Capturing CO2 from the environment

Since a buildup of humanmade carbon dioxide is causing the planet to warm, why not just suck this greenhouse gas straight out of the atmosphere?

That's one strategy scientists have proposed to combat climate change. But a new analysis suggests that the approach may be neither economical nor practical...Before widespread industrial activity began spewing CO₂ into the air in the mid-1700s, atmospheric concentrations of the gas were around 280 parts per million (ppm). They now exceed 390 ppm and are growing rapidly, about 2 ppm per year. Rather than reducing emissions of the greenhouse gas by shifting to carbon-neutral sources of energy—wind, solar, and nuclear power, for example—and then letting vegetation and the oceans gradually absorb CO₂ in the long term, humans could lower concentrations more rapidly by actively pulling CO₂ from the air, some scientists have suggested.

In such a scheme, researchers would leave large vats out in the open, filled with solutions of sodium hydroxide, potassium hydroxide, or chemicals called amines. When CO₂ in the air reacts with these solutions, it becomes trapped in carbonate-rich compounds. Scientists can later heat these compounds and release the CO₂ and dispose of it, typically by injecting it into deep geologic formations beneath impermeable rock, such as natural reservoirs of oil and natural gas.

Previous studies have hinted that capturing CO₂ directly from the air could cost a few hundred dollars per metric ton of CO₂. At a rate of $300 per metric ton, that would total more than $10 trillion to completely counteract the estimated 33.5 billion tons of CO₂ emissions generated by humans—a tremendous cost, yet one that is still economically viable.

Among other techniques, the researchers estimated the costs of this form of carbon capture by comparing it with the price of scrubbing other pollutants such as oxides of sulfur and nitrogen from industrial emissions before they leave a power plant's smokestack. Although pulling CO₂ from ambient air rather than a smokestack, where CO₂ concentrations can be as high as 12%, would be more difficult, it is technically possible. The problem,  is that it's energetically as well as economically expensive to do so. Capturing CO₂ once it's in the atmosphere takes about four times the energy generated by burning the fossil fuel in the first place.

Overall, just to capture CO₂ would cost at least $1100 per ton, the researchers estimate. That's a total price tag of at least $33 trillion just to hold atmospheric concentrations of CO₂ steady Then, once the gas is captured, even more energy must be expended to compress the gas into a liquid and then dispose of it. And unless the energy needed to drive these processes are carbon-neutral—that is, unless they produce no CO₂ emissions of their own—the net result might add CO₂ to the atmosphere, not reduce it...Seems like Capturing CO₂ is yet Too costly to combat climate change so the best approach, many suggest, is simply to find greener sources of energy.

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