Negative emissions

I went to some Departmental talks recently and discovered that some of my colleagues are researchering possible carbon sequestration technologies. This could be very important, but appealing to negative emission technologies is often quite strongly criticised. The basic argument (which has some merit) is that presenting this as a possibility can provide policy makers with an argument for delaying action that might reduce emissions sooner.

Although I have some sympathy with these criticisms, I do have some issues with them. One is that it often involves criticising climate models that include negative emission pathways. The problem I have with this is that they seem to use “climate model” as a catch all for any kind of model associated with climate change. However, there are a large number of different models. Some are trying to understand how our climate responds to changes, and – typically – use concentration pathways. Others try to associate concentration pathways with emission pathways. Then there are others that try to understand the impact of various emissions pathways, how we could follow different pathways and, in some cases, if it is possible to actually do so. Given how easily what is said can be mis-interpreted, I generally think it would good to be clear about what type of models are actually being criticised.

The other issue I have relates to the idea that maybe we should avoid providing these pathways to policy makers. My view is that we should be very careful of selecting what information is presented. If there is a desire to understand what pathways might keep warming below 2oC, for example, and it turns out that many would require negative emission technology, then I think that this should be made clear. However, it should also be made clear that such technology does not yet exist (at scale, at least) and that there is a chance that it will never exist, on the required timescale at least. I don’t have much faith in policy makers myself, but if they can’t even get that it would be silly to base policy on technology that does not, and may never, exist, then we should probably just give up now.

What partly motivated this post, though, was a recent article that argues that we should not assume that land-based measures will save the climate. It’s pretty readable, so I would encourage you to do so and won’t say much more. It argues that negative emissions may either not be technological feasible, that they have unacceptable social and economic impacts, and that they may ultimately not be as effective as hoped. Therefore we should assume that it is unlikely to be a technology on which we can rely. I’ll leave you to make up your own minds, but I just wanted to quote the concluding remarks, as I think they do illustrate a crucial point.

If the expected negative emissions cannot ultimately be achieved, the decades in which society had allowed itself a slower, softer transition would turn out to be a dangerous delay of much-needed rapid emission reductions. Saddled with a fossil fuel-dependent energy infrastructure, society would face a much more abrupt and disruptive transition than the one it had sought to avoid. Having exceeded its available carbon budget, and unable to compensate with negative emissions, it could also face more severe climate change impacts than it had prepared for.

Update: Andy Skuce’s article ‘We’d have to finish one new facility every working day for the next 70 years’—Why carbon capture is no panacea is also worth reading. Kevin Anderson and Glen Peters also have an article called The trouble with negative emissions.

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34 Responses to Negative emissions

  1. Mike Coday says:

    I could not agree more.
    One typo: left out “not” in the following line: that does, and may never, exist, then we should probably just give up now. end of third paragraph.

    I think our species is going to crash into the situation where only negative emissions will be able to reduce and mitigate environmental destruction. I wish we might choose another path, but I read the news that a new, large oil patch has been discovered in West Texas recently. Nuff said?

  2. Mike,
    Thanks, fixed. I’m hoping that what you’re saying in your second paragraph is wrong, but I worry that that is pretty much exactly what will happen.

  3. Mike Coday says:

    Yes, I would love to be wrong about paragraph two. My grandkids hope I am wrong about that one.

  4. Andy Skuce says:

    So, ecosystem restoration and afforestation can buy us about 10 years or so of emissions at our current rate until saturation. The SEI report did not cover biochar and soil carbon enrichment and perhaps those technologies might buy us a few more years. In his recent submitted paper Hansen et al (page 20) estimate that 100GtC is a reasonable total for agricultural and forestry combined.

    Enhanced weathering of basalts may give us a few more years of current emissions, at a cost, providing there are no unforeseen snags.

