Carbon Dioxide removal through enhanced weathering—knows and unknows

[Grigory Bronevetsky]

Modeling Talks

Carbon Dioxide removal through enhanced weathering—knows and unknows Noah Planavsky, Yale University Tuesday, Oct 24 | 9am PT Meet | Youtube Stream Hi all, The presentation will be via Meet and all questions will be addressed there. If you cannot attend live, the event will be recorded and can be found afterward at https://sites.google.com/modelingtalks.org/entry/carbon-dioxide-removal-through-enhanced-weathering-knows-and-unknows Abstract: Dramatically reducing emissions is the most important factor in meeting climate goals. But even in the best possible emission reduction scenarios removal of billions of tons of atmospheric carbon dioxide is likely going to be necessary to meet the international climate goal of keeping mean warming below 2 degrees. However, low-quality, reversible, and poorly quantified carbon dioxide removal will likely further erode public and academic trust in carbon trading schemes and payments. Enhanced weathering (also often called enhanced rock or mineral weathering) is a long-term (>1000 year) carbon dioxide removal strategy that—by using existing infrastructure—has the potential to rapidly scale. The carbon capture potential of enhanced weathering, although still poorly defined, may rival or surpass methods based on sequestration in organic carbon (e.g., afforestation or soil organic carbon storage). I will give an introduction to enhanced weathering, review key recent advances and areas of uncertainty, and end with future research directions that could unlock the potential for enhanced weathering to provide a cost-effective and robust means of carbon removal. Bio: Dr. Noah Planavsky is Professor of Geochemistry in the Department of Earth and Planetary Sciences at Yale University and at the Yale Center for Natural Carbon Capture. He is also an Assistant Curator of Mineralogy at the Yale Peabody Museum. He obtained his Bachelor's from Lawrence University and his Ph.D. in Earth Sciences from the University of California, Riverside. He is a geochemist who uses empirical measurements and geochemical modeling to track the carbon cycle. He has demonstrated track record of research at the forefront of understanding carbon dioxide regulation through weathering, the mechanics of enhanced weathering in natural and managed soils, and the downstream fate of captured carbon in natural systems. Lastly, he is a Senior Contributing Scientist at the Environmental Defense Fund.   More information on previous and future talks: https://sites.google.com/modelingtalks.org/entry/home

[Grigory Bronevetsky]

Video Recording: https://youtu.be/HiLo9pPbs7I

Summary:

• Focus: Enhanced rock weathering (ERW)

  • Take rocks from queries

  • Spread them in agricultural soils

  • Use them to capture and store CO2 and improve crop growth

• Motivation:

  • High CO2 emissions are driving climate change

  • Need to reduce emissions

  • But on top of that, need to

    • Remove CO2 that has already been emitted

    • Reach net-negative emissions to meet climate goals

• Carbon offsets are one mechanism for funding CO2 removal

  • Many examples of removing CO2 via nature-based projects

  • Very challenging to ensure validity of offsets: permanence, additionality and leakage

  • Enhanced rock weathering can capture/store CO2 more effectively with fewer questions about offset validity

• Enhanced Rock Weathering

  • Process:

    • Take silicate rock that can sequester atmospheric CO2 (e.g. basalt, olivine)

    • Spread on agricultural field and capture the CO2

    • Periodically measure the amount of sequestration that has happened

    • Trace the weathered rocks as they are transported via groundwater/rivers into the ocean

  • Chemistry

    • CO2 + Water -> Carbonic Acid (normally happens in soils)

    • Carbonic Acid + Calcium Silicate (added crust rocks) + Water -> Calcium Carbonate (carbon captured)

    • Calcium Carbonate propagates through the ecosystem and travels to the ocean

      • Calcium Carbonate is a base

      • Reduces ocean acidification caused by CO2 being absorbed by the ocean

    • Ultimately buried in ocean sediments

• Modeling cradle-to-grave flow of carbon

  • Measurement of rock weathering at deployment sites

  • Soil reaction-transport model

  • Catchment/river network flow modeling

  • Ocean storage model

• Impact of ERW on agriculture

  • Soil are too acidic for crops

  • ERW increases pH

  • This is currently done by applying lime to soils

  • ERW reduces N2O emissions and sequesters CO2

• Deployment

  • Costs are becoming much cheaper

    • 2023 cost/ton CO2: $354

    • 2023 cost/ton CO2: $90

  • Deployment model: 

    • Give silicates to farmers for free (instead of paying for limestone)

    • Complementary to applying biochar to soils

• Measurement/Verification

  • Currently challenging/expensive soil sampling

    • though, easier than sampling for organic carbon because ERW sequestration varies less with time and depth

  • Need more work on modeling to reduce the number of samples needed

• Soil cycle model (SCEPTER: https://gmd.copernicus.org/articles/15/4959/2022/gmd-15-4959-2022-discussion.html)

  • Developed simulation of fluid transport and geochemical reactions

  • Needs to be primed with weathering rates

  • Currently poor at tracking rate of silicate weathering (depends on local weather conditions)

    • Uncertainty: surface area of rock grains

  • Appropriate for planning and optimizing ERW deployments

  • Not appropriate for monitoring/verification

• Modeling Propagation of Calcium Carbonate

  • Model of river network

  • Flow of material through rivers to the ocean

  • North American rivers have excellent data

  • Model is dynamic: river flow driven by weather/precipitation

  • Rivers are very effective at transporting sequestered carbon before it can be re-released

  • Loss of carbon due to degassing is overall small

• Flow into the ocean

  • Grid Enabled Integrated Earth System Model (cGENIE: https://www.seao2.info/mymuffin.html)

    • Computationally cheaper than fully-detailed models and makes it possible to incorporate atmosphere and ocean

  • Modeling a large-scale ERW deployment

    • Removal of CO2 in atmosphere

    • Deposition of CO2 into the ocean

  • Model shows that the loss of carbon from the shallow ocean is ~5-10%

  • Results have low uncertainty

• Alternative opportunities for ERW: roadway storage

  • Highway medians and land adjacent to roads

  • Can use satellite imagery to identify roads with non-built area near them where silicates can be placed

  • Can use de-icing salt spreaders or similar vehicles for deploying silicates