Get Ready for Air Capture

December 15th, 2005

Posted by: Roger Pielke, Jr.

I have often joked that the solution to increasing greenhouse gases was simple: simply invent a tabletop device (solar powered of course) that turns the CO2 in ambient air into diamonds and releases oxygen. While I am still awaiting this invention, the issue of “air capture” of CO2 is becoming less and less far-fetched. Whether or not air capture proves technologically, economically, or politically feasible in the long run, the technology, or more precisely the idea of the technology, has the potential to fundamentally transform debate on climate change.

The idea of air capture of CO2 is simple in principle: ambient air is taken in, CO2 is taken out, and air is released. (Those interested in an introduction to the technical details should see this PDF by David Keith and Minh Ha-Duong. For a look at a a prototype system see this PDF.)

Currently air capture of CO2 is a political third rail of climate policy. Here is why:

For most of those people opposed to greenhouse gas regulation advocating air capture would require first admitting that greenhouse gases ought to be reduced in the first place, an admission that most on this side of the debate have avoided. When so-called climate skeptics start advocating air capture (which I have to believe can’t be too far off), then you will have a sign that the climate debate is really changing.

If such a transformation occurs, then we have the irony of seeing the climate skeptics become the technology advocates and the greenhouse gas regulation advocates become technology skeptics. Why? For most of those people who support greenhouse gas regulations, even admitting the possibility of air capture is anathema, because it would undercut the entire structure of the contemporary climate enterprise. Consider that the Kyoto Protocol and all of its complex mechanisms would largely be rendered irrelevant. So too would be most research on carbon sequestration (though point source sequestration would likely remain of interest) and management, as well as much of research on reducing emissions in autos, homes, cities, etc.. As well, because among many much of the motivation for climate mitigation lies in changing peoples lifestyles, securing advantages in international economics, and changing energy policies, air capture represents a tremendous threat to such agendas. As a 2002 Los Alamos National Laboratory press release trumpets, “Imagine no restrictions on fossil-fuel usage and no global warming!”

Now for a moment imagine that the technological, economic, and political obstacles to air capture could be successfully overcome. For the record, I have no idea if this is in fact the case, however some very prominent researchers think that it is possible, see e.g., this PDF. What would this mean?

This would mean that policy makers could then tune the atmosphere to whatever concentration of CO2 that they desired, and people around the world could continue to consume fossil fuels with abandon. (The entire prospect of geoengineering would of course require some very, very careful thought that I am obviously overlooking for the moment.) Now of course, this argument presumes that the climate problem is one of stabilizing CO2 concentrations at a particular level, such as described in the Climate Convention, a framing that I have critiqued (e.g., here in PDF), but let’s go with it for purposes of discussion. The problem of increasing CO2 in the atmosphere would then simply be turned into a technical exercise in scrubbing the atmosphere clean, of course, at some cost.

Critics of air capture that I have spoken to dismiss air capture almost reflexively as undoubtedly forever remaining too costly and technologically infeasible. But given its potential to reshape the climate debate, I am amazed that air capture has not captured more attention from researchers and, especially, policy makers. For example, the recent IPCC report on Carbon dioxide Capture and Storage discusses capture from point sources, like power plants, but not from air. Should air capture start getting attention you can just about predict who will argue against it as being infeasible and work to keep it off of technology research agendas. (Question: Does anyone know how much research money is currently devoted to air capture?)

According to estimates by David Keith and colleagues, the costs of air capture are about one order of magnitude higher than the price that carbon trades for in the European carbon exchange. In the history of technological innovation, this is really not very far apart (think computers). Imagine if governments around the world set up a $50 billion prize for the first technology that demonstrated economic viability for air capture of carbon dioxide at, for instance, $20 per ton, $5 per ton or $1 per ton. The resulting investment in innovation would be massive. To scale the cost of awarding such a prize, it is a fraction of some projections of the annual costs of implementation of the Kyoto Protocol, which would deal with about 99% less of the problem than cost-effective air capture.

Can air capture solve the problem of increasing greenhouse gas emissions? I don’t know. But if scientists and policy makers frame the climate problem as one of stabilizing concentrations of atmospheric CO2, then given the potential payoff, air capture deserves to be at the center of international climate policy debate. Presently it is not, but I’d bet that it will be soon.

(Note: Thanks to David Keith for providing useful background information on air capture!)

