Direct air capture – the technology that pulls carbon dioxide straight out of the atmosphere – has attracted enormous attention and significant investment as a potential climate solution. 

However, a new study suggests that it’s a poor use of money compared to simply building more wind and solar. 

In most parts of the United States, and under almost every scenario modelled through 2050, renewables deliver more climate and health benefits per dollar spent. 

The study was led by Yannai Kashtan, an air quality scientist at PSE Healthy Energy, alongside collaborators at Boston University School of Public Health and the Harvard T.H. Chan School of Public Health.

Most previous assessments of direct air capture, or DAC, have asked the following question: does the technology remove more carbon than its own operations emit, or does the cost per ton of CO2 fall below some benchmark for what carbon is worth? 

Both of those tests compare DAC against doing nothing at all. This study asks something harder. 

It compares DAC against what the same money could buy if spent on wind or solar instead. That’s a stricter standard – and, the researchers argue, the one that actually matters when governments and investors are deciding where to put limited climate funding.

“Our study underscores that being carbon negative isn’t enough to make direct air capture a good investment,” Kashtan said.

The team ran the numbers across 22 U.S. grid regions from 2020 through 2050, comparing the climate and health benefits of cost-equivalent deployments of DAC, utility-scale solar and onshore wind. They tested four DAC scenarios. 

The first was anchored at today’s commercial performance – roughly 5,500 kilowatt-hours of energy and $1,000 per ton of CO2ù captured. 

The most optimistic was a so-called “breakthrough” scenario at 800 kilowatt-hours and $100 per ton, the extreme low end of what published projections consider possible.

In between sat an “ambitious progress” scenario in which DAC’s energy use falls by more than two thirds and its cost by half.

Even in the ambitious progress scenario – a dramatic leap well beyond anything the technology has actually achieved – renewables still delivered several times more climate and health benefit per dollar at the national level. 

Only under the most extreme breakthrough assumptions did grid-connected DAC come out ahead nationally.

And even then, wind and solar continued to beat it across large parts of the country, including most of the Upper Midwest.

Under today’s real-world performance, the picture was worse still. Grid-connected DAC actually produced more greenhouse gases and air pollution damage through 2050 than it offset.

One of the things that makes this analysis different from conventional carbon accounting is that it factors in local health impacts, not just CO2.

When DAC draws power from a grid that still runs partly on fossil fuels, it creates new demand for that electricity – which means more sulfur dioxide, nitrogen oxides, and fine particulate matter being pumped out near the power plants supplying it. 

Those pollutants don’t drift off. They concentrate in communities near those plants, affecting real people’s health.

Renewable deployment works in the opposite direction, displacing fossil fuel generation and producing health benefits in every region and every scenario the team modelled.

“There’s a rapidly growing variety of interventions out there to mitigate greenhouse gases, and potentially affect public health as well,” said study senior author Dr Jonathan J. Buonocore.

“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 authors are careful to say this isn’t a case for scrapping direct air capture entirely. 

The technology may yet play a useful role later in the century, once ongoing emissions have been largely reduced and the remaining challenge is drawing down the legacy CO2 already built up in the atmosphere. At that point, the comparison with renewables looks different.

But right now, we’re nowhere near that point. Spending heavily on DAC while cheaper, more effective alternatives exist carries a real opportunity cost.

Money that could reduce emissions and improve public health may instead be redirected to a technology that, under current conditions, could be making things marginally worse.

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

The study is published in the journal Communications Sustainability.

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