Carbon Sequestration Rate Formula
Estimate CO2 absorbed by trees based on species, age, and size.
An average tree absorbs about 22 kg of CO2 per year.
The Formula
Carbon sequestration refers to the process by which trees and other plants absorb carbon dioxide from the atmosphere and store it as solid carbon in their wood, roots, and leaves. The formula works in three steps: first, estimate how much dry biomass a tree gains per year. Then multiply by 0.5 because roughly half of a tree's dry weight is carbon. Finally, multiply by 44/12 (approximately 3.67) to convert the weight of carbon atoms into the weight of CO2 molecules, since each CO2 molecule is heavier than the carbon atom alone.
An average mature tree absorbs approximately 22 kg (48 lbs) of CO2 per year, though this varies enormously by species, age, and growing conditions. Fast-growing species like poplars or eucalyptus can absorb 35 to 50 kg per year. Slow-growing hardwoods like oak may absorb only 10 to 15 kg per year but store carbon for centuries. Young trees in their rapid growth phase absorb more carbon annually than very old trees that have reached their full size.
For forest-scale calculations, you can estimate total sequestration by multiplying per-tree rates by the number of trees per hectare. A typical temperate forest has 400 to 600 trees per hectare and sequesters roughly 5 to 10 tonnes of CO2 per hectare per year. Tropical rainforests can sequester 15 to 25 tonnes per hectare per year due to faster growth rates and longer growing seasons.
These estimates are used by governments, corporations, and environmental organizations to plan carbon offset programs and evaluate reforestation projects.
Variables
| Symbol | Meaning |
|---|---|
| CO2 sequestered | Mass of CO2 removed from atmosphere (kg/year) |
| Dry weight gain | Annual increase in tree dry biomass (kg/year) — varies by species and age |
| 0.5 | Carbon fraction — approximately 50% of dry wood mass is carbon |
| 44/12 (≈ 3.67) | Molecular weight ratio of CO2 to C — converts carbon mass to CO2 mass |
Example 1
A young oak tree gains 8 kg of dry biomass per year. How much CO2 does it sequester annually?
Carbon stored = 8 × 0.5 = 4 kg of carbon per year
CO2 sequestered = 4 × (44/12) = 4 × 3.67
CO2 sequestered ≈ 14.67 kg per year
Example 2
A reforestation project plants 500 fast-growing poplar trees per hectare. Each tree gains about 15 kg of dry biomass per year. How much CO2 does one hectare sequester?
Per tree: CO2 = 15 × 0.5 × 3.67 = 27.5 kg/year
Per hectare: 500 × 27.5 = 13,750 kg/year
≈ 13.75 tonnes of CO2 per hectare per year — equivalent to the annual emissions of about 3 average cars
When to Use It
Use the carbon sequestration formula to estimate how much CO2 trees and forests remove from the atmosphere.
- Evaluating carbon offset programs and reforestation projects
- Estimating the climate benefit of planting trees on your property
- Comparing sequestration rates between different tree species
- Calculating how many trees are needed to offset a given amount of CO2 emissions
- Environmental impact assessments for land development or deforestation