"Normal ecosystem efficiencies are typically around 0.5 %. " Exactly. Nature doesn't do very well Peter ----- Original Message ----- From: Ken Caldeira To: Stephen Salter Cc: Manu Sharma ; Peter Read ; [email protected] ; geoengineering ; [email protected] ; [email protected] Sent: Monday, September 28, 2009 7:41 AM Subject: Re: Grass root answer to Ken's question
Total land area is around 1.5 x 10^14 m2 and grazing might cover 25% of this (Asner et al, 2004), so there must be an error in your calculation. Please give me a calculation in units of watts per m2. What kind of efficiencies are you assuming for using sunlight to produce reduced carbon in soils? This will tell us how much land area you need to store the 5.5 to 9.5 PgC / yr claimed by Lehmann et al. (2006). Reversing the calculation and taking the upper bound. Let's assume it takes about 470 kJ/mol to reduce CO2 to C (I am assuming something like glucose). This works out (unless I have made an error to about 1.2 * 10^13 W. Normal ecosystem efficiencies are typically around 0.5 %. If we assume average sunlight at ground at 200 W/ m2, we get 1 W/m2 ecosystem rates of producing reduced carbon. What fraction of total ecosystem net productivity will be converted to biochar after taking into account processing costs etc? Let's say 10%. So this is 0.1 W/m2. Therefore, we will need about 1.2 * 10^14 m2 or the same order of magnitude as all of the land in the world. You can argue with particular numbers, but it seems that it will take a great leap of faith to be confident that we can feasibly get more than 10% of this number. On Sun, Sep 27, 2009 at 10:59 AM, Stephen Salter <[email protected]> wrote: Ken Slide 10 of the Lovell Ward PowerPoint says grazing land is 5 E15 m2. I would expect that this will include a lot of what we might think of as desert but this is because it has been badly grazed and they show that they can get it back. In another presentation Tony Lovell showed a photograph of a slice through the topsoil of some land that had been managed by his technique. I recall a deep black layer of what looked very carbonish. Tony, if I am correct, can you circulate that photograph? If we multiply that land area by a soil depth of 0.3 metres and my guess of soil density of 1800 kg/m3 we get 27000 G tonne of earth. Each 1% of additional carbon mass that gets embedded is 270 G tonne. Nature keeps the herds concentrated with lion power. We would have to do it by fences and gate control. I am not sure where solar power or food mass comes in. Lovell and Ward are not charring the roots or doing any digging. They are just leaving roots where they grew holding onto their carbon. The food is only a tiny fraction of vegetable matter. Stephen Emeritus Professor of Engineering Design School of Engineering and Electronics University of Edinburgh Mayfield Road Edinburgh EH9 3JL Scotland tel +44 131 650 5704 fax +44 131 650 5702 Mobile 07795 203 195 [email protected] http://www.see.ed.ac.uk/~shs Ken Caldeira wrote: Steven, What is the total area of the world that is susceptible to such processes? I think what the Royal Society report basically said is that in order of magnitudes, if we think 10 GtC/yr is the order of magnitude of the 100% solutions, biochar is not a 100% solution but could potentially be a 10% solution. I repeat my basic logic: /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 scale. / Nothing in this conversation has induced me to change this perspective. Best, Ken PS. Please not that I am not speaking for the Royal Society in making these comments. ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA [email protected] <mailto:[email protected]>; [email protected] <mailto:[email protected]> http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968 On Sun, Sep 27, 2009 at 4:36 AM, Stephen Salter <[email protected] <mailto:[email protected]>> wrote: Hi All I may be able to answer Ken's questions about the ultimate potential for bio-char by pointing to some work by the Australians Tony Lovell and Bruce Ward. The number Ken needs for energy to make the root equivalent of bio-char is very close to zero and depends on the energy you need for ranch fencing. We need to build fences and control gates between grazing grounds and so manage the way livestock are allowed to move around ranches. We want it to be more like the way wildebeest move around the Serengeti and Masai Mara. We want them to eat all the grass from a small area in a short time and then leave it alone for a long time rather than nibbling a moderate fraction all the time. The amount of root matter below ground is set by the amount above ground when the grass is at its tallest and affect the rates at which it can recover. The photograph below makes the point. Below are a pair of photographs from the Lovell and Ward presentation taken from adjacent ranches with the same soil type on the same day. They quote a UN FAO figure of 1500 GT capacity for soil uptake. As the reflectivity of grass is higher than bare earth and grass roots transfer carbon to the soil it looks like a useful technique for albedo increase as well as carbon removal. For more, PLEASE go to http://www.soilcarbon.com.au/case_studies/pdf/08TL_SCCPPP_En.pdf Then contact Tony Lovell Soil Carbon (Australia) Pty Ltd PO Box 157, BOND UNIVERSITY QLD 4229 Suite 102, 20 Lake Orr Drive, VARSITY LAKES QLD 4227 Ph: +61 (0)7 5553 7900 Fax: +61 (0)7 5553 7999 Mob: +61 (0)418 730340 Email: [email protected] <mailto:[email protected]> It should be very cheap to test the idea on a small scale and grow it progressively. But in the short term why not mosey down Mexico way and take your own photographs of La Inmaculada and next door ranch? Stephen Emeritus Professor of Engineering Design School of Engineering and Electronics University of Edinburgh Mayfield Road Edinburgh EH9 3JL Scotland tel +44 131 650 5704 fax +44 131 650 5702 Mobile 07795 203 195 [email protected] <mailto:[email protected]> http://www.see.ed.ac.uk/~shs <http://www.see.ed.ac.uk/%7Eshs> Ken Caldeira wrote: 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] <mailto:[email protected]>; [email protected] <mailto:[email protected]> http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968 The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. ------------------------------------------------------------------------------ No virus found in this incoming message. 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