Can Carbon Dioxide Be Cheaply Removed From Our Atmosphere?


I recall a hare-brained experiment discussed on the news some years ago that proposed using cryonics to separate moisture and carbon dioxide from the Earth’s atmosphere. The experiment relied on the fact that both water and carbon dioxide liquefy and solidify at much higher temperatures than oxygen and nitrogen, the primary components of the air we breathe, so that by cooling air sufficiently one could extract both water and CO2 and send the pure nitrogen and oxygen back out into the world. The fresh water, of course, could be used for any of multiple useful purposes, especially in desert countries, and the CO2 could also be put to industrial uses in various existing businesses.

It turns out that this experiment may not be so outlandish after all, though the energy requirements of cooling vast quantities of air would be prodigious. These and other technologies are discussed at length in a new ebook, Suck It Up, by Marc Gunther, who has previously written about the environment. The ebook takes a look at technologies, existing and developing, to extract carbon dioxide from the air to, in effect, undo two centuries of carbon pollution by the Industrial Revolution. Some of these are called “direct air capture” of carbon dioxide, technologies that remove CO2 directly from the atmosphere by solidifying it or converting it into a non-gaseous compound.

Gunther begins his narrative by assessing how well governments have done in achieving reductions in carbon dioxide. As we know from reading news reports, little has been accomoplished so far. Reducing carbon emissions requires reliance on non-fossil fuel energy alternatives, and no serious efforts have yet been made to actually extract carbon dioxide artificially from the air. This leads him into the grand subject of “geo-engineering” which is the term used by scientists to describe methods available on a colossal, planetary scale to create significant atmospheric change worldwide. The Industrial Revolution itself is an example of geo-engineering, albeit a project that has had consequences we now need to try to reverse, namely the accumulation of greenhouse gases in concentrations not seen in the our atmosphere for tens of millions of years.

Taken as a matter of high school science, removing CO2 from breathable air is easily accomplished. Navies manage it all the time in submarines with relatively simple chemical technology. The problem is one of scale and cost. An accepted way to accomplish CO2 removal is to run air through giant tanks filled with algae. The carbon dioxide dissolves in the water where it is sucked up by the algae to make sugars and other carbohydrates that confine the CO2 in solid molecules. But this, too, cannot be done cheaply enough and on scales large enough to offset the tens of millions of tons of new CO2 we add to the air annually through burning coal and gasoline in our cars.

One surprising result of all these efforts to a non-scientist like myself is that, while CO2 removal is not cheap, it is comparatively less expensive than the alternatives, which involve cutting CO2 emissions by switching to energy systems that don’t release carbon dioxide at all. There are also clever technologies that would tackle global warming indirectly, not by reducing greenhouse gases but rather by reflecting back out into space more solar energy. If there is less heat coming into the atmosphere from sunlight, the earth’s average temperature would tend to rise more slowly or not rise at all. This would save the poles and keep the oceans from rising, two of the potentially catastrophic outcomes of global warming most feared by environmentalists.

I also learned that there is a tradeable market for carbon dioxide, beyond the folks at Omaha Steaks who use it to keep your steaks frozen on the way to your house. Carbon dioxide can fetch prices of $50 or more per ton in the oil and gas industry, where it is injected by oil companies into oil reservoirs to displace fluids from permeable rock and up to the surface where these hydrocarbons can be collected and sold. This use of carbon dioxide has the added benefit that once injected into the ground, it tends to stay there, safely out of the atmosphere for a long time.

Gunther then goes on to look at the small spectrum of startup ventures, including at least one that has earned the backing of Bill Gates, which are just now building feasibility plants. There are no clear front-runners — and all of them suffer from a possibly insurmountable problem, namely energy use. It clearly makes no sense at all to use dirty energy (and thus release more carbon) to remove existing carbon from the atmosphere. This is one of those fields where some sort of exogenous technology or new discovery would be most welcome.

Gunther’s book is the length of a long Atlantic Monthly article, and for the interested layperson like myself, it is an excellent introduction to the subject.

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