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Response: Enhanced rock weathering

Weathered basalt, Reynisfjara Iceland image: Sonny Whitelaw

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Enhanced rock weathering

Summary

“Biogeochemical improvement of soils by adding crushed, fast-reacting silicate rocks to croplands is one such CO2-removal strategy. This approach has the potential to improve crop production, increase protection from pests and diseases, and restore soil fertility and structure.” – Beerling et al, 2018.

“Our findings suggest that widespread adoption of EW across farming sectors has the potential to contribute significantly to net-zero greenhouse gas emissions goals while simultaneously improving food and soil security.” – Beerling et al, 2024

  • However, a two year study has revealed that while soil inorganic C increases significantly, mineral-bound organic C decreases, and total soil organic C remains the same.
  • A parallel plan is to add crushed rocks to the ocean to make it more alkaline, and reduce ocean acidification:

“In theory, olivine dust spread on beaches or in the ocean would break down in a matter of years, locking up carbon as it dissolves. (This might also help address ocean acidification) – Prof. Oliver Jagoutz, MIT

  • These plans require mining, crushing, and transporting the right types of crushed rocks to agricultural lands and the ocean, all processes that emit large volumes of CO2.
  • Deliberately making the ocean more alkaline also has the potential to slow down the natural oceanic alkalinity cycle in some locations.

  Response

Other sections

Home > Climate wiki > Response > Enhanced mineral weathering

Summary

“Biogeochemical improvement of soils by adding crushed, fast-reacting silicate rocks to croplands is one such CO2-removal strategy. This approach has the potential to improve crop production, increase protection from pests and diseases, and restore soil fertility and structure.” – Beerling et al, 2018.

“Our findings suggest that widespread adoption of EW across farming sectors has the potential to contribute significantly to net-zero greenhouse gas emissions goals while simultaneously improving food and soil security.” – Beerling et al, 2024

  • However, a two year study has revealed that while soil inorganic C increases significantly, mineral-bound organic C decreases, and total soil organic C remains the same.
  • A parallel plan is to add crushed rocks to the ocean to make it more alkaline, and reduce ocean acidification:

“In theory, olivine dust spread on beaches or in the ocean would break down in a matter of years, locking up carbon as it dissolves. (This might also help address ocean acidification) – Prof. Oliver Jagoutz, MIT

  • These plans require mining, crushing, and transporting the right types of crushed rocks to agricultural lands and the ocean, all processes that emit large volumes of CO2.
  • Deliberately making the ocean more alkaline also has the potential to slow down the natural oceanic alkalinity cycle in some locations.

How does it work?

The following is an extract from Carbon Brief: How ‘enhanced weathering’ could slow climate change and boost crop yields’ (Fig. 1)

Chemical weathering is a natural process that continuously erodes away rocks and stores atmospheric CO2 over millions of years. As natural rock weathering absorbs around 0.3% of global fossil fuel emissions, enhanced weathering can provide a boost to remove even more CO2 from our atmosphere.

The process begins with rain, which is usually slightly acidic having absorbed CO2 from the atmosphere on its journey to the ground. The acidic rain reacts with rocks and soils, gradually breaking them down into rock grains, forming bicarbonate in the process. Eventually, this bicarbonate washes into the oceans, where the carbon is stored in dissolve form for hundreds of thousands of years or locked up on the sea floor.

Fig. 1: Advanced rock weather to drawdown carbon dioxide and improve soils (image: Carbon Brief)
Fig. 1: Advanced rock weather to drawdown carbon dioxide and improve soils (image: Carbon Brief)

Enhanced weathering scales up this process. Pulverising mafic rocks
such as basalt – left over from ancient volcanic eruptions – bypasses
the slow weathering action because powder has a greater surface area
that large rocks, so it absorbs carbon much faster.

When spread on large areas of agricultural land, plant roots and microbes in the soil speed up the chemical reactions, boosting nutrient levels, improving crop yields and helping restore degraded agricultural soils (Video 1).

Potential downsides

A two year study has revealed that while soil inorganic C increases significantly, mineral-bound organic C decreases, and total soil organic C remains the same.
 

Mining, grinding and transporting  the right kind of rock takes a lot of energy, most of it from climate-polluting fossil fuels.

Deliberately making the ocean more alkaline has the potential to slow down the natural alkalinity cycle:

“However, the problem can potentially be mitigated by dilute dosing of anthropogenic alkalinity into the ocean environment and the avoidance of OAE in natural alkalinity cycling hotspots, such as in marine  sediments.” – Bach, 2024

Video 1: Concept and testing in different parts of the world to determine viability and efficiency at scale.

More information

  • Explainer: What rocks are suitable?

     
    Olivine and other mafic rocks – igneous rocks rich in magnesium and iron – are suitable.

    “Our preliminary investigations have shown Mg can also be extracted from basalt; however, we will primarily focus our discussion on two enriched and accessible olivine deposits: the Semail ophiolite (Oman) and the Red Hills Ultramafic Complex (New Zealand) which conservatively contain 1.4 × 105 and 871 billion tonnes of olivine, respectively.“   –  Scott et al (2021)

    But Maungakura Red Hills near St Arnaud is part of the Mt Richmond Forest Reserve; it’s surrounded by native ecosystems that already store massive quantities of carbon dioxide (images). The whitish area in the centre of the second image is an ephemeral riverbed, not a road.

    How much carbon-absorbing and life-supporting ecosystem services provided by biodiversity are we prepared to destroy through carbon-emitting mining and processing activities?

    (Images: Cody Whitelaw)