Noah Planavsky, Yale University
Department of Earth and Planetary Sciences; Yale Center for Natural Carbon Capture
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.
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