🔄 Updated 2025-11-24
As global warming intensifies, reducing atmospheric carbon dioxide (CO₂) has become a central challenge. In addition to mitigating emissions at their source, society must actively remove existing CO₂ from the atmosphere and store it in stable reservoirs — an approach known as carbon sequestration. In recent years, emerging strategies such as biochar-based carbon sequestration have gained increasing attention due to their long-term stability and environmental co-benefits. This review examines the mechanisms of biochar-based sequestration and compares it with other major carbon removal pathways.
Introduction to Biochar: How It Captures and Stores Carbon
Biochar is a carbon-rich solid formed by pyrolyzing biomass at ~350–700°C under low-oxygen conditions. Its aromatic carbon structure resists microbial degradation, enabling long-term carbon storage in soils. Typically, 30%–60% of original biomass carbon is retained in biochar after pyrolysis—much higher than natural decomposition.
Biochar Carbon Storage Process
- Carbon capture: Plants absorb CO₂ through photosynthesis and store it in biomass.
- Carbon stabilization: Pyrolysis converts a portion of this biomass carbon into stable biochar that can persist in soils for hundreds to thousands of years.
Biochar vs Natural Carbon Cycle
| Biochar vs Natural Carbon Cycle | |||
|---|---|---|---|
| Feature | Plant Residues | Soil Organic Matter | Biochar |
| Source | Plant residues after harvest or litter | Decomposed residues and microbial products | Biomass converted through pyrolysis |
| Decomposition | Rapid microbial breakdown | Slow microbial breakdown | Highly resistant to decomposition |
| Carbon Retention | 1–20 years | 10–100 years | ~100–1000 years |
| Cycle Type | Short-term natural cycle | Medium-term natural cycle | Human-designed long-term storage |
| Return to Atmosphere | Fast | Moderate | Very slow |
Biochar vs Forest-Based Carbon Sequestration
Forest-based carbon sequestration means forests absorb CO₂ from the atmosphere through photosynthesis and store carbon in woody biomass, roots, leaf litter, and soils. This approach is well-established and provides multiple ecosystem benefits. However, the stored carbon is vulnerable to disturbances such as wildfires, pests, disease, and harvesting, which reduce long-term permanence. Large-scale forest expansion may compete with other land uses.
| Dimension | Biochar | Afforestation |
|---|---|---|
| Source | Waste biomass | New plant growth |
| Carbon Stability | High | Medium–High (released when trees die) |
| Land Dependence | Medium (requires soil application) | High (requires large-scale land) |
| Co-benefits | Soil improvement, yield increase | Biodiversity, habitat restoration |
| Risks | Cost, feedstock supply | Fire, pests, logging |
Biochar vs Soil Carbon Sequestration
Soil carbon sequestration includes various ways of managing land, especially farmland, so that soils absorb and hold more carbon. Increasing soil carbon is accomplished in various ways, including: (1) reducing soil disturbance by switching to low-till or no-till practices or planting perennial crops; (2) changing planting schedules or rotations, such as by planting cover crops or double crops instead of leaving fields fallow; (3) managed grazing of livestock; and (4) applying compost or crop residues to fields.
This approach is cost-effective, compatible with existing farming systems. However, soil carbon is relatively dynamic and can be released back into the atmosphere under changes in management or climate. Additionally, soil carbon stocks may eventually reach a saturation point.
| Feature | Biochar | Soil Carbon Sequestration |
|---|---|---|
| Carbon Source | Waste biomass | Crop residues, organic amendments, and soil management practices |
| Carbon Stability | High | Medium, easily re-emitted |
| Cost | Medium | Low |
| Risks | Feedstock availability, production cost | Poor management can lead to carbon loss |
Biochar vs Ocean Carbon Sequestration
Ocean Carbon Sequestration occurs as oceans store carbon through physical processes like physical solubility (CO₂ dissolution), biological pumps (phytoplankton uptake and sinking), and carbonate chemistry. Human interventions, such as iron fertilization or alkalinity enhancement, are being explored to enhance this natural carbon storage.
| Feature | Biochar | Ocean Carbon Sinks |
|---|---|---|
| Carbon Source | Plant residues or organic waste converted through pyrolysis | Atmospheric CO₂ absorbed by seawater or captured by marine life |
| Carbon Stability | High; long-term fixed in soil | High; but human interventions carry ecological risks |
| Controllability | Production and soil application are controllable | Difficult to control; monitoring and verification are challenging |
| Additional Benefits | Improves soil and agricultural productivity | Large-scale natural carbon reservoir, ecosystem services |
| Risks | Feedstock, production cost | Ecological impact, uncertainty of enhanced sequestration |
