Some Simple Economics of Taking Air Capture to the Limit

April 20th, 2006

Posted by: Roger Pielke, Jr.

A while back we discussed the notion of “air capture” which refers to the direct removal of carbon dioxide (CO2) from the atmosphere and referenced the work of David Keith at the University of Calgary. David has an excellent paper on this in the journal Climatic Change, available here, and David’s views on my earlier post can be found here.

With this post, I’d like to engage in some simple math on the economics of air capture. Think of this exercise a bit like the mathematician’s tendency to take things to their limit. In a policy sense, exploring air capture is also a bit like taking things to the limit. If climate change is defined as a problem of increasing atmospheric concentrations of CO2 (and other greenhouse gases), then it is logical that the solution would be to stop that increase, and some form of air capture is a logical way to do that (please note that I have not said anything about technical feasibility or economic efficiency). The exercise below explores what sort of costs air capture implies using the lower end of Keith’s cost estimates of $200 per ton of CO2 removed from the atmosphere (the upper end is simply 2.5 times higher, for those interested in those numbers). I’d like to motivate some discussion on this subject, because I’d like to understand it further. A central question that I have been pondering is: Given the numbers below, why isn’t air capture technology at the center of debate on climate change?

If the end of the world is at risk, as some have warned, should a politically-neutral technology (i.e., requires no change in behavior, no complicated negotiations, no oversight or compliance regimes, no carbon markets, nada) that may cost as little as 1% of today’s global GDP (yes, a big number I realize) at least be on the table with other options of similar magnitude costs, but with huge political obstacles to their implementation? At a minimum why isn’t air capture technology research at the center of the governmental investment in climate change technologies? I remain completely baffled by this oversight in the policy debate.

Here is the math:

Starting points: 1 ppm of CO2 equals 2.08 billion tons (Thanks to CU faculty colleague Jim White for this info!) At $200/ton air capture cost this equals $416 billion per 1 ppm CO2 scrubbed from the atmosphere.

A. Total Cost for US to reduce emissions to 1990 levels:

A1. Annual cost

1990 US CO2 emissions: 5,005,300,000 tons
2004 US CO2 emissions: 5,988,000,000 tons
Source: US EPA

Lets just say roughly 1 billion tons, annual cost of compliance to 1990 levels via air capture = $200 billion or approximately 1.5% of US GDP.

A2. Incrementally increasing costs

Yearly increase in CO2 emissions = roughly 150,000,000 tons
Annual increase in costs = $30 billion or (0.2% of US GDP)

B. Cost for Global reduction of emissions

B1. To pre-industrial values

From 380 ppm to 280 ppm requires a reduction of 100 ppm or $41.6 trillion dollars (~67% of global GDP, assuming ~$60B global GDP), with an average annual recurring cost of reducing approximately 1.5 ppm or $624 billion (~1% of global GDP).

B2. Brute force stabilization to 350 ppm

Presumably, air capture could be used to “tune” the atmospheric concentrations of CO2 to some desired concentration. From 380 to 350 ppm requires an initial reduction of 30 ppm or $12.5 trillion dollars (~21% of global GDP), with an average annual recurring cost of reducing approximately 1.5 ppm or $624 billion (~1% of global GDP).

B3. Brute force stabilization to 400 ppm

From 380 ppm to 400 ppm implies ~10 years of business as usual, and then with an average annual recurring cost of reducing approximately the annual increase of 1.5 ppm or $624 billion (~1% of global GDP). The US share of this cost would initially be approximately 25% (or somewhat less) of this total or $151 billion. Developing country costs would start out small and would increase as their economies (and emissions) grow. My first impression is that these numbers and time frame seem surprisingly reasonable.

How would any of this be paid for? I don’t know and haven’t given this much thought. But the numbers at the lower end, e.g., $151 billion for the U.S., seem to be well within the range of a gasoline or carbon tax, which could be phased in very gradually over the next 10 years.

