FAQ to Accompany Pielke (2009) on Air Capture
February 3rd, 2009Posted by: Roger Pielke, Jr.
What is your new paper?
Pielke, Jr., R.A., An idealized assessment of the economics of air capture of carbon dioxide in mitigation policy. Environ. Sci. Policy (2009), doi:10.1016/j.envsci.2009.01.002
How can I get a copy?
The final version will be placed online here. Until that is available you can find the corrected proofs here in PDF.
What is the paper about?
Here is the abstract:
This paper discusses the technology of direct capture of carbon dioxide from the atmosphere called air capture. It develops a simple arithmetic description of the magnitude of the challenge of stabilizing atmospheric concentrations of carbon dioxide as a cumulative allocation over the 21st century. This approach, consistent with and based on the work of the Intergovernmental Panel on Climate Change (IPCC), sets the stage for an analysis of the average costs of air capture over the 21st century under the assumption that technologies available today are used to fully offset net human emissions of carbon dioxide. The simple assessment finds that even at a relatively high cost per ton of carbon, the costs of air capture are directly comparable to the costs of stabilization using other means as presented by recent reports of the IPCC and the Stern Review Report.
Is air capture technically possible?
Yes, it is possible.
Is air capture a magic bullet? Why don’t we just capture carbon dioxide directly from the air and be done with it?
Air capture is not a magic bullet to stopping the carbon dioxide build-up in the atmosphere. There are several obstacles to deployment of air capture at a scale significant enough to play a role in mitigation policy.
The first obstacle is the immaturity of the technology. Some scientists and engineers are working on it, but it really has not received significant attention or resources. There are various proposals for air capture technologies and some of these proposals have been prototyped.
The second obstacle is sequestration. What do you do with the carbon dioxide when it is captured? This is the same obstacle to the carbon capture and storage from coal power plants. Because the IPCC, IEA, G8, US, EU and others are all banking in a big way on such storage being possible, we’ll know soon, perhaps within a decade how viable an option sequestration is –for both CCS and air capture. There is also the possibility that people will react negatively to sequestration, like some do to nuclear waste. So there could be social objections.
The third obstacle is how air capture changes the debate. If air capture is a possible contribution to mitigation some believe that it will lessen the ability to use climate policies to get at other agendas. So for some there is a reflexive almost irrational opposition to air capture simply because it is a technological fix. For example, commenting on air capture a representative of an environmental NGO explained that it took away the ability to use climate change to get at other issues:
Such techno-fixes also miss the point of the environmental degradation brought on by the use of fossil fuels, he said.
Carbon scrubbers won’t stop oil spills, habitat-destroying strip mining and ozone, he said. “It’s like having cancer and putting a Band-Aid on it,” he added.
Or as Ted Parsons, a professor at the University of Michigan, commented on air capture (PDF):
Can we continue to rely on specific technical correctives for each problem as it arises – whether these are changes in production processes to further reduce environmental burdens per unit of output, or direct environmental interventions to offset those burdens like air capture? Alternatively, can we continue to rely on narrowly drawn policies to motivate reductions in whatever specific forms of production and consumption pose the clearest immediate risks? Or must we somehow find a way to address the larger-scale question of limiting the aggregate scale of human population and economic activity, and seek to identify some means to achieve this that is compatible with humane, democratic states that value individual liberty?
Such concerns about technical fixes are commonplace.
A fourth obstacle is cost, which is what my paper focused on.
What did you learn about the costs of air capture?
The analysis in my paper concludes:
To summarize, the idealized exercise conducted here finds that air capture using 2008 technology is of about the same costs as the costs estimates for stabilization at 450 ppm or 550 ppm carbon dioxide presented by IPCC (2007a) and Stern (2007). If the costs of air capture decrease to $100 per ton of carbon, then over the 21st century air capture would in fact cost much less than the costs estimates for stabilization presented by IPCC (2007d) and Stern (2007). This surprising result suggests, at a minimum, that air capture should receive the same detailed analysis as other approaches to mitigation.
This should not be too surprising a result for people familiar with the marginal cost curves of abatement of carbon dioxide which are similar to (or large than) the costs of air capture presented in my paper. I took efforts in my paper to ensure that my simple analysis erred on the side of overestimating the costs of air capture. Another way of looking at the costs of air capture is with respect to the damages associated with doing nothing. Air capture easily costs less than these damage costs as presented by IPCC and the Stern Review. So whatever other objections one might have to air capture, costs do not seem to be among them.
In short, if air capture costs too much as an approach, then so too do other forms of mitigation, because they costs about the same. If other forms of mitigation are judged to be worth the expense, then air capture deserves more attention than it has received in the past, because its costs are in the same ball park .
