Focus on Arts and Ecology

A high-tech approach to combating climate change — often thought of as a futuristic last resort, decades away from reality — may now be a step closer to a commercial future.

Researchers from the Canadian company Carbon Engineering have just published an in-depthreport in the journal Joule on a technology designed to pull carbon dioxide straight out of the air, a process known as "direct air capture." Afterward, the climate-warming gas can either be compressed and stored away or converted into fuel.

They're not the first or only scientists working on developing direct air capture systems. Last year, the company Climeworks became the first to open a commercial direct air capture plant, currently operating at a small scale — capturing less than 1,000 tons of carbon dioxide each year — in Switzerland. But the new report is the first in the peer-reviewed literature to outline a complete engineering process with a detailed cost breakdown included, says lead researcher and Harvard University engineer David Keith.

And the analysis suggests the technology may be cheaper than previously thought. Depending on what happens to the gas after it's collected, the whole process may cost from just over $232 per metric ton of CO2 captured to less than $100 per ton.

"What I really hope is this kind of calms down the shouting match about the cost of direct air capture," Keith said.

Prior cost analyses for direct air capture have been few and far between, he told E&E News. One2011 report from the American Physical Society concluded that the technology would likely cost at least $600 per ton of carbon dioxide removed. At that price, the process is probably "not currently an economically viable approach to mitigating climate change," the authors said.

"What is new and important here is not just the technology but also the transparency around estimated engineering costs," David Victor, a University of California, San Diego, expert on energy and climate change policy, said in an email to E&E. "There's been a lot of talk about DAC [direct air capture] but nobody really knows what it costs."

The new cost breakdown would seem to place the technology a step closer to economic viability. For now, the company is focusing on finding partners for air-to-fuel plants, which would convert the captured carbon dioxide into fuels for cars, jets and other vehicles. It's hoping to have the first commercial plants running in the next three to four years.

As global temperatures continue to rise, scientists have grown increasingly concerned that they'll blow past certain dangerous thresholds. Currently, the Paris climate agreement calls for world leaders to keep global temperatures within at least 2 degrees Celsius of their preindustrial levels and within a more ambitious 1.5 C limit if possible.

Now, some researchers suggest that overshooting the 1.5 C goal is increasingly likely — meaning the only way to meet the target would be to cool the climate back down again after the fact. One of the most widely discussed methods is the use of "negative emissions" — technology designed to pull carbon dioxide back out of the atmosphere.

Scientists have proposed a variety of negative emissions strategies, including everything from enormous carbon-guzzling tree plantations to special carbon-storing minerals (Climatewire, June 4). Direct air capture machines have been widely discussed, as well, but have often been dismissed by experts as too expensive and unproven at the needed scales.

Carbon Engineering is one of several groups now working to make the technology a commercial reality. It already operates one pilot plant in British Columbia, and its researchers say the technology is easily scalable.

The technology itself relies on a series of carefully engineered chemical processes. First, outside air flows through a structure known as the contactor, which contains an alkaline (or chemically basic) solution. This solution reacts with the air's slightly acidic carbon dioxide and converts it into a different chemical compound known as carbonate.

Another series of processes is used to remove the carbonate from the liquid solution and turn it into pellets. These pellets can then be converted back into carbon dioxide, which may then be either compressed for storage or used in the making of hydrocarbon fuels.

If the captured carbon is stored away (most proposals involve stashing it deep underground), the whole process becomes carbon negative — that is, it results in a net removal of carbon dioxide from the atmosphere. If it's converted into fuel, those emissions eventually go back into the atmosphere, but the fuels may be considered carbon neutral — they release the same amount of carbon that was captured to create them.

The Climeworks operation in Switzerland currently feeds its captured carbon dioxide into greenhouses, for use in fertilizing plants. But a second direct air capture plant, currently testing in Iceland, aims to pump the captured carbon dioxide underground — the classic negative emissions strategy.

Carbon Engineering's technology can be applied in this way, as well. But for now, the company is mainly focused on finding partners for commercial air-to-fuel plants — an easier market, for the time being, according to CEO Steve Oldham. The problem with direct air capture purely for negative emissions, he noted, is that "nobody's paying for that right now."

In the meantime, he said, "we wanted to do something where economically it made sense, but also we can make a significant difference in reducing emissions. And we believe the fuels market achieves both of those." Currently, emissions from the transportation sector account for around a fifth of global greenhouse gas emissions.

Renewable or low-carbon fuel standards in the United States, Canada and abroad, have already created a market for zero-carbon fuels. At the moment, Oldham said, the costs for Carbon Engineering's fuels would probably hover around 20 percent higher than the cost of the equivalent fossil fuels. But he said that "anybody who uses our fuel and sells our fuel will be able to claim carbon credits that more than offset that 20 percent extra cost."

As far as direct air capture purely for negative emissions, there are far greater challenges in finding a market. According to Victor, the UC San Diego policy expert, the government would likely have to introduce specific types of incentives to make it worthwhile for industries to invest in the technology. These could include either some sort of penalty for emissions, such as a carbon tax, or a subsidy for carbon removal.

Even if those came to pass, challenges would still exist. According to Christopher Knittel, an energy economics expert at the Massachusetts Institute of Technology, the cost range presented in the new paper — $94 to $232 per ton of carbon dioxide removed — is still "very high," despite being significantly lower than previous estimates.

A useful standard for comparison is the social cost of carbon, a metric used to evaluate the monetary costs of emitting carbon dioxide into the atmosphere, given all the damages associated with climate change. While the Trump administration has proposed substantially lower values, the Obama administration placed the cost at around $40 per ton, a value many experts still cite (Climatewire, Nov. 22, 2017).

Assuming the social cost of carbon would be used as a standard to help set future carbon-pricing programs (in the past, it's been used in all sorts of cost-benefit analyses used to develop environmental regulations), even $94 per ton of carbon dioxide would still be a high price, Victor noted.

For now, most carbon capture projects — including those that capture carbon emissions directly from industrial plants rather than straight out of the atmosphere — have a necessary interest in other streams of revenue. For instance, many groups are exploring the possibility of selling captured carbon (typically, emissions captured on-site from factories or other industrial activities) for use in enhanced oil recovery, a process that injects CO2 and water into oil wells to increase the production of oil.

Should the market for it open up, the Carbon Engineering researchers say, their process could be expanded for use in large-scale negative emissions projects — which may become an increasing focus of international discussion on climate action in the coming years. In the meantime, the researchers are hoping to fill a new niche by tackling the transportation sector first.

"Right now, I think we're certainly the only company in the world that's making a zero-carbon fuel from atmospheric CO2," Oldham said.