wind

Renewable Energy is More Cost Effective than Direct Air Capture at Reducing Carbon

A new study shows that direct air capture is, and will continue to be, one of the most expensive ways to reduce carbon dioxide in the atmosphere, and using it may actually increase health harms.

The case for investing in direct air capture weakens substantially once it is directly compared against solar and wind, according to a peer-reviewed analysis published today in Communications Sustainability. Across nearly every U.S. region and every year through 2050, an amount of money spent deploying wind or solar delivers more combined climate and public health benefit than if it is spent on direct air capture, even under extremely optimistic assumptions of the development of direct air capture.

Prior assessments of direct air capture, or DAC, have largely asked whether the technology removes more carbon than its operations emit, or whether the cost per ton clears a social-cost-of-carbon benchmark. Both tests implicitly compare DAC against doing nothing. The new study by researchers at the School of Public Health, PSE Healthy Energy, and Harvard T.H. Chan School of Public Health instead compares DAC against the renewable energy the same dollars could fund. This is a stricter and, the researchers argue, more policy-relevant bar.

The researchers modeled the health and climate benefit of cost-equivalent deployments of DAC, utility-scale solar, and onshore wind across 22 U.S. grid regions from 2020 through 2050. They tested four DAC scenarios anchored at today’s commercial performance (about 5,500 kilowatt-hours and $1,000 per ton of CO₂ captured) at one end, and at the other an ambitious progress scenario in which DAC’s energy use falls by more than two-thirds and its cost by half (1,500 kWh and $500 per ton). They also modeled a “breakthrough” (800 kWh and $100 per ton) at the extreme low end of published projections.

Even in the ambitious progress scenario, a dramatic technological advance well beyond anything DAC has demonstrated, renewables still delivered several-fold more climate and health benefits per dollar nationally. Only under the more aggressive breakthrough scenario did grid-connected DAC do the best nationally, and even then wind and solar continued to beat DAC across large portions of the country, including most of the Upper Midwest. Under today’s commercial performance, grid-connected DAC produced more greenhouse gases and air pollution damage through 2050 than it offset.

“There’s a rapidly growing variety of interventions out there to mitigate greenhouse gases, and potentially affect public health, as well,” says study senior author Jonathan Buonocore, assistant professor of environmental health and a core faculty member at BU’s Institute for Global Sustainability. “Our research here shows the power of cost-effectiveness analysis to ensure that capital invested in climate mitigation has the most ‘bang for the buck’ for the climate, while having the fewest side effects.”

The new analysis also incorporated both climate and local health impacts, and underscored a reality that conventional carbon accounting misses. If DAC is connected to a grid powered even in part by fossil fuels, building DAC will generate new sulfur dioxide, nitrogen oxides, and fine particulate matter concentrated in the communities near the power plants supplying that electricity. Renewable deployment does the opposite, producing health benefits in every region and scenario modeled.

“Our study underscores that being carbon negative isn’t enough to make direct air capture a good investment,” says study lead author Yannai Kashtan, an air quality scientist at PSE Healthy Energy.

The analysis isn’t an argument against DAC, the researchers note. The technology may still help draw down legacy atmospheric CO₂ once ongoing emissions are largely abated. What the analysis offers is a sharper, opportunity-cost-based benchmark for when DAC deployment becomes worthwhile, substantially stricter than the carbon-neutrality and cost-parity tests the field has traditionally relied on.

“If your sink is overflowing, turn off the tap before you begin mopping the floor,” says Kashtan.