Some caveats and notes: CO2 isn’t the only important greenhouse gas, but it is important. Cost estimates are estimates, Keith says they might be accurate to within a factor of 3, and given what I know about the uncertainty in past efforts at technological forecasting the costs could be much higher or much lower, and it is worth noting that cost estimates of this sort often wind up being far too high than what proves to be the case in reality. Nonetheless, the best data on air capture technologies will come from actual engineering experiments. As David Keith writes in his Climatic Change paper and on our blog, in reality air capture would make the most sense as a complement to other forms of mitigation and sequestration. My point here is not to propose an optimal policy in any way, but to take air capture to the limit. I am not advocating air capture as a solution (I simply don’t know enough), but I am advocating air capture as a contribution to the debate on climate change. And of course none of this addresses adaptation to climate or climate change. And above all – caveat emptor!

38 Responses to “Some Simple Economics of Taking Air Capture to the Limit”

  1. Bob_K Says:

    Since no one can as yet accurately quantify the percentage warming due to humans, I’m inclined to believe there is very little to worry about.

    I won’t comment on the feasability of air capture since I’m not up on the subject.

    The reason it’s not on the table is likely because the bureaucracy required to manage the system would be minimal.

    CO2 control by means of carbon credits is a much larger and more fertile ground for lurcrative shenanigins to be perpetrated.

  2. 2
  3. Chip Knappenberger Says:


    Who gets control of the thermostat? Does it revolve through the major countries of the world? Russia turns it up a bit during its turn, India turns it down a bit…

    As control of the thermostat is a contentious affair (to say the least) at my house, and even more so at my office, I can’t help but to worry that if the scale of the contention increases with the scale of the parties affected, things could get out of hand fairly quickly.

  4. 3
  5. Roger Pielke, Jr. Says:

    Chip- Thanks. A good question, but it is the exact same question that arises under any policy focused on stabilization. Air capture holds the prospect, I would think, of less “leakage” or cheating.

  6. 4
  7. Chip Knappenberger Says:


    In my view, reducing emissions is far different than actively removing CO2. I am much more comfortable trying to limiting what we put into the atmosphere than I am with the idea of actively taking things out of the atmosphere. To me, the latter, can lead to far more problems than the former…”hey, my country really liked the increased precipitation–so quit tinking with the climate” seems a much more valid concern than “hey, my country really liked the increased precipitation–so stop making cars in your country more efficient.” (even if the precipitation/climate change link was simply perceived)

  8. 5
  9. Paul Says:

    Well, this tells you all you need to know about this whole subject:

    “Presumably, air capture could be used to “tune” the atmospheric concentrations of CO2 to some desired concentration”

    How absurd

  10. 6
  11. Ben Says:

    Forgive me if I seem naive on this subject, because I really am. But haven’t we already got some CO2-scrubbers? By this I mean trees and other plants. Maybe we should work on keeping those capture devices functional.
    And besides, fundamental separations principles suggest that capturing CO2 should be most efficient when input is high in concentration of CO2 and these concentrations should be highest at the exhaust pipes of coal burning power plants. It makes more sense to capture the CO2 before it is diluted in the atmosphere.

  12. 7
  13. Steve Hemphill Says:

    Isn’t the “rate of change” of the “rate of change” (aka acceleration) of CO2 concentration concave downward, so that we must be naturally doing something like that already?

  14. 8
  15. Hinheckle Jones Says:

    Pardon me, But may we put a BILLION TONS of CO2 in your back yard?

  16. 9
  17. William Connolley Says:

    I can’t read the Cl Ch paper, so its hard to assess the tech feasability. Would the $200/t be applicable no matter how much you want to remove, or are there limits to whereever it is being deposited? (And, is the $200/t just the finance cost? How much CO2 is emitted in the process? I saw (somewhere, sometime) figures that direct capture from power plant exhaust about doubles the total fuel use).

    Assuming for the sake of argument that it does all work fine… how does this play against the EU CO2 trading, which is currently at $35/t (I think; you’ll probably be able to find better numbers). If that price means anything, there is little point paying 10* as much for direct capture.

  18. 10
  19. James Annan Says:


    Conventional power produces ~1kg of CO2 per kWh. Renewable power (eg wind) costs about ~5cents per kWh, and produces very little CO2. So, for $50, we can cut emissions by 1 tonne, and this is 1/4 the cost of your best-case (so far rather pie-in-the-sky) scenario for air capture.

    And I haven’t even mentioned the most obvious efficiency measures that could be free or even make money, such as switching tax breaks from the most inefficient vehicles to the most efficient ones.

