Google, Salesforce, H&M and other brands have turned to unlikely allies to help them clean up their carbon pollution: sewage treatment plants and paper mills. The companies joined an $80 million plan to take CO2 out of the atmosphere, though the strategies they’re using have yet to show whether they can have a meaningful impact on climate change.

They’re paying $32.1 million to a startup called CREW that aims to trap carbon dioxide emissions produced at wastewater treatment facilities. And $48 million will go to another startup called CO280 that retrofits pulp and paper mills with controversial carbon capture technologies. The two agreements were facilitated by a carbon removal initiative called Frontier that’s led by led by Stripe, Google, Shopify, and McKinsey Sustainability on behalf of those founding companies and other brands trying to meet their own sustainability goals.

Companies are increasingly looking for ways to try to cancel out the damage caused by their greenhouse gas emissions. They’ve funneled millions into startups building new-fangled industrial plants that filter CO2 out of the ambient air or seawater. Frontier’s latest announcement shows they’re also open to backing even more novel tactics for drawing down carbon dioxide.

“We do need to be looking at a lot of different kinds of approaches,” says Wil Burns co-director of the Institute for Responsible Carbon Removal at American University, who is also part of an assessment committee for Frontier. “Some of these approaches still remain extremely expensive, notably direct air capture, so we’re looking for approaches that potentially are less expensive.”

The first generation of industrial facilities built over the past decade or so to filter CO2 out of the air — called direct air capture — cost companies including Microsoft upwards of $600 per ton of captured carbon. The deals Frontier just brokered come out to around $447 per ton of CO2 removal by CREW (for a total of 71,878 tons), and $214 per ton for CO280’s services (for a total of 224,500 tons).

That’s still well above the $100 per ton that industry leaders often say they’re targeting. And for a company like Google that was responsible for 14.3 million metric tons of carbon dioxide pollution last year, you can see how prohibitively expensive the technology still is.

While CREW’s strategy is more expensive, Burns says he’s particularly excited about its potential. The idea is to capture carbon dioxide that otherwise would have been released by microbes that break down organic waste in water treatment tanks. To do this, CREW adds alkaline minerals to the tanks. Those minerals react with the CO2 microbes produce, trapping it in water as bicarbonate. Eventually, the bicarbonate travels with the treated wastewater out to oceans, which are natural sinks that keep CO2 out of the atmosphere.

CO280, on the other hand uses technologies initially developed by the fossil fuel industry to capture CO2 emissions from smokestacks before they can escape into the atmosphere. These kinds of devices have been added to industrial facilities and power plants in the past, and can collect CO2 that companies might then shoot back into the ground to push out hard-to-reach oil reserves.

CO280 takes a different approach by adding carbon capture devices to facilities that burn “black liquor,” a bi-product from pulp manufacturing that’s used to generate heat and power. The devices are supposed to capture the CO2 from burning black liquor so that it can be permanently stored in underground wells. Since the fuel is made from trees, the process essentially sequesters CO2 that those trees drew in through photosynthesis during their lifetimes.

To be sure, there are still major concerns about how effective carbon capture technologies are as a way to mitigate climate change. They use a lot of energy, which generates its own greenhouse gas emissions. There are also additional emissions from cutting down trees and transporting wood for paper mills, and it can be difficult to ensure that tree plantations are managed sustainably.

Companies buying carbon removal services also get flak from environmentalists concerned that it’s a distraction from more critical efforts to transition from fossil fuels to clean energy. At the end of the day, the only surefire way to stop climate change is to prevent the greenhouse gas emissions from fossil fuels that are causing the crisis in the first place.

To try to counteract the impact their pollution has on the climate, Google and other big companies have bought into a plan to trap carbon dioxide using rocks. They recently announced multimillion dollar deals with a Sheryl Sandberg-backed startup called Terradot.

Google, H&M Group, and Salesforce are among a gaggle of companies that collectively agreed to pay Terradot $27 million to remove 90,000 tons carbon dioxide from the atmosphere. The deals were brokered by Frontier, a carbon removal initiative led by Stripe, Google, Shopify, and McKinsey Sustainability.

Separately, Google announced its own deal to purchase an additional 200,000 tons of carbon removal from Terradot. Both companies declined to say how much that deal is worth. If the cost is similar to the Frontier agreement — roughly $300 per ton of CO2 captured — it could add up to $60 million, although Google says it expects the price to come down over time for this larger deal.