24 Responses to “Get Ready for Air Capture”

  1. James Annan Says:


    While I certainly wouldn’t suggest that such research is worthless, it seems pretty much pie in the sky for now. Arguing that it should be “at the center of international climate policy debate” on the basis of the existing rather speculative research is a bit silly – would you say the same about nuclear fusion, even cold fusion? If not, why not? If that works, it would be great too…

    Focussing on the financial cost (and expecting it to drop massively) is rather misleading. Ultimately it’s the energy cost that matters. Using the rather handwavy-values in the Lackner pdf, if the 700kJ of heat from gasoline generates usable power at 30% efficiency, then 95% of this useful output is going to be needed to capture the CO2. And coal of course is substantially worse (higher carbon content). The 10% value quoted by Keith is very much a theoretical best-case scenario assuming perfect efficiency at each stage of the process. Sure, transistors have got smaller and cheaper, but power stations cannot increase their efficiency by an order of magnitude each decade, or ever!

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  3. TCO Says:

    I agree with the above. Plus what about the iron filings in the ocean thing?

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  5. Roger Pielke Jr. Says:


    Thanks. I’d actually have no objections to setting up a prize for proof of fusion success. I can’t imagine that from the standpoint of technology investments that anyone would object to a prize for air capture, given the exceedingly low cost. There is good reason to believe that prizes are effective as a component of technology policies:

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  7. Lisa Dilling Says:

    Hi Roger,
    I actually think any of the carbon sequestration options constitute a “third rail” of policy. There’s not that much different about David Keith’s proposed air capture system vs. capture and storage (say at power plants), mineral carbonation, terrestrial sequestration, and so on in terms of offering a third option that does not involve alternative energy sources or behavior change regarding energy. The “air capture” system is just another type of method for removing CO2 from the air, similar to mineral carbonation or terrestrial sequestration (but not requiring a concentration stream of CO2, like capture and storage at power plants). Keith himself admits in his documentation that would be currently expensive, but of course I see no reason why research might not bring down the cost. The issue then falls squarely into all the issues you have not addressed in the post– the issues of geoengineering, dialing up a specific concentration in the atmosphere (and what should that be), etc. As far as I can tell, industrial carbon capture and storage at power plants seems to be the current favorite for implementation, simply because we currently have the technology that can be adapted, it’s already deployed to recover oil and gas, and the cost estimates are therefore calculatable.

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  9. Oliver Morton Says:

    The baseline here is sugarcane, no? Grow it at 80 tonnes a hectare, turn it to charcoal, bury the charcoal. (Don’t know who much co2 you lose back in charcoal step, but obviously not all of it). Alternatively drop the sugarcane in deep oceans.
    It’s not an idea original to me, but biomass fuels with CCS are a real world possibility for carbon negative fuel energy generation, if you pick the right biomass crop in teh right place.

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  11. Interested Lurker Says:

    Crystal sponges appear to be an up and coming technology as well.

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  13. EliRabett Says:

    I see you are still building strawmen. Serious people who think about greenhouse gas driven climate change are quite happy with technical devices that help. They would, in the Ghandian sense, be a good thing. Hansen for one has thought quite hard about practical effective tactics although his strategy does not involve constructing specific gimicks.

    In keeping with that idea, one wants to go for the low hanging fruit first. Things like improving power generating and heating and cooking devices to limit forcing emissions of all sorts (CO2, soot, etc.) are negative or lower cost compared to air capture.

    OTOH, being around the aerosol lye used in the prototype air capture device is not necessarily good for your health, especially respiration. Operating enough of those things in a safe manner to have an effect on CO2 mixing ratios would be difficult, obviously much more difficult than the links or you imply. The best solution would be a passive matrix in which the gas can be captured and released. Such matricies exist, but they are not yet inexpensive. Chemically, this is very similar to the hydrogen gas storage problem.

    Since you don’t have a clue about how practical air capture devices are, rather than jumping on the bandwagon, a more prudent attitude would be to not jump into the fire. Instead you proclaim that air capture is job 1. What we don’t need is another fad cure.

    Politically that is like saying that we are in a bad situation, but you don’t know if the cure is worse than the disease, and then throw a fit because other people don’t agree with your plan of action.

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  15. Roger Pielke Jr. Says:

    Thanks Eli for your standard response, however, I am remain a bit confused, your objection to setting up a prize awarded to a successful demonstration of air cature technology would be what?

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  17. James Annan Says:


    I’m sure that few would object to prizes being offered for reasonably energy- (not just financially-) efficient air capture and storage of CO2. Indeed, it would be a great way of encouraging engineering students to do something more socially responsible than designing ever more efficient ways of killing foreigners (google DARPA challenge). But in saying it “deserves to be at the center of international climate policy debate” you’ve simply fallen hook line and sinker for what at the moment seems little more than speculative puffery.