    That, in a nutshell, is why air capture is not “at the centre of the debate”, and not likely to be for some time to come. By all means let the research continue, but it’s hardly a credible approach at this time.

    The hypothetical possibility of a hideously expensive solution that might not work on the large scale anyway is hardly a credible reason to not focus on the practical measures that can make a difference right now.

  20. 11
  21. Mark Bahner Says:

    Hi Roger,

    You write, “At a minimum why isn’t air capture technology research at the center of the governmental investment in climate change technologies? I remain completely baffled by this oversight in the policy debate.”

    And I’m completely baffled why you’re completely baffled. ;-) Here are the reasons why CO2 capture by big CO2 scrubbers is not now being considered, and almost certainly never will be:

    1) As Ben pointed out, it’s almost always much less expensive to capture a pollutant before it gets diluted by the atmosphere than before. Therefore, people will look at CO2 scrubbers for power plants way before they will ever look at ambient air scrubbers.

    2) If anyone ever did do ambient air scrubbing, it would probably be with ocean iron fertilization, which has estimated costs more like $2-10 per ton of CO2 scrubbed, versus $250-625 with mechanical scrubbers.

    3) CO2 scrubbing doesn’t bring any co-benefits at all; switching coal plants to natural gas or nuclear, for example, dramatically reduces particulate, SO2, and NOx emissions.

    4) For reducing emissions by 1 billion tons per year (going from 2006 to 1990 emissions for the U.S.) you’re talking about talking about $200 billion A YEAR!(!!!!!!!!!!!)

    a) With less than HALF that amount, it is virtually guaranteed that non-tokamak fusion energy could be brought to commercial status. (That’s why I want you to do the paper! :-) You’ll get the Nobel Prize of Public Policy Research for it! ;-) )

    b) And with $200 billion, photovoltaics could EASILY be brought down in cost to be competitive with coal, natural gas, and nuclear for electrical generation.

    5) You have calculated to remove 1 ppm of CO2 from the atmosphere, but you haven’t calculated the cost to lower temperature by, for example, 1 degree Fahrenheit. And it’s temperature that everyone is supposedly worried about. You’ve presented the value of 1 ppm = 2.08 billion tons of CO2. Then, taking a sensitivity of 3 degrees Celsius for doubling CO2 from it’s current value of 370 ppm, that means that 370 ppm = 3 degrees Celsius, or 1 ppm = 0.0081 degrees Celsius.

    Soooo…at $250 per ton, and 2.08 billion tons per ppm, and 1 ppm = 0.0081 degrees Celsius…to reduce the world temperature by a mere 1/2 degree Celsius, the cost is…

    $250 x 2.08 billion x (0.5 degC/0.0081 deg C) = $32 TRILLION!

    Don’t you see the insanity there?

    As I mentioned, with a mere $100 billion, non-tokamak fusion could almost certainly be commercialized…or photovoltaics could easily be brought to costs comparable to coal-fired or fission-fueled electrical production.

    That’s why ambient CO2 scrubbing with big mechanical scrubbers isn’t being seriously investigated, and almost certainly never will be.

  22. 12
  23. laurence jewett Says:

    Roger Posted: “Starting points: 1 ppm of CO2 equals 2.08 billion tons”

    Unfortunately, the number “2.08 billion ton” is NOT consistent with the number that one arrives at if one uses the total weight of CO2 given by the wikipedia source below (2.94 trillion metric tons) which is itself consistent with the number that one calculates from the latest values for CO2 concentration and total weight of the atmosphere**

    “As of 2006, the earth’s atmosphere is about 0.038% by volume (381 µL/L or ppmv) or 0.057% by weight CO2. This represents about 2.94 trillion tonne of CO2″ (metric ton)

    2.94 trillion metric ton is the total weight equivalent of the current 381 ppm atmospheric CO2 concentration ….

    Soooo…. by my calculation, the weight equivalent of a 1ppm atmospheric CO2 concentration is
    (2.94 trillion metric tons) divided by 381

    OR about 7.7 billion metric tons.

    This value (7.7 billion metric tons) should be compared to “2.08 billion tons” given as the starting point for the cost estimates provided.

    Not to be nitpicky or anything, but there IS nearly a factor of 4 discrepancy between the two values.

