HOW CRUSHED STONE COULD HELP FIGHT CLIMATE CHANGE?
Why in News
- On June 24, 2025, reports highlighted that crushed rock is being spread across farmland—from sugar plantations in Brazil to tea estates in India—as part of a novel method to combat climate change.
- This method, known as Enhanced Rock Weathering (ERW), is attracting global attention and investment for its potential to remove carbon dioxide (CO₂) from the atmosphere.
WHAT IS ENHANCED ROCK WEATHERING?
- Enhanced Rock Weathering (ERW) is a climate change mitigation technique that aims to accelerate the natural process of rock weathering in order to capture and store atmospheric carbon dioxide.
- It involves spreading finely ground, quick-weathering rocks such as basalt over agricultural land.
- These rocks react with carbonic acid (formed when CO₂ dissolves in rainwater or soil moisture), triggering a chemical reaction that locks CO₂ into bicarbonates, which eventually form limestone.
HOW ERW WORKS?
- Under natural conditions, rocks undergo weathering when rainwater containing dissolved CO₂ forms carbonic acid (H2 CO3 ) and reacts with minerals in the rocks.
- This process binds carbon and washes it into oceans where it can precipitate as limestone (CaCO3 ).
ERW speeds up this natural carbon capture process by:
- Using rocks like basalt, which weather quickly.
- Grinding them into a fine powder to increase surface area and reaction speed.
- Spreading them over farmland where moisture and microbial activity facilitate the reaction.
Effectiveness of ERW
- The effectiveness of ERW as a carbon removal method is still being evaluated.
- According to a U.S. study, applying 50 tonnes of basalt per hectare annually could remove up to 10.5 tonnes of CO₂ over four years.
- However, field trials in Malaysia (on oil palm plantations) and Australia (on sugarcane farms) showed much lower CO₂ removal rates, indicating that initial estimates may have been overly optimistic.
EFFICIENCY OF ERW
The efficiency of ERW depends on several factors:
- The type and grain size of the rock used.
- Soil composition and land management practices.
- Climate conditions, especially temperature and rainfall.
CHALLENGES IN MEASUREMENT
- One of the major challenges in ERW is accurately measuring the amount of carbon dioxide removed from the atmosphere.
- The most commonly used method measures cations (positively charged ions) released during the weathering process.
- However, these cations are released not only by reactions with carbonic acid but also by other stronger acids present in soil.
- As a result, there is a risk of overestimating the actual amount of carbon captured through ERW.
- Experts suggest that more scientific funding and improved verification techniques are needed to accurately quantify carbon removal through this method.
ADDITIONAL BENEFITS OF ERW
ERW provides multiple co-benefits beyond carbon capture:
- It increases soil alkalinity, which can boost crop yields and improve soil structure.
- The application of rock dust adds essential nutrients to the soil, aiding long-term soil health.
- Even if the rock reacts with non-carbonic acids, it may still neutralize acidic runoff, reducing ocean acidification and potentially preventing indirect CO₂ emissions from water bodies.
- Moreover, basalt is abundantly available and often a quarrying byproduct, making the process relatively cost-effective and scalable.
RISKS & CONCERNS
While ERW is generally considered safe, there are some associated risks:
- Some types of quick-weathering rocks may contain toxic heavy metals, which could contaminate soil or water.
- Workers applying the finely ground rock must wear protective gear to avoid inhaling dust.
- The greatest concern is the overestimation of carbon credits. If companies purchase ERW-based credits based on inflated carbon capture figures, they may fail to truly offset their emissions, resulting in a net increase in atmospheric CO₂.
GLOBAL IMPLEMENTATION OF ERW
ERW projects are being piloted and implemented in several countries across Europe, North America, Latin America, and Asia.
- In India, crushed basalt is being applied to tea plantations in Darjeeling.
- In Brazil, a project recently delivered the world’s first verified carbon-removal credits from an ERW initiative.
- In the United States, ERW is being trialed in soybean and maize fields.
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