With global carbon emissions continuing to rise, the climate target of 1.5C is looking less and less likely without interventions like this.

“The number of things that would have to happen without direct air capture are so stretching and multiple it’s highly unlikely we can meet the Paris Agreements without it,” says Ajay Gambhir, senior researcher at the Imperial College Grantham Institute for Climate Change and an author of a 2019 paper on the role of DAC in climate mitigation.

The IPCC does present some climate-stabilizing models that don’t rely on direct air capture, but Gambhir says these are “extremely ambitious” in their assumptions about advances in energy efficiency and people’s willingness to change their behaviour.

“We’re past the point where reducing emissions needed to take place,” says Zelikova. “We’re locking in our reliance on DAC more and more.”

DAC is far from the only way carbon can be taken out of the atmosphere. Carbon can be removed naturally through land-use changes such as restoring peatland, or most popularly, planting forests. But this is slow and would require huge tracts of valuable land – foresting an area the size of the United States, by some estimates, and driving up food prices five-fold in the process. And in the case of trees, the carbon removal effect is limited, as they will eventually die and release their stored carbon unless they can be felled and burned in a closed system. (Read more about why planting trees doesn’t always help with climate change)

The scale of the challenge for carbon removal using technologies like DAC, rather than plants, is no less gargantuan. Gambhir’s paper calculates that simply keeping pace with global CO2 emissions – currently 36 gigatonnes per year – would mean building in the region of 30,000 large-scale DAC plants, more than three for every coal-fired power station operating in the world today. Each plant would cost up to $500m (£362m) to build – coming in at a cost of up to $15 trillion (£11tn).

Climeworks’ facility near Zurich, Switzerland, sells the CO2 it captures to nearby vegetable growers for their greenhouses (Credit: Alamy)

Every one of those facilities would need to be stocked with solvent to absorb CO2. Supplying a fleet of DAC plants big enough to capture 10 gigatonnes of CO2 every year will require around four million tonnes of potassium hydroxide, the entire annual global supply of this chemical one and a half times over.

And once those thousands of DAC plants are built, they also need power to run. “If this was a global industry absorbing 10 gigatonnes of CO2 a year, you would be expending 100 exajoules, about a sixth of total global energy,” says Gambhir. Most of this energy is needed to heat the calciner to around 800C – too intense for electrical power alone, so each DAC plant would need a gas furnace, and a ready supply of gas.

Costing the planet

Estimates of how much it costs to capture a tonne of CO2 from the air vary widely, ranging from $100 to $1,000 (£72 to £720) per tonne. Oldham says that most figures are unduly pessimistic – he is confident that Climate Engineering can fix a tonne of carbon for as little as $94 (£68), especially once it becomes a widespread industrial process.

A bigger issue is figuring out where to send the bill. Incredibly, saving the world turns out to be a pretty hard sell, commercially speaking. Direct air capture does result in one valuable commodity, though: thousands of tonnes of compressed CO2. This can be combined with hydrogen to make synthetic, carbon-neutral fuel. That could then be sold or burned in the gas furnaces of the calciner (where the emissions would be captured and the cycle continue once again).

Surprisingly, one of the biggest customers for compressed CO2 is the fossil fuel industry.

As wells run dry, it’s not uncommon to squeeze the remaining oil out of the ground by pressuring the reservoir using steam or gas in a process called enhanced oil recovery. Carbon dioxide is a popular choice for this and comes with the additional benefit of locking that carbon underground, completing the final stage of carbon capture and storage. Occidental Petroleum, which has partnered with Carbon Engineering to build a full-scale DAC plant in Texas, uses 50 million tonnes of CO2 every year in enhanced oil recovery. Each tonne of CO2 used in this way is worth about $225 (£163) in tax credits alone.

It’s perhaps fitting that the CO2 in our air is eventually being returned underground to the oil fields from whence it came, although maybe ironic that the only way to finance this is in the pursuit of yet more oil. Occidental and others hope that by pumping CO2 into the ground, they can drastically reduce the carbon impact of that oil: a typical enhanced-recovery operation sequesters one tonne of CO2 for every 1.5 tonnes it ultimately releases in fresh oil. So while the process reduces the emissions associated with oil, it doesn’t balance the books.