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  19. EliRabett Says:

    Dear Roger, What on this earth caused you to that exceedingly odd and misleading statement about what I said? In no way shape or form have I objected to a prize being given for design, implementation or theoretical improvements to air capture of CO2 or any pollutant. I simply know something about NaOH.

    May I suggest a simple experiment you can probably do at home. Go under the sink and grab the heavy duty Easy Off or whatever standard brand of oven cleaner you use. Spray it into the air in the kitchen. Watch how it soaks up CO2. Then breath deeply. On second thought don’t. Easy Off oven cleaner in a spray bottle is aerosolized lye.

    Were I to wish to bring this discussion down to your level, I would use the old saw “So’s your old man, but your old man don’t deserve that.”

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  21. Roger Pielke Jr. Says:

    Eli- If you’d like to discuss substance, I’d be happy to, please send me an email. Otherwise, I assume that you are more interested in slinging insults and sophistry while anonymous. Thanks though for reading.

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  23. Roger Pielke Jr. Says:


    Thanks for your response. You write, “But in saying it “deserves to be at the center of international climate policy debate” you’ve simply fallen hook line and sinker for what at the moment seems little more than speculative puffery.”

    Now what is more “speculative puffery” air capture technology or successful implementation of the Kyoto Protocol? Seriously. Since you are a betting man ;-) perhaps we might think about wagering on the cost per ton of air capture technologies in 2030?

    The center of the climate debate ought to be a big place, e.g., as represented by various policy options discussed in the IPCC. Does air capture deserve to be considered by he IPCC? It does not appear (that I can see) in its recent report on Carbon dioxide Capture and Sequestration, and it probably should. Shouldn’t the IPCC strive for inclusiveness in its discussion of policy options for adaptation and mitigation?

    Given the highly politicized nature of the climate issue, it is abundantly clear that air capture is a “politically incorrect” technology, which I find very interesting.

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  25. Roger Pielke Jr. Says:

    Some numbers on air capture

    If the world emits 6 billion tons of CO2 annually then the cost of removing this via air capture at $200/ton (using a middle estimate from the work of David Keith) is $1.2 trillion or about 2% of global GDP (assuming $60 trillion).

    Now if the increase in global greenhouse emissions is indeed among the (if not the single) greatest challenges facing humanity, shouldn’t a technical solution that requires essentially no change in behavior at a cost of 2% of GDP be on the table with options that are estimated to cost 1% or 0.1% of GDP but require changing the energy consuming habits of >6.2 billion people? Or is climate change a problem at a cost of 1% of GDP but not a problem at 2%?

    OK, gentle readers, have at it, what is wrong with this back-of-the-envelope calculation?

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  27. James Annan Says:


    What is wrong with it is exactly what I started off with: if the energy cost of capture matches or exceeds the useful output of the fuel that generated the CO2 in the first place, it’s a complete waste of time regardless of how cheap it is in dollar terms. Overall, emissions would increase by more than the amount sequestered. You might as well try to generate wind power by putting turbines on car roofs.

    Until it can reliably get well past this emissions break-even point on a large scale, it’s simply a non-starter as a realistic solution. And as other have said, there are plenty of lower-cost or even money-saving options to start with – it is surely these possibilities which should surely be “at the centre of the debate”.

    As to the wager: the figure of 4MJ/tonne is presented as a hard lower bound. How close to that do you think they’ll get by 2030?

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  29. Rich Conant Says:

    Hi Roger,

    Congratulations on a very interesting post! I anxiously await a reponse from DeBeers and their proposal for alternative products to be produced.

    CO2 sinks are limited under Kyoto – they are there at all largely there due to US negotiations. If the goal is to reduce atmospheric CO2 concentrations, shouldn’t sinks of any kind be included? There are legitimate worries about all C sinks. But I think that most are derived from the feeling that efforts devoted to sinks reduce focus on what ought to be core efforts to reduce emissions. If I were a regulator of CO2 reduction activities, I would restrict activities to those that led to a net reduction on CO2 concentration. If a complete evaluation was not feasible, I’d attempt to discount those activities accordingly.

