Can ‘enhanced rock weathering’ help combat climate change?

In a quarry surrounded by the rumble of heavy machinery, Jim Mann bends down and picks up a handful of tiny black rocks.

“This is my magic dust,” he says with a smile, rubbing them gently between his fingers.

He’s holding pieces of basalt. It is a hard volcanic rock that is not rare or particularly notable.

But through a process known as ‘enhanced rock weathering’ it could help cool our overheated planet.

UN scientists are now clear that reducing greenhouse gas emissions alone will not be enough to stop dangerous levels of warming. They say that some carbon dioxide will need to be removed by actively removing it from the atmosphere.

Planting trees is the most natural way to do it, but it has its limitations; the CO2 that is captured is released when the wood rots or burns, and there are limits to how many trees can be planted.

Meanwhile, Direct Air Capture (DAC) mechanically sucks CO2 out of the atmosphere and stores it underground; it’s permanent, but does it make sense to build such an energy-intensive process when we’re trying to move away from fossil fuels?

Enhanced rock weathering falls somewhere between natural and man-made. It takes the natural but very gradual aging process and turbocharges it to remove carbon faster.

I’ve come to a quarry across the Firth of Forth from Edinburgh to see Jim, whose enhanced rock weathering company UNDO has just secured £12m of new investment and is looking to expand its operations.

All around us, the black hillside is constantly being eaten away, scraped away by huge bulldozers to make concrete and asphalt for the roads. The environment is more of a post-nuclear apocalypse than saving the planet.

But the tiny bits of basalt rock left over are prized by Jim’s company. They have a useful property: when worn in the rain, they remove carbon dioxide from the atmosphere.

For millennia, volcanic rocks and cliffs have been slowly removing carbon as they erode in the rain. Enhanced rock weathering uses tiny pieces to increase the amount of contact between rain and rock, and therefore the amount of weathering and carbon removal.

Like a cliff, or piled up in the quarry, basalt wears away very slowly. To maximize carbon removal, it needs to be spread over a larger area.

And that’s where local farmers come in, helping the planet and getting free fertilizer in return. In addition to sequestering carbon, basalt has been shown in trials to improve both crop yields and grazing quality.

A half hour drive from the quarry I see how it spreads across a field.

It does not require specialized equipment. A trailer is loaded with 20 tons of basalt before it is pulled up and down by a tractor, a spinning wheel at the rear dispersing the small rocks.

“It’s free, which is very important for a farmer,” John Logan tells me with a smile as he lays the basalt in his field. He had seen UNDO tests at a neighboring farm.

“It looks like it’s going to improve the grass, so that can only be good for the cattle because they eat better grass.”

Some experts worry that carbon removal techniques like this could distract people from the more urgent priority of reducing emissions and even be used as justification for continuing to live our carbon-intensive lives.

“CO2 reduction has to come first,” Jim tells me as we watch the GPS-guided tractor move up and down, “but we also need to develop these technologies that can eliminate scale. What we’re doing with enhanced rock weathering is that it’s permanent.”

The math, it must be said, is overwhelming. UNDO scientists estimate that it takes four tons of basalt rock to capture one ton of CO2.

With the CO2 emissions of a typical Briton estimated at around 7 tonnes a year, that means each of us needs around thirty tonnes, or one and a half trailers of basalt to be spread annually just to break even.

UNDO has plans to expand rapidly in the coming years and has attracted some serious fans. Microsoft has agreed to pay for 25,000 tonnes of basalt to be spread across UK fields. As part of the agreement, Microsoft will also help audit the project and verify that it is working as intended.

“The essential chemistry makes sense,” Dr. Steve Smith, an expert in carbon removal at the University of Oxford, told me.

“Measuring how much CO2 would be removed and where it would ultimately go is one of the key challenges, and there is no standardized system at the moment.”

Ultimately, Dr. Smith thinks the idea could end up just being a standard part of the way the land is farmed.

“It’s something that can be built into how we use land right now and provide a carbon removal benefit alongside other benefits in terms of how we use land for food and crops,” he says.

There are still a lot of questions about how scalable it is. UNDO projects use by-products from local quarrying, but if this expands massively, the energy and emissions required to crush the basalt and then transport and disperse it will need to be considered.

“Right now, there’s no downside, it’s a win-win situation for everyone involved.” Jim Mann tells me.

This year UNDO plans to spread 185,000 tons of basalt and hopes to have eliminated one million tons of CO2 by 2025. It is still a drop in the ocean compared to emissions. In 2022, the world is believed to have released around 37 billion tons of CO2 into the atmosphere.