Carbon markets come with their own language. If you’ve ever tried to read a project methodology document, a certification report, or even a news article about carbon credits, you’ve probably hit a wall of unfamiliar terms.
This glossary covers the 20 terms that come up most often, defined simply and without the jargon. Bookmark it, and you’ll be able to navigate the voluntary carbon market with confidence.
The Core Concepts
Carbon credit. The fundamental unit of the carbon market. One carbon credit represents one metric tonne of CO₂ equivalent (CO₂e) that has been reduced, removed, or avoided. Credits are issued on registries, assigned unique serial numbers, and retired permanently when purchased. For a deeper look at how credits and offsets differ, see our guide to carbon offsets vs. carbon credits.
Carbon offset. A carbon credit purchased voluntarily to compensate for your own emissions. When you buy an offset, you’re funding a project that reduces or removes an equivalent amount of CO₂ on your behalf. Offsets exist in the voluntary carbon market, not the compliance market. Our complete guide to carbon offsets covers how they work from start to finish.
CO₂ equivalent (CO₂e). A standard unit that expresses the warming impact of different greenhouse gases in terms of the equivalent amount of CO₂. Methane, for example, is roughly 80 times more potent than CO₂ over a 20-year period. CO₂e allows all greenhouse gases to be measured and traded on a common scale.
Additionality. Perhaps the most important concept in carbon markets. A project is “additional” if the emissions reductions it achieves wouldn’t have happened without the financial support from carbon credits. If a forest was already legally protected and never at risk of being logged, a credit claiming to protect it isn’t additional. If a cookstove program only exists because carbon revenue makes it financially viable, it is. Additionality is what ensures that credits represent real, new climate action, not things that would have happened anyway.
Baseline (or reference scenario). The emissions trajectory that would have occurred without the project. To calculate how much carbon a project saves, you need to know what the alternative was. The baseline is that counterfactual. Establishing a credible baseline is one of the harder technical challenges in carbon project development, and one of the things independent verifiers scrutinize most closely.
Permanence. Carbon reductions need to stay reduced. A forest that sequesters carbon for five years and then burns down hasn’t delivered permanent climate benefit. High-quality projects address permanence risk through buffer pools: reserves of unissued credits held back to cover losses. If a project suffers a setback, credits are drawn from the buffer rather than asking buyers for a refund.
Leakage. When a project prevents deforestation in one area but drives it somewhere else, that’s leakage. A protected forest that pushes logging activity to an adjacent valley hasn’t actually saved the net carbon it claims. Good project methodologies account for leakage risk and discount credits accordingly.
Verification and Standards
Verified Carbon Standard (VCS). The most widely used voluntary carbon standard in the world, operated by Verra. Projects certified under VCS go through an independent audit before credits can be issued. The VCS registry publicly tracks every credit issued and retired. Many Cool Effect projects carry VCS certification.
Gold Standard. A voluntary certification standard established by the Gold Standard Foundation, with a particular focus on sustainable development co-benefits. Gold Standard-certified projects must demonstrate positive impacts on communities and ecosystems beyond carbon reduction. Often used for clean energy and clean cookstove projects.
American Carbon Registry (ACR). One of the oldest voluntary carbon registries in the US, run by Winrock International. Certifies projects primarily in North America but increasingly internationally. ACR is approved as an offset program under California’s cap-and-trade system. More at americancarbonregistry.org.
Climate Action Reserve (CAR). A US-based standard focused on North American emissions reduction projects, with a strong emphasis on rigorous quantification protocols. CAR protocols are publicly available and well-regarded for their technical quality. More at climateactionreserve.org.
Retirement. When a carbon credit is retired, it’s permanently removed from the registry and can never be sold or used again. Retirement is the moment a credit fulfills its purpose: the emissions reduction it represents is officially claimed by the buyer. Every credit Cool Effect sells is retired in the buyer’s name.
Project Types
Nature-based solutions (NbS). Carbon projects that work with natural carbon cycles rather than technology. Forests, wetlands, soils, and grasslands all store carbon, and protecting or restoring them generates carbon credits. Nature-based solutions often deliver significant co-benefits for biodiversity and local communities. Read about tree-planting projects in Kenya, mangrove restoration in the Sundarbans, and peatland conservation for real examples.
Blue carbon. Carbon stored in coastal and marine ecosystems: mangroves, seagrasses, and salt marshes. “Blue” refers to the ocean context. Blue carbon ecosystems store carbon at very high densities compared to terrestrial forests, primarily in waterlogged soils where organic matter decomposes slowly. When these ecosystems are degraded, that stored carbon is released rapidly.
REDD+. Reducing Emissions from Deforestation and Forest Degradation. A mechanism that compensates developing countries and project developers within them for protecting forests that would otherwise be cleared. The “+” refers to additional activities like sustainable forest management and carbon stock enhancement. REDD+ projects are among the most common nature-based offset projects globally.
Soil carbon (or soil organic carbon). Carbon stored in the organic matter of agricultural soils. Healthy soils hold roughly three times as much carbon as the atmosphere above them. Practices like cover cropping, reduced tillage, and managed grazing can rebuild soil carbon that industrial agriculture has depleted, generating credits while also improving soil health, water retention, and crop yields. Our Fertile Ground project is a detailed example of this approach.
Emissions Accounting
Scope 1, 2, and 3 emissions. A framework for categorizing where an organization’s greenhouse gas emissions come from. Scope 1 covers direct emissions from sources the organization owns or controls: a factory’s combustion, a company’s fleet. Scope 2 covers indirect emissions from purchased energy like electricity, heat, and steam. Scope 3 covers all other indirect emissions in the value chain: supply chain, business travel, employee commuting, use of sold products, and more. For most companies, Scope 3 is the largest category and the hardest to reduce directly, which is part of why high-quality offsets matter.
Carbon neutral. A state in which the net carbon emissions from an entity (person, company, product, or event) are zero. Typically achieved by reducing emissions as much as possible and then offsetting the remainder with verified credits. The term has varying definitions across different certification bodies, so it’s worth checking what standard is being used when you see a “carbon neutral” claim.
Net zero. A more ambitious target than carbon neutral, typically applied to organizations or economies. Net zero means reducing emissions across all scopes to as close to zero as possible, then removing any residual emissions through carbon removal. Science-based net-zero targets usually require deep, real-world reductions rather than primarily offset purchases before claiming the label.
Co-benefits. The positive effects of a carbon project beyond carbon reduction. A forest protection project might protect biodiversity, secure watershed function, and provide income to local communities. A cookstove project reduces indoor air pollution, lowers wood fuel costs for families, and often specifically benefits women and children who spend the most time near cooking fires. Co-benefits are not secondary features. For Cool Effect, they’re a core part of what makes a project worth supporting.
Want to go deeper? Our guide to how carbon offsets work covers the full picture. And when you’re ready to put these terms into practice, browse our verified projects. Every one of them has been vetted against the standards described here.