Carbon terminology and conversions

Glossary of terms

The following presents a glossary of terms we use when referring to forest carbon concepts, measurements, and markets. 

Aboveground biomass: All living biomass above the soil, including stems, stumps, branches, bark, seeds, and foliage.[1]

Biomass: Organic material, living or dead, such as trees, crops, grasses, tree litter, and roots.

The FIA defines biomass as “The aboveground weight of wood and bark in live trees 1.0 inch (2.5 cm) DBH and larger from the ground to the tip of the tree, excluding all foliage. The weight of wood and bark in lateral limbs, secondary limbs, and twigs under 0.5 inch (1.3 cm) in diameter at the point of occurrence on sampling-size trees is included but is excluded on poletimber and sawtimber-size trees. Biomass is typically expressed as green or oven-dry weight and the units are tons.”[2]

Belowground biomass: All living biomass of live roots, except for roots too small to be distinguished empirically from soil organic matter, and the below-ground part of the stump.[3]

Carbon budget: An assessment of carbon sinks and sources; OR the amount of carbon dioxide emissions deemed permissible based on such an assessment.[4]

Carbon credit: A standardized unit equal to one metric ton of CO₂ or CO₂e that has been reduced, avoided, eliminated, or sequestered instead of emitted. Carbon credits are often used in the calculation of a carbon budget or carbon footprint.[5]

Carbon cycle: The processes by which carbon moves between the atmosphere, oceans, and living things.[6]

Carbon dioxide (CO₂): A naturally occurring gas of one part carbon and two parts oxygen. It is produced as a by-product of burning biomass and fossil fuels. The IPCC describes CO₂ as “the principal anthropogenic greenhouse gas (GHG) that affects the Earth’s radiative balance.”[7]

Carbon dioxide emission: Release of CO₂ into the atmosphere.[8]

Carbon dioxide equivalent (CO₂e or CO₂eq): A measure used to compare emissions of different greenhouse gases by standardizing them against CO₂. This value is calculated by determining the global warming potential (GWP) of a gas across a 100-year time horizon and comparing it to the equivalent amount of CO₂ that would have the same GWP across that horizon.[9]

Carbon flux: Fluctuations of CO₂ in the atmosphere, oceans, and land. [10]

Carbon market: A system to reduce GHGs by putting a price on carbon and trading carbon credits.[11]

Carbon offset: Reducing sources of GHGs, or increasing storage of GHGs, to compensate for other GHG emissions.[12]

Carbon pool: A part of a system that can store, accumulate, or release carbon. Five carbon pools are commonly used to describe forest carbon pools: aboveground biomass, belowground biomass, soil, litter, and dead wood.[13]

Carbon registry: – An independent authority that approves, lists, and tracks a carbon credit’s ownership.[14]

Carbon sequestration: The process of storing carbon in a carbon pool. For example, plants sequester carbon by using photosynthesis to convert carbon dioxide into plant biomass.[15]

Carbon sink: A source that removes CO₂ from the atmosphere.[16]

Carbon source: A source that places CO₂ into the atmosphere.

Carbon stock: The quantity of carbon in a reservoir or system which has the capacity to accumulate or release carbon.[17]

Carbon tax: A fee for GHG emissions, usually levied on companies rather than individuals, states, or countries.[18]

Cost-benefit analysis (CBA): A monetary assessment of all negative and positive impacts associated with a given action. A CBA can enable comparison of different interventions, investments or strategies and reveal how a given investment or policy effort pays off for a particular person, company or country.[19]

Down woody material (DWM): Dead material on the ground in various stages of decay. It includes coarse and fine wood material. The FIA includes the duff layer, litter layer, residue piles, and overall fuel bed as part of the DWM category.[20]

Dead wood biomass: Carbon in all non-living woody biomass not contained in the litter, either standing, lying on the ground, or in the soil. Dead wood includes wood lying on the surface, dead roots, and stumps.[21]

Emissions trading:  An approach to reducing GHG emissions through the economic market. A cap or limit is set on the total amount of allowable emissions, and companies can trade “shares” of these emissions through buying and selling of permits.[22]

Greenhous gas (GHG): Gaseous components of the atmosphere that absorb and emit radiation emitted by the Earth’s surface, the atmosphere, and by clouds. This trapping of radiation resembles the way greenhouses trap heat, hence the name greenhouse gas. Some examples of greenhouse gases are carbon dioxide (CO₂), nitrous oxide (N₂O), methane (CH₄), and hydrofluorocarbons (HFCs). [23]

Land use: Land use refers to the total of arrangements, activities and inputs undertaken in a certain land cover type (a set of human actions). In national greenhouse gas inventories, land use is classified according to the IPCC land use categories of forest land, cropland, grassland, wetland, settlements, and other.[24]

Land-use change: Land-use change involves a change from one land use category to another. For example, forest land that has been converted to agricultural land.[25]

Life cycle assessment (LCA): Compilation and evaluation of the inputs, outputs and the potential environmental impacts of a product or service throughout its life cycle.[26]

Litter: all non-living biomass (undecomposed or only partially decomposed) above the mineral or organic soil.[27]

Soil carbon: Organic carbon in mineral and organic soils (including peat).[28]

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Carbon Units & Conversions

1 lb = 0.453592 kg

2,000 lbs = 1 US ton

1 megagram (Mg) = 1 metric ton

1 metric ton = 1.10 US tons

1 teragram = 1 million metric ton (MMT)

1 lb/acre = 1.120851 kg/ha

1 ton/ac = 2.2417 Mg/ha

1 unit C = 3.667 units CO₂ equivalent

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Sources

Cool Effect. “Important Definitions in the Carbon Market.” Cool Effect. 6 Aug 2021. https://www.cooleffect.org/important-definitions-in-the-carbon-market  Accessed 15 Jan 2022.

Forest Inventory and Analysis. “Forest Inventory and Analysis Glossary.” Forest Inventory and Analysis: Northern Research Station. 22 June 2016. https://www.nrs.fs.fed.us/fia/data-tools/state-reports/glossary/ Accessed 14 Jan 2022.

Forest Resources Assessment Programme. “Global forest resources assessment update 2005: Terms and Definitions.” 2005. https://www.fao.org/3/ae156e/AE156E03.htm#TopOfPage Accessed 14 Jan 2022.

IPCC, 2018: Annex I: Glossary [Matthews, J.B.R. (ed.)]. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. https://www.ipcc.ch/site/assets/uploads/sites/2/2019/06/SR15_AnnexI_Glossary.pdf Accessed 16 Jan 2022.

Texas A&M Forest Service. “Carbon Market Simplified Glossary.” Texas Forest Service. 2013. https://tfsweb.tamu.edu/uploadedFiles/TFSMain/Data_and_Analysis/Contact_Us(3)/CarbonMarketSimplifiedGlossary.pdf  Accessed 15 Jan 2022.

Walters, Brian F.; Domke, Grant M.; Nowak, David J.; Smith, James E.; Ogle, Stephen M. 2021. Greenhouse gas emissions and removals from forest land, woodlands, and urban trees in the United States, 1990-2019: Estimates and quantitative uncertainty for individual states. Fort Collins, CO: Forest Service Research Data Archive. https://doi.org/10.2737/RDS-2021-0035  Accessed 14 Jan 2022.