Google says it’s the biggest purchase yet of carbon removal through enhanced rock weathering (ERW), the strategy Terradot uses to try to slow climate change. It’s a relatively low-tech tactic for taking carbon dioxide out of the atmosphere that now has significant backing from some big names.

“I mean, it’s a big deal, says Oliver Jagoutz, a professor of geology at MIT. “I think it should go a little out of the academic world into the industrial world. And I wish these guys all the best.”

Terradot grew out of a research project at Stanford, where CEO James Kanoff and CPO Sasankh Munukutla were undergraduate students at the time. Shortly before graduating in 2022, they co-founded the company along with Kanoff’s former professor, Scott Fendorf, who is now Terradot’s chief scientist and technical advisor.

Before starting that research project, Kanoff had briefly dropped out of Stanford during the covid pandemic to co-found a nonprofit called the Farmlink Project that connects food banks to farms with excess produce. Kanoff met Sandberg through that initiative, which is how he was able to get the former Facebook COO’s support for Terradot as an investor.

“I’ve known James, the CEO, since long before this company started,” Sandberg said in a press release. “These are proven leaders, which is rare to find in an early-stage company. They have the drive, the right technology and a strong focus on execution to succeed.”

Enhanced rock weathering attempts to speed up a natural process that might otherwise take thousands of years. Rainfall naturally “weathers” or breaks down rock, releasing calcium and magnesium and triggering a chemical reaction that traps CO2 in water as bicarbonate. Groundwater carrying that bicarbonate eventually makes its way to the ocean, which stores the carbon and keeps it out of the atmosphere.

Accelerating the process, in theory, is simple: crush up rock and spread it out over a large area, increasing the surface area of exposed rock that reacts with CO2. Terradot has a 2029 deadline to make good on the 90,000-ton Frontier deal. It’s supposed to capture the additional 200,000 tons for Google by the early 2030s.

Terradot takes basalt from quarries in southern Brazil to nearby farms. Farmers can use the finely-ground basalt to manage the pH of soil, and carbon removal is a bonus. Terradot struck up a partnership with Brazil’s agricultural research agency (EMBRAPA), allowing the startup to use this strategy on more than one million hectares (roughly 2,471,054 acres) of land. Another perk in Brazil is a hot, humid climate that also helps to speed up the weathering process.

The tricky part will be trying to count how much CO2 Terradot actually manages to trap. Google admits this in its announcement:

Right now, it’s hard to measure with precision how much CO2 this process removes from the atmosphere. But the only way to develop highly rigorous measurement tools is to deploy this approach widely in the real world. That’s why our support aims to help Terradot’s solution get out of the lab more quickly.

Terradot says it’ll take soil samples to assess how much CO2 is captured based on how the rock degrades over time. But it’s harder to figure out how much calcium, magnesium, and bicarbonate makes it to the ocean to permanently sequester CO2. Fertilizer in the soil can also potentially limit how much carbon is captured through enhanced rock weathering.

“How much they sequester is still the outstanding question,” Jagoutz says. But he doesn’t think that uncertainty needs to stop trials in the real world. “I also think, why not try? … I don’t think we have the luxury to overthink it right now.”

Carbon dioxide emissions from fossil fuels are already making heatwaves, droughts, wildfires, storms, and other climate disasters more dangerous. And Google’s carbon footprint has grown as it builds out energy-hungry AI data centers. The company has recently announced plans to help develop advanced nuclear reactors and new solar and wind farms to power its data centers with carbon pollution-free electricity. When it comes down to it, switching to clean energy is the only effective way to stop climate change.

Carbon removal, at best, is just an attempt to counteract some of a company’s legacy of pollution while they make that energy transition. And even though Google says it signed the biggest ERW deal to date, 200,000 tons of carbon removal is still a small fraction of the 14.3 million metric tons of carbon dioxide pollution it was responsible for last year.

“It’s very clear that this is not a substitute for emissions reductions at all … we need both of these tools,” Kanoff says. “Any of the partners we’re even thinking about working with, they have some of the most aggressive emission reduction strategies of any of the companies really in the world. And those are the groups that we really want to partner with to advance carbon removal.”