    Artisanal approaches to CO2 reduction will be necessary but not sufficient to undo the damage we have caused. We’ll likely need industrial-scale processes to undo industrial-scale damage. This will be expensive, disruptive and probably not scalable within required time periods. I wrote about this recently for the Bulletin of the Atomic Scientists.‘we’d-have-finish-one-new-facility-every-working-day-next-70-years’—why-carbon-capture-no-panacea9949

    What an unholy mess we’ve made.

  5. Andy,
    Thanks, I remember reading your article. One new facility every working day for the next 70 years is a pretty tall order.

  6. T-rev says:

    They talk about negative emissions and a few other topics

  7. So I read the article. Yawn. Bio-clueless rocket scientists. BECCS is of course dangerous nonsense, an idea of earth detached rocket scientists not worth much consideration. There is a simpler way – but alas it would require an agro-ecological revolution. And forests need not compete with food production if sparse enough.
    A proven, but stone age, method of carbon sequestration and soil build-up is to not burn the wood completely but to leave some char coal and add it to compost. It has multiple synergistic benefits to soil and society (small farmers, CAFO operators,…). Combine it with irrigated afforestation of desert. Make food production a sink, not a source. The effective C sequestration could be 3x the char input, esp. in the tropics.

    Keywords: Biochar, Terra preta, agroforestry, food sovereignty, biosphere recarbonization, pyrolysis, syngas, soil life, water storage, cation exchange capacity, …

  8. Florifulgurator,
    According to the Hansen paper that Andy Skuce mentioned in his comment, biochar would probably be limited to around 100GtC (a decade at current emissions). Are you suggesting it could do better than that?

  9. Andy Skuce says:

    That 100 GtC was for agricultural processes (biochar and soil recarbonization) plus forest processes.

    I wish it were true that these processes could solve the problems, but their aficionados do seem to indulge in unquantified arm-waving. Also, I can’t see us escaping from industrial-scale intensive agriculture with 10 billion mouths to feed.

    If we had fifty more years and only two billion people, we’d be able to ace this test. Alas.

  10. Reblogged this on Hypergeometric and commented:

    If the expected negative emissions cannot ultimately be achieved, the decades in which society had allowed itself a slower, softer transition would turn out to be a dangerous delay of much-needed rapid emission reductions. Saddled with a fossil fuel-dependent energy infrastructure, society would face a much more abrupt and disruptive transition than the one it had sought to avoid. Having exceeded its available carbon budget, and unable to compensate with negative emissions, it could also face more severe climate change impacts than it had prepared for.

    The risky promise of ‘negative emissions’.

  11. Given that the time for action is short, and growing shorter as mitigation-to-zero is put off, and given that clear air capture of CO2 is hard enough by itself, never mind if emissions are still underway, and given that by the time we start there are likely to be appreciable if not yet dominant natural emissions of CO2 underway atop whatever agriculture produces, even if emissions for transport, harvesting, and production are zeroed, a “drawdown to save climate” is likely to be initiated post-crisis, and so may be fast. I hope that in the interim the climate dynamicists like John Marshall at MIT might learn what it will mean if, having driven climate hard and fast with radiative forcings, a rapid pullback is initiated which drives it the other way. Sure, the oceans will damp some of that since they will release their own CO2 over time.

    But my ongoing concern is we have no real way of assessing the climate implications of magnitude of forcing one way or another, and this is an area which is starkly different than almost all natural instances of forcing, save the end-Permian mass extinction, which was similar but qualitatively worse in many respects.

  12. Sorry for unquantified arm waving. 🙂 If I had seen Andy’s response I might have kept quiet…
    Dunno latest estimates, but my old books tell between 1500Gt and 3200Gt soil carbon, plus 500-650Gt plant matter carbon. I forgot the C content of pre-Columbian Amazon terra preta soil, but from my experiments it could well be 50% vol. biochar and 1m deep – in places where natural soil C would be almost 0%. (I have a 8y old pot with >70% char crowded with an old black currant and varying malva or oenothera, growing well. One bonsai pot has 90% C.) Industrial-agricultural soil is loosing lots of carbon, in many areas it is already equivalent to desert soil, which can only be kept productive by huge artificial fertilizer input. This needs to be stopped anyway, if we want to feed a crazy 10 billion people (overpopulation is suigenocide, BTW, as exemplified in Syria). A German book says 800Gt CO2 by enhancing agri soil to 10% C.

