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Could weathered rock be the magic dust that vaults us towards our climate goals?


Could weathered rock be the magic dust that vaults us towards our climate goals? 

Building on previous research, a new study estimates how much carbon farmers could lock away by spreading crushed rock on croplands. Their numbers are enormous.
August 18, 2023

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Scattering carbon-absorbing rock dust across global farmland could sequester 217 gigatons of CO2 by 2100, according to a new study. This could vault us towards the carbon drawdown target we need to reach to keep global temperature increases below 1.5 °C.

What’s more, the study shows that the absorbent powers of volcanic rock dust, like basalt, are amped up in tropical, humid climes. Therefore, strategically adopting this measure in some regions could drive agricultural investment into developing nations, while simultaneously bringing a global benefit. 

Previous research has looked at the huge potential of rock weathering—the process through which rain that captures CO2 from the atmosphere as it falls, reacts with rock to form carbonates which capture the carbon. From here, the carbon either precipitates into the soil or flows into the ocean where it can then be sequestered for centuries in marine sediments.

‘Enhanced’ rock weathering is a process that relies on first grinding the rock up to increase the available surface area for the weathering action to occur. Vast tracts of farmland provide the ideal real estate where this technology can be applied at scale—and farmers benefit, as weathered basalt enriches the soil with crop-boosting minerals over time.

But until now, few researchers have really scrutinized the global potential of rock weathering to soak up emissions—not just now, but in the critical decades ahead. The scientists on the new study stepped in with a model to fill that gap. Their simulation incorporated 963 agricultural sites globally, and explored what would happen if farmers applied 10 tons of ground up basalt rock per hectare per year, across all these lands, during a period of 75 years. Then they extrapolated the results of this simulation to all croplands worldwide to see what would happen if we took this especially ambitious step. 


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Enhanced Rock Weathering


Across those initial 963 farms, the researchers found that basalt could sequester about 64 gigatons of carbon dioxide—an amount equivalent to the emissions from 35 years’ worth of coal burning in the United States.

This is already an impressive figure—but if spread across all the world’s croplands the potential is astronomical: rock dust could lock away 217 gigatons of carbon over the next 75 years.

The researchers also found that size matters, with the model revealing that fine-grained basalt rock captures carbon far more successfully than coarse fragments of rock which take decades longer to weather, thereby slowing down the process of carbon capture that’s needed now. Perhaps most intriguingly, they found that weathering is accelerated and therefore more effective in humid, warm environments—helping to pinpoint the regions where bringing in this technology would create the quickest and most efficient gains. 

The Intergovernmental Panel on Climate Change estimates that in addition to crucial emissions-curbing measures, we’ll need to sequester somewhere between 100 to 1000 gigatons of carbon dioxide by century-end, to keep global temperature increases within acceptable limits. So, depending on what’s needed, this straightforward, low-tech solution could hit that sequestration target, or at the very least, get us a significant portion of the way there. 

Getting basalt to where it needs to be may be costly and require new infrastructure to spread it across fields. But these costs could be dovetailed with agricultural investments in the countries where rock weathering will have its biggest benefit—which also typically overlap with those nations where global support for farm tech, innovation, and food security is needed most.

“There’s tremendous potential here,” the researchers say

Baek et. al. “Impact of Climate on the Global Capacity for Enhanced Rock Weathering on Croplands. Earth’s Future. 2023

Image: ©Anthropocene Magazine

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