Gravel helps farmers capture carbon

Dan Prevost grows corn, soybeans and cotton on about 1,000 acres of farmland near the town of Raymond in central Mississippi. Since the soil tends to become too acidic from the heavy rains in the Deep South, he does what many farmers do and buys gravel to control the pH in the fields. When Prevost got the offer to get gravel for free, he immediately liked the idea.

“That represents a significant saving for me,” he said Newsweek.

It’s not just any stone. Prevost worked with a company called Eion to spread the volcanic rock olivine on his field. When rain falls, olivine and some other silicate volcanic rocks undergo a chemical process that absorbs carbon dioxide from the air as the rock wears away. Suddenly, Prevost’s common agricultural practice of spreading rock dust became a possible climate solution.

“If we can do something that makes financial sense, increases the profitability of the operation, and at the same time provides environmental benefits, then I’m 100 percent for it,” Prevost said.

The technique is called enhanced rock weathering, and studies show that if enough farmers use the right types of rock in the right way, they could help combat climate change by storing huge amounts of CO2 warms the planet₂– all while improving their soil.

A study in the August issue of the American Geophysical Union’s monthly journal The future of the earth found that rock dust spread on all arable land worldwide could sequester more than 200 billion tons of CO₂ until the end of the century.

Climate scientists say that in addition to reducing greenhouse gas emissions, we also need such large-scale removal of atmospheric CO₂ to keep warming below dangerous levels. While some high-tech (and expensive) approaches to removing carbon from the atmosphere are attracting attention, Prevost’s diagram shows that part of the solution could be as simple and cheap as crushed rock.

Accelerate nature

Simon Manley is head of the carbon department UNDO, a London-based company working with farmers in the UK and US on improved rock weathering. Manley explains the process as, in the process of erosion, it simply speeds up the natural carbon cycle by finely crushing silicate rock and exposing it to more rain, soil and air.

“This shortens the time frame of the carbon cycle from tens of thousands of years to dozens of years,” Manley said Newsweek. “It has the potential to have a significant impact on the task of removing what we need from the atmosphere.”

UNDO uses basalt in its application and has found that five tons of the crushed volcanic rock can emit one ton of CO2₂. Manley said basalt and other similar rocks are abundant and the low-tech nature of the technique means there are few barriers to implementation.

“You pick it up with equipment that everyone is used to, you know, excavators and loaders, you load it on a truck and take it down the road to a farm site,” he said.

However, a technological challenge is to accurately measure and therefore monetize carbon removal results. You can’t manage what you don’t measure, as the old saying goes. So how can you measure the exact amount of CO?₂ removed by gravel?

“The core of this is trust,” said Eion co-founder and CTO Elliot Chang Newsweek. “Ultimately we have to build the confidence that we are actually quantifying that a ton means a ton, right?”

Eion has patented its process for tracking certain “fingerprints” of trace elements left by rock weathering. Chang said these are reliable indicators of the chemical process and provide a way to measure the amount of CO₂ Absorption.

“This shines a light on what’s happening in the ground in a way that hasn’t been done before,” Chang said.

Such evidence of carbon removal allows companies to participate in carbon markets, promising an economic boost that can lead to faster growth.
This month, Eion announced that it had met the technical criteria for carbon credits managed by financial services company Stripe.

Further studies are still needed to optimize enhanced rock weathering. The same study, which predicted a carbon removal potential of 200 gigatons, also warned that not all stone applications are created equal. Increased rock weathering appears to work best in hot, humid conditions and with finely ground materials, but less well in cold, dry places.

Carbon-free plants

Amplifying increased rock weathering will also require getting more farmers on board, and that could mean taking a more locally informed approach to climate communication. Prevost said it’s not easy to talk to his fellow farmers in Mississippi about global warming.

“It will definitely cause excitement,” he said. However, he suggested that a deeper conversation about things like weather extremes, changing rainfall patterns and soil health will pique a farmer’s interest.

Prevost said some farmers also feel a little disadvantaged when they are blamed for environmental impacts such as nutrient runoff, erosion and emissions.

“I mean, agricultural activities do contribute to greenhouse gases, but at the same time people need to eat,” he said. Prevost said proposed environmental improvements that involve additional costs or major changes to existing practices are leaving farmers “a little exhausted.”

What he likes about improved rock weathering is that it is simple, inexpensive, and helps farmers as well as the environment. He also uses other environmentally friendly practices such as cover crops and reduced tillage to reduce erosion and emissions.

“I’m very close to, if not below, a carbon-free crop,” Prevost said, “and I’m personally proud of that.”

But if increased rock weathering proves it can supply CO₂ Through large-scale reductions, Prevost and other farmers could grow a climate solution along with their crops.