Enhanced Rock Weathering (ERW) for Climate Mitigation

25 Jun 2025 GS 3 Environment
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Enhanced Rock Weathering (ERW)

What is ERW?

Enhanced Rock Weathering (ERW) is a carbon dioxide removal (CDR) technique that accelerates the natural process of rock weathering to capture and store atmospheric CO₂ in a stable form for thousands to millions of years.

Natural Process Behind ERW:

  • CO₂ + Rainwater → Carbonic Acid

  • Carbonic Acid + Rocks → Bicarbonates (which eventually form limestone, storing carbon for geological timescales)

  • This natural process is slow, taking centuries to remove meaningful amounts of CO₂.

How ERW Works:

  • Rocks like basalt or wollastonite are crushed into fine powder.

  • This powder is spread on agricultural land.

  • The increased surface area of finely ground rocks accelerates chemical reactions with CO₂ in rainwater and soil.

  • Carbon is locked up as bicarbonate, stored for 100,000+ years.

  • ERW speeds this up using fast-weathering rocks with increased surface area through fine grinding.

Why Use Agricultural Land for ERW?

  • Co-benefits to farmers:

    • Releases essential nutrients (magnesium, calcium, potassium, phosphorus)

    • Improves soil health and pH

    • Reduces fertilizer dependency

  • Supports climate-resilient agriculture and offers free soil amendments to farmers.

Climate Significance:

  • IPCC Target: To avoid catastrophic climate change, we must remove 10 billion tonnes of CO₂/year by 2050.

  • ERW Potential: Can contribute up to 4 billion tonnes/year, covering 40% of the global removal target.

Scientific Challenges and Concerns:

  • Actual CO₂ Removal Rates Vary: A U.S. study showed 10.5 tonnes CO₂/ha/year removal; trials in Malaysia and Australia showed much lower rates.

  • Depends on:

    • Rock type and grain size

    • Temperature and rainfall

    • Soil pH and microbial activity

    • Farming practices

  • Measurement Issues:

    • Popular metric: Cation release from rocks (e.g. Ca²⁺, Mg²⁺)

    • Problem: Cations are released regardless of which acid (carbonic or stronger) caused weathering, leading to overestimation of CO₂ capture.

Recent Developments:

UNDO–Microsoft Partnership (2024–25)

Highlights:

  • Microsoft funds UNDO’s scientific ERW trials in Canada and the UK.

  • Trials at:

    • University of Guelph farm (Ontario)

    • Newcastle University farm (UK)

  • Purpose: Improve Monitoring, Reporting and Verification (MRV) of carbon removal.

Scientific Importance:

  • Focus on wollastonite, a fast-weathering mineral, enabling quicker data generation.

  • Emphasis on field-level MRV accuracy for open environmental systems.

  • Helps move ERW toward scalable, verifiable carbon removal technology.

Canada as a Strategic Hub:

  • Canadian government’s Net Zero by 2050 commitment

  • Canada hosts 70+ CDR companies

  • UNDO working with Canadian Wollastonite to supply minerals and verify carbon capture



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