Learn

Enhanced Rock Weathering is a fascinating subject with lots of different dimensions to dig into. Here’s a solid sample of resources to help you get started on your Carbon Gardener learning journey.

Reads: Media and Journals

Videos

Some excellent backgrounders on ERW on Youtube.

Science in Motion: Can enhanced weathering help slow climate change?

Carbon Gardener co-founder Dr. Garret Boudinot’s Introduction to ERW (aka “Rock Dust”)

Carbon Dioxide Removal: Enhanced Weathering As a Billion Ton Solution?

Enhanced Weathering in the Global South with Shantanu Agarwal, CEO, Mati.

Enhanced Rock Weathering FAQ

  • What is Enhanced Rock Weathering (ERW)?+

    Rock weathering happens naturally when rocks are broken down through chemical, physical, and biological processes. For the CDR pathway explored in this project, we will focus on chemical rock weathering, a process through which rock is broken down, exposing reactive minerals to dissolved CO2. Methods to accelerate this process, referred to as Enhanced Rock Weathering (ERW)1, include grinding up the rock to make “rock dust.” This increases the amount of exposed surface area, and consequently, can speed up the reaction rate.

  • How much carbon could ERW potentially remove from the atmosphere per year?+

    Many parameters affect weathering rates including rock type, temperature, precipitation, particle size, and mixing depth. Natural rock weathering is estimated to remove on the order of a gigaton (billion tons) of carbon per year. 2,3 Studies project that ERW could remove 2-4 billion tons of carbon by midcentury and could possibly scale to the order of 20 gigatons by 2100.4 One study found that enhanced weathering could lower atmospheric CO2 by 30–300 ppm by 2100.5

  • How quickly does Rock Dust remove carbon?+

    The speed at which rock dust can remove carbon varies widely depending on factors including size of particles, climate, and dissolution time of a given mineral. For example, a 1mm sphere of calcite can dissolve in months while a 1mm sphere of quartz would take on the order of tens of millions of years.6

  • How long does carbon removed by ERW stay removed?+

    ERW is considered a relatively durable carbon removal pathway as it can store carbon either as carbonate minerals in soils, which are stable for thousands to millions of years, or bicarbonate in soil waters, which flows through groundwater and rivers into the oceans, where it is stable for ~10,000-100,000 years.7 The exact fate of carbonate and bicarbonate over long timescales, as soils change and water flows, is still an active area of study.

  • How do we know that ERW is happening?+

    MRV methods are still under development, but see here for an example of a verification framework. The purpose of this project is to help accelerate the development of a useful MRV approach to measure the rate and amount of carbon removal via ERW.

  • What types of rocks result in ERW and why?+

    The most reactive rocks for ERW include basalts, periodites, or serpentinites. These particular rocks contain alkaline cations (for example, Magnesium or Calcium) that react with CO2 in acidic aqueous solutions to form carbonates.8 ERW could also work well with certain alkaline industrial waste products such as mine tailings.

  • Does ERW result in other benefits in addition to carbon removal?+

    While more research is needed, evidence indicates that ERW could improve soil health and increase agricultural productivity.9 Given that ERW increases soil pH, it could serve as a potential substitute for lime – a source of significant agricultural emissions.10 Over time, the alkaline runoff from soil waters to the ocean at scale could provide a  co-benefit of reducing ocean acidification.11

  • What about potential risks or harms?+

    Potential risks and harms include emissions from grinding and transport, leaking of heavy metals into ecosystems and water sources from certain materials, increased mining, and adverse effects on soil ecology.12 Some of these risks can be mitigated easily by, for example, sourcing rocks from nearby-locations to reduce transport emissions, or using materials that have low or no trace metal contents. Other risks require more research to assess their probability, like adverse impacts on soil ecology such as increased respiration ((which releases more CO2), or harm to soil microbiology.

  • Do the emissions caused by grinding up rock dust and transporting it outweigh the emissions removed via ERW?+

    The footprint of ERW depends strongly on the energy sources used in grinding and transport – one study found that they could account for up to 94% of emissions from the ERW process.13 These can be reduced by using pre-ground material (i.e., biproducts of existing mining operations), deploying near material sources, and using low-energy methods for transport

  • How extensive is the prior research on ERW, and what does it tell us?+

    Academic research on the efficacy of ERW for carbon removal is relatively nascent. Existing studies, from models, to potted plant studies, to field trials, show a wide range of impacts, which depend on the type and amount of rocks used, soil and climate conditions of the study, plants introduced to the soils, and measurement techniques (see for example table 1) . Overall, research indicates that ERW *could* be a useful method for CDR at scale, but much more research is required to ensure it is deployed safely and effectively.

  • Does Rock Dust work better in some soils/conditions than others?+

    Understanding the efficacy of ERW in different soil types is an active area of research and a major motivation behind this project.  Overall, soils with lower pH (acidic) and more moisture will more rapidly dissolve rock dust and convert CO2 to bicarbonate. Temperature and plant type may also control the weathering rate and efficacy.14 One modeling study indicated that India, Brazil, South-East Asia, and China hold 75% of the global ERW potential.15

  • How expensive is Rock Dust?+

    Rock dust is estimated to cost $24-578 per ton of CO2 removed.

  1. ERW is sometimes referred to as enhanced mineralization or accelerated weathering.
  2. Taylor, L., Quirk, J., Thorley, R. et al. Enhanced weathering strategies for stabilizing climate and averting ocean acidification. Nature Clim Change 6, 402–406 (2016). https://doi.org/10.1038/nclimate2882
  3. Hartmann, Jens, et al. “Global CO2-consumption by chemical weathering: What is the contribution of highly active weathering regions?.” Global and Planetary Change 69.4 (2009): 185-194.
  4. American University Fact Sheet
  5.  Taylor, L., Quirk, J., Thorley, R. et al. Enhanced weathering strategies for stabilizing climate and averting ocean acidification. Nature Clim Change 6, 402–406 (2016). https://doi.org/10.1038/nclimate2882
  6. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/rog.20004
  7. Andrews, M. G., & Taylor, L. L. (2019). Combating Climate Change Through Enhanced Weathering of Agricultural Soils. Elements, 15(4), 253–258. doi:10.2138/gselements.15.4.253
  8. https://cdrprimer.org/read/chapter-2#sec-2-1
  9. Edwards, David P., et al. “Climate change mitigation: potential benefits and pitfalls of enhanced rock weathering in tropical agriculture.” Biology letters 13.4 (2017): 20160715.
  10. https://www.sciencedirect.com/science/article/abs/pii/S1750583618300057
  11. https://iopscience.iop.org/article/10.1088/1748-9326/ac1818
  12. Edwards, David P., et al. “Climate change mitigation: potential benefits and pitfalls of enhanced rock weathering in tropical agriculture.” Biology letters 13.4 (2017): 20160715.
  13. Renforth, Philip. “The potential of enhanced weathering in the UK.” International Journal of Greenhouse Gas Control 10 (2012): 229-243.
  14. Edwards, David P., et al. “Climate change mitigation: potential benefits and pitfalls of enhanced rock weathering in tropical agriculture.” Biology letters 13.4 (2017): 20160715.
  15. Jessica Strefler et al 2018 Environ. Res. Lett. 13 034010
  16. Renforth, Philip. “The potential of enhanced weathering in the UK.” International Journal of Greenhouse Gas Control 10 (2012): 229-243.