    While Roger may be correct in noting that there are probably OTHER factors (of 3 or even more) involved in such back-of-the-envelope cost estimates, I believe it is best to start with a CO2 weight equivalent for 1ppm that is as close as possible to the correct one (and near as I can figure, that is about 7.7 billion metric tons)

    ** The 2.94 trillion number (for TOTAL metric ton of atmospheric CO2) provided by the above (wikipedia) source is consistent with the number one obtains if one uses the mean weight of the atmosphere provided by the National Center for Atmospheric Research (5.1480 x 10^18 kg – or 5148 trillion metric ton ) and multiplies this by 0.00057 (atmospheric CO2 concentration by weight)

    (5148 trillion metric ton)x 0.00057 = 2.93 trillion metric ton,

    (essentially the same as the 2.94 trillion metric tons provided by wikipedia)

  24. 13
  25. Roger Pielke, Jr. Says:

    Laurence- Thanks for your comment. Here is what I got from Jim White (

    “Its about 2.08 GtC per ppm. GtC is gigatons of carbon.

    You need the relative masses of carbon to the bulk atmosphere. I used 22% oxygen (mass 32) and 78% nitrogen (mass 28). Using a carbon mass of 12 yields the formula: 12/(28×0.78 + 32×0.22) for the mass ratio. Note that this is carbon based, not CO2 based, which is the normal convention used. There’s about 5 x10^18 kg of atmosphere (+/- a bit). There’s 1000 kg in a metric ton, and a gigaton is a billion tons.”

  26. 14
  27. Roger Pielke, Jr. Says:

    William- Good questions. I would assume that air capture would have to be powered by nuclear. My example is simply an “end point” analysis. David Keith makes the point that if there are other, cheaper methods of removing CO2, then air capture is a “backstop” technology.

  28. 15
  29. Roger Pielke, Jr. Says:

    James- Thanks for your comment. You write:

    “By all means let the research continue, but it’s hardly a credible approach at this time.

    The hypothetical possibility of a hideously expensive solution that might not work on the large scale anyway is hardly a credible reason to not focus on the practical measures that can make a difference right now.”

    I am not advocating air capture as a “solution.” But discussing it does open up the conversation a bit, as I think the comments suggest here.

    How much research do you think is going into air capture? i don’t know but I’d bet it is mesaured in the millions of $$ (not tens of millions or more), if even that amount.

    Don’t confuse political questions (what makes a difference now) from reseach questions, e.g., what technologies might we need in 30 years if international policy fails to stabilize CO2? I for one see little harm in air capture research or discussing it.

  30. 16
  31. Roger Pielke, Jr. Says:

    Mark and Jim- Good comments, good questions. (I don’t have answers for you;-) These seem to be the sorts of questions that don’t usually get asked on this issue, and if raising the notion of air capture brings them into the dicsussion good.

    Mark- Your comment about co-benefits is important, and one that we raise here a lot.


  32. 17
  33. James Annan Says:


    Looking at the numbers, perhaps someone is confusing tonnes of C as CO2, and tonnes of CO2 itself – it’s a common point of confusion. I can’t be bothered wading through the numbers again to see who (if anyone) is wrong though.

    As for the money spent on research – well, make the case for more money if you like. But you’ll have to find out (a) how much is being spent and (b) what are the likely benefits of spending more and (c) what we should fund less of instead. Simply waving around a few vague ideas with “hey, it could work” isn’t very convincing IMO. As I remember, last time you mentioned this you were shot down with a pretty good list of reasons as to why it was basically a non-starter on technical and economic grounds, and was likely to remain so indefinitely.

    I sense some rapidly shifting ground from “centre of the debate” to “research questions” :-) Sure, let’s research it, like we research cold fusion and space elevators and string theory. It’s unlikely to be less useful than any or all of those :-)

  34. 18
  35. Hans Erren Says:

    I use 2123 MtC/ppm CO2, which is in the same order of magnitude.

  36. 19
  37. Douglas Hoyt Says:

    At one cent per square foot for aluminum foil, it would take about 5.5 trillion dollars to cover 1% of the Earth’s surface and reflect back to space about 2 W/m2. That is equivalent to about 28 years of the air capture solution or 37 years of Kyoto. Something to think about.

    Probably even cheaper to do iron fertilization or use GM to create microbes that can take lots of CO2 out of the air.

