Stuart, etal:
1. Per your Tuesday message repeated below, I believe an upper limit of 50 tons char per hectare is on the low side of what is possible or desirable. Last week, I was in Brazil looking at depths of terra preta soil that were approaching 1 meter (I have seen photos with 2 meter depths). Using the same but more visionable measure of 5 kg char in a square meter (or 50 grams on a 10cm x 10 cm patch), and assuming a density the same as water, this would be only 5% as high as the standard 10 cm height size (1000 cm^3) for a liter/kg, then the height to be applied is on the order of 0.5 cm = 5 mm. Obviously the final char/soil density that would be attained is a function of the tilling depth. In Brazil, that is apparently often 20 cm - so the percent char would be about 0.5/20 = 2.5% - and we hear larger % numbers are fine. 2. Looking at it in larger scale, in terms of removing 400 Gt C total (roughly needed for fixing 100 ppm, including the present excess in the oceans) to be placed on 2 Gha of land (about 15% of global total land area), this would be 200 t C/ha or 20 kg C/m2 (roughly a 2 cm height of char, but not that much in any one application). Using the above numbers, this is a quadrupling of your suggested limit of 5 kg C/m2 . 3. These numbers are certainly approaching upper limits. However, the amount required can be smaller for several reasons. a. Hopefully going all the way back to 290-300 ppm will not be required. Maybe getting to 350 ppm will be enough? Pick up a factor of maybe 2 or more here (depending on when we get underway) b. There will be other means developed to remove atmospheric CO2. If Biochar only does half the job (using BECS?, some oceans-related approaches? some sequestration through solid carbonates?), then another factor of 2 is possible?? c. All the char produced does not have to go into the ground. Perhaps some can go into light-weight concrete, asphalt, carbon fiber, etc. This could also include new approaches to producing carbonates? Maybe a few tens of GtC here?? d. Maybe more than 15% global land area can be considered viable - for deposition, if not for production? e. Much of the needed sequestration can take place in 1) the added biochar-caused soil organisms, 2) the trees/plants grown to produce the biochar, and 3) the added plant growth on soils augmented by biochar. Maybe 100 Gt C of new "almost permanent" added standing biomass in these three categories?? If we can pick up a factor of 2-4 out of the above, then we can still stay below 5-10 kg/m2 . 4. In sum, I still believe that Biochar can do a very large percentage of the needed CO2 removal. Whether it is the least cost approach is crucial. I feel it is - for reason of the added energy and soil benefits that don't occur for the other sequestration approaches. I am also now more strongly believing that the Biochar approach can provide both more sequestration and more carbon neutral energy than BECs or the other bio approaches. I look forward to hearing what is wrong with this view, and will be supplying that added important detail soon 5. The above is not the whole story - which I am still working on. Here I am only addressing your issue (below) on allowable added char.- total and per unit area. I don't think the issue is related much or at all to the crops being assumed (you have maize below). Thanks for the chance to have these added discussions. Ron ----- Original Message ----- From: "Stuart Strand" <[email protected]> To: [email protected] Cc: [email protected], "marty hoffert" <[email protected]>, "andrew lockley" <[email protected]> Sent: Tuesday, September 21, 2010 10:22:01 PM Subject: RE: [clim] Re: [geo] Carbon sequestration workshop Sep 9-10, Heinz Center, Washington DC Sorry, premature send again…. “ Finally, I goofed in stating…” should be: I goofed in stating a saturation level for biochar of 50 kg/ha. Mea culpa, I meant 50 Mg biochar C/ha (only off by 1000x!). My reference for this rate is Chan et al., Australian Jour. Soil Research 2007, 45:629. I should have checked before pressing send. So my point is that biomass harvested from maize cultivation, used to produce biochar (assuming 10Mg aboveground CR produced /ha, 0.5 g biochar C yield/g CR C), and returned to a fraction of the soil at 50 t biochar C/ha, would saturate the soil in 35 years or less. My apologies for the errors. = Stuart = Stuart E. Strand 490 Ben Hall IDR Bldg. Box 355014 , Univ. Washington Seattle, WA 98195 voice 206-543-5350, fax 206-685-9996 skype: stuartestrand http://faculty.washington.edu/sstrand/ -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