Who else thinks air capture is important?
Lots of people. Jim Hansen is a notable example. In my paper I quote him as follows:
‘‘a feasible strategy for planetary rescue almost surely requires a means of extracting [greenhouse gases] from the air”
Realistically, what role do you think air capture will play in mitigation?
Well, it seems fairly obvious that mitigation policies are going to face serious difficulties in slowing down, much less reversing, the growth in carbon dioxide emissions. But let’s take an optimistic view that the world sets forth immediately on a path of decarbonization and sustains that effort over the next few decades. Even under such an optimistic scenario, the world may wish at that time to further reduce concentrations in the atmosphere, as mitigation efforts may not be 100% successful. Air capture will be the only way to do that, and so could be a form of “mopping up” whatever is left of the task of mitigation.
Of course, there is a pessimistic scenario as well, which has the world not doing much to reduce emissions and seeing concentrations grow rapidly. Under such a scenario, the world may wish to remove carbon dioxide directly from the air. Air capture would of course be necessary under such a scenario as well, and at a much larger scale.
In either case, there can be little reason not to pursue the technology of air capture even though it may or may not have a significant role to play in future mitigation policies. In the end ask yourself this question:
Would it be easier to transform the global energy system and change the energy consuming habits of 6.5 (going to 10) billion people around the world in a period of a few decades, or to engineer a solution to removing carbon dioxide directly from the ambient air? I don’t know what the answer is, but I lean pretty strongly toward the latter.
My paper is certainly not the last word on this subject, and I would expect that we’ll be hearing a lot more about air capture, especially if progress on other forms of mitigation continues as it has recent decades. If climate change is indeed a planetary emergency, how can we afford to ignore air capture?
February 3rd, 2009 at 6:14 pm
[...] From Roger’s posting today in Prometheus: [...]
February 4th, 2009 at 12:02 pm
Roger:
You make it clear that is this work, “air capture” is to be distinguished from CCS at coal-fired plants, as well as other ‘capture’ modes.
Yet you say “Air capture will be the ONLY way to do that (drawdown CO2), and so could be a form of “mopping up” whatever is left of the task of mitigation.”
This statement is patently false, since CCS and bio-capture and sequestration are other competing ways. And it is also unwise to seem to be suggesting that drawdown technology should probably be used AFTER other mitigating efforts, for “mopping up”.
As Susan Solomon and others, including you;-) have noted, the more a given magnitude of drawdown is delayed, the less effective it will be because of the buffering effect of accumulated CO2 in the oceans.
So drawdown efforts should be preferred as early parts of, and in parallel with, ’standard’ mitigation efforts.
In this connection, I have 2 papers in the pipeline at the journal, Climatic Change, that describe 8 to 13 GtC/yr. of sustainable bio-sequestration. One involves irrigated afforestation of subtropical deserts. The other the sustainable eco-neutral conservation harvest of old-growth tropical forests. Both depend upon already mature technologies. The second is extremely inexpensive, and the first, cheaper than either CCS or “air capture”{.
February 4th, 2009 at 1:29 pm
Len-
Thanks for your comments, and congrats on your papers.
When I say “left with the task of mitigation” I am including CCS as part of conventional mitigation. As I state in the paper (have you read it?):
“Carbon dioxide emissions from power plants, representing perhaps as much as half total emissions over the 21st century could be captured at the source for a cost considerably less than direct air capture.”
I am assuming that air capture technologies will not be available for some time, but perhaps you differ on this. Finally, “bio-sequestration” is a form of air capture, as I use the term. If this approach to removing CO2 from the ambient air is cheaper than the cost estimates that I reviewed, then my arguments are that much stronger.
February 4th, 2009 at 9:14 pm
Roger:
I’ve now read your comp0lete paper.
As you note, your cost estimates for chemical “air capture”, don’t include the follow up costs of sequestration.
For CCS at power plants, this typically turns out to involve extensive, large-volume, high-pressure, pipeline systems to transport the CO2 to underground or undersea storage sites. Such will also be necessary for chemical “air capture”. This increases capital/maintenance costs considerably. These would often have to course their way through populated areas. They represent potential hazards. And, as you note, sequestering CO2 underground or undersea involve hazards of ‘unexpected releases’ – one of the serious problems that has also plagued the nuclear power industry. In addition, the various methods for concentrating the ambient, dilute CO2 require power/heat, with potentially very large CO2 footprints.
By comparison bio-sequestration, in wood (or bio-char/charcoal), poses much less risk, and minor costs, essentially no new technology, and usable, salable products.