  38. 20
  39. Roger Pielke, Jr. Says:


    Thanks for your comments, On the trackbacks, yes, we’ve got issues, sorry about that and thanks for the (attempted) link!

    On air capture, I still think you miss my point. It is not about getting “shot down” or not. It is about opening up a conversation about climate policy that might be a bit different from the stale one about skeptics/non-skeptics.

    For instance, having a few folks here (who might be closer to the skeptics camp) underscore the importance of “co-benefits” is very interesting to me, and points to what factors might lead to breaking the preset gridlock through convincing such folks about what are valid criteria for action.

    As well, if, as some commentators have suggested, we have 10 years to save the earth from destruction, then I would think optimal cost efficiency is not necessarily the defining criteria in selecting a policy. The fact that these folks don’t seem to be too warm to AC suggests to me that they may not in fact believe their own hype. Let’s be honest, the global energy system is not going to be completely overhauled in 10 years.

    In short, the issue of AC is interesting to me not because it is a solution, but because it is a nice, fixed end point on the debate that provides some grounding with which to explore options. Perhaps it is the mathematician in me, but it seems that some sense of boundaries in policy debates can help to properly frame issues — hence the notion of “center of the debate.” (At the other boundary we might discuss “saturation policy” — the consequences of complete liberation of fossil energy from the earth into the atmosphere — perhaps I’ll write a post on this as a companion to AC. The point would not be to advocate “saturation policy” but explore its implications).

    Finally, yes, I think you are right about the confusion between C and CO2. I may have added to this confustion by being less precise on this point than I should have. Prices of CO2 reduction are typically discussed in terms of C. So sorry for any confusion!

  40. 21
  41. Laurence Jewett Says:

    Roger Pielke posted”Note that this is carbon based, not CO2 based, which is the normal convention used.”
    James Annan posted: “Looking at the numbers, perhaps someone is confusing tonnes of C as CO2, and tonnes of CO2 itself – it’s a common point of confusion.”

    You are both correct: this IS the source of the discrepancy (ie, of my error)

    If you take the 7.7 billion metric ton that I got using total CO2 weight for my claculation and multiply this by the mass fraction of carbon in CO2 (12/44), you get 2.1 billion ton, which is basically the number provided by Roger (2.08)

    Please forgive my ignorance.

  42. 22
  43. Roger Pielke, Jr. Says:


    Your question caused me to go back to some of the orginal sources and see if I/they had conflated CO2 and carbon, and that may be the case.

    For instance, the EPA site I referenced cites CO2 emissions in tons, and it does not look like they are referring to C only.$File/06ES.pdf

    If this is indeed the case the my calculations under A. above (but not B.) would in fact be a factor of 4 too large. Does this make sense?

    So thanks for raising this.

  44. 23
  45. laurence jewett Says:

    James Annan posted” “Conventional power produces ~1kg of CO2 per kWh. Renewable power (eg wind) costs about ~5cents per kWh, and produces very little CO2. So, for $50, we can cut emissions by 1 tonne, and this is 1/4 the cost of your best-case (so far rather pie-in-the-sky) scenario for air capture.”

    After reading this this — and looking at a description of a CO2 capture system — I am struck by a thought, which has undoubtedly occurred to others as well. (Forgive me if I am simply rehashing a previous discussion on this blog.)

    Why does this have to be an Either/OR proposition?

    Why not combine CO2 capture with a renewable electrical generating system like a wind turbine?

    I’m not suggesting merely operating the two systems simultaneously but actually integrating them into a single system.

    Perhaps it might be possible by combining them into a single housing to reduce the cost and/or increase the profitability of BOTH systems simultaneously — thereby killing two birds with one windmill, so to speak. (My apologies to any bird lovers, of which I must admit I am actually one. But, unfortunately, every technology has bad as well as good aspects).

    The climate Decision Making Center (University of Calgary) describes their vision for a CO2 capture system thus:

    “A real system would be … an open tower
    about 390 feet (120 meters) high and about 330 feet(100 meters) in diameter. The sorbant would be
    sprayed from the top while air is blown down
    through it.”

    The system requires an energy source (preferably one that is on site and non-CO2 producing) to compress the CO2 for storage.

    This sounds to me like it has a lot in common with a wind tower with regard to required real estate and infrastructure.