    Air capture sinks ought to be evaluated by the same terms as any other sink or emission reduction activity. All sinks ought to be evaluated on how much CO2 they store, how long that CO2 remains there, secodary environmental impacts/benefits, and cost. A prize could entice research, development, and/or application, but IMHO it ought to be structured to address these four key areas. A prize focused on air capture could lead to reduced atmospheric CO2 concentrations, but could lead to investment in an option that is not the best option for one of several reasons.

    Energy-dense fossil fuels drive modern industrial economies. They are so entrenched and valuable that any country, industry, etc that gave them up would be missing an opportunity for growth/prosperity. But emitting CO2 to the atmosphere has a cost. Sinks are a logical response to these observations and I suspect their appeal will grow in parallel with efforts to reduce atmospheric CO2 concentrations. The real STP issue here is how should scarce research dollars be best used to identify and evaluate competing options. How can existing programs (e.g, that at DOE: be improved? This is must be all the more challenging in the current environment in which, as prometheus suggests, research may be supported to allay action.

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  31. Jim Clarke Says:


    From the point of view of a skeptic, I have to wonder why you think skeptics would start to advocate sequestering CO2? Although a skeptic would not find sequestering in itself, harmful, I believe it would be considered a waste of time and energy, unless a viable and profitable use could be found for the sequestered carbon (which is another interesting speculation. See below).

    At the core of the skeptics understanding is the theory that CO2 is NOT a major driver of climate change, so tweaking the amount of CO2 in the atmosphere either way, is not likely to produce a significant difference in climate!

    I must, however, strongly disagree with the sentiments you expressed in this statement:

    “If such a transformation occurs, then we have the irony of seeing the climate skeptics become the technology advocates and the greenhouse gas regulation advocates become technology skeptics.”

    There is no irony in climate skeptics becoming technological advocates, for that is what we are today. While the term ’skeptic’ refers to our skepticism that CO2 is a major climate driver, we are also strong advocates of the idea that technology will make the debate a mute point. For example, Roy Spencer’s latest editorial on the TCS website illustrates this perfectly. Most climate skeptics recognize the inevitable progress in technology and view the IPCC projections of increasing CO2 emissions for the next 100 years as totally irrational.

    Advocates of greenhouse gas regulation, on the other hand, are already skeptical of technology, referring to the undeniable march of progress as ‘pie-in-the-sky’, and ‘wishful thinking’!

    I, for one, find no compelling reason to damage the biosphere by depriving plants of essential nutrients, but if it makes people feel better about themselves and they are willing to pay for it, who am I to complain! The problem is that these people are not willing to pay for it, but will certainly insist that we all contribute.

    (On the other hand, would it not be ironic if a private company found a way to extract the carbon from the atmosphere and turn it into a highly profitable product? Imagine the consternation that the environmentalists would have as this corporation ‘rapes’ the atmosphere for money! Presidents will be persuaded to proclaim whole sections of the atmosphere as ‘National Atmospheric Parks’ to prevent industry from profiting off the atmospheric CO2, which rightfully belongs to the people! Now THAT would be ironic!)

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  33. Kit Stolz Says:

    The claim that air capture would be anathema to environmentalists (assuming for a moment its practicality) is very dubious. Already a number of prominent environmentalists (such as Stewart Brand) have suggested the time has come to reconsider nuclear energy, because it can produce large amounts of power with no carbon emissions. This stance in years past would be heresy within the movement, and is still controversial.

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  35. Tom Rees Says:

    Roger, I think that your line: “For most of those people who support greenhouse gas regulations, even admitting the possibility of air capture is anathema” is unsubstantiated and captures pretty neatly your inherent bias. That said, air capture would be fantastic if practicable.

    Reasonable people might worry about where all the energy is going to come from (and whether it might not be more efficient just to use that energy to replace fossil fuel power generation). Also, if the practibility is possible but tendentious at this stage, they might worry that a ‘jam tomorrow’ technological fix might be used by advocates of complacency to avoid taking practical steps today. It would be a gamble to rely on this hope, in other words – and your attitude to that gamble would depend upon your political preconceptions.

    The best way to make the judgment independently of such preconceptions is to leave it to market forces. With this in mind, your post also (inadvertently, I’m sure!) underlines the value of Kyoto. As a result of Kyoto, a value for CO2 emissions has been set by carbon trading. Companies now have a calculable incentive to undertake the research that would lead to air capture – and they can judge whether risk is worth the potential profit.

    Giving a prize is less effective, because the prize is for a specific technology achievement, rather than for a policy achievment. In other words, a prize means that a bureacrat has decided that ‘technology X’ is what should be researched. A carbon marketplace leaves the choice of technology (free air capture, point of source capture, alternative energy, energy efficiency, or some optimal combination of all four) up to the market.

