Carbon Drawdown Initiative

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Climate Hacker's Cheat Sheet: Enhanced Rock Weathering on Croplands

Dirk Paessler

Update in 2024

Since this cheat sheet was published in June 2022 a lot of new studies and papers have been published which essentially show that coming up with such a simplified cheat sheet is not possible. Even our own scientific work in our greenhouse shows that we did not find a rock that works well on all soils or a soil that works well with all rock dusts.

So please consider this cheat sheet only as a rough guide for thinking about EW projects and consider our more recent blog articles with much more in-depth analysis of the situation.

Enhanced Rock weathering works, there is no question about it

We think it is fair to say that nobody disputes that rock weathering actually works. Nature’s own carbon-in-ambient-air control process has been working on earth for billions of years and actually made our planet inhabitable in the first place: Rocks are dissolved by acidic water that contains CO2 from the air which sequesters the carbon and takes it out of the atmosphere..

Many scientists working on rock weathering as a climate solution also think that enhanced rock weathering is undisputed, too: We speed up the natural weathering process by several orders of magnitude by grinding the rocks and putting them in a favorable place. If we’d do this at a massive scale, millions or even billions of tons of rock, we would be able to counter balance 10-20% of the remaining emissions in 2050 (after lowering the emissions by 80-90%). ERW is not THE climate solution, but one of the several solutions we need to apply together.

We still don’t know exactly how fast rock weathering on e.g. farmland is, but we know from lab experiments that the rate of weathering is at least in the single digit percent per year of the total weathering potential (3 tons of basalt capture 1 ton of CO2) and we expect it to be much faster (10x ?) in open nature. From the preliminary data that we have seen in our experiments in the last year we think that ERW can be done economically and within a price range of 50-400 Euro per ton of CO2 soon.

We don’t need to know more than we already do to at least get started with the business part

It will take a few years to sort all the details and run all the necessary field experiments, but we can’t wait for that because we not only have a scientific problem, we also have a practical challenge with ERW: We need to scale up a new basalt-based industry to millions of tons of rock per year in 2-3 decades. This is a massive challenge and we just can’t wait another 2-3 years for some tiny bits to be sorted out.

So…. Today we would like to add one building block for an expedited scale-up of ERW which enables everyone to start scaling the practical part without waiting for the last and final study to be written: Our new cheat sheet makes it possible to design early ERW pilot-projects today even without having those glitzy models of the future and before all those field tests have been done. Let’s start scaling now!

Of course we will need much more detailed and thorough MRV (Monitoring, Reporting and Verification) in the near future, but this will take some time to develop. And it would actually be quite helpful for the MRV development process to already have more than a few “aged” fields where the weathering process has already been “in-action” for a few years!

What is a Cheat Sheet?

According to Wikipedia a cheat sheet is “a concise set of notes used for quick reference” and “The act of preparing such reference notes can be an educational exercise in itself”.

This is exactly how we feel about this document and how it came about. We started to make notes about the various parameters that we would need to take into account in our enhanced weathering projects and experiments to make sure the desired weathering outcomes would actually be possible. We discussed the data with many of the scientists we work with to achieve a kind-of-peer-review-process. We are now sharing this cheat sheet with the community because we believe our work could be of help to others working on ERW projects.

Two words of caution:

  1. Work in progress: This cheat sheet has been changed more than 100 times in 6 months. We improved, corrected, and added stuff all the time. This will surely continue and we will publish updated versions when it becomes necessary.

  2. Simplifications: To compress this much information onto one page we had to make simplifications and intentionally leave away some complexity.

Our ERW on croplands Cheat Sheet (Version 0.9)

The cheat sheet covers 10 parameters (top to bottom) and rates their good or bad influence on the intended climate positivity from “really bad” to “very good”.

  • Annual rainfall

  • Temperature

  • Soil pH

  • Rock dust size (energy and practicality!)

  • Rock surface area (reactivity!)

  • Rock application rate (every few years)

  • Soil type

  • Irrigation

  • Secondary minerals, Clay formation

  • Rock type

It will be hard to impossible to find any location on earth and any project where all parameters will be in the “very good” column. Generally for your ERW projects you should try to stay in the two green columns for most parameters, or at least in the middle “ok” column.

“Really Bad” and “Bad” means that you might be ADDING CO2 to the ambient air (e.g. creating more emissions than removal) instead of removing carbon, so stay away from that! There are dependencies between the parameters and also some parameters may be able to become “good” when combined in the right way. But this can quickly become hauntingly complex and you can’t solve these situations without either an extensive model or many experiments - which we don’t have yet.

If you would like to make suggestions on what to add or correct in this cheat sheet, please let us know via email or send a tweet to @carbon_drawdown.

Appendix: Some Maps