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Why the tech giant is so high on Heirloom Carbon

Microsoft is betting millions on the promise of some magic dust spread on a bunch of giant baking sheets stacked in 50-foot-tall towers to reverse the company's carbon emissions.
I’m being cheeky, but the truth is really not much more complicated than that.
Heirloom Carbon, a startup that has pioneered a method to absorb CO2 from the air using crushed rocks, just signed the tech giant to one of the biggest carbon removal deals to date. Microsoft has agreed to pay Heirloom to capture 315,000 metric tons of carbon from the atmosphere over 10 years. For a sense of scale, that’s equivalent to about 75% of the carbon Microsoft emitted in 2022 through its direct operations and energy usage. Neither company would disclose the price, but the Wall Street Journal estimated it would likely cost Microsoft a minimum of $200 million, “based on market prices,” or $635 per ton.
Climate scientists warn that we won’t be able to keep global warming in check solely by cutting emissions, no matter how rapidly the world acts to get off fossil fuels in the coming decades. Finding ways to pull what we’ve already emitted back out of the atmosphere and permanently sequester it can help balance out emissions from industries that might take longer to decarbonize, like aviation. In the long term, it could even cool the planet.
There are now hundreds of startups around the world racing to develop a variety of methods to do this. But many of them, including Heirloom, are still operating at a tiny scale, if they are even at the point of removing carbon at all. So this latest Microsoft deal stands out for signaling a high degree of confidence in Heirloom’s unique approach.
“Heirloom is quickly building a runway to low-cost CO2 removal at the gigaton scale,” a Microsoft spokesperson told me in an email. “This agreement accrues to our goal to become carbon negative by 2030 and remove our historic emissions by 2050.”
Heirloom harnesses the natural ability of minerals to absorb carbon from the atmosphere. The process starts with limestone, which is formed from the detritus of corals, clams, and other sea creatures that use the dissolved carbon and calcium in the ocean to build their shells. Heirloom grinds up limestone and does something that humans have been doing for thousands of years — heats it in a kiln. This loosens carbon dioxide from the rock, leaving behind calcium oxide, a white powder commonly called quicklime. The ancient Romans are believed to have done the same thing, using quicklime in the construction of many of their famous architectural marvels that are still standing today.
But Heirloom's modern kiln, which heats the limestone to about 1,650 degrees Fahrenheit, is electric, meaning it can run on renewable energy. Also, because no fuels are being combusted, the CO2 comes out in a pure gas stream that's easy to capture. Heirloom can either pump it permanently into underground wells, or inject it into long-lived products, like concrete.
This is only the first step. The real trick to Heirloom’s solution is what happens next. The leftover calcium oxide is “super thirsty for CO2,” the company's CEO Shashank Samala told me. “If you put that on your desk, it will start pulling out carbon.”
And that’s more or less what the company does. It spreads the powder on large trays stacked in 40- to 50-foot-tall towers, so that the maximum amount of surface area is exposed to the air. This, along with a proprietary bit of engineering that Heirloom has not disclosed, speeds up the material’s ability to absorb carbon even more. On your desk, it might take a year. In Heirloom's system, it takes a matter of days. Then the company pops the powder, which is now chemically similar to limestone, back into its kiln, and starts all over again.

It’s already been a big year for Heirloom. The company was selected by the Department of Energy to receive funding for a commercial-scale plant in Louisiana under the federal government’s $3.5 billion Direct Air Capture Hubs program. Heirloom will fulfill at least some of its contract with Microsoft at that facility, and has plans in the works to build a second plant as well.
Giana Amador, executive director of the Carbon Removal Alliance, an industry association, told me the deal with Microsoft illustrates this positive reinforcing loop that’s happening between the public sector and the private sector, helping the industry to scale faster. She wants to see the federal government do more to set standards around what high quality carbon removal looks like, in order to encourage more deals like this from companies that maybe want to purchase carbon removal, but can’t afford to hire whole teams to vet projects the way Microsoft can.
