Estimate carbon stored in a tree from its diameter.
Trees sequester carbon through photosynthesis, converting CO2 and water into glucose and oxygen: 6CO2 + 6H2O → C6H12O6 + 6O2. About 50% of a tree's dry biomass is carbon. The carbon stored in a tree is estimated from its aboveground biomass using allometric equations based on diameter at breast height (DBH, measured at 1.3m). Total biomass includes a root-to-shoot ratio of approximately 1.2× (roots add ~20%). One kg of carbon stored equals 3.67 kg of CO2 removed from the atmosphere (molecular weight ratio: 44/12). Young, fast-growing trees sequester carbon more rapidly per year, but old-growth trees store vastly more total carbon — a single large oak can store 5+ tonnes of CO2. The world's forests store approximately 861 billion tonnes of carbon (more than the entire atmosphere). Deforestation releases 4.8 billion tonnes of CO2 annually, making forest conservation as important as afforestation for climate mitigation.