    Perhaps there is some unused space inside wind towers (even existing ones) — space that might be retrofitted to house CO2 sorbant for the capture system.

    Wind might provide the energy to run the fan to blow the air through the sorbant chamber and to compress the CO2.

  46. 24
  47. William Connolley Says:

    James point seems to me to be a very good one: if you can do renewable energy generation far cheaper than air capture, why even think about air capture? There are enough ideas floating around already seeking valuable attention time, there is no point pushing up ones that are doomed (if James figures are right, and I don’t see anyone disputing them).

  48. 25
  49. Roger Pielke, Jr. Says:


    Thanks. You ask: “if you can do renewable energy generation far cheaper than air capture, why even think about air capture?”

    When you say ” … can do …” do you mean technologically feasible? Politically viable? Both?

    Here is the answer to your question:

    Until a policy focused on changing energy infrastructure shows some actual promise in terms of emissions reductions, why would anyone recommend putting all of their eggs in this basket?

    Laurence- David Keith makes clear that he doesn’t see this as an either/or proposition. I simply wrote up this exercise to see what sort of costs would be involved if policy focused only on air capture. It is an idealized thought experiment.


  50. 26
  51. laurence jewett Says:

    Roger: I fully understand your purpose here and appreciate that you take the position of exploring the different options to see where they lead.

  52. 27
  53. Kooiti Masuda Says:

    I understand that technical details are not the subject here. But we must consider the laws of thermodynamics.

    Concentrating CO2 from the atmosphere is against the natural tendency of diffusion, and it means that we want entropy of the target system of the process (CO2 plus the atmosphere) to decrease. It requires some resources (energy or matter) whose entropy increase more than the decrease of entropy in the target system. Also, captured CO2 must be converted into some stable form to be sequestered. It requires some more resources. Those resources to be employed are likely to be energy resources, for we do not want material pollution.

    Thus, I think that this kind of technology is not helpful until the availability of renewable energy resources significantly exceeds our consumption of fossil fuel. By then it is wiser to directly replace fossil fuel with renewable energy.

    By the way, I have come to an idea that air capture technology is helpful, in a sense different from yours, to reduce our dependence on fossil fuel. The weak point of renewable energy resources, such as solar light, wind power, and hydropower without large dams, is large temporal heterogeneity. Some buffer is necessary for them to cover many of our energy needs. If it becomes possible to produce some fuel easier to store than hydrogen (e.g. hydrocarbon or elemental carbon) from the atmospheric CO2 with low-density, highly variable energy input, it will work as temporary storage of renewable energy.

  54. 28
  55. laurence jewett Says:

    David Keith adresses the above thermodynamic question in his publication “Climate strategy with CO2 capture from the air”

    “the overall energy requirement for air capture with geologic
    sequestration is about 4 GJ/tC.
    The .4 GJ/tC minimum may be compared to the carbon-specific energy content
    of fossil fuels: coal, oil, and natural gas have about 40, 50, and 70 GJ/tC respectively.
    Thus if the energy for air capture is provided by fossil fuels then the amount of
    carbon captured from the air can — in principle — be much larger than the carbon
    content of the fuel used to capture it.”

    from David W. Keith, Minh Ha-Duong and Joshuah K. Stolaroff (2005). Climate strategy with CO2 capture from the air. Climatic Change, published on line, DOI: 10.1007/s10584-005-9026-x.

    which can be downloaded from Keith’s website:

  56. 29
  57. laurence jewett Says:


    While it appears that Keith is giving two different values in the quote above, this is NOT the case.

    It actually appears as “4″ in both places in the original pdf document.

    The “.4″ posted above (in the line “The .4 GJ/tC minimum may be compared to the carbon-specific energy content”)

    should ACTUALLY read “~4″ (ie, about 4)

    The “~” got transposed to “.” when I copied the text from the pdf document.
    I did not notice this until after I posted it. Sorry.

  58. 30
  59. Kooiti Masuda Says:

    I have browsed the paper by Keith et al. and found the thermodynamical discussion of the theoretical limit case as introduced by Laurence Jewett above. But, about the two more concrete examples of technologies, the paper includes cost analysis in monetary terms only.

