Cooling the world by filtering excess carbon dioxide from the air on an industrial scale would necessitate the development of a new, massive global industry – what would it take to function?
We have a climate change problem and it’s caused by an excess of CO2. With direct air capture, you can remove any emission, anywhere, from any moment in time – Steve OldhamIt is the year 2050. When you walk out of the Permian Basin Petroleum Museum in Midland, Texas, and drive north through the sun-baked scrub where a few remaining oil pumpjacks nod lazily in the heat, you’ll see it: a glittering palace growing out of the pancake-flat field. The land is reflected here: the choppy silver-blue waves of a vast solar array reach out in all directions. In the distance, they can see a massive grey wall five storeys high and nearly a kilometre long. A chemical plant’s snaking pipes and gantries can be seen behind the wall.
When you get closer, you realise that the wall is shifting and shimmering – it is entirely made up of enormous fans whirring in steel boxes. You imagine it to be a massive air conditioning unit, blown up to enormous proportions. In certain ways, that is exactly what this is. You’re looking at a direct air capture (DAC) facility, one of tens of thousands worldwide. They’re working together to cool the earth by squeezing carbon dioxide out of the atmosphere. This Texas landscape is renowned for the billions of barrels of oil mined from its depths during the twentieth century. The legacy of those fossil fuels – CO2 in our atmosphere – is now being pumped back into the depleted reservoirs.
If the world is to achieve the Paris Agreement’s target of restricting global warming to 1.5 degrees Celsius by 2100, sights like this will be expected by the mid-century.
But fast forward to 2021, to Squamish, British Columbia, where a barn-sized device covered in blue tarpaulin is being finished against a bucolic skyline of snowy mountains. Carbon Engineering’s prototype direct air capture plant will begin removing a tonne of CO2 from the atmosphere every year when it becomes operational in September. It’s a small start, and a slightly larger plant in Texas is expected, but this is the standard size of a DAC plant today.
“”We have an issue with climate change, and it’s exacerbated by an excess of CO2,” says Carbon Engineering CEO Steve Oldham. “With DAC, you can eliminate any pollution from any location and at any time. It’s an extremely useful tool to have.”
The majority of carbon capture technology focuses on cleaning pollutants at the source, such as scrubbers and filters on smokestacks that prevent toxic gases from entering the atmosphere. This, however, is impractical for limited, multiple point sources such as the world’s billion or so automobiles. It also does not answer the CO2 that is already in the atmosphere. This is where direct air capture comes into play.
Switching to a carbon-neutral society would not suffice if the planet is to prevent catastrophic climate change. The Intergovernmental Panel on Climate Change (IPCC) has cautioned that restricting global warming to 1.5 degrees Celsius by 2100 would necessitate “large-scale implementation of carbon dioxide reduction steps” – large-scale meaning several billions of tonnes, or gigatonnes, every year. Elon Musk recently committed $100 million (£72 million) to develop carbon capture technology, and companies such as Microsoft, United Airlines, and ExxonMobil are investing billions of dollars in the sector.
“According to current projections, we’ll need to extract 10 gigatonnes of CO2 per year by 2050, and that figure will need to double to 20 gigatonnes per year by the end of the century,” says Jane Zelikova, a climate scientist at the University of Wyoming. At the moment, “We’re eliminating almost none. We have to start at the beginning.”
Carbon Engineering’s Squamish plant is intended to act as a testing ground for various technologies. However, the company is developing plans for a much larger plant in the oil fields of west Texas, which will repair 1 million tonnes of CO2 annually. “When one is finished, it’s a cookie cutter model, and you simply create replicas of that plant,” Oldham explains. Nonetheless, he acknowledges that the magnitude of the challenge ahead is dizzying. “We need to remove 800 gigatonnes from the atmosphere. It will not happen immediately.”