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  37. Roger Pielke Jr. Says:

    Lots of good stuff here, thanks. Some quick replies:

    James – Nuclear power?

    Rich – Welcome! Excellent points, and I certainly agree with your 4
    criteria for evaluating sinks.

    Jim Clarke- Thanks for these comments and for clarifying a skeptical perspective!

    Kit- Ditto for a non-skeptical perspective!

    Tom- You dismiss prizes a bit too quickly I think. Also, extending your argument to its logical conclusion there would be essentially no directed government investment in technology research. Have a look at this paper:

    Thanks all!

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  39. Lisa Dilling Says:

    A few quick notes here on semantics and other odds and ends. The term “air capture” can cover both chemical (such as Keith et al.’s method) and photosynthetic (such as planting forests or changing tillage practices). So, in a sense, air capture is already at the heart of the Kyoto protocol in the form of the carbon sink debate. As far as the feasibility of air capture, Lackner (cited for his 2001 work in the post), writes in the June 2003 issue of Science: “Currently, photosynthesis is the only practical form of air capture.” It’s possible that the chemical method of air capture had simply not yet progressed beyond the “white paper” concept stage at the time of the IPCC carbon capture and storage report, which would explain its omission, as the IPCC generally relies on peer-reviewed published literature for its assessment process. The Carbon Capture and Storage report explicitly did not cover biological land sequestration through land use changes, forestry, ocean fertilization etc. (see the Preface. This is probably because these were covered elsewhere, e.g. for land in the Land Use Land Use Change and Forestry report in 2000).

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  41. John Vermylen Says:

    A quote from Paul and Anne Ehrlich is instructive: “Giving inexpensive and abundant energy to Americans today would be like giving a machine gun to an idiot child.” ( Many of Roger’s predicted “greenhouse gas regulation advocates become technology skeptics” might agree with this statement. Is the climate change debate for many simply a proxy argument for an energy/technology debate? (i.e., can we solve the climate problem using technological progress to provide abundant energy, or must the solution, as Roger writes, “require changing the energy consuming habits of >6.2 billion people?”)

    If we simplify the climate change debate to a Pascal’s Wager-like 2×2 grid, with Climate Change a Problem/Not a Problem on one axis and Technological Progress a Solution/Not a Solution on the other, how would most fill in the probabilities on this grid? Assuming its possible to simplify a very “shades of gray” problem into two “black-white” questions, my expectation is that answers to these seemingly objective questions would be strongly influenced by one’s feelings toward current resource and energy consumption levels.

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  43. Paul Says:

    “When so-called climate skeptics start advocating air capture (which I have to believe can’t be too far off), then you will have a sign that the climate debate is really changing.”

    That is a classic fallacy I have encountered before.

    If you happen to find yourself as the only person in a row boat, which you believe is going n the wrong direction, the only rationql thing to do is abandon the oars and grab the rudder.

    I though you of all people would appreciate the political motivation of such behaviour

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  45. Mark Bahner Says:

    Hi Roger,

    You write, “For most of those people opposed to greenhouse gas regulation advocating air capture would require first admitting that greenhouse gases ought to be reduced in the first place, an admission that most on this side of the debate have avoided.”

    Your wording strongly implies that those against greenhouse gas regulation are simply avoiding admitting a truth. Otherwise, why would you use the words “avoid” and “admission”?

    But why do you think governments need to regulate CO2 (either emissions or atmospheric concentrations)?

    What do you have against plants?


    P.S. Seriously, what significant harm do ***you think*** will be avoided by governments regulating CO2 (emissions or atmospheric concentrations)?

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  47. Mark Bahner Says:

    Sorry, a bit off-topic, but did anybody actually read the link John Vermylen gave?

    Specifically, there is this outrageous and ludicrous statement, passed on without a shred of supporting evidence. (Why? Because no evidence is available, obviously!) It’s Paul Ehrlich (remember him?), quoting John Holdren:

    “As physicist John Holdren has written, ‘A CO2 climate-induced famine, killing a billion people before 2020, certainly cannot be ruled out.’”

    Absolutely appalling.

    P.S. Actually though…it’s not so off-topic after all. Roger, if you also think that “A CO2 climate-induced famine, killing a billion people before 2020, certainly cannot be ruled out”…I can certainly understand why you would think government regulation is necessary! (What I can’t understand is why you would ever accept such a statement without volumes of supporting evidence!)