The choice about which of the two deserves most attention in a global effort to stop and reverse warming, seems to me to be a no-brainer.
February 5th, 2009 at 5:34 am
Received by email:
—————————
This is totally outside my field of interest, but I wondered if you had anything to say about David MacKay’s physics-based prognoses for air capture in Chapter 31 of this:
http://www.inference.phy.cam.ac.uk/sustainable/book/tex/cft.pdf
I would have commented on Prometheus (I’ve lost my login details) as I’d be interested to hear Len’s views as well…considering MacKay’s equally pessimistic words about bio-seq.
—————————–
February 5th, 2009 at 10:11 am
With respect to #5:
I’ve just read Chapter 31 of David McKays excellent book. I find that I agree with virtually everything he says – BUT he made an ENORMOUS error when he said
“The best plants in Europe capture carbon at a rate of roughly 10 tons
of dry wood per hectare per year – equivalent to about 15 tons of CO2 1 hectare = 10 000m^2 per hectare per year – so to fix a European’s output of 11 tons of CO2
per year we need 7500 square metres of forest per person. This required
area of 7500 square metres per person is twice the area of Britain per person.”
This is wrong because it should be “twice the area of Britain
February 5th, 2009 at 10:27 am
(Continuing #6:
“twice the area of Britain to sequester the TOTAL CO2 OUTPUT of Britain”.
That’s why my proposal involves the “irrigated afforestation of subtropical deserts”, namely the Sahara and the Australian Outback.The growing season becomes 12 months, the photosynthetic efficiency at such latitudes is greater, and with the appropriate choice of tree species, the standing forest, itself, is the storage device for at least 100 years. And with appropriate conservation harvest, can continue indefinitely to sequester about 8 GtC/yr forever. The harvest becomes a source of renewable solid and liquid fuel for the transportation and some energy sectors.
McKay made a ’small’ numerical error, and quickly, and incorrectly, rejected bio-sequestration, out of hand.
February 5th, 2009 at 10:47 am
“This is totally outside my field of interest, but I wondered if you had anything to say about David MacKay’s physics-based prognoses for air capture in Chapter 31 of this:…”
I’ve just skimmed portions of David MacKay’s book. I agree with Len Ornstein that it seems wonderful. Especially so since it’s provided for free. (I’ll have to look for a “tip jar” tonight.)
One comment I have regarding MacKay’s Figure 31.6 (on “ocean nourishment”). He makes the 120 areas separated from one another (even though I know of no practical reason why they would need to be separated). This has the visual effect of making the total area seem bigger. Also, he cuts off the figure just at the limit of the areas of nourishment (not showing the rest of the Atlantic Ocean). This also has the effect of making the areas look larger.
His central point that the total ocean area involved is a significant fraction of the land area of a country is well-taken. But it’s also important to remember that the earth is more than 2/3rds ocean.
P.S. Just FYI, his calculation of the ocean area needing nourishment to remove the United Kingdom’s CO2 emissions is 120 areas, each 900 square kilometers. That’s a total of 108,000 square kilometers. The land area of the United Kingdom is approximately 240,000 square kilometers (or about twice as large). And the total area of the oceans of the world is 361,000,000 square kilometers…or approximately 3,300 times larger than the area needed to absorb the United Kingdom’s CO2 emissions.
February 8th, 2009 at 2:16 am
What role then for the large amounts of new “secondary tropical forests”? Given that they appear to be growing at 40 times the pace of rainforest deforestation, surely they must be doing some carbon capturing by themselves already?
http://www.iht.com/articles/2009/01/30/america/forest.1-419181.php
February 16th, 2009 at 11:08 am
Corrected proof posted here:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VP6-4VKDH06-1&_user=918210&_coverDate=02%2F11%2F2009&_rdoc=2&_fmt=high&_orig=browse&_srch=doc-info(%23toc%236198%239999%23999999999%2399999%23FLA%23display%23Articles)&_cdi=6198&_sort=d&_docanchor=&_ct=33&_acct=C000047944&_version=1&_urlVersion=0&_userid=918210&md5=768e34359f3f6782ea259894b0efc053
February 24th, 2009 at 3:31 am
The technology currently exists for “Air Capture”. Atmospheric carbon dioxide mitigation can take place while producing a zero footprint motor fuel. A motor fuel that reduces dependence on petroleum imports and produces employment.