Though there are other uses that may become more commercially viable. Another direct air capture company, Climeworks, has 14 smaller-scale units in operation sequestering 900 tonnes of CO2 a year, which it sells to a greenhouse to enhance the growth of pickles. It’s now working on a longer-term solution: a plant under construction in Iceland will mix captured CO2 with water and pump it 500-600m (1,600-2,000ft) underground, where the gas will react with the surrounding basalt and turn to stone. To finance this, it offers businesses and citizens the ability to buy carbon offsets, starting at a mere €7 (£6) per month. Can the rest of the world be convinced to buy in?

Enhancing the growth of vegetables in greenhouses is one application for the CO2 captured from the air by DAC (Credit: Alamy)

“DAC is always going to cost money, and unless you’re paid to do it, there is no financial incentive,” says Chris Goodall, author of What We Need To Do Now: For A Zero-Carbon Future. “Climeworks can sell credits to virtuous people, write contracts with Microsoft and Stripe to take a few hundred tonnes a year out of the atmosphere, but this needs to be scaled up a millionfold, and that requires someone to pay for it.

“There are subsidies for electric cars, cheap financing for solar plants, but you don’t see these for DAC,” says Oldham. “There is so much focus on emission reduction, but there isn’t the same degree of focus on the rest of the problem, the volume of CO2 in the atmosphere. The big impediment for DAC is that thinking isn’t in policy.”

Zelikova believes that DAC will follow a similar path to other climate technologies, and become more affordable. “We have well-developed cost curves showing how technology can go down in cost really quickly,” says Zelikova. “We surmounted similar hurdles with wind and solar. The biggest thing is to deploy them as much as possible. It’s important for government to support commercialization – it has a role as a first customer and a customer with very deep pockets.”

Goodall advocates for a global carbon tax, which would make it expensive to emit carbon unless offsets were purchased. But he recognizes this is still a politically unpalatable option. Nobody wants to pay higher taxes, especially if the externalities of our high-energy lifestyles – increasing wildfires, droughts, floods, sea-level rise – are seen as being shouldered by somebody else.

Zelikova adds we also need broader conversation in society about how much these efforts should cost. “There is an enormous cost in climate change, in induced or exacerbated natural disasters. We need to do away with idea that DAC should be cheap.”

Risk and reward

Even if we agree to build 30,000 industrial-scale DAC plants, find the chemical materials to run them, and the money to pay for it all, we won’t be out of the woods yet. In fact, we might end up in a worse position than before, thanks to a phenomenon known as mitigation deterrence.

Facilities in Iceland are among those aiming to mineralize CO2, to lock it out of circulation in the atmosphere as a long-term solution (Credit: Sandra O Snaebjornsdottir)

“If you think DAC is going to be there in the medium- to long-term, you will not do as much near-term emissions reduction,” explains Gambhir. “If the scale-up goes wrong – if it turns out to be difficult to produce the sorbent, or that it degrades more quickly, if it’s trickier technologically if turns out to be more expensive than expected, then in a sense by not acting quickly in the near-term, you’ve effectively locked yourself into a higher temperature pathway.”

Critics of DAC point out that much of its appeal lies in the promise of a hypothetical technology that allows us to continue living our carbon-rich lifestyles. Yet Oldham argues that for some hard-to-decarbonize industries, such as aviation, offsets that fund DAC might be the most viable option. “If it’s cheaper and easier to pull carbon out of air than to stop going up in the air, maybe that is what DAC plays in emission control.”

Gambhir argues that it’s not an “either-or” situation. “We need to rapidly reduce emissions in the near-term, but at the same time, determinedly develop DAC to work out for sure if it’s going to be there for us in the future.” Zelikova agrees: “It’s a ‘yes, and’ situation,” she says. “DAC is a critical tool to balance out the carbon budget, so what we can’t eliminate today can be removed later.”

As Oldham seeks to scale up Carbon Engineering, the biggest fundamental factor is proving large-scale DAC is “feasible, affordable and available”. If he’s successful, the future of our planet’s climate may once again be decided in the oil fields of Texas.

The emissions from travel it took to report this story were 0kg CO2. The digital emissions from this story are an estimated 1.2g to 3.6g CO2 per page view. Find out more about how we calculated this figure here.

CO2, to lock it out of circulation in the atmosphere as a long-term solution (Credit: Sandra O Snaebjornsdottir)

Source: https://www.bbc.com/future/article/20210310-the-trillion-dollar-plan-to-capture-co2