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Sequestration Revisited

"Carbon Sequestration" is sometimes suggested as a parallel process alongside a significant shift away from carbon-producing technologies. The logic is straightforward: carbon dioxide is still produced, but rather than remaining concentrated in the atmosphere for a century, it is extracted. This extraction can take place at the point of production (so-called "carbon capture") or more generally, using CO2-loving plants. Although some may hope to use carbon sequestration as an excuse to delay or ignore a move towards non-carbon-emitting technologies, the reality is that the planet is close enough now to a potential climate tipping point that we should not rule out any effort that might help us forestall disaster. Moreover, as much as we would like to see all manner of CO2-producing industries (such as power production or cement manufacturing) move to cleaner technologies, even in the best likely scenario it's going to take decades for the transition to be complete. In principle, if CO2 output can be reduced from those industries during the transition, we're all better off.

But the IPCC (Intergovernmental Panel on Climate Change) wondered just what kind of effort would be required to make a real difference in CO2 output. The IPCC commissioned a study, and the preliminary results are now in. Read on for a discussion of our sequestration options.

The PDF summary report (which is all that's currently available) starts out by describing in detail the currently available processes for carbon capture and storage; the document doesn't address biological sequestration options, as they are largely useful for reduction of existing concentrations, not reduction of new emissions. The three broad families of capture systems -- "post-combustion," "pre-combustion," and "oxyfuel" -- are described, and discussions of costs, geographic requirements for storage, and risks (from the environmental to the legal) close out the document.

The summary report runs a brief 25 pages, and it makes for sobering reading. Under best case scenarios, carbon capture and storage wouldn't make a significant difference in CO2 levels until the mid-point of this century; in addition, the current available sequestration options all pose significant challenges, including the possibility of actually exacerbating the global environmental situation rather than ameliorating it. That said, under some scenarios the addition of carbon capture and storage to the overall mitigation mix could reduce the overall costs of reducing greenhouse emissions by as much as 30%.

It's notable, however, that the greatest reduction of CO2 output from fossil-fuel-based power plants comes from new systems built with scrubbing and capture technologies built-in, perhaps as much as a 80-90% reduction in emissions. Bolt-on retrofits provide "significantly reduced overall efficiencies" of CO2 reduction. How the costs of new CCS-equipped power plants compare to the costs of carbon-free renewable systems appears to be outside the scope of this document, but stands as a key research question; moreover, it will be important to project the degree to which those costs will decline over time.

The other big question is just where the captured and compressed CO2 will be stored. Several options are presented in the report: deep storage in saline formations and depleted oil and gas fields (with deep injection in order to increase oil production or coal bed methane recovery as a variant); deep water "dissolution" and sea floor dispersal; and locked up in metal oxides (such as serpentine). Leaving aside the irony of using industrial CO2 output as a means of increasing carbon-based fuel production, each of these options has serious drawbacks:

  • Metal oxide reactions are slow, and the CO2 has to be pre-processed, which is currently very energy-intensive;
  • Ocean dispersal runs a strong risk of increasing ocean acidity and promoting a serious disruption of the ecosystem;
  • Geological storage has a slight risk of leakage (although lower than is sometimes feared), but faces a more daunting prospect -- finding the space to put it all.

    In general, the overall available space is sufficient. The report makes an estimate of about 2,000 gigatons of CO2 worth of storage space, total, around the world, but admits that this number is a guess, at best. Current global CO2 output is listed in the document as being just under 13.5 gigatons annually from stationary emitters (as current CCS systems wouldn't work with vehicles). Even taking into account the uncertainty of the total space figure and an increase in emissions before a real overall decline starts, geological storage would likely be enough for this century's emissions.

    But it turns out that, while there may be space for 2,000 gigatons of CO2, it will only be available in many thousands of much smaller sites. The current largest CO2 storage site in the world, the Weyburn Project in Canada, is projected to hold 25 million tons of CO2 by 2033. We'd need 80,000 Weyburn Project-scale sites to hold 2,000 gigatons of CO2 -- and in reality, many more than that, as not all geological storage sites are as big as Weyburn. Even if the total output would be much less than that, we'd still need tens if not hundreds of thousands of sites around the world.

    Of course, the question remains of how quickly the sequestration technologies and sites could come on line, given the accelerated timetable we face for atmospheric greenhouse gas concentrations.