    So, from the uncertainty of soil C numbers and the possibility of extremely high C terra preta I would guess 500-1500Gt C soil sequestration would be easily possible. (Given an agricultural revolution to work intensive small scale farming and agroforestry, “Nature’s Matrix”, a socially beneficial byproduct. Food sovereignty.)

    The only limit is forest soil combustibility (we don’t want Indonesian style C release from forest fires).

  13. Pardon if I’m restating the obvious, so this suggests that emissions driving the Hyperanthropocene began with the clearing of North American forests, well before oil and coal. And the latter made it much worse, and amplified the problem because, then, one could grow crops without good soil. At the time I imagine that was considered a big win. (Didn’t Haber win the Nobel?) Wikipedia from Haber’s bio: “The ability to produce much larger quantities of nitrogen-based fertilizers in turn supported much greater agricultural yields and prevented billions of people from starving to death.”) Alas, looks like the Debt is coming due. Seriously, it’s not like people were not warned.

  14. Andy Skuce says:

    Forgive my “arm-waving” comment, it wasn’t aimed particularly at you, but at the folk who always seems to show up on any discussion about negative emissions with their own pet solution, whether it’s no-till farming, grazing ungulates or biochar.

    According to the latest Global Carbon Budget (table 10), in the past 265 years, land use emissions amounted 190 GtC +/- 65. That includes both deforestation and soil carbon loss. To sequester 500-1500 GtC in soils alone (2-8 times the amount of post-industrial land use emissions) seems to be stretching credulity. Presumably, most preindustrial soils were in a near-stable equilibrium with regards to their carbon content, since intensive industrial agriculture had not started yet. Could soils really hold that much more? How stable will that carbon be in a >2°C world? And how quickly could we do this? We need serious reductions over decades, not centuries.

    The total of all human emissions, fossil fuels and land use together, since 1750 is about 600 GtC. Can we really sequester that amount (or double that amount) in the soil?

    I’m all for better, sustainable agriculture that enriches soils and for increased afforestation. I hope that, apart from other benefits, such processes could take a significant wedge out of our excess atmospheric carbon problem. However, I think it’s just as problematic to imply that any particular soil technology, untried at scale, provides a solution to AGW, as it is for BECCS or Direct Air Capture promoters to do the same. It is going to be a stretch to get us to where we need to be using any combination of negative emissions technologies.

  15. On the rate of sequestration: Alas forestry statistics is in cubic meter, not tonnes. But from Hansen’s paper (p.20) I read (rounded) 1GtC/y from afforestation/reforestation plus 1GtC/y from biochar.

    The sink saturation of maturing forests isn’t such a problem, as they can be cut (rejuvenated) to produce more biochar. (One of my Holzknecht pipe dreams was putting up a fleet of ox drawn mobile wood gas/oil refineries leaving biochar in situ. Bayerwald Standard Wood Oil Inc. 🙂 )

    So, 2GtC/y. That should suffice, if mankind decides to behave well and take an organic approach to living on Earth. But with some rocket science help it could be 1GtC/y more, e.g. irrigated afforestation of Sahara and Australian outback, where surplus solar/wind could be used for water desalination. But it seems the Desertec project is dead…

  16. Andy, you’re right, stable natural soil doesn’t hold that much organic carbon, only 5-20% methinks. And one problem is of course the growing instability: Warming soil means more microbial activity means more C oxidation. (Recently there was an article on European Alpine soil C loss, which meanwhile has become statistically significant.)

