Rock dust could put a drain on atmospheric carbon — will this technology work?

Faced with the daunting task of rapidly curbing global warming to reduce the most devastating effects of climate change, humanity finds itself confronted with something akin to a “bathtub” problem: Just because you turn off the faucet doesn’t mean that the water instantly goes down the drain. 

In the context of climate change, this means that even if we can dramatically reduce carbon dioxide emissions, the high levels we’ve already emitted and the future emissions we can’t avoid will keep us well above 2 degrees Celsius of warming compared to the pre-industrial era. At this point, humanity needs to increase the size and speed of the atmospheric carbon dioxide drain, removing billions of tons of carbon dioxide each year and securely transforming this greenhouse gas to a solid-state. 

So, just how will this new atmospheric plumbing feet be accomplished? Many ideas have been proposed and to some extent tested, including deep injection of carbon dioxide in the planet’s deep rocks, giant machines that capture carbon dioxide and convert it to stable non-atmospheric forms, and natural climate solutions such as tree planting and carbon farming by feeding microbes in the soil. No solution is without its set of issues. There is no free lunch when it comes to carbon dioxide removal. 

The most viable solutions must hit that sweet spot between economic realities, the opportunity for local financial benefits, and — perhaps most importantly — impart permanence to carbon dioxide removal so that it won’t return to the atmosphere after it’s been captured.

One of the most promising approaches that tick these boxes involves the repurposing of rock dust into agricultural soils, which can be gathered in hoards from the mining industry, demolition of buildings, or cement and steel manufacturing. Adding rock dust derived from volcanic geology can soak up carbon dioxide and convert it to a form of carbon that is highly protected from atmospheric return, and these rocks can provide agronomic benefits in terms of yield enhancement, lower fertilizer costs and maybe even support healthier crops that have a higher density of nutrition for people and animals.  

Depending on the rate of rock breakdown, estimates suggest that between 0.5 to 2 billion tons of carbon dioxide could be removed each year if rock dust fines were applied to all of Earth’s croplands. There is a large uncertainty around these numbers, however, and much need for additional refinement and testing — from lab to field scales and across regions and countries. Model calculations suggest that the U.S., China and India have the most to gain in terms of net carbon dioxide removal from the technology. 

A critical question centers on deployment — and how effective rock dust is at capturing carbon dioxide across diverse agricultural settings. Not all rocks are created equally when it comes to capturing carbon dioxide. The most important candidates include volcanic rocks that are rich in calcium and magnesium silicates. The stockpile of rock dust of this kind is vast around the planet — the byproduct of leftover rock shattering and grinding processes used to create raw materials for building and manufacturing. 

Furthermore, soils vary widely on the planet as do the kinds of crops and how they are grown. What may work in one setting won’t work in another. The economics of carbon farming need to be met with simple payment systems so farmers can cash in on the commoditization of carbon, and the science of rock weathering and field-level quantification of carbon is lagging well behind the potential. 

I have been leading a study examining over 100 acres of rock dust additions to soils in both California and New York, working with farmers, ranchers and tribes. We are in the third year of our study and have found evidence for high rates of carbon dioxide removal when rock dust is applied to the soil. We have found some increases in large-scale crop yields and soil nutrients traced back to the rocks, suggesting a fertilization effect that not only benefits soil carbon but also soil health and agricultural production. 

However, we still need more research and development to determine how to optimize materials for things that matter most to farmers — grain yield, water use, fertilizer use, costs and benefits. Scientifically, where the carbon goes and how long it stays around requires large-scale testing over many years. 

As the world clamors for solutions to the global climate crisis, science and evidence must lead the way. The new science of climate solutions needs to infuse multiple stakeholders, from inception to testing to results and delivery of solutions, if we are to meet the urgent challenges of carbon dioxide removal without imposing further problems. Rock dust has its own set of issues that need careful analysis, including social-economic perspectives. What if this leads to more rock mines that could negate the environmental and climate benefits of the practice? Could there be negative consequences of adding rock dust to the soil for decades? Does the carbon that is removed stay in the ground and waterways even under extreme weather events?

I argue that the answers to these questions will come from large-scale demonstrations that link industry, academia, governments and stakeholders in new “innovation ecosystems” that can work rapidly, fail fast and succeed quicker. Rock dust is one of the more exciting test cases in this regard — which may ironically help to get us out of the rock and hard place we find ourselves in today. 

Benjamin Z. Houlton is the Ronald P. Lynch Dean of Cornell University’s College of Agriculture and Life Sciences and a professor of ecology and evolutionary biology as well as global development. His research interests include global ecosystem processes, climate change solutions, and agricultural sustainability.

Dr. Garrett Boudinot is a research associate in the Department of Ecology and Evolutionary Biology, and faculty fellow of the Cornell Atkinson Center at Cornell University.