Insider Brief:
- Airlines like United Airlines are investing in Direct Air Capture startups, as a way to significantly cut emissions
- United’s investment in DAC startup Heirloom is one of a series of investments into the DAC space
- However, a recent study has found that DAC approaches will have to be coupled with sustainable aviation fuel to attain net-zero levels.
On February 28, United Airlines announced it had invested in direct air capture (DAC) company Heirloom via its UAV Sustainable Flight Fund, as the industry continues to work towards decarbonizing aviation. Scientists estimate that aviation accounts for 2.5% of all global emissions, and 4% of all global warming to date.
United will also enter into an agreement for the right to purchase up to 500,000 tons of carbon dioxide removal (CDR) to make sustainable aviation fuel.
“Carbon capture is one of our country’s fastest growing, energy enabling pathways,” said head of United Airlines Ventures Andrew Chang.
“Heirloom’s technology aligns directly with this objective, offering a scalable and commercially viable approach and complements United’s commitment to net zero by 2050.”
The UAV Sustainable Flight Fund has more than US$200 million in investment commitments from United Airlines, as well as other corporate participants such as Google, Embraer, GE Aerospace, and several other airlines.
Heirloom, founded in California in 2020, uses limestone to accelerate carbon dioxide absorption. It then stores the gas underground.
The carbon removal company raised C$150 million in Series B fundraising in December, from companies including Japan Airlines, Mitsubishi, Mitsui, and Siemens Financial Services. Heirloom said it will use the funds to increase carbonation rates, expand automation in its factories, and reduce overall energy use.
How DAC Works to Decarbonize Aviation
Aviation is an industry which remains stubbornly difficult to decarbonize, but there are promising technological advancements which makes lowering emissions a less daunting prospect.
United Airlines, before investing in Heirloom, has been a longtime support of DAC technologies.
In March 2023, the Sustainable Flight Fund invested US$5 million in carbon capture technology company Svante, which produces materials for the carbon capture supply chain. In 2020, the fund invested several million dollars in 1PointFive, which aimed to build a carbon capture plant in the U.S. that would permanently sequester 1 million tons of CO2 every year. 1PointFive is a partnership between Oxy Low Carbon Ventures, a subsidiary of Occidental Petroleum Cor, and California-based Rusheen Capital Management.
But could DAC effectively bring down emissions enough to meet international climate guidelines?
It’s certainly a possibility, according to scientists and industry associations.
The International Air Transport Association has found that while DAC could certainly move the needle, the technology will need to be supplemented with “long-term (geologic time-scale) storage,” according to a February 2023 report.
Carbon dioxide removal must be “verifiable, permanent, net (total emissions removed versus emitted), and based on a robust life cycle assessment.”
What remains to be seen, the IATA says, is whether DAC technologies can be scaled up to a level where they can make an appreciable dent in aviation emissions.
“The … challenge is scaling up DAC capacity quickly enough to ensure that sufficient volumes are available to reach net zero by 2050, as DAC capacity will be required for both removals and as a feedstock for synthetic fuels,” the IATA report said.
Carbon dioxide removals can become cost-effective if more airlines and companies operating in the sector develop and adopt CDR technology, IATA noted.
The technology should become a “strategic investment for airlines,” the industry organization emphasized, as it will help drive down the costs for CDR development and application.
IATA also encouraged the sector to engage in offtake agreements, to further spur development and investment in CDR technologies.
Will DAC be enough to attain net-zero?
However, others caution that CDR will not be sufficient for aviation to meet its net-zero objectives.
Scientists writing in Nature in January found that “synthetic fuels could achieve climate neutrality at lower cost than an emit-and-remove strategy based on DACCS”.
The best shot at synthetic fuels, write authors Niccoletta Brazzola, Amir Meskaldji, Anthony Patt, Tom Trondle, and Christian Moretti, will come in the form of renewable Fischer-Tropsch synthetic fuels developed from air-captured CO2 and green hydrogen.
The authors reject biofuel as a possible replacement for fossil fuels, due to limitations in the availability of sustainable biomass.
According to the study, synthetic fuels generated from captured CO2 and green hydrogen would lead to a gradual replacement of fossil fuels, culminating in 100% synthetic fuel usage by airplanes by 2050.
Using captured carbon in the production of synthetic fuels also has another benefit: these fuels are expected to burn with fewer emissions, therefore reducing the number of emissions generated by the industry and less need for carbon capture, while also requiring less mitigation for other problematic gases.
Either way, whether the industry adopts carbon capture only, or a combination of carbon capture plus synthetic fuel production, the costs will increase from current levels.
However, using carbon capture for both capture and fuel generation is more cost-effective than adopting a carbon-capture only approach, the study finds. The authors note that policy interventions will be necessary to push the sector to adopt either pathway.
There are several factors which make adopting the carbon capture plus fuel generation approach more amenable to airlines now. These include the rising costs of fossil fuels (including fossil kerosene, used to propel aircraft) and the possibility of taking advantage of zero-cost renewable energy (available during periods of excess production), the authors note.
While moving towards net-zero objectives are important for airlines, there are concerns that these technologies could lead to higher ticket prices. However, the authors found that applying the two-tiered approach (carbon capture and fuel generation) would only result in a slight increase in ticket prices.
“This small price difference for customers sheds light on the attractiveness of [the technology], which has a lower cost per emissions and is consistent with broader societal goals of climate mitigation and fossil fuels phase-out,” the authors said in the study.
United Airlines appears to be taking this dual-track approach.
In addition to its investment in Heirloom, United was the first airline to purchase sustainable aviation fuel in July 2024 for use at Chicago’s O’Hare International Airport.
United then followed this up with a deal with fuel company Phillip 66 in December 2024 to supply the airline with 3 million gallons of SAF for use at Chicago O’Hare, with a possible increase of up to 8 million gallons in the first half of 2025.
Phillip 66 also agreed to provide 600,000 gallons of SAF to United at Los Angeles International Airport.
“At United, we’re building on that approach by investing in both companies that can capture CO2 and others that can turn it into fuel,” United CEO Scott Kirby said in March 2023.
