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HOW CRUSHED STONE COULD HELP FIGHT CLIMATE CHANGE?

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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 CO dissolves in rainwater or soil moisture), triggering a chemical reaction that locks CO into bicarbonates, which eventually form limestone.

HOW ERW WORKS?

  • Under natural conditions, rocks undergo weathering when rainwater containing dissolved CO 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 CO 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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