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The cost of removing carbon dioxide directly from the atmosphere could be double previous estimates. Researchers from the university ETH Zurich also warn that the technology should not be treated as a substitute for carbon reduction policies.
Carbon removal is considered a possible solution to the problem of limiting global warming to within 2°C above pre-industrial levels. It could be particularly useful for sectors such as aviation and agriculture, which are particularly hard to abate using current technologies.
The researchers compared the potential costs of three direct air capture (DAC) technologies already in use. These included the method used by ETH spinoff Climeworks, as well as carbon capture using aqueous solutions and calcium oxide.
They estimate that the cost of removing one tonne of CO2 from the air will fall to between $230 and $540 by 2050 – nearly twice as high as previous estimates. None of the technologies studied have clear cost advantages over the others, but all three require further development, the researchers said. Climeworks operates a plant in Iceland that captures 4,000 tonnes of CO2 a year, at a cost per tonne of between $1,000 and $1,300.
The Intergovernmental Panel on Climate Change (IPCC) estimates that up to 13 billion tonnes of CO2 will need to be removed from the atmosphere every year from 2050. These targets will be hard to achieve unless ways can be found to reduce the cost of DAC technologies.
The ETH researchers said they have developed a new method that provides a more accurate estimate of their future cost. As the technologies are scaled up, DAC will become significantly cheaper – although not as cheap as some stakeholders anticipate.
Bjarne Steffen, ETH professor of climate finance, said: “Just because DAC technologies are available it certainly doesn’t mean we can relax our efforts to cut carbon emissions. That said, it’s still important to press ahead with the expansion of DAC plants, because we will need these technologies for emissions that are difficult or impossible to avoid.”
The ETH researchers applied their method to the three technologies and found that Climeworks’ method – in which a solid filter with a large surface area traps CO2 particles – could cost between $280 and $580 per tonne by 2050.
The estimated costs of the other two DAC technologies also fall within a similar range: between $230 and $540 using an aqueous solution of potassium hydroxide, and between $230 and $835 for carbon capture using calcium oxide derived from limestone.
“At present, it is not possible to predict which of the available technologies will prevail. It is therefore crucial that we continue to pursue all the options,” said Katrin Sievert, lead author of the study.
Climeworks started building its largest DAC facility, called Mammoth, in a remote area of Iceland in 2022. After an 18-month construction phase, its core infrastructure is finally in place and most systems are operational.
