Carbon Sequestration Calculator

Sequestration is a flux, not a stock: it describes how fast carbon moves from the atmosphere into vegetation and soil each year, measured in tonnes of carbon per hectare per year, whereas a carbon stock is the accumulated total sitting on the land at one moment. The default rates used here reflect that distinction. Established forest accumulates on the order of 5 tonnes of carbon per hectare per year under natural regeneration and up to roughly 12 under intensive silviculture, agroforestry systems fall between about 3.5 and 9, urban tree canopy between 2 and 5, and grassland typically under 2 because carbon accrues mainly below ground in slow soil pools. Soil texture modifies these figures because clay and organic soils physically protect carbon from decomposition while sandy and rocky soils cannot, hence multipliers above 1 for peat and clay and well below 1 for coarse or shallow substrates. The age factor encodes the standard yield curve: seedlings fix little, increment peaks somewhere between roughly 20 and 40 years in most temperate systems, then declines as respiration and mortality approach gross production. The main caveats concern permanence and saturation. A hectare cannot sequester indefinitely; as a stand matures the net rate trends toward zero, and any stored carbon returns to the atmosphere if the site burns, is cleared, or is drained. Wetland and peat soils are the sharpest example, since a drained peatland switches from sink to a substantial source. Soil carbon gains are also slow and hard to verify, requiring repeated sampling over years to resolve change against a large background stock.

Quantifying the land carbon sink became possible once atmospheric measurement was put on a reliable footing. Charles David Keeling began continuous carbon dioxide observations at Mauna Loa in 1958, and the resulting record showed both a steady rise and a pronounced annual sawtooth caused by the growth and senescence of northern hemisphere vegetation, the first direct evidence of the biosphere breathing at global scale. Through the 1980s carbon budget accounting exposed a discrepancy: fossil fuel emissions exceeded the sum of atmospheric accumulation and ocean uptake, implying a large unaccounted terrestrial sink. Micrometeorological eddy covariance towers, coordinated from the 1990s through the FLUXNET network, allowed net ecosystem exchange to be measured directly rather than inferred. Policy turned these measurements into accounting rules. The Kyoto Protocol of 1997 admitted afforestation, reforestation, and deforestation under Article 3.3 and additional land management activities under Article 3.4, with the operational details settled in the Marrakesh Accords of 2001. The IPCC published Good Practice Guidance for Land Use, Land-Use Change and Forestry in 2003 and folded it into the 2006 national inventory guidelines, which supply the tiered default sequestration rates by land use and climate zone that calculators of this kind rely on. Soil carbon research has a much longer lineage, running back to the continuous field experiments started at Rothamsted in 1843. Interest broadened again after France launched the 4 per 1000 soil carbon initiative at COP21 in 2015 and after work on natural climate solutions published in 2017 quantified the mitigation available from land management.