Samala emphasized that the deal is significant not only for its size but for what he called its “bankability.” It’s “take or pay,” meaning Microsoft has to pay up as long as Heirloom delivers on its end of the bargain. Even though no money is exchanging hands up front, Heirloom can take this binding contract showing a predictable, durable, revenue stream to the bank, and use it to secure financing at a much lower cost than it would otherwise get from a venture capital firm.
Right now, much of the nascent carbon removal industry is being supported by venture capital. One of the obstacles to financing projects is that nobody knows what the business model will ultimately look like. Will this be a public service, like waste disposal? A regulated requirement, where polluters are asked to pay? Something else? And in the meantime, how do you raise enough money to scale your idea up to where you can credibly sell it?
The Heirloom deal shows the industry is increasingly looking to replicate the experience of early wind and solar projects. This long-term contract is similar to a power purchase agreement, where wind and solar developers finance new projects by pre-selling the electricity to corporations like Google or Walmart at a set price.
At 315,000 tons over 10 years, this isn’t the biggest carbon removal deal to date, but it may be the biggest for such a fledgeling company. The oil giant Occidental, which is building a facility in Texas designed to suck 500,000 tons of carbon dioxide from the atmosphere per year, has pre-sold 400,000 tons’ worth of carbon removal credits, over four years, to the aircraft manufacturer Airbus. In May, a coalition of tech companies signed a 112,000-ton offtake agreement, over six years, with a small startup called Charm Industrial, for $53 million. Charm is working to turn agricultural waste into oil that can be pumped underground.
Microsoft was an early investor in Heirloom through its Climate Innovation Fund, providing some of the company’s Series A funding last year. “They’ve seen this in the front row seats as we made progress from pulling grams of CO2 from a Petri dish to pulling kilograms and hundreds of kilograms, to tons and hundreds of tons,” Samala told me when I asked what he thought gave Microsoft confidence in the deal.
Part of it was also showing them that this solution is modular, Samala said.
“It helps to see that okay, you just need to build more of these stacks, more of these trays. If you want to pull more carbon, you stack more trays and you put more stacks of trays around."
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In Providence, at least, climate change is still on the ballot.
Here’s some trivia for you: What was the first state to see its average temperature break the 2-degree Celsius threshold for warming above pre-industrial levels? It wasn’t Alaska, the fastest-warming state, nor was it California or Florida, states with some of the most visible impacts of the extreme weather crisis. It was not Arizona or Texas, either, though “hot” and “warming” are often conflated.
The answer, in fact, is humble Rhode Island, which passed the international benchmark for accelerated climatic impacts back in 2019. It is perhaps less surprising, then, to learn that in the Ocean State’s largest city, Providence, climate change and how to adapt to it have become one of the central talking points in a heated mayoral race, which in the deep-blue city is likely to culminate in the September 9 primary.
There is plenty to worry voters. Providence sits at the head of Narragansett Bay, which has warmed 1.6 degrees Celsius, enough to drive lobsters from the region and convert the local lobstermen into crabbers, fishing for crustaceans they previously considered bycatch. The sea level has risen on Rhode Island’s 400-plus miles of coastline by more than 10 inches since 1930, more than in Venice or Miami, meaning the city floods frequently. Locals hold their breath every hurricane season; a hit from a category 4 or larger storm could tally billions in damages. And as home to the biggest port in the region, Providence is also an unfortunate case study in industrial and fossil-fuel-related pollution affecting historically redlined neighborhoods.
“Since I’ve been in office, we’ve had dramatic, chronic flooding. We’ve had high heat days in the fall that have closed public schools, which is not something that ever happens here in September,” Providence Mayor Brett Smiley told me. “We had some of the highest snowfall in recorded history [in the city]. We’re seeing the effects.”
Smiley, who was elected in 2022, has described investing in infrastructure upgrades for the nearly four-century-old city as one of his “principal responsibilities” as mayor. During his second year in office, he signed an ordinance requiring all of the 122 city-owned buildings to decarbonize by 2040, and that fall published a 10-year plan that introduced air quality, heat, and stormwater management goals, provisions aimed at curbing pollution at the Port of Providence, and would have effectively banned the construction of new gas stations. (A later amendment relaxed the restrictions.) He’s also invested in long-overdue repairs to the city’s hurricane barriers.
