Land Use Change Emissions Calculator

Land use change emissions are computed by the stock-difference method: carbon held per hectare under the original cover minus carbon held under the new cover, multiplied by area, then multiplied by 3.667, the mass ratio of CO2 to carbon (44 divided by 12). Two pools are tracked here. Living biomass ranges from roughly 200 tonnes of carbon per hectare in tropical moist forest and 250 in mangrove down to about 15 in grassland and 5 in cropland. Soil organic carbon is reported to the IPCC reference depth of 30 centimeters, where tropical forest holds around 80 tonnes per hectare, boreal forest about 150 because cold slows decomposition, and mangrove and wetland soils 250 to 300 because waterlogging suppresses it further. The two pools behave differently in time. Biomass carbon is released quickly, largely within one to five years through burning and decomposition, while soil carbon declines gradually, the top 30 centimeters typically losing 25 to 40 percent over decades once forest becomes tilled cropland. Negative results indicate sequestration and should be read as a potential reached only at maturity, which for reforestation means 50 to 100 years rather than the conversion period entered. The default carbon densities are IPCC Tier 1 global averages and can be wrong by a factor of two for a specific site. They also exclude deep peat, where organic soils several meters thick hold thousands of tonnes of carbon per hectare, and exclude the methane and nitrous oxide released when land is burned or drained.

Quantifying the land flux began with the realization in the 1970s that fossil fuel emissions alone could not close the global carbon budget. Bert Bolin argued in 1977 that clearing of the biosphere was a significant net source, and George Woodwell and Richard Houghton, working at the Marine Biological Laboratory in Woods Hole, built the first bookkeeping model, tracking areas converted and the subsequent decay of each carbon pool over time. Houghton's bookkeeping estimates remained the principal basis for the land use component of the annual Global Carbon Budget for decades afterward. Methodology was standardized once land entered climate treaties. The Kyoto Protocol's land use, land-use change and forestry provisions were given operational rules in the Marrakesh Accords of 2001, prompting the IPCC's Good Practice Guidance for LULUCF in 2003, the 2006 National Greenhouse Gas Inventory Guidelines with their Tier 1 to Tier 3 structure, and the 2019 Refinement. Deforestation-specific crediting grew from a proposal by Papua New Guinea and Costa Rica at COP11 in Montreal in 2005, becoming REDD+ under the Warsaw Framework in 2013. Verification improved sharply after the US Geological Survey opened the Landsat archive without charge in 2008, enabling the global forest-change mapping published by Matthew Hansen and colleagues in Science in 2013 and the Global Forest Watch platform built on it.