Climate Change – Looking outside the box
The science of direct air capture is simple. Carbon Engineering’s device uses fans to pull air containing 0.04 percent CO2 (today’s ambient levels) through a filter drenched in potassium hydroxide solution – a caustic chemical widely known as potash, used in soapmaking and many other applications. The potash absorbs CO2 from the air before being piped to a second chamber and mixed with calcium hydroxide (builder’s lime). The lime clings to the dissolved CO2, resulting in small flakes of limestone. These limestone flakes are sieved and heated in a third chamber known as a calciner before they decompose, releasing pure CO2 that is collected and processed. The leftover chemical residues are recycled back into the process at each step, creating a closed reaction that repeats indefinitely with no waste materials.
With global carbon emissions continuing to increase, meeting the 1.5°C temperature goal is becoming increasingly unlikely in the absence of measures like this.
“The number of items that would have to happen without direct air capture is so vast and numerous that it’s highly unlikely we’ll be able to reach the Paris Agreements without it,” says Ajay Gambhir, senior researcher at the Imperial College Grantham Institute for Climate Change and author of a 2019 paper on the role of DAC in climate mitigation.
The IPCC does present some climate-stabilizing models that do not rely on direct air capture, but Gambhir describes them as “highly optimistic” in their assumptions about energy efficiency advances and people’s willingness to change their actions.
“We’ve passed the point where reducing emissions was needed,” Zelikova says. “We’re being more reliant on DAC.”
DAC is far from the only method for removing emissions from the atmosphere. Carbon may be eliminated naturally by modifying land usage, such as restoring peat bogs or, more generally, planting forests. However, this is a slow process that would necessitate the acquisition of vast swaths of fertile land, potentially covering a region the size of the United States and pushing up food prices by a factor of five. In the case of trees, the carbon reduction effect is minimal since they will ultimately die and release their accumulated carbon unless they are felled and burned in a closed system. (To read more about why planting trees does not always help with climate change, click here.)
The size of the challenge for carbon removal using technologies such as DAC rather than plants is no less massive. According to Gambhir’s paper, merely keeping up with global CO2 emissions – currently 36 gigatonnes per year – will necessitate the construction of 30,000 large-scale DAC plants, more than three for every coal-fired power station in operation today. Each plant will cost up to $500 million (£362 million) to build, for a total cost of up to $15 trillion (£11 trillion).
Each of those facilities will need to be supplied with CO2 absorbent solvent. Supplying a fleet of DAC plants large enough to capture 10 gigatonnes of CO2 per year would require approximately four million tonnes of potassium hydroxide, which is one and a half times the current annual global supply of this chemical.
And once those thousands of DAC plants are installed, they will need electricity to operate. “If this were a global industry absorbing 10 gigatonnes of CO2 each year, you’d be expending 100 exajoules, or around a sixth of total global electricity,” Gambhir says. The majority of this energy is needed to heat the calciner to about 800 degrees Celsius, which is too high for electrical power alone, so each DAC plant will need a gas furnace and a ready supply of gas.
Expenses on the environment
Estimates for the expense of capturing a tonne of CO2 from the atmosphere range widely, ranging from $100 to $1,000 (£72 to £720) per tonne. Most estimates, according to Oldham, are overly pessimistic; he believes Climate Engineering can fix a tonne of carbon for as little as $94 (£68), particularly once it becomes a widespread industrial method.
A bigger challenge is deciding where to submit the bill. Surprisingly, financially, saving the planet turns out to be a difficult sale. However, direct air capture yields one useful commodity: thousands of tonnes of compressed CO2. This can be combined with hydrogen to create carbon-neutral synthetic fuel. This could then be sold or burned in the calciner’s gas furnaces (where the emissions would be captured and the cycle continue once again).
Surprisingly, the fossil fuel industry is one of the largest users of compressed CO2.
When wells run dry, it’s not uncommon to pressurise the reservoir with steam or gas to remove the remaining crude, a method known as enhanced oil recovery. Carbon dioxide is a common option for this because it has the added advantage of burying the carbon, completing the final stage of carbon capture and storage. Occidental Petroleum, which has collaborated with Carbon Engineering to develop a full-scale DAC plant in Texas, uses 50 million tonnes of CO2 in enhanced oil recovery per year. Each tonne of CO2 emitted in this manner is worth approximately $225 (£163) in tax credits alone.
