CDR (Carbon Dioxide Removal) Calculators

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Carbon dioxide removal (CDR), also called negative emissions technologies (NET), refers to approaches that actively remove CO₂ from the atmosphere and store it durably in terrestrial, oceanic, or geological reservoirs. CDR is distinct from emissions reduction — it removes CO₂ that has already been emitted. The IPCC's climate pathways limiting warming to 1.5–2°C universally require large-scale CDR alongside deep emissions cuts. Key CDR approaches include afforestation and reforestation, bioenergy with carbon capture and storage (BECCS), direct air capture (DAC), enhanced weathering, ocean alkalinity enhancement, and soil carbon sequestration.

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Major CDR Approaches

  • Afforestation/reforestation: Planting trees to sequester carbon in biomass and soil; low cost, large co-benefits; but competes with land for food and biodiversity; reversible (fire, harvest)
  • BECCS (Bioenergy + CCS): Grow biomass → burn for energy → capture CO₂ → store geologically; net-negative energy with permanent storage; requires large land areas
  • Direct Air Capture (DAC): Chemical sorbents capture CO₂ from ambient air; energy-intensive (~300–400 kWh/tCO₂); scalable if clean energy is available; high current cost (~$300–1000/tCO₂)
  • Enhanced weathering: Spread silicate minerals (basalt) on agricultural land; CO₂ reacts with minerals during weathering; also adds soil nutrients
  • Ocean alkalinity enhancement: Add alkaline minerals to ocean to increase CO₂ uptake; large theoretical potential; ecological risks uncertain
  • Soil carbon sequestration: Improved land management (no-till, cover crops, biochar) to increase soil organic carbon

Monitoring, Reporting, and Verification (MRV)

CDR must be measured, reported, and verified to count toward climate targets. Permanence is critical — CO₂ stored in trees or soil can be released by disturbance. Geological storage (DAC + CCS) is considered most permanent.

Glossary

CDR (Carbon Dioxide Removal)
Active removal of CO₂ from the atmosphere and durable storage; distinct from emissions reduction; required alongside decarbonization to meet 1.5–2°C climate targets.
Direct Air Capture (DAC)
Technology using chemical sorbents to capture CO₂ from ambient air; energy-intensive (~300–400 kWh/tCO₂); current cost ~$300–1000/tCO₂; most scalable permanent CDR approach.
BECCS (Bioenergy with CCS)
Grows CO₂-absorbing biomass for energy production; captures and geologically stores the resulting CO₂; theoretically net-negative but requires large land areas.

Frequently Asked Questions

CDR (also called negative emissions or carbon removal) removes CO₂ from the atmosphere and stores it durably. It is needed because: (1) Cumulative past emissions have pushed atmospheric CO₂ to ~420 ppm — even stopping all emissions now won't bring CO₂ back to safe levels without active removal; (2) Many economic sectors (aviation, shipping, some agriculture) are difficult to fully decarbonize — CDR can compensate for residual emissions; (3) IPCC scenarios for 1.5°C require net-negative CO₂ by mid-century, meaning removal must exceed residual emissions.

Direct air capture uses chemical sorbents or solvents to capture CO₂ directly from ambient air (~420 ppm CO₂). Solid DAC: air passes over solid sorbents (amine-functionalized materials); CO₂ binds; heating regenerates the sorbent and releases concentrated CO₂. Liquid DAC: air contacts KOH solution; CO₂ reacts to form K₂CO₃; heated to release concentrated CO₂. The CO₂ is then compressed and stored geologically or used. Current challenges: energy intensity (~300–400 kWh/tCO₂); cost (~$300–1000/tCO₂); scale-up. Climeworks (Iceland) and Carbon Engineering (Canada) are leading commercial developers.

BECCS (Bioenergy with Carbon Capture and Storage) grows biomass that absorbs CO₂ during growth, burns it for energy, captures the CO₂ emitted, and stores it geologically — achieving net-negative emissions while producing energy. Limitations: (1) Land requirement — large-scale BECCS would require hundreds of millions of hectares, competing with food production and biodiversity conservation. (2) Water use — high water demand for biomass crops. (3) Governance — where is CO₂ stored and who monitors it? (4) Food price effects — diverting cropland raises food prices. BECCS appears in many IPCC scenarios but at scales many experts consider unrealistic.

IPCC AR6 scenarios limiting warming to 1.5°C with no or limited overshoot require cumulative CDR of ~100–1000 GtCO₂ by 2100 (median ~300 GtCO₂), peaking at ~10 GtCO₂/year by 2050. Current CDR is dominated by natural land sinks (~10 GtCO₂/year) plus early-stage engineered CDR (<0.01 GtCO₂/year from DAC). Scaling engineered CDR to gigatonne scale by 2050 requires massive investment, policy support, and technological development. No single CDR approach can provide sufficient scale — a diverse portfolio is required.