Let me be clear upfront: trees are wonderful. Plant them. Protect them. Love them. But if your entire carbon removal strategy is “plant more trees,” we have a problem.

The Scale Problem

Humanity emits roughly 37.4 billion tonnes of CO₂ per year from fossil fuels (Global Carbon Budget, 2024). The IPCC says we need to remove 5–16 billion tonnes per year by 2050 on top of aggressive emissions cuts (IPCC AR6 WGIII, 2022). Afforestation and reforestation can contribute meaningfully — the IPCC estimates a technical potential of 0.5–10.1 GtCO₂/yr by 2050, with median estimates around 3.9 GtCO₂/yr (IPCC AR6 WGIII, Ch. 7) — but they can’t do it alone.

Here’s why:

Land competition. Growing enough trees to remove billions of tonnes of CO₂ requires enormous amounts of land — land that’s also needed for food production, biodiversity, and, well, the people who already live there. A 2024 study in Nature Climate Change found that when accounting for implementation costs and land-use competition, realistic reforestation potential is significantly constrained (Mo et al., Nature Climate Change, 2024). A separate analysis limiting negative impacts on biodiversity and food security put the maximum at about 3.8 GtCO₂/yr by 2050 (Deprez et al., via npj Climate Action, 2026).

Permanence. Trees burn. They die. They decompose. A forest planted today could release its stored carbon back into the atmosphere in a wildfire decades from now. The 2023 Canadian wildfire season released an estimated 480 megatonnes of carbon — equivalent to roughly 1,760 Mt CO₂ — making it the fourth-largest emitter globally that year, behind only China, the US, and India (Copernicus/CAMS, 2023; Walker et al., Nature, 2024). That’s not a theoretical risk; it’s already happening.

Saturation. Trees don’t grow forever. A mature forest reaches a rough carbon equilibrium where new growth roughly equals decay. The big sequestration happens during the growth phase, then tapers off.

The Portfolio Approach

This is why the CDR field talks about a portfolio of removal methods:

  • Enhanced weathering (EW): Spreading crushed silicate rocks on agricultural land to accelerate natural CO₂-absorbing chemical reactions. Added benefit: it can improve soil health and crop yields (Beerling et al., Nature, 2020). Companies like UNDO and Lithos are scaling this now.

  • Direct air capture (DAC): Giant machines that chemically scrub CO₂ from ambient air. Energy-intensive and expensive today (~$400–1,000/tonne), but costs are falling and permanence is essentially guaranteed when combined with geological storage (WRI, 2024). Climeworks and 1PointFive are leading the charge.

  • Biochar: Heating biomass in low-oxygen conditions creates a stable carbon-rich material that can persist in soil for hundreds to thousands of years (Frontiers in Soil Science, 2024). It also improves soil fertility. Win-win.

  • Ocean alkalinity enhancement (OAE): Adding alkaline minerals to the ocean to increase its capacity to absorb CO₂. The ocean already absorbs about 25–30% of our emissions (NOAA; Global Carbon Project via Carbon Brief) — OAE helps it do more.

  • Biomass carbon removal and storage (BiCRS): Burning or gasifying biomass for energy while capturing and storing the CO₂. If the biomass is sustainably sourced, the net effect is carbon removal.

Why This Matters

No single method can scale to the gigatonnes we need. Each has trade-offs in cost, permanence, land use, energy requirements, and co-benefits. The smart bet is diversification — just like an investment portfolio.

Trees are a critical piece. But they’re one piece. The CDR community is building the rest, and the pace of innovation is genuinely exciting.

I’ll be tracking all of it. Stay tuned. 🌍

Sources

  1. Global Carbon Budget (2024). “Fossil fuel CO₂ emissions increase again in 2024.” globalcarbonbudget.org
  2. IPCC AR6 WGIII (2022). Carbon Dioxide Removal Factsheet. ipcc.ch
  3. World Resources Institute. “How Effective Is Land At Removing Carbon Pollution? The IPCC Weighs In.” wri.org
  4. Mo, L. et al. (2024). “Cost-effectiveness of natural forest regeneration and plantations for climate mitigation.” Nature Climate Change. doi:10.1038/s41558-024-02068-1
  5. Deprez, A. et al., via Harfoot, M.B.J. et al. (2026). “Charting our forest future.” npj Climate Action. doi:10.1038/s44168-026-00335-9
  6. Copernicus Atmosphere Monitoring Service (2023). “2023: A year of intense global wildfire activity.” atmosphere.copernicus.eu
  7. Walker, X.J. et al. (2024). “Carbon emissions from the 2023 Canadian wildfires.” Nature. doi:10.1038/s41586-024-07878-z
  8. Beerling, D.J. et al. (2020). “Potential for large-scale CO₂ removal via enhanced rock weathering with croplands.” Nature, 583, 242–248. doi:10.1038/s41586-020-2448-9
  9. World Resources Institute (2024). “Direct Air Capture: 6 Things To Know.” wri.org
  10. Kalu, S. et al. (2024). “Biochar – a sustainable soil conditioner.” Frontiers in Soil Science. doi:10.3389/fsoil.2024.1376159
  11. NOAA. “Ocean Acidification.” noaa.gov
  12. Friedlingstein, P. et al., via Carbon Brief (2020). “The oceans are absorbing more carbon than previously thought.” carbonbrief.org