    The lesson from this is neither that sequestration will save us nor sequestration is useless. Carbon storage will have an important role in our efforts to stay below the carbon concentration tipping point, but not as great a role as many of its proponents might hope. We're better off focusing our efforts on shifting away from carbon-intensive industrial and energy processes, using sequestration as an option for those few remaining systems that can't be moved as quickly as the others. There's also a chance -- not mentioned in the IPCC report -- that carbon capture technologies might one day be able to pull CO2 directly from the atmosphere instead of only at the point of production (something that biological systems do every day). If this became possible, we may well want to have that geological space available as a way to more than just store extra emissions -- we might want it for efforts to reduce existing CO2 levels.

  • Comments (25)

    This morning, Le Devoir, a popular newspaper in Quebec, had a frontpage article about carbon sequestration. I guess it's starting to become more mainstream.

    As long as it doesn't delay other things, I say why not?


    Well the thing to remember is its likely they wont just be pumping the co2 into the earth. Very likely they will trap all the stuff they have to scrub out of the exaust gases and dump all of it including co2 all into a well.

    As they had to trap so much gunk anyway and as they already had to expend alot of money dealing with that dumping the entire lot down a spent oilwell is prolly not so expensive... specialy if the well is right next door.


    considering geosequestration, could similar happen as with high pressure leaks as with the lakes in Cameroon which occasionally leaks large volumes of CO2 after it builds up then kills all animals & people within 25km. And more remote chance: if it is stored underground lithosphere, could the pressure cause plate movements, earth quakes??

    Sequestration should be used as a complement to other activities that aim to reduce emissions, not as a license to burn baby burn fossil fuels which is what many of its backers want.

    And WHO is developing the technologies, I'd like to know? Who is funding? Patents & fat license fees?


    Ditto that, Daisy. I'm with her; I remember reading a sizeable piece within the last year in Foreign Affairs magazine on the issue of carbon sequestration. The authors were so gung-ho-do-it-now -- but they weren't exploring the topic, they were more than advocates for it, bordered on outright promotion. I pictured exactly the example that Daisy cited, a catastrophic release of CO2 likely to impact a population that can least afford to resist the creation of a sequestration facility in the vacinity of their homes. What bugs me is the most obvious method for dealing with CO2 is the one least cited: plants. A CO2 tax should be levied on carbon fuels that is directly utilized in planting grasses and trees in areas where deforestation has occurred and where both consumption and energy generation is heaviest. Let's start here as we investigate future technological options; this is something we can do right now, along with conservation and consumption reduction.

    Martin Hastings:

    Ever thought why carbon capture and storage economics never seem to reach the surface - so to speak? The technique is UNECONOMICAL and not feasible. Get the numbers from the promoters, then a valid comparison from those capable of doing this type of work and do the sums - and don't forget the monitoring costs. Reducing emissions is a far more cost effective way to go but that's not going to happen is it? And by the way, how many new coal fired generating facilities WITHOUT capture and storage facilities are currently planned around the globe? I fail to see how any intelligent person can take this whole discussion seriously.

    Martin, I started by seeing this nearly as you do, but I've had to think again. Please realize that Jamais entirely agrees with the need to reduce emissions, increase efficiency, and develop alternative energy sources. But that very likely will not be enough. Consider: the climate change we're starting to see is from gasses emitted in the 1970's and 80's. There's a delay in the climate system, and the effects of our current emissions haven't been fully felt yet. So, in addition to the sensible measures hinted at in your post, we're likely to need some "geo-engineering" too, not as a palliative, or a substitute for reform, but as another tool in the tool kit.


    All the carbon sequestration in the world won't save us from the pending, massive release of methane. Methane will overwhem carbon as a greenhouse problem. I fear it is too late. Someone, please, show me that I am wrong, because I surely want to be.

    Sounds like we're not just going to have global warming, we're going to have global extinction on a massive scale.

    Among all carbon sequestration scenarios, I've found nowhere studies about sequestration in long-lasting solid materials, likely to be used in building and civil engineering. Why not trap carbon inside our walls, basements, furniture, equipement, roads and bridges in any possible sustainable form? There are a lot of possible robust carbon composite materials, and OTOH cement industry is an heavily polluting and energy consuming one. I've not investigated the quantities at stake (e.g tons of carbon vs tons of concrete produced each year), but maybe it's worth considering.

    More on the same topic. I looked out for some figures. According to this canadian source http://www.ecosmart.ca/enviro_statistics.cfm
    - Global production of cement worldwide in 2000 was 1.56 billion tones.
    - Producing one ton of cement releases about one ton of C02 in the atmosphere.
    - The manufacturing of cement accounts for 5% of the non-energy related greenhouse gas emissions (in Canada)

    It figures that turning building and civil engineering into a carbon pit instead of carbon source is a fascinating challenge ...