This year, Smiley also announced the creation of a Green Revolving Fund to support Providence’s ambitious carbon neutrality goals. “I’ve been in government long enough to know that operating budgets can change as priorities change, and so having a dedicated recurring revenue stream is vital to ensuring that this work continues,” he said.
In the face of federal headwinds, and at a time when the political currency of “climate change,” at least in so many words, is on the downswing, Smiley’s focus on climate issues stands out. That is especially true against the backdrop of a broader state-level reassessment of environmental goals, with Democratic Governor Dan McKee proposing a budget earlier this year that would have slashed climate programs funded by monthly utility charges in the name of affordability. Though Rhode Island lawmakers ultimately rejected that rollback, McKee’s move fits into a larger trend in the region of blue-state politicians in places like Maryland, Massachusetts, and New York curbing or weakening climate ambitions under the pressure of affordability politics. (McKee also faces his own competitive primary.)
“Providence alone can’t solve the climate crisis. But our actions, at least in Rhode Island, are pushing other communities in the state to take action,” Smiley said.
But there are others — including Smiley’s progressive challenger, State Representative David Morales — who say the mayor’s tenure has been a lot of talk and little action, and that he’s neglected Providence’s low-income and frontline communities.
Morales’ campaign did not get back to me for this article, despite requests through multiple channels. But Steve Ahlquist, an independent reporter who follows environmental justice-related issues in Rhode Island, also told me that “over the years, and also in dealing with Mayor Smiley as an incumbent, I’ve had some real difficulty with what I would even call basic honesty out of his administration.” He added that the mayor’s office has a history of downplaying and denying police harassment of unhoused people in particular, including lying about the presence of police officers at a homeless encampment and their involvement in an “illegal search” in 2023.
When I asked the Smiley administration about Ahlquist’s accusations, press secretary Carl Austin Miller Grondin told me the city has a “multi-department approach” for addressing encampments of which “Providence Police are one piece,” though he didn’t address the 2023 incident directly. As for the idea that Smiley represents the status quo, Grondin said the mayor has made “significant investments” in programs for underprivileged groups including affordable housing, eviction prevention, public schools and youth programming, and public safety.
Ahlquist also finds Smiley’s talk about affordability and clean energy false, however. Smiley notably vetoed a rent control ordinance, despite the city having some of the highest rates in the country, and while serving as former Governor Gina Raimondo’s chief of staff between 2016 and 2019, he helped push for the expansion of fossil fuel infrastructure in the form of a $1 billion fracked gas and diesel oil power plant that was ultimately thwarted by community pushback. (Grondin told me “rent control policies do not lower rents” and that the mayor “has instead taken a disciplined, results-driven approach to lowering housing costs.” The power plant project was proposed before Smiley’s tenure in Raimondo’s administration, he added.)
Morales, 27, is a Democratic Socialist and has won the backing of Vermont’s Independent Senator Bernie Sanders. His scrappy campaign against an establishment incumbent Democrat has earned him comparisons to New York City’s young, charismatic Mayor Zohran Mamdani. Unlike Mamdani, however, Morales has made climate central to his campaign.
Morales has gone after Smiley particularly hard on environmental justice issues, sensing a weak spot in his record. “Industrial facilities near the Port of Providence have polluted our neighborhoods for decades,” his issues page reads. “David will require them to contribute more toward the city services and infrastructure our communities deserve.”
A nearly two-mile stretch of Allens Avenue, which flanks the port, is home to asphalt plants, scrap metal recyclers, oil and gas companies, and petroleum storage tanks with a history of leaks, spills, dumps, and other forms of contamination. Locals complain that even just driving along the avenue is enough to make you sick, with 11 identified polluters within a mile radius of National Grid’s newest LNG plant. Traffic to and from the port adds to the odor — and health impacts — in the neighboring communities of South Providence and Washington Park, which have some of the highest hospitalization rates in southern New England. Notably, South Providence’s population is 90% people of color; Washington Park’s is above 60%.