It’s only fitting that the CO2 in our atmosphere will finally be returned underground to the oil fields from which it came, but it’s ironic that the only way to fund this is to dig for even more oil. Occidental and others hope that by injecting CO2 into the field, they will be able to dramatically reduce the carbon footprint of the oil: a standard enhanced-recovery operation sequesters one tonne of CO2 for every 1.5 tonnes of fresh oil released. So, although the process lowers oil-related pollution, it does not balance the books.
Other applications, however, may become more commercially viable. Climeworks, another direct air capture company, has 14 smaller scale units in service, sequestering 900 tonnes of CO2 per year, which it sells to a greenhouse to boost pickle output. It is now working on a longer-term solution: an Icelandic plant is being built that will combine captured CO2 with water and pump it 500-600m (1,600-2,000ft) underground, where the gas will react with the surrounding basalt and transform to stone. To fund this, it allows companies and individuals to purchase carbon offsets for as little as €7 (£6) a month. Will the rest of the planet be persuaded to join in?
“DAC will still cost money, and unless you’re paying to do it, there’s no financial motivation,” says Chris Goodall, author of What We Need To Do Now: For A Zero Carbon Future. “Climeworks will sell credits to good people and sign contracts with Microsoft and Stripe to remove a few hundred tonnes of CO2 from the atmosphere each year, but this has to be scaled up a millionfold, and that requires someone to pay for it.”
“There are subsidies for electric vehicles and low-cost financing for solar plants, but you don’t see these for DAC,” Oldham says. “There is a lot of attention on reducing emissions, but there isn’t as much emphasis on the other side of the issue, which is the amount of CO2 in the atmosphere.” The biggest impediment for DAC is that policy does not promote thought.”
Zelikova claims DAC will follow in the footsteps of other climate innovations and become more affordable. “We have well-developed cost curves that demonstrate how technology can rapidly reduce costs,” Zelikova says. “We overcame similar challenges with wind and solar.” The most important thing is to use them as soon as possible. It is important for the government to promote commercialization because it serves as a first customer with deep pockets.”
Goodall advocates for a global carbon tax, which would make carbon emissions prohibitively costly unless offsets were bought. However, he acknowledges that this is still a politically unpalatable choice. Nobody wants to pay more taxes, particularly if the externalities of our high-energy lifestyles – increasing wildfires, droughts, floods, and sea level rise – are perceived to be borne by someone else.
Zelikova adds that there needs to be a wider debate in society about how much these efforts can cost. “Climate change has a huge cost in terms of caused or intensified natural disasters.” We must abandon the notion that DAC should be inexpensive.”
The definition of risk and reward
Even if we agree to create 30,000 industrial-scale DAC plants, find the chemical materials to fuel them, and find the money to pay for it all, we won’t be out of the woods for long. In fact, due to a phenomenon known as mitigation deterrence, we could end up in a worse place than before.
“If you believe DAC will be there in the medium to long term, you will not do as much near-term emission reduction,” explains Gambhir. “If the scale-up goes wrong – if it turns out to be difficult to manufacture the sorbent, or that it degrades more quickly, if it’s trickier technologically, if it turns out to be more costly than anticipated, then in a sense, you’ve essentially locked yourself into a higher temperature pathway by not moving quickly in the near-term.”
Critics of DAC argue that much of its allure is based on the promise of a hypothetical technology that will enable us to continue living our carbon-intensive lifestyles. However, Oldham contends that for certain difficult-to-decarbonize sectors, such as aviation, offsets that finance DAC might be the best choice. “If it’s cheaper and quicker to take carbon out of the air than it is to stop it from going up in the air, then that’s the role DAC plays in pollution control.”
Gambhir contends that the case is not “either-or.” “We need to minimise pollution quickly in the short term, but we also need to work hard to figure out whether DAC will be there for us in the long run.” “It’s a ‘yes, and’ scenario,” Zelikova admits. “DAC is an effective tool for managing the carbon budget, so that what we can’t remove now can be reduced later.”
The most important fundamental factor in Oldham’s efforts to scale up Carbon Engineering is demonstrating that large scale DAC is “feasible, inexpensive, and usable.” If he succeeds, the future of our planet’s atmosphere will be determined once more in the oil fields of Texas.