    But that’s the point of biochar. Wood rots, but char coal does not f.a.p.p. The half life is between 100y and 1000y.

  17. David B. Benson says:

    By all means use irrigated afforestation of the Sahara desert and the Australian outback! This won’t be cheap but the Ornstein et al. paper introducing this concept states that the carbon dioxide removed from the atmosphere is about 2 ppm per annum, once this vast expanse of new forest is growing.

    Of course, this is to be in addition to stopping the use of fossil fuels.

  18. angech says:

    David B. Benson says: “By all means use irrigated afforestation of the Sahara desert and the Australian outback!”
    The Australian outback is desert due to lack of water and extreme heat.
    Not all the goodwill in the world is going to provide enough water to irrigate great swathes of it. It is a pipedream.
    Some hope would be by diverting water flow through the Eastern mountain ranges via tunnels [That makes me one of “the folk who always seems to show up on any discussion about negative emissions with their own pet solution] a geo-engineering solution.
    To get this through when we are currently doing a California re dams, where we are closing down our Victorian irrigation systems, when it would detract flow of nutrients to the endangered great barrier reef, and drown the eastern ridge frilled neck lizard would require great cooperation which does not exist.

  19. izen says:

    @-Andy Skuce
    “the folk who always seems to show up on any discussion about negative emissions with their own pet solution, whether it’s no-till farming, grazing ungulates or biochar.”

    It is a feature shared with geoengineering solutions, or which it is a component.

    There is often an abundance of grand global schemes for modifying agriculture or atmospheric chemistry or ocean dynamics. Ideas that have obviously had much thought and effort devoted to their development. Epic in scale and requiring a level of international cooperation and social change unprecedented in human history.

    In stark contrast to the paucity of options when the issue is stopping emissions. I am reminded of ATTPs comment that “It seems we can adapt to anything but stopping fossil fuel use.”

  20. Mike Coday says:

    this problem requires an “all of the above” solution approach and the top of that list has to be drastic reduction in burning of fossil fuels. A lot of folks know what needs to be done. There is a of pushback about what needs to be done. The pushback and widespread frustration with the income inequality of our current global economic model give us results like Brexit and Trump.

  21. John Hartz says:

    Every now and then there is a glimmer of hope on the carbon sequestration front. Here’s a “hot-off-the press” case in point…

    Earlier this year, a project in Iceland reported an apparent breakthrough in the safe underground storage of the principal greenhouse gas, carbon dioxide — an option likely to be necessary if we’re to solve our global warming problem.

    The Carbfix project, run by a leading Icelandic producer of geothermal power, Reykjavik Energy, announced that it had successfully injected 250 tons of carbon dioxide, dissolved in water, into an underground repository of volcanic rocks called basalts — and that the carbon carbon dioxide hadn’t just stayed there. No — it was way better than that. Instead the carbon dioxide had apparently become one with the basalt, undergoing a fast chemical reaction and forming a type of rock called a carbonate in two years’ time.

    That’s a big deal because it means the gas would not escape back to the atmosphere again even if the underground repository were somehow compromised. And now, a group of American researchers has taken the science even farther, once again suggesting that storing carbon dioxide stripped from industrial processes, or sucked from the atmosphere, in basalt rocks may be a key part of the solution to climate change.

    They may save us yet: Scientists found a way to turn our carbon emissions into rock by Chris Mooney, Energy & Environment, Washington Post, Nov 18, 2016

  22. David B. Benson says:

    angech — The irrigation water is desalinated sea water.

  23. angech says:

    David, I did remove a line about the Saudis using their oil it run a desalination plant/s because I thought the idea of burning up more fossil fuels to produce water was too extreme. While one could imagine doing it for potable water the amount needed for those hot deserts would be far too extreme and counter productive.
    Non fossil fuels would be at an even greater disadvantage trying to produce enough water.
    A post on practical an imaginative geoengineering would be good.

