Dramatically reducing carbon dioxide emissions is the first step towards stopping catastrophic climate change — but it’s not the last. If all emissions stop tomorrow, the atmosphere will still be clogged with 200 years’ worth of human-produced CO2. The planet will continue to warm. The seas will continue to rise.

“The question is, what do we do with all this excess CO2 in the atmosphere,” said Noah Deich, Executive Director and co-founder of the non-profit Center for Carbon Removal.

In 2014, the United Nation’s Intergovernmental Panel on Climate Change reported that preventing a 2°C increase in global temperatures above pre-industrial levels would likely require a global strategy to remove CO2 from the atmosphere.  

The question is, what do we do with all this excess CO2 in the atmosphere?

Despite its outsized impact on climate, CO2 molecules represent only .04 percent of the air — that’s one in 2,500 molecules. An industrial-scale machine that could remove meaningful amounts of CO2 would need to move huge amounts of air, requiring lots of energy, which means lots of money.It turns out that capturing airborne carbon is less of a scientific challenge – technology for removing CO2 from ambient air has been around since the 1940s – than an economic one.

For years, this strategy of CO2 removal, known as direct air capture, has been viewed as an exotic pipe dream, too expensive to be practical. A paper published in 2011 estimated the cost of direct air capture could be as much as $1,000 per metric ton of CO2.

But David Keith, the Gordon McKay Professor of Applied Physics at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Professor of Public Policy at the Harvard Kennedy School, thinks it can be done for a lot less.

Keith and his colleagues estimate that their company, Carbon Engineering, could capture CO2 at a price between $94 to $232 per metric ton. In the journal Joule, the Carbon Engineering team outlined the material and engineering costs of their system – the first time the costs of a commercial direct air capture process have been published.

The paper could have major ramifications across the industry.

“Until now, basically no one in the industry has published an open book number that will give credibility that direct air capture costs less than the $500 to $1000 per metric ton that has been estimated,” said Deich.

“We need enormous volumes of CO2 removal and to achieve that, we need accurate economic analysis and hard engineering data,” said Julio Friedmann, CEO of Carbon Wrangler LLC and senior advisor at The Global Carbon Capture and Storage Institute. “This paper provides that transparency.”

Keith co-founded Carbon Engineering in 2009, when direct air capture was still on the fringes of industrial climate solutions. Carbon Engineering’s goal is to use direct air capture to produce carbon-neutral fuels, enabling carbon-free energy to be converted into high-energy fuels for difficult-to-electrify vehicles such as planes and barges.

Keith and his team’s approach is fundamentally different than their few competitors in the field.

“At Carbon Engineering, we’re not developing a fundamentally new product or unit operation,” said Keith. “That’s the design choice we made. We’re making something that’s never been done before — commercial large-scale air capture — but we’re doing it on a basis of technology that already exists."

Using existing technology in novel ways is the ultimate engineering challenge.

CE’s pilot pellet reactor and associated equipment

CE’s pilot pellet reactor and associated equipment (image courtesy of Carbon Engineering)

The Carbon Engineering system uses a remodeled industrial cooling tower which contains a liquid hydroxide solution that captures CO₂ and converts it into carbonate. Next, the carbonate is converted into pellets in equipment created to extract minerals in water treatment plants. Those carbon pellets are heated with a kiln originally designed for gold roasting and transformed into pure carbon dioxide gas, which can be turned into synthetic fuel.

The Carbon Engineering team worked directly with commercial suppliers of each of these pieces of repurposed equipment to design tests, engineer alterations, and develop cost estimates to adapt the hardware for a commercial direct air capture plant.

“In a post-Paris Accords world, everyone has been talking about carbon removal but most of the analysis is secondary literature or policy perspectives,” said Keith. “This is the first paper to estimate the cost of direct air capture based on a detailed engineering design and cost analysis. While uncertainties, of course, remain, the fact that it can be build using established processes and suppliers gives us confidence to develop industrial-scale plants.”

With that cost breakdown, direct air capture — especially direct air capture that can be used to make synthetic fuel — may look less exotic and more attractive to investors and policy makers.

CE’s direct air capture pilot plant in Squamish, B.C. Shown are the air contactor (foreground) and calciner (upper left)

CE’s direct air capture pilot plant in Squamish, B.C. Shown are the air contactor (foreground) and calciner (upper left) (image courtesy of Carbon Engineering)

In addition, direct air capture technology is location independent, which should make it even more attractive to investors, said Joe Lassiter, retired Senior Fellow and Senator John Heinz Professor of Management Practice in Environmental Management at the Harvard Business School.

“A commercial carbon capture facility could be located anywhere in the world where renewable or nuclear is inexpensive,” said Lassiter. “This is an example of how engineering and human cleverness can find economically feasible and sustainable solutions to the problems that society faces.”

Keith and the Carbon Engineering team have raised about $30 million to date, the next step is to raise funds for a plant that can deliver fuels to market, which depends on finding a renewable power supplier who wants to supply high capacity power at a low price and incentives for low carbon fuels.

“I hope this paper will launch 1,000 master’s students to figure out how to create an even better future using this technology,” said Friedmann.