storage Works own the physical CCUS chain. This article owns the economic coordination layer: carbon taxes, emissions trading, allowances, carbon credits, registries, retirement and international Article 6 transfers.

Finance retains financial disclosure, securities analysis and investment valuation. Carbon Markets explains how carbon units and prices are created and governed before they become inputs to those financial decisions.

Current evidence and further reading

The final lesson is simple: carbon markets work only when the tonne is stronger than the trade.

How Energy Works | Main Series

How Carbon Markets Work | Carbon Pricing, Emissions Trading, Carbon Credits, Registries and Article 6