    I think that the overall viability of this kind of technology crucially depends on certainty of CO2 sequestration. I doubt that there can be places where compressed CO2 will certainly be stable for millenia. I admit a relative merit of air capture over power plant exhaust capture that the capture plant can be located at best places in this respect. But it is just relative.

    If sequestration is certain, the idea using biomass seems to work. But as usual in schemes employing biomass energy, its requirement of land competes with food production and nature conservation.

    I guess that it is difficult to achieve high energy efficiency in chemical cycle processes involving CaO and/or NaOH to capture CO2. But this is just a guess and it seems worthwhile to make technology assessment if (but only if) there is outlook of sure sequestration.

    By the way, it seems strange to me (a climatologist) that the authors assume that future people will certainly be wealthier than us (unless either the abatement cost or the damage related to climate change be too high). I think this is just a wishful thinking that we should not depend on (though we should not exclude that possibility either).

  60. 31
  61. laurence jewett Says:

    I must admit I know nothing about the sequestration side of the coin, but it seems reasonable to assume, as Kooito points out, that “the ability to KEEP the CO2 captured” could very well be the “make or break issue” in this case.

    Also, Kooito’s point about “theoretical limits” is well taken.

    Actually, there are TWO “theoretical limit” issues involved here. One is the theoretical MINIMUM energy required by the capture system to capture a ton of carbon (in CO2) (which is system dependent, of course, but is given as ~4 GJ/tC by Keith, presumably for the Sodium hydroxide system that he has proposed).

    The other is the “carbon-specific energy content” of fossil fuel: 40, 50, and 70 GJ/tC for coal, oil and natural gas, resp (given by Keith).

    From the numbers I have found elswhere, these would appear to be primary energy contents (ie, max numbers for available energy provided). Eg, Keith’s 70 Gj/tC is consistent with a 14.92 carbon coefficient factor (Metric ton carbon per quadrillion BTU) — equivalent to about 67 Gj/tC — that I found elsewhere

    If one used electricity produced at a central generating station to power the capture system (compressor and fan), for example, the USABLE energy delivered by fossil fuel (to power the capture system) per ton of carbon produced would have to be reduced significantly from the 40, 50, and 70 GJ/tC numbers provided by Keith (bringing them closer — in some cases MUCH closer to the 4 GJ/tC MINIMUM need for capture).

    For example, if one used coal to produce ELECTRICITY at a central station and assumed about a 15% overall efficiency, one would already be very near to the “break even point” — ie, only about 6 GJ/tC would be provided, while at least 4 GJ/tC are required, according to keith.

    If one assumed worse than the best case minimum energy required for capture (eg, assume that 7GJ/tC required for capture instead of 4GJ/tC), then it would not even make sense to do the capture at all using electricity provided by a central coal-powered electical generating station, since more carbon would be released in powering the system than was captured.

    Of course, there is nothing saying that the compressor and fan could not be powered DIRECTLY ON SITE(by natural gas, for example), which would certainly be a better scenario than the centralized electrical power one from an overall efficiency standpoint, though even this would require reducing the 40, 50, and 70 GJ/tC numbers provided by Keith, of course.

    I assume that Keith must have made some adjustments in his COST estimate calculations to take the above efficiency issues into account, but I must admit I do not know if that is the case.

  62. 32
  63. laurence jewett Says:

    I just noticed I misspelled Kooiti’s name as “Kooito”.

    Please forgive me.

  64. 33
  65. Hans Erren Says:

    My favourite scenario for 2100 is nuclear fusion which makes diesel for transport vehicles from air captured CO2 and water.

    As for J/kg diesel still outweighs batteries, and it’s far safer to handle than hydrogen.

    As byproduct you also have a CO2 sequestering programme. You could store the diesel in oilfields.

  66. 34
  67. Mark Bahner Says:

    “My favourite scenario for 2100 is nuclear fusion which makes diesel for transport vehicles from air captured CO2 and water. As for J/kg diesel still outweighs batteries, and it’s far safer to handle than hydrogen.”

    Yes, diesel presently delivers more energy per kilogram than batteries. But the energy per kilogram of batteries is increasing significantly (and charging time is decreasing significantly), due to nanotechnology:

    A 200-250 mile range is good enough for me. And that 3-minute charging time…pretty impressive!