    Daisy Flower:

    Bernard they have actually developed a concrete that absorbs rather than releases CO2. Make city buildings like trees. Been around a coupla years but it's slightly more expensive so the horrid stuff gets used instead. But you're looking mainly at new buildings only, which use more land & more materials. How to capture the CO2 in building products that essentially make the stuff? And it's not jsut CO2 as someone said above, it's methane & others.

    1. we need to treat possible future technological fixes as a possible future bonus, a happy surprise if they do work, and do today what we can do today to fix the problem, not hope that the future holds the perfect solution. ie caution over high-risk strategies when lives are at stake. A stitch in time as yr grannie might say

    2. we shoudl bear in mind that most technological solutions to suit the problems of today actually create problems tomorrow that were either unforeseen or conveniently ignored to suit someone's agenda or only do a portion of what it was suggested they could do (ie remove new emissions from large-scale industrial sources, not small-scale emissions eg cars or prior emissions) or all 3.

    3. we need to cut down on stuff, all stuff, all of it, & stop generating gases & waste today today today today today today today now now now now now. Conserve energy today. Everyday in little ways.

    4. no matter what the technology, we will still require social & institutional changes. SO why put them off until it's even more difficult & complex?

    Riot for austerity!! I might make that my new WC post identity.

    Rather than spending energy to extract carbon from the atmosphere and sequester it, it makes more sense to design an energy cycle around sequestration.  I found a way to do it with biofuels and a zinc cycle and wrote it up as Going negative (warning, highly technical content not edited for lay audiences and author [me] is not the clearest writer in the world).

    What I keep wondering is whether there might not be a way to turn CO2 sequestration into a profit-making enterprise. I mean, to some extent agriculture works along those very lines. I wonder if there's any way that some form of CO2-to-diamond or -fullerene process could be developed that would consume atmospheric CO2 at a volume sufficient to be both environmentally effective and profitable, either inherently or with reasonable subsidies.


    Oh thats already starting to happen.

    Carbon fiber use is on the rise rapidly and they expect amazingly enough that some day carbon fibers and carbn nanotbes will replace alot of the building materials we currently use.

    In 2070 we might watch teams of robots spin towering buildings out of carbon wires and entire cities might be woven of it even down to the streets themsevles and the streetlights.

    Carbon-fiber products are not going to reduce atmospheric CO2 as long as the energy to make them comes from fossil fuels.


    But in the end its gona lock up billions of tons of carbon and likely be powered by various non fossil fuel sources.

    Jamais Cascio:

    Okay, then, here's a question for you folks who want to play with the math & science: what would be involved in converting the carbon dioxide from industrial emissions into source material for nanotubes? Leave aside whether it would be efficient, for the moment -- is it even possible?

    Bonus question: the non-burial form of sequestration locks up the carbon in serpentine minerals. What sort of non-carbon-emitting industrial/construction/material use can we think of for the resulting compound?

    The kind of sequestration Jamais describes does one thing: sequester carbon. Here's another approach. The top 20 cm. of soil typically weighs about 270 kg. per square meter. If you increase soil organic matter, the soil grows better crops, erodes less, holds water longer, develops better tilth and structure, requires less artificial fertilizer, increases beneficial soil microbes, etc., etc. Soil organic matter is about 58% carbon. If you raise soil organic matter 1%, you've sequestered (58% of 1% of 270 kg.) about 1.57 kg. of carbon per square meter. That works out to about 15.7 metric tons of carbon per hectare. There are approximately 1.5 billion hectares of cropland on the planet. Raising its organic matter by 1% would sequester roughly 23,550,000,000 metric tons of carbon. It is, of course, necessary to replenish the organic matter in soil to maintain it as a carbon sink. But we should be doing that anyway.

    I should have added that the IPCC report said that current CO2 emissions from fossil fuel are about 14 gigatonnes per year. A 1% soil-organic-matter increase only deals with about 1 2/3 years' worth of emissions, and raising soil organic matter above 8% to 10% is very, very hard. So, like other sequestration schemes, this doesn't overcome the need for drastic, quick, reductions in CO2 emissions. I think the quickest, cheapest way to do that is to focus on serious, determined energy efficiency. We also need to get to work on alternatives, perhaps including E-P's biofuel/zinc cycle. But the time cycle for efficiency is faster, and requires less capital, than retooling our energy systems. To stabilize the atmosphere at around 450 ppm of CO2, we need a roughly 70% reduction in emissions, and we need it fast.