  24. David B. Benson says:

    angech — I assure you that a combination of solar panels and nuclear power plants will certainly provide all the water needed for growing trees in the desert. Try reading the full paper; the pdf is freely available:
    Irrigated afforestation of the Sahara and Australian Outback to end global warming

  25. bill shockley says:

    Thanks for posting this. Wow, wouldn’t it be nice?

    Surprisingly old — from 2009. Hansen is obviously aware of this work but evidently prefers a more distributed plan for bio-sequestration that wouldn’t be so capital-intensive and therefore politically unfeasible. The proposed project would require a very large tax on fossil fuels, at least initially, that the FF companies would pass on to the public, and would be very regressive. Whereas a rev-neutral carbon tax could be progressive and would therefore be popular if its advantages could be explained to the voting public, i.e., “popularized”, or if it somehow could get its foot in the door and thereby become its own popularizer.

  26. David B. Benson says:

    Actually reading the Ornstein et al. paper one will find a claim equivalent to stating that US $150 billion per annum suffices for the irrigated afforestation of the Sahara desert and much of the Australian outback.

  27. I did not read Ornstein, et al. Perhaps I should some day. Three questions: (1) Does afforestation REALLY sequester Carbon on 1000 year timescales? (2) Are there ancillary requirements and assumptions? For example a recent paper (can give/find ref but not handy now) found that only old growth forests in Europe sequestered Carbon, the remaining forests returning it to atmosphere on decade time scales. (3) Are the costs calculated correctly, including proper accounting for having to purchase or incentivize siting lands?

  28. bill shockley says:

    $150 billion/year is really cheap compared to the 5 or 6 hundred billion in discretionary military spending by the US with the outcome of spreading terror over the world, or the 3 trillion in health care per year, half of which is wasted since we spend twice as much per capita as some other developed countries and get poorer outcomes.

  29. Read Ornstein, et al. Also read Keller, Feng, Oschlies. Translation? Cold water.

  30. KFO: We find that even when applied continuously and at scales as large as currently deemed possible, all methods are, individually, either relatively ineffective with limited (<8%) warming reductions, or they have potentially severe side effects and cannot be stopped without causing rapid climate change.

    The only thing I critique KFO about is their assumption that emissions (RCP 8.5) continue while afforestation is underway. No geoengineering technique works if a substantial portion emissions continue, and where they can the cost of reduction of CO2 is higher than otherwise.

    So, the very first thing champions of these technologies should say is that doing what we should do now is a precondition for any of these to work. At best, a negative emissions technology might buy us a little time more to get to zero emissions, but they are not without their own complications and repercussions.

    It would be interesting to examine aforestation once emissions were zeroed compared with direct air capture. The situations are not strictly exchangeable, but KFO’s simulations indicate that while the techniques may work, they’ll be much slower than direct air capture, meaning that residual disruptive impacts from a found-to-be-intolerable level of climate disruption would linger. KFO’s effectiveness charts (their Figure 4) suggests about 20 ppm per 80 years.

  31. David B. Benson says:

    Yes, afforestation sequesters carbon on, at least, millennia scales. Once the trees are old the wood is converted to biochar and buried. This is a well known soil conditioner which improves growth. Some of the biochar can be compressed, forming artificial anthracite, and buried to remove the carbon for tens of millions of years.

    The Sahara desert is worthless and the countries of the Maghreb and the Sahel will be more than happy to find the work for their citizens.

    I live in Washington state and I assure all that new forests sequester carbon at a great rate. The problem is clearcuts. Not only the wood is taken away but the stumps rot and the forest soils otherwise lose some carbon. The coppice method reuses the stumps and clearcuts would not be practiced in this project, rather, selective thinning.

    As I understand it, each of the Sahara desert and the Australian outback would remove about 1 ppm of carbon dioxide per annum. Obviously burning fossil fuels has to stop.

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