As Occidental Petroleum and BlackRock prepare to bring Stratos — the world’s largest direct air capture plant — online in the Permian Basin, a familiar debate has reignited: Does direct air capture actually remove more carbon than it emits? 

But that question, while important, isn’t the right one for policymakers and investors to ask. 

The more instructive questions are: For a given amount of money, which technology delivers the greatest public health and climate benefit? And how efficient does direct air capture need to be, and how clean does the electrical grid have to be before direct air capture investments outperform wind and solar? Our new research, produced by a team of scientists at Boston University, PSE Healthy Energy, and the Harvard T.H. Chan School of Public Health, answers these questions.

We modeled deployments of direct air capture, utility-scale wind, and utility-scale solar across the U.S. through 2050, and asked which delivers the most health and climate benefit per dollar. Under realistic assumptions about DAC’s current cost and energy requirements, wind and solar won in nearly every region, in every year. The technology approached competitiveness only under a cost and efficiency “breakthrough” scenario requiring electricity usage and costs to plunge far below anything demonstrated today. Even then, direct air capture barely edged out renewables nationally and still lost to wind in the Upper Midwest.

The comparison looks even worse for DAC when we consider the health of people living near power plants that produce the electricity it requires. A grid-connected DAC plant is a new source of electricity demand. On today’s U.S. grid, that demand is met in part by fossil fuel combustion, which means more sulfur dioxide, more nitrogen oxides, and more fine particulate matter, all concentrated in the communities near power plants. 

Building out renewables can displace fossil generation and reduce that air pollution, whereas DAC does not. In our analysis, grid-connected direct air capture produced negative health impacts in every scenario and every year, while renewable deployment produced positive ones. This asymmetry is invisible in analyses that only count tons of carbon dioxide emitted or mitigated.

Where DAC makes sense depends on how clean the local grid is. In regions with relatively low-carbon electricity — such as in California, the Pacific Northwest, and parts of the Northeast — it gets closer to being competitive with renewables under highly optimistic technology assumptions. In the coal-heavy Midwest, however, renewables win by a wide margin even in our most favorable direct air capture scenario. 

Our analysis quantifies a threshold that should guide deployment decisions: How clean does a region’s grid need to be before a dollar invested in direct air capture delivers more benefit than a dollar invested in renewables? Put more specifically, how much carbon dioxide and other pollutants would need to be produced per unit of electricity delivered before DAC is competitive?

For most of the U.S., the answer is much cleaner than today. Even if DAC technology improves dramatically — meaning cutting its energy consumption by two-thirds and its costs in half, roughly in line with the industry’s own targets — our analysis finds it would only outperform renewables in California, which has one of the cleanest grids in the country, at about one-fifth the national average carbon intensity. 

Some have proposed sidestepping the grid problem entirely by requiring that DAC be powered with dedicated new renewables. But this concedes the underlying point: Diverting renewables to power direct air capture is a less effective use of clean electricity than simply displacing fossil generation on the grid. 

But that doesn’t mean we should give up on DAC entirely. It may still have a role in the climate fight because it can do something wind and solar cannot: remove CO2 that is already in the atmosphere. Once electricity generation comes almost entirely from renewables and ongoing emissions are extremely small, DAC may prove essential for drawing down our historical carbon debt. Therefore, continued research funding makes sense so that the technology is ready to deploy after electricity generation is mostly decarbonized. However, we are far from a place where deploying this technology at scale is the best strategy. 

Some argue that deploying DAC today will help it ride technological learning curves and bring costs down. That argument holds for modular technologies that move electrons, like solar panels, batteries, or cell phones, which have fallen in cost by orders of magnitude. But direct air capture is a large-scale industrial process that moves large quantities of matter, more akin to a gas or nuclear plant than a solar cell. Large power plants have much slower learning and cost curves, so DAC research is not the same as deployment. And from a climate standpoint, reducing carbon dioxide today is much more important than potentially reducing it tomorrow.

Before committing billions to large-scale direct air capture deployment, policymakers, climate investors, and philanthropists should ask: Would this money deliver greater climate and health benefits if it were invested into wind and solar? For now, and until the grid gets vastly cleaner, the answer is yes. If your sink is overflowing, turn off the tap before you begin mopping the floor.

Yannai Kashtan, PhD is an air quality scientist at PSE Healthy Energy. Jonathan Buonocore, ScD, is an assistant professor of environmental health at Boston University School of Public Health, core faculty at the Boston University Institute for Global Sustainability, and a member of the Science Roundtable on Carbon Capture and Storage. The opinions represented in this contributed article are solely those of the author, and do not reflect the views of Latitude Media or any of its staff.

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