Thanks Ron. I agree that "irreversible" is a poor choice of words given that once we stop emitting fossil CO2, air CO2 and global T (+- inertia) will eventually decline back to pre-industrial levels due to nature's CDR, but in a time frame of say 50 kyrs. The paper does acknowledge that once we stop emitting, air CO2 will start to decline, but the possibility that we might be able to accelerate or augment this air CO2 removal is ignored. I'd say that this might be an opening for a letter to Science from the CDR community perhaps with the title "CO2: Reversible and Avoidable". Anyway, count me in. -Greg
As for your wording, here's what I'd say, open to further discussion: Given the reversibility of air CO2 concentrations and hence CO2-induced warming, every increment of reduced or avoided temperature increase represents less warming [x, y] that would otherwise persist for many millenia (Archer et al., 2009). Because post-emissions (i.e., air CO2) removals can return global CO2 and temperatures to preindustrial levels, they do have the power to avert additional warming or affect cooling on the same time scale as the emissions reductions or removals themselves. Climate warming tomorrow, this year, this decade, or this century is predetermined by both past and future CO2 emissions as well as the rate of CO2 removal. The climate benefits of both emissions reductions and enhanced CO2 removal [CDR] will thus occur on the same time scale as the political decisions that lead to CO2 emissions reductions and/or CDR. One little caveat here is that CDR must operate by not only removing CO2 from air, but also in removing the excess, ocean-absorbed CO2 that will degas back into the air, al la Cao and Caldeira (2010). So the response of air CO2 conc to air CO2 removal alone will be (very) sluggish. This is why I'm a big fan of consuming excess CO2 in the ocean (via base/alkalinity addition). This addresses multiple birds with one stone: ocean-->air CO2 flux is reduced or reversed, ocean acidity is neutralized, and the bio effects (on calcification) of ocean acidity are offset by alkalinity addition. Given earth's past successes in mitigating excess global CO2 in this fashion, it would seem unwise to ignore Mother Nature's example, but I'm open to better ideas. -Greg ________________________________ From: "[email protected]" <[email protected]> To: Geoengineering <[email protected]> Sent: Sat, May 4, 2013 3:06:48 PM Subject: [geo] New climate article, peripherally related to CDR List: 1. I believe this article from last week's Science could be valuable to this list, although there is (close to) zero mention of either side of geoengineering: Irreversible Does Not Mean Unavoidable; H. Damon Matthews 1 and Susan Solomon 2 Science 26 April 2013: Vol. 340 no. 6131 pp. 438-439DOI:10.1126/science.1236372 2. I hope someone can help me understand the use of "Irreversible" in the title and, as an example, in the final paragraph: "Given the irreversibility of CO2-induced warming ( 5, 6), every increment of avoided temperature increase represents less warming that would otherwise persist for many centuries. Although emissions reductions cannot return global temperatures to preindustrial levels, they do have the power to avert additional warming on the same time scale as the emissions reductions themselves. Climate warming tomorrow, this year, this decade, or this century is not predetermined by past CO2 emissions; it is yet to be determined by future emissions. The climate benefits of emissions reductions would thus occur on the same time scale as the political decisions that lead to the reductions." Cites 5 and 6 are: 5. S. Solomon, G. K. Plattner, R. Knutti, P. Friedlingstein, Proc. Natl. Acad. Sci. U.S.A. 106, 1704 (2009). 6. H. Matthews, K. Caldeira, Geophys. Res. Lett. 35, L04705 (2008). 3. Believing that CDR is real and alive, I would have preferred to see this (my emphasis added) as: Given the reversibility of CO2-induced warming, every increment of avoided temperature increase represents less warming [x, y] that would otherwise persist for many centuries. Because emissions removals can return global temperatures to preindustrial levels, they do have the power to avert additional warming on the same time scale as the emissions reductions themselves. Climate warming tomorrow, this year, this decade, or this century is predetermined by both past and future CO2 emissionsand removals The climate benefits of emissions reductions and removals would thus occur on the same time scale as the political decisions that lead to the reductions. My cites (x and y) might be from Jim Hansen and Bill McKibben, but also this list, the Royal Society and the new NRC study all of which describe various CDR approaches. All mistaken? I ask why this second version should not be the more accurate. 4. In defense of the authors, whose work I otherwise uniformly admire, I think the intended word rather than "irreversiblity" might have replaced "ir" with (awkwardly) "non-utilized" or "un-utilized". The "ir" strikes me as guaranteeing a physical impossibility, for which no proof is offered. I think this important as CDR gets too little attention anyway, to be saddled with "irreversible" Thoughts? Ron -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering?hl=en. For more options, visit https://groups.google.com/groups/opt_out. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