Smiley bristled at Morales’ plan to tax polluters. “Many of my opponent’s proposals — which continue to evolve, by the way — are illegal or not allowed, and he leaves some of those details out, and sometimes changes his position,” he told me. Ahlquist, who issued a rare endorsement of Morales last spring, contends that “we know for a fact it is not illegal” to tax polluters at a different rate. (In truth, it’s a bit of a legal gray area; Providence’s tax code allows it to adopt a classification system with different rates for industrial properties, but whether that classification can be used to single out specific polluters on Allens Avenue is murkier.)
In an interview with Ahlquist, Morales has also proposed buying out the Rhode Island Recycled Metals property — where some of the worst contamination has originated — and pursuing “brownfield mediation” in the area. “I find it shameful that Public Street, one of the few shoreline access points around the Port of Providence, is not a very welcoming environment,” he said. On the adaptation side, he’s proposed passing a green energy bond to invest in renewable energy and upgrade the sewage system with an eye on future flooding.
A week ago, it might have seemed as though Morales had progressive momentum on his side. But after the upset of Democratic Socialist Francesca Hong in Wisconsin on Tuesday night and the narrow victory by progressive up-and-comer Abdul El-Sayed in Michigan the week before, the narrative is now more complicated. Meanwhile, the first primary poll shows Smiley with a 4-point edge — within the margin of error, but still likely to have the Morales campaign in a state of jitters.
Climate adaptation can sometimes fall under a variation of the refrain parodied in urban infrastructure circles: One more study would fix this. That’s especially true in Rhode Island, where study after study has highlighted the problems Morales and Smiley are circling, and yet here they still are, at the center of yet another mayoral race.
“One of the things that frustrates me is when you write a plan and then put it on the bookshelf, and that’s the end of it,” Smiley told me, sounding genuinely irked as we spoke on the phone. “That’s not how I do plans.” He told me stormwater infrastructure would be a major focus of his administration if he’s elected to another term, while he hopes his decarbonization roadmap and the green revolving fund will outlast his mayoralty, whenever and however it may end.
Morales has been stymied before, too. Ahlquist recalled watching the young legislator in the State House at the end of a legislative session, when, in the waning hours, he was told by leadership that a bill he’d been working on wasn’t going to get through. “David, when he’s in public, he’s very controlled, very managed,” Ahlquist said. But from his vantage point, Ahlquist could see Morales had started to cry.
“It’s midnight, the last days of session, and I just saw something raw in him then,” Ahlquist said. “It was like, Wow, this is a guy who really gives a shit.”
Editor’s note: This story has been updated to include responses from the Smiley campaign.
Chatting about win-win solutions with the Abundance Institute’s Ryan Norris.
This week’s conversation is with Ryan Norris, senior fellow for energy policy at the Abundance Institute. The libertarian-leaning institute — whose name cleverly shortens to AI — is a new-ish entity with increasing relevance in energy and tech spaces. As Norris and I discussed, it’s starting to help shape policy on data center development and the generation that’ll power it all, especially in Republican circles. Norris himself previously worked with Americans for Prosperity, a right-wing political organization. I reached out to him and asked if we could chat because I wanted to know more about the institute’s work within the energy space. He wound up saying a lot more than I expected. So let’s dive into it.
The following conversation was lightly edited and abridged for clarity.
So let’s start with what you’re working on. What’s on your desk these days?
Here at Abundance, we sit at the juncture of emerging technology and the energy they need to bring that new technology to bear to impact life positively. We are always in a constant state of learning and researching what the latest thoughts and feelings are around certain policies, particularly around AI and data centers, and then energy technology. How do they feel about nuclear? Geothermal? Solar and battery arrays?
A lot of what I’m working on is Project Gigawatt, a body of policy that fits into permitting, generation, the grid, transmission, and then market and demand. Policies that we believe will generate more, transmit more, and as much of a free market approach as possible. Knowing that a lot of states have regulated utilities, when the state utility can’t produce what the state can potentially actually generate or would need to in order to accommodate large loads, we think there needs to be other opportunities to either bring that power or purchase it in a different way.
When it comes to this policy set, how are you taking into account the intensifying backlash to data center and AI infrastructure, as well as the energy attached to it?
