Ken, Manu, I did not go into primary data but had in front of me one or two respectable secondary sources that led to the "about 15Gt" number
Strand and Benford , 2008 Env Sci and Tech, quote 4.98 Pg/yr for residues from maize, wheat, soybeans, sugar cane, rice, sugar beet and barley. Jason Clay in World Agriculture and the Environment (Island Press 2004) provides additional data for Cassava, Potatoes, Sorghum, Bananas, Sweet Potatoes, Plantain and Millet which I did not trouble to add in. Hall, et al in Renewable Energy (Eds Johansson et al, Island Press 1993) turn it all into EJ to get 35EJ for Maize, Wheat, Rice and Sugar Cane residues only, 41EJ for animal dung, (excluding human dung which pyrolyzes fine) and 35 EJ for timber residues. Roughly 3 x 4.98 led to 15Gt Haberl et al must have it wrong since the global food yield for Strand and Benford's seven crops only (with an average harvest index of 0.44) is about 4 Pg/yr or ~2PgC 9.5 Gt is actually about one sixth of global net primary productivity, not one tenth, but one must be cautious of treating global NPP as a given, as many ecologically focused writers seem to do. Nature (and much subsistence agriculture) optimises on resilience to secure survival of the fittest and is not productively efficient. Read and Parshotam, 2007, cited in the RS report, provide Illustrative calculations which show that, if managed efficiently, and with plausible technological progress, only about 2.2GHa is needed (at a take up rate of .088 GHa for 25 years) to shift 1120Gt from linked ocean and atmosphere (in ratio ~45:55) by 2060, leading to pre-industrial levels around mid-century. I do not favour the vast monocultural developments that may seem to be implied, but rather a wider dissemination of carbon conservative and productively efficient management methods to land users worldwide. The obstacle is not shortage of land but shortage of investment in land (and in land users' human capital) -- investment on a scale comparable with current investments in ever harder to get fossil fuels (i.e. tilling for bio-oil not drilling for fossil oil). Peter. ----- Original Message ----- From: Ken Caldeira To: Manu Sharma Cc: Peter Read ; [email protected] ; geoengineering Sent: Sunday, September 27, 2009 8:18 PM Subject: [geo] Re: Manifesto for Geoengineering How many watts per square meter of solar energy can be used to reduce carbon that can be stored as biochar? How many watts per square meter is needed to process this organic matter? Do you really think it reasonable to think that 10% of global primary productivity of land plants can be stored as biochar? Note that Haberl et al (2007) estimate that total global total food harvest is about 1.7 GtC / yr and global wood extraction is about 1 GtC / yr, so the 9.5 PgC / yr number cited by Lehmann et al (2006) represents carbon flows that are more than 5 times bigger than all the food harvesting in the world and more than 9 times bigger than all wood extraction in the world. These kinds of flows may be physically possible, but I remain skeptical regarding the practical feasibility of producing biochar at this scales. Haberl, H., K.-H. Erb, F. Krausmann, V. Gaube, A. Bondeau, C. Plutzar, S. Gingrich, W. Lucht, M. Fischer-Kowalski, 2007. Quantifying and mapping the human appropriation of net primary production in earth’s terrestrial ecosystems. Proceedings of the National Academy of Sciences of the USA 104, 12942-12947. ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA [email protected]; [email protected] http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968 On Sat, Sep 26, 2009 at 8:32 PM, Manu Sharma <[email protected]> wrote: Thank you, Peter. Your arguments are well made. Have you considered making a formal submission to the Royal Society for a review of their position on this issue? Manu On Sat, Sep 26, 2009 at 5:50 PM, Peter Read <[email protected]> wrote: Ken, Simon As it was I that said it, I had best front up. My objection on first reading was to the passage immediately following Simon's quote, which is a gratuitous shift from policy relevance to policy prescription, viz: "Biochar and other forms of sequestered biomass have not yet been adequately researched and characterised, and so should not be eligible for carbon credits under the UNFCCC flexible mechanisms until there is a reliable system in place for verifying how much carbon is stored, and the wider social and environmental effects have been determined. Substantial research will be required to achieve these conditions for methods other than BECS". However, as regards the words that Simon quotes, one concern is a matter of emphasis, interpretation and tone. For instance, there are in aggregate about 15Gt p.a. crop and forestry residues and animal dung, which may be expected to rise to 20Gtp.a. (with ~10Gtp.a. C content) with population increase to 9billions. If the lot were pyrolyzed with 50 per cent C capture, and the product used for soil improvement, that would yield the lower end of the Lehman et al quoted range without any growth at all "in the resources devoted to producing" [[not "biofuels" but biochar is presumably intended]]. There would not be conflict with the use of agricultural land but synergy, with improved soil leading to increased crop yield. In a single sentence the RS writer manages to state that "using crops [PRESUMABLY HE/SHE MEANS CROP RESIDUES] for renewable fuels would be in conflict with using agricultural land for the production of food AND/OR BIOFUELS" !! Beyond the circular non-sequitur, the sentence is about biofuels and not about biochar at all. Next, a negativistic sentence "However, unless the sustainable sequestration rate exceeds around 1 GtC/yr, it is unlikely that it could make a large contribution." contains a false premise [as per the numbers above] which is then carried through to a prominent conclusion of low effectiveness in table 2.4 As regards final sentence that Simon quotes "might increase the cost and reduce the availability of food crops" is precisely the opposite of what would happen with conversion of currently largely wasted or inefficiently used farm and forestry residues to soil productivity enhancing biochar. As Ron Larson has noted, there is an extraordinary failure to quote the enormous positive literature on biochar, conveniently referenced and summarized in book format published in London IN MARCH 2009, within 2 miles of the RS Carlton House Terrace headquarters [Biochar for Environmental Management, Eds J Lehmann and S Joseph, Earthscan] which contrasts strangely with the Report's favourable attitude to BECS where the literature is sparse (possibly a convenience) and where success is entirely dependant on the infant CCS technology. There is not the slightest doubt that we know how to pyrolyze. As regards the gratuitous policy prescriptive paragraph, the establishment of a reliable system for verifying how much C is stored through commercial biochar application to soil is no different from estimating fossil fuel emissions - quantities and quality assay will.become available through normal accountancy procedures and can be aggregated in the same way as is done for coal, except the movement is down into the gropund rather than up out of it. As biochar is "finely divided pyrolyzed biomass prepared [expensively] for soil improvement" purchasers are not going to waste if for fuel (especially as preparation will likely involve wetting and doping with nutrients and/or fungal spores etc., somewhat spoiling combustion properties). Nobody is talking about carbon credits for increased labile soil C resulting from increased productivity or about unregulated backyard operations, though much valuable experimentation is going on in that way. As regards the RS concern over "the wider social and environmental effects " it would be good to see the same applied to already large scale bioenergy before getting too excited about the (likely beneficial) social and environmental effects of infant biochar. While I do not generally favour ad hominem arguments it may be noted that there is not a single member of the working group and review panel that has a publishing record in the field of biochar. Hope that helps Peter ------------------------------------------------------------------------------ No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.113/2396 - Release Date: 09/26/09 05:51:00 --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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