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Climate change: Why removing CO2 from the air won’t be enough

Posted July 31, 2019

Pulling carbon dioxide out of the air using a technology called “direct air capture,” or DAC, will not be the silver bullet for curbing climate change that some hoped it would be, according to new research from the University of Michigan.

A more aggressive and early move toward renewable energy will be less expensive in the long run, as nations aim to keep global temperatures from exceeding a 1.5-to-2-degree Celsius increase over pre-industrial times. The researchers estimate that each day the U.S. electricity sector fails to take more aggressive steps toward renewables, it adds $100 million to its future tab for stalling the 2-degree limit.

In the coming decades, various climate change impacts are likely to compound, making it more difficult to adapt. Image credit:, CC0 Public Domain.

In the coming decades, various climate change impacts are likely to compound, making it more difficult to adapt. Image credit:, CC0 Public Domain.

“DAC is inherently more expensive than if we started an immediate transition to renewable energy on a larger scale,” said Steve Skerlos, an Arthur F. Thurnau Professor and professor of mechanical engineering at U-M.

In order to stay below the 2-degree mark, all sectors must reduce emissions by 70%. This study looks at a 70% reduction in the electricity sector. The study makes clear that if the U.S. electricity sector waits more than a decade, it will have no choice but to rely in part on direct air capture to meet its share of the emissions budget that the 2-degree limit implies.

“Too many policymakers think that if we wait, carbon capture and sequestration technology will get better and cheaper, and cheap enough to address the problem,” said Skerlos, who is also a professor of civil and environmental engineering.

“They’re wrong.”

If electricity providers maintain their “business as usual” approach, they will disproportionately push Earth past the point where it can stop the 2-degree increase as early as 2030. The U.S. electricity sector is responsible for roughly 4% of all greenhouse gases generated annually on Earth.

DAC pulls carbon dioxide from the air, concentrating the gas so it can be stored underground. The technology has garnered plenty of media attention in recent years with its potential impacts being debated in the scientific community.

U-M’s team developed a computer model that can project the cost of installing, operating, and replacing utility-scale electricity technologies. Based on existing infrastructure in the U.S., the model estimates the optimal scale and timing of technology transitions, early retirements, capacity expansions and DAC deployment that results in the least overall cost to reduce emissions by 70% and meet the 2-degree mandate.

They found that even a high-efficiency, low-cost version of DAC that’s ready to be scaled up would still cost much more than speeding up the switch to renewables.

“Our results are conservative, as we stacked our assumptions into an optimistic picture of ‘business as usual,’” said Tae Lim, a graduate student in mechanical engineering. “We also did not consider other sectors of the U.S. economy such as transportation, buildings and industry. It’s generally more expensive to find low carbon alternatives in those sectors than in the electric sector.”

The $100-million-a-day figure U-M’s team cites encompasses a variety of costs, not the least of which is the reshuffling of power sources over the next two decades.

“We’re now building new natural gas plants to replace coal plants,” Skerlos said. “But those same gas plants, which produce large quantities of carbon dioxide, will need to be retired in 10 or 15 years to hit the climate targets. So those relatively new plants will have to be paid off over time and then retired early in favor of renewable energy sources like wind and solar.”

“That’s an incredibly inefficient use of resources. It’s cheaper to build out more wind and solar now.”

Source: University of Michigan

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