Information may be obtained at:
NEGATIVE FOOTPRINT http://sites.google.com/site/negativefootprint/
Atmospheric Carbon Dioxide Removal:
http://sites.google.com/site/maketheworldgreenorg/
Electric Car: http://sites.google.com/site/jreed4301electriccar/
February 24th, 2009 at 5:24 am
I’m not an expert in the field, but I read the pop literature and I remember some time ago reading about an experiment where plants grown in a greenhouse with elevated (x4 IIRC) levels of CO2 caused tremendous proliferation of plant growth – the plants in the conditioned greenhouse were much larger than those in the control one.
Do you reckon we could marry these two ideas? Can we think of a local CO2 sequestering plant that could either bottle CO2 (or CO2 rich air that is less expensive to produce) or pipe it to local greenhouse farms to boost yield? Of course this still “leaves” the carbon hanging around after you harvest, but that could be taken care of in some other way (?).
There are also other technical issues such as insulating the greenhouses.
February 24th, 2009 at 5:28 am
[...] possibility, Dr. Pielke says, would be to remove carbon dioxide from the atmosphere in the future. He calculates that it could cost about the same, in the long run, as making drastic cuts in emissions today, and [...]
February 24th, 2009 at 9:03 am
How is capturing the CO2 at some time in the future, when failure is even less of an option than it is now, a reasonable approach? As with current carbon capture and sequestration proposals, the big question is where will the CO2 be sequestered?
February 26th, 2009 at 2:05 pm
A plug for the work of some colleagues on the potential to sequester CO2 in the basaltic ocean crust:
David S. Goldberg, Taro Takahashi, and Angela L. Slagle
Carbon dioxide sequestration in deep-sea basalt
Proceedings of the National Academy of Sciences, 2008 105:9920-9925; doi:10.1073/pnas.0804397105
February 26th, 2009 at 6:15 pm
[...] possibility, Dr. Pielke says, would be to remove carbon dioxide from the atmosphere in the future. He calculates that it could cost about the same, in the long run, as making drastic cuts in emissions today, and [...]
May 25th, 2009 at 8:01 am
Roger,
Your article attempts to calculate the macro-economic costs of air capture by taking different estimates of the ‘individual’ costs from the literature. A question which would need to be addressed as well concern the energetic costs of the process: If capturing a ton of CO2 costs more energy than the production of that energy emits to the atmosphere, than it’s not a useful strategy to decrease the carbon loading of the atmosphere; to the contrary. (That would still be the case even if the energy comes from renewable sources; those energy sources could better be used to replace fossil energy than to capture carbon out of the air.)
There are slightly conflicting results out there regarding the energy costs of air capture, and of course it depends on the process used (and on how ‘inclusive’ one calculates the energy costs). According to the IPCC report the process currently produces as much CO2 from coal-generated energy usage as it strips from the air, so it is not (yet) at the stage of useful deployment [IPCC WG3, 2007]. Bachiocchi et al (2006) conclude that it is not (yet) energy efficient, while Zeman (2007) comes to the opposite conclusion. The recent Nature Climate Crunch special (2009) quoted some numbers from Roger Aines (Livermore Nat Lab) that enable a more macroscopic view: Taking 0.25 Gt carbon out of the air per year would cost 900,000 GWh of energy per year according to their assessment. That means that capturing 1 ton of carbon costs 3.6 MWh, or that 0.28 ton C is captured per MWh of invested electricity costs. (I’m assuming they’re talking about tons of C, not CO2, which would be a factor of 3.6 more.)
I compare that to the emission rate of electricity generation from http://www.eia.doe.gov/cneaf/electricity/page/co2_report/co2report.html. Here, the emissions from coal are roughly 2 pounds of CO2 per kWh, which equals 0.28 t C per MWh, the same as the energy costs of capturing the same CO2 (in line with the IPCC statement cited above).
That implies that if coal fired energy is used to capture CO2, we’re not changing the carbon content of the atmosphere by a single bit, and that if cleaner energy is used, we may as well use it to replace coal generated energy instead, since that would decrease the CO2 content of the atmosphere by the same amount as using it to capture CO2 from the air.
The bottom line is that the energy costs of air capture needs to be reduced before it could be considered to play a role in mitigating climate change. Now the expectation is of course for that to happen as a consequence of more R&D, and for the relative CO2 emissions (CO2/kWh) of energy generation (including coal fired power plants) to decrease.
I believe this to be relevant to your paper, and to any estimation of monetary costs of air capture, since the costs per ton of CO2 needs to include these energy costs. At the current break-even point (assuming the numbers above to be correct), these costs reach infinity. And the real monetary costs will not be nearly as low as found when only the captured CO2 is taken into account, and not the required CO2 from fuelling the process.
That said, if and when the energy costs are low enough, it may be a useful technology to use to help averting dangerous climate change.
Bart