As everyone can sense, things are moving rapidly, and there is a natural inclination to question how fast we’re going. I think these concerns need to be addressed seriously and respectfully. You can’t just say negative things about people who care about water quality or impacts to their local economies. Those are valid. I’ve lived through those. I come from a rural place in Arkansas that had oil and gas plays. And I’ve seen there needs to be conversations with people living in those areas too.
We cannot discount the backlash. When you take the legitimate concerns and pair them with the opportunities coming, I think there’s actually a chance to set up win-win solutions. It shouldn’t be a win-lose scenario here. They have skepticism about AI in the short and long term — that’s a natural inclination and not a negative, per se. But educating people and policymakers about data centers, that’s important.
What is your approach to the rise in land use regulation around data centers and energy infrastructure, moratoria and restrictive ordinances?
As much as possible, you want the infrastructure and cost allocation to be borne by the business causing it. That’s the motivation behind a lot of colocation partnerships happening right now, like the Kilby project in Texas, with natural gas powering a Microsoft hyperscale.
To us, it’s about setting up the opportunity for private property owners to sell to those hyperscalers and those generating the energy. Setting up situations where you’re not stopping people from benefiting. A lot of the “bring your own power” concept, we really like that. Maybe having it where power purchase agreements are more in the mix, things along those lines. That’s where I see things.
The energy increases to our utility bills, people are concerned about it, and that’s a bread and butter issue. That’s the approach: We know we need grid upgrades and want to have the most cost effective versions of those as possible, but you want those needing the power paying for it and not putting it on the backs of residents.
I’m curious, what’s you and your organization’s approach to the rise of gas infrastructure built for AI and the potential impacts that could have on climate change?
I don’t discount the issue of climate change.
Let’s say we’re not able to decarbonize enough to reverse the effects of warmth. We know we’ll have to create energy. We know we have other options for energy that need to be in the mix — more nuclear, which now even some of those who are climate-minded understand is an abundant energy source. I’m also interested in new technologies in geothermal where it can be viable in more places than we thought. You can drill down and tap hot rocks, a basin of water, turn a turbine, and that’s more acceptable for those who care about the climate. And states are looking at it, including my state of Arkansas. I bring these up because I also care about sources that provide firm, consistently available power.
We attended the American Legislative Exchange Council, and one of the things we do, we’re voting members on the energy, environment, and agriculture task force. We’re pro letting the market decide what they need. So we took opposite stances from what people typically consider normal standards on the center-right about banning “net-zero” for local governments. It did pass as model legislation but if we believe “all of the above” is the approach, we also want to be principally correct to ourselves that it doesn’t mean banning wind or solar where it’s viable.
My last question: What’s your thought on the future of politics around AI infrastructure and energy generation for it?
There’s definitely headwinds to those in that industry. I think the sense is, they understood what they wanted and didn’t see any barriers to the way they’d go about it. That’s causing ripple effects in our politics at the local level, including here in Arkansas, where I live in Pulaski County. I think it’ll stay important particularly as it connects to affordability concerns around energy. We know we need more energy, but we want it at the lowest cost possible to the residential side. If people are feeling like data centers are driving the demand for the energy and aren’t on the hook for it, that’s going to position them to be more negative towards the technology.
But we have to expand the conversation. There are folks out there talking about 3D printing for homes, using proprietary cement mixes to build homes in a few weeks when they took months. Agriculture is using robotics in lieu of pesticides and herbicides. Advanced manufacturing is improving the quality of medical equipment. No one completely understands the end goal of new energy to fuel the data centers and AI to get us where there’s a net benefit to them.
Plus more of the week’s biggest development fights.
1. Shelby County, Alabama — The Trump administration’s widening effort to intervene in rural energy project fights is facing an early test: What happens if companies don’t take it seriously?
2. Ozaukee County, Wisconsin — Speaking of walls, we just saw the political power of the data center resistance hit one in the Badger State.
3. Everywhere in Texas — Texas Governor Greg Abbott is getting a lot of love for his data center standards, with major developers rolling out press statements claiming they’ll comply.
4. Herkimer County, New York — Something weird is going on in upstate New York with a monastery, a wind farm, and the Trump administration. I’m not sure what to make of it yet.