    Well most likely the emmisions from coal power plants will be the primary co2 source by 2050 or so as oil getting more expensive falls in use and natural gas also gets more expensive and falls in use.

    In coal power plants they will likely trap a percentage of co2 exuast in whatever cheap material they can fling through thier icky goop catcher emission scrubbers.

    Then the entire icky goop parade will likely be slurried and pumped into a well where 1 billion years from now aliens will wonder how the heck did that form!?

    Meanwhile escess co2 in the atmostphere will likely be gobbled up by carbon fiber makers using feedstocks that themsevles eat co2 from the atmosphere.

    In the end by about 2200 we likely are talking about 10-20 trillion tons of carbon fibers. Depending that is on just how cheap the suckers get. In the end its likely they will be both the new steel and the new concrete... thats ALOT of stuff.

    Atmospheric CO2 to nanotubes (or graphite fiber)?  Start by growing anything; from there, it's just chemistry.  There are bioplastic processes but you can do the conventional route by gasifying and then going Fischer-Tropsch to get hydrocarbons.  I understand that ethylene can be made directly from CO2 and H2.

    How much in the way of carbon fiber, plastic, etc. can a person expect to consume (non-recyclable) in a year?  What does a 2-liter pop bottle weigh, a couple of ounces?  An acre of switchgrass at even 7 tons yield would supply the annual wrappings for one heck of a lot of fizzy-water addicts.

    martin Hastings:

    David Foley
    You fail to address the COST OF CAPTURE AND STORAGE under the present financial system. Failing to do so results in just another lot of hot air and wishful thinking.

    Daisy Flower:

    Martin H: the approach David mentioned would reduce the need for expensive fertilisers & irrigation. So perhaps you should be enquiring after the long-term cost SAVINGS under the present fin system.

    Irrigation is currently realatively cheap, but not for long at current depletion rates: increasing numbers of disputes will be over water shortages. David's plan has an added bonus of reducing irrigation needs (greater absorption & retention) which in turn reduces leaching of nutrients which further reduces the need for fertiliser. Extra soil organic matter increases nutrient levels, also reducing the need for fertiliers which are more expensive than indicated by sale prices as they're subsidise by govt, & being derived from petroleum, may increase in price. Reducing leachin woudl also reduce the need for phosphorous which is being depleted beyond it's renewable capacity & releases more GHG when it's mined.

    Therefore this approach has an important added benefit of increasing food security and reducing dependence on non-renewable resources that have negative externalities (climate irregularities which is likely to make crops more thirsty & reduce rainfall, requiring more irrigation) that threaten the very productivity that fertilisers try to improve.

    To expect someone to comprehensively factor in such complicated numbers in a quick post is unreasonable, but at least David proposed and intelligently explained a potential solution. The only hot air is deconstructing & criticising his suggestion without suggesting and rationalising an alternative.

    martin hastings:

    Daisy Flower

    I don't disagree with david's sentiment or ideas.
    Please read my first post to understand the context of my second comment. I didn't ask for a complicated cost structure - simple, but realistic would be fine. Fact is, the costings don't fit the current business model. One can wish and come up with all sorts of positive ideas
    in this whole area but if it don't fit the CURRENT business model it ain't going to happen. That is, unless the powers that be in your part of the world have suddenly started making sensible decisions based on the long term good rather than the short term - as in the life of a parliament!


    I expect the efficacy of the method to be a bigger hurdle than the cost, altho they go hand in hand. The costs I saw weren't rediculous but they're prob not reliable & no-one will want to wear them. What I see: govts & big business are now acknowledging climate disruption & the fact that industry contributes to this. Simultaneously they're expanding coal-powered elect generation and encouraging (minor incentives) investment in abatement technologies. Even though these technologies do increase costs, their development is put fwd as necessary, needing future investment + planning --> therefor it likely is a lot of hot air to excuse the fact of doing nothing in the meantime cos that would be bad for business. Ahhhhhh losing my head over the madness of it all, someone pls geosequester me under tonnes of crude oil.

    *BUT* govts will have to do something, eventually, when they can't ignore it anymore (& they realise the rapture hasn't happened), so what should it be?? It may be too late for cutting-back alone. What's our contingency plan? Martial law & development funds to engage in reforestation frenzies & fertilising phytoplankton blooms amid fossil-fuel bans?

    martin hastings:


    You said it - they're expanding coal fired power generation - doesn't seem to make much sense does it? Keep talking to people about your concerns, every little helps.


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