The Next Big Climate Tool: Little Chunks of Rock

When we talk about carbon removal, we often focus on “direct air capture” facilities — big factories that suck carbon dioxide out of the ambient air.

But a simpler and easier way to remove carbon from the atmosphere may exist. It’s called “enhanced rock weathering” — grinding up rocks, spreading them out, and exposing them to the ambient air — and it works, essentially, by speeding up the Earth’s carbon cycle. Enhanced rock weathering recently got a major vote of confidence from Frontier, a consortium of tech and finance companies who have teamed up to support new and experimental carbon removal technologies.

Frontier’s members include Stripe, Meta, Alphabet, Shopify, and McKinsey & Company. It aims to buy nearly $1 billion of various forms of carbon removal in the next few years — an intervention meant to spur commercial and investor interest in the sector.

In this episode, Jesse Jenkins, an energy systems expert and professor at Princeton University, and I talk with Jane Flegal, a former Biden White House climate adviser and now the market development and policy lead at Frontier, about the promise of enhanced rock weathering and why Frontier just spent $57 million to do it.

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Here is an excerpt from our conversation:

Jane Flegal: So enhanced weathering is a carbon removal process that speeds up a natural process which is weathering of alkaline materials. And so weathering happens naturally, it actually drives what makes the earth habitable in the first place. It just happens over very, very long periods. So essentially what happens is that rocks slowly erode when they come into contact with acid rain essentially and —

Robinson Meyer: Naturally acidic rain?

Flegal: Yeah, not like acid rain the way we think of it, rain that is acidic because it has some dissolved CO2. And so that acidic rainwater interacts with rocks and erodes them, and it results in CO2 being stored either as a solid carbonate or as a bicarbonate. So that happens naturally, again, on very long time periods.

Meyer: And I just want to interrupt before we go any further. What then happens, right, is that the CO2 winds up being dissolved as a bicarbonate. It goes into the ocean.

Flegal: Into the ocean.

Meyer: And then what happens? It’s turned into ...

Flegal: It sinks and becomes part of the Earth’s crust.

Meyer: Right. Or it gets turned into a shell, a creature’s shell, and then it sinks again.

Flegal: It is functionally stable. It is thermodynamically pretty much impossible to reverse.

Meyer: And you kind of said this, but I do want to draw it out: This is the carbon cycle. This is a central Earth science process. There’s nothing fancy about this.

Jesse Jenkins: The problem is it takes centuries to play out. It’s just moving on geologic time. But this idea of enhanced weathering means we can potentially speed that up, right?

Meyer: Sorry, I just want to — this is, like, the whole problem of climate change, right? The problem of climate change is that we take fossil fuels and carbon that’s stored in geological storage out of the ground on historic time scales, on decadal ... you know, every year we take millions of tons of it out of the ground, and then it would only be restored back to the ground by this extremely slow process.

Flegal: One way to think about carbon removal is, like, taking stuff out of the fast cycle and putting it into the slow cycle, basically. And essentially, you either inject CO2 underground, where it’s where it’s stable, or you turn it into salt. These are kind of the options.

And so enhanced weathering, to exactly this point, it’s enhanced for a reason, right? There’s regular old weathering, and then there’s the enhanced kind, which aims to speed up this process that typically takes millennia to years or days by either using more reactive materials than the normal rocks that would just weather naturally or increasing the surface area of the material that is exposed to CO2. So grinding up rocks into very, very fine fine powder and exposing that material to more favorable environments.

This episode of Shift Key is sponsored by Advanced Energy United, KORE Power, and Yale …

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Music for Shift Key is by Adam Kromelow.