  68. 35
  69. laurence jewett Says:

    “My favourite scenario for 2100 is nuclear fusion which makes diesel for transport vehicles from air captured CO2 and water. As for J/kg diesel still outweighs batteries, and it’s far safer to handle than hydrogen.”

    The hydrogen saftey issue is obviously very important, but IF this issue could be properly addressed, hydrogen would undoubtedly trump both diesel and batteries as an energy storage solution.

    The following link addresses the safety issue (along with a lot of other stuff about a hydrogen economy on the site

    Particulalry relevant is the authors’ statement that “hydrogen can be safer than gasoline if it is used properly”. They explain why, in a very straightforward manner.

  70. 36
  71. laurence jewett Says:

    I realize most people are probably no longer reading this topic** but just in case:

    Here’s a link to “Twenty Hydrogen Myth’s”, also from the above Rocky Mountain Institute (RMI) website referenced above

    This adresses the hydrogen saftey issue, along with lots of other issues related to hydrogen.

    **Blog topics, even MORE than traditional news topics, seem to have an exceedingly short shelf-life, making me wonder a little about the value of posting to one, particularly on an “outdated” (a few days old) topic like this one. To be honest, I just recently started posting on this blog, and my judgement on its value is still not in. I’m still trying to figure out if it indeed HAS value. The problem is that, while there may be useful information somewhere here, it might be more readily accessed elsewhere (with a simple search) without having to wade through all the opinion (some of which, I admit I have expressed).

  72. 37
  73. Hans Erren Says:

    Thanks for the hydrogen myth backgrounder!

    Still, IMHO a diesel based infrastructure for transport will live a long life, in particular in remote areas, as it is low tech.

    Time will tell.

  74. 38
  75. Mark Bahner Says:

    laurence jewett wrote, “The hydrogen saftey issue is obviously very important, but IF this issue could be properly addressed, hydrogen would undoubtedly trump both diesel and batteries as an energy storage solution.”

    Hans Erren responded, “Still, IMHO a diesel based infrastructure for transport will live a long life, in particular in remote areas, as it is low tech.”

    A couple comments:

    1) I knew that batteries had a much lower energy density (energy per unit mass) than diesel fuel, but I didn’t realize quite how much lower. Wonderful Wikipedia (;-)) has good information on the difference:

    hydrogen: 120 MJ/kg
    diesel: 63.47 MJ/kg
    lithium ion battery: 0.54 to 0.72 MJ/kg

    However, it should be noted that the diesel and the hydrogen have to be put in a container, which adds additional mass (though not much for a diesel gas tank). And even more important, they both have to go through an engine/transmission (or with hydrogen, it could be a fuel cell) to change the energy form into something more usable, whereas the electricity in a battery goes through an electric motor to drive the wheels.

    Further, the cost advantage for batteries that get their energy from central generation is currently pretty large. For example, if a diesel car gets 30 mpg, at $3/gallon (just to use some easy numbers), that works out to 10 cents/mile. Whereas, at 9 cents per kilowatt-hour, I’ve read that the cost per mile for electricity from the grid (assuming appropriate battery charging efficiencies and electric motor efficiencies) is about 3 cents per mile.

    2) Diesels are becoming amazingly clean (particulate-wise, anyway) as very-low-sulfur diesel fuel is starting to come on the markets in all developed countries, and as particulate filters are beginning to be very common in developed countries.

    3) However, the long term trend seems very clear to me. All forms of internal combustion engine will eventually be replaced by completely electrified cars…which could very well involve cars having fuel cells. That’s what I was commenting on, Hans…your mention of the year 2100. I don’t see diesels surviving to 2100 (not that anyone can realistically see anything in 2100!).

    4) Regarding diesels’ lifetime: I’m working on project that looks at international transportation regulations. One thing that has struck me is that the world is rapidly becoming much more unified in its transportation regulations. I’m thinking of developing countries like China and India. Their regulations are at most a decade behind those in Europe and the United States. And they are catching up, rather than falling further behind. I think that will work against internal combustion engines, even in countries like China and India. If fuel cell vehicles begin to displace significantly displace hybrids circa 2020-2030 in the most advanced countries, I don’t see more than 1-2 decade delay for equal market penetration in China and India.

    5) Soo…I see the last diesel (or gasoline) automobile engine rolling off an assembly line before 2050.