Ron, If your objective is only to help stabilize or reduce air CO2 then one air CO2 removal system is as good (or bad) as another, all else being equal (e.g., as treated by Sabine et al.). However, CDR systems that removal excess CO2 from the ocean instead of or in addition to air help reduce the excess CO2 load in the ocean that otherwise will be very slow to be removed by air removal alone and whose negative chemical imprint will otherwise be long lasting, as Sabine et al show. Excess ocean CO2 can be removed (actually transformed) via alkalinity addition. The addition of this could be taylored to effect removal of excess CO2 from air, ocean or some combination via addition to surface waters that are otherwise naturally CO2-undersaturated or -supersaturated, respectively, relative to air. Alkalinity addition can also be used to (help) rebalance pH, CO2, and carbonate saturation state in subsurface waters if that is your concern (as in the case of Sabine et al.).
Another (geo)chemistry based CO2 removal system that would directly benefit ocean chemistry would be to react waste CO2 streams with mineral carbonate and (sea)water to capture and convert the CO2 to ocean alkainity (Rau and Caldeira 1999). If your waste stream is derived from biomass combustion, then you have an air CO2 capture and storage system generating ocean alkalinity, in contrasts to oh-so-popular BECCS that simply stuffs the CO2 in the ground, with no additional environmental benefit. I could go on, that's my thinking in brief. Greg -------------------------------------------- On Tue, 8/11/15, Ronal W. Larson <[email protected]> wrote: Subject: Re: [geo] Long-term response of oceans to CO2 removal from the atmosphere To: [email protected] Cc: "Sabine Mathesius" <[email protected]>, "Geoengineering" <[email protected]> Date: Tuesday, August 11, 2015, 2:44 PM Greg: cc Sabine and list Can you give your own cite or two to support this sentence from below? “I also think that your modeling could make a strong case that CDR that generates ocean alkalinity is the preferred CDR method.” I have been thinking that every molecule (or tonne or Gigaton of C) taken from the atmosphere has the same impact (all being quite quick) on ocean acidity/alkalinity. So I would think cost is the main criterion, assuming no major negative down sides. Ron On Aug 11, 2015, at 2:36 PM, Greg Rau <[email protected]> wrote: I'm with you on the idea that there is no better way to manage GHG's and their impact than to reduct GHG emissions. Thanks for pointing this out. But if we continue to fail to adequately reduce emissions, wouldn't CDR be better than no action at all, as you modeling shows? And what is the better alternative to CDR for mitigating all of the CO2 that has already been and will be emitted (and associated climate and ocean effects) before we get to zero emissions? I also think that your modeling could make a strong case that CDR that generates ocean alkalinity is the preferred CDR method. How about modeling the ocean chem recovery rate when 5Gt or 25 Gt CO2/yr are consumed via via enhanced mineral weathering and the resulting alkalinity added to the ocean? Get in touch if you want to collaborate on this. Greg -------------------------------------------- On Sat, 8/8/15, Sabine Mathesius <[email protected]> wrote: Subject: Re: [geo] Long-term response of oceans to CO2 removal from the atmosphere To: "Greg Rau" <[email protected]>, "geoengineering" <[email protected]> Cc: [email protected] Date: Saturday, August 8, 2015, 9:10 AM Hi, just a short clarification: The main point of our study is not that CDR is useless, but that it is not effective enough to counteract business as usual CO2 emissions. Our results stress, once again, that there is no alternative to immediate emissions reduction - CDR can be deployed as a supplemental measure (and maybe it should), but it would not be effective enough to reverse severe changes caused by a delay in emissions reduction. On alkalinity addition: How likely is it that we would be able to do this on a global scale? I could imagine that alkalinity addition might be a way to protect a coral reef, being deployed locally, but globally? I guess it would be much harder to do than atmospheric CDR and you would have to be very careful how much alkalinity you add and how often, to not further stress marine organisms? As far as I know, there are hardly any studies on this? (By the way, our study is not only about ocean acidification, but also about warming and oxygen depletion.) Best, Sabine On 08/08/15 12:50 am, Greg Rau wrote: If the goal is to restore ocean chemistry, it would indeed seem inherently inefficient to do so via CO2 removal from air. Better to remove excess CO2 from the ocean by chemical, geochemical, or biological means (1), my favorite being alkalinity addition. Secondly, according to the IPCC (2) and now UNEP (3), RCP 2.6 scenarios cannot be achieved without CDR - in the UNEP estimate, 300 Gts CO2 worth by 2100. So while I don't think anyone is asking CDR to do all of the heavy lifting, it would appear that at least some CDR is essential to achieve RCP 2.6 and probably even less ambitious scenarios, depending on when/if we ever get serious about emissions reduction. What then is the point of dissing CDR if emissions reduction alone isn't going to save the ocean and the planet either? 1) http://link.springer.com/referenceworkentry/10.1007/978-94-007-5784-4_54 2) http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter06_FINAL.pdf 3) http://www.unep.org/emissionsgapreport2014/ Greg -------------------------------------------- On Mon, 8/3/15, Andrew Lockley <[email protected]> wrote: Subject: [geo] Long-term response of oceans to CO2 removal from the atmosphere To: "geoengineering" <[email protected]> Date: Monday, August 3, 2015, 1:02 PM http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2729.html Long-term response of oceans to CO2 removal from the atmosphere Sabine Mathesius,1, 2, Matthias Hofmann,1, Ken Caldeira3, & Hans Joachim Schellnhuber1, 4, Nature Climate Change (2015): doi:10.1038/nclimate2729 Published online 03 August 2015 Abstract Carbon dioxide removal (CDR) from the atmosphere has been proposed as a measure for mitigating global warming and ocean acidification. To assess the extent to which CDR might eliminate the long-term consequences of anthropogenic CO2 emissions in the marine environment, we simulate the effect of two massive CDR interventions with CO2 extraction rates of 5 GtC yr−1 and 25 GtC yr−1, respectively, while CO2 emissions follow the extended RCP8.5 pathway. We falsify two hypotheses: the first being that CDR can restore pre-industrial conditions in the ocean by reducing the atmospheric CO2 concentration back to its pre-industrial level, and the second being that high CO2 emissions rates (RCP8.5) followed by CDR have long-term oceanic consequences that are similar to those of low emissions rates (RCP2.6). Focusing on pH, temperature and dissolved oxygen, we find that even after several centuries of CDR deployment, past CO2 emissions would leave a substantial legacy in the marine environment. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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