Keith cc list 1. Since this is a thread with a biochar theme, I thought we should compare a hypothetical biochar scenario with your solar power satellite (SPS) scenario.
2. Because char is lighter than oil (I assume relative density of 1/3), I got 1200 km3 of char, assuming 400 Gt of carbon needing to be removed for a 100 ppm drop in CO2. This assumes almost as much has to come out of the ocean as the atmosphere. Was your assumption similar on ocean CO2 release? 3. To achieve the 1200 km3 of char, and an assumed depth of a uniform char layer of 2.5 cm (roughly an inch) requires spreading over about 20% (2.4 Gha) of the global land area. Yours would be a thinner layer of course, but an oil would have to be deep underground to avoid conversion back to CO2. Also a despoil sequestration can provide no out-year benefits. 4. Assuming that about half of biomass carbon will go to char and half to energy (at 30 GJ/tonne C), means that the 2.5 cm layer (400 Gt C) will also provide a beneficial (carbon neutral) release of about 12,000 EJ. 5. You estimate about 300 TWyrs for the SPS scenario. I calculate (using 5 kWh = 18 MJ [about the energy in 1 kg wood] and 3600 seconds in an hour) about 1 TWyr = 30 EJ (we are globally using near 600 EJ/yr in 2013), so the 12,000 EJ is about 400 TWyr to compare to your 300 TWyrs. The difference is that the biochar scenario supplies 1/3 more (not requires that much more). This is also handling the required ocean carbon - I am not sure of your “ocean” assumption. You suggest a new 15 TW for 20 years; this is 8 TW for 50 years. >From here on is an extension of the SPS scenario 6. If we accomplish the 400 Gt C transfer at about today’s fossil input rate of 8Gt C/yr (about 1% removal rate), all with biochar only) this would supply in a carbon neutral sense about 240 EJ/yr = about 40% of today’s total supply. (The SPS scenario would also be carbon neutral.) But biochar also supplies out-year carbon negative benefits from increased above and below-ground living matter. This augmentation is not well known at all, but assuming 2 Gt C per year of afforestation, and placed-char having this assumed eventual out-year doubling potential, then 3 Gt C/yr of placed-char would be sufficient to meet the 8 Gt C/yr goal (this assumes zero fossil and land disturbance positive contributions). 7. Because of this projected doubling of char impact, we are down to 3*30 = 90 EJ/yr of supplied energy - about 15% of today’s supply - which is in addition to today’s approximately 10% through biomass of 60 GJ/yr. Biomass contributions in the neighborhood of 25% appear in some projections for 2050. 8. The above was to try to get an annual average biomass tonnage of carbon, with each tonne of carbon in wood supplying 1/2 tonne of carbon in biochar and 9 GJ. So 3 Gt C/yr of biochar sequestration requires 6 Gt of C in wood-input (or about 12 Gt dry biomass or 24 Gt of wet biomass). This amount of input wood provides a new 54 EJ to be added to today’s roughly 60 - approaching a needed doubling in wood supply going to energy. 9. The total needed added supply is 2 (afforestation) + 2*3 (biochar) = 8 Gt C, which is to be compared with today’s global NPP of about 60 Gt C/yr. Today’s standing biomass is about 500 Gt C, so this would increase to perhaps 650 by a combination of afforestation and biochar annual and short rotation feedstock. Today’s roughly 1500 Gt C of below ground carbon would similarly increase by 50 years * 2 Gt C/yr = 100 Gt C. Together, after 50 years, these assumptions change from about 2000 Gt C up to 2250 Gt C. This (1/4% per year) seems conservative, compared to the annual productivity improvements seen for grain crops over the last 50 years. Disclaimer: These are only intended as rough numbers to correspond to the SPS scenario. Obviously there should be a ramping period in both scenarios. The most important difference is the sign on the energy contribution. It would be interesting to compare costs; none are shown here, but my guess is that the bio alternative would be considered cheaper and nearer to commercial readiness. Ron On Nov 19, 2013, at 1:14 PM, Keith Henson <[email protected]> wrote: > Some years ago I calculated how much energy it would take to convert > 100 ppm of CO2 into synthetic oil which could be stored in old oil > fields safely for millions of years. > > 100 ppm of CO2 would be 470 cubic km of the stuff. It's what humans > added to the atmosphere since ~1960. > > Had to define a new measure of energy, it would take about 300 TW > years (check it if you want to quote it). > > I was doing this in the context of space based solar power. If you > kept building power plants in space beyond replacing fossil fuels, to > another 15 TW, it would take 20 years to put 100 ppm back in the > ground. > > Much less energy if you take it out as CO2, but less of a blowout problem > > Keith Henson > > http://en.wikipedia.org/wiki/L5_Society > > > On Tue, Nov 19, 2013 at 5:45 AM, Ning Zeng <[email protected]> wrote: >> Or simply CRS (Carbon Removal and Storage). A few years back when this group >> came up with the names SRM and CDR, I argued for CRS, reasoning that any CO2 >> removal method has to be accompanied by storage as a truly workable carbon >> sequestration strategy. many cheers, -Ning >> >> >> On Monday, November 18, 2013 5:59:10 PM UTC-5, kcaldeira wrote: >>> >>> Folks, >>> >>> The question about whether biochar is a CDR technique and therefore >>> "geoengineering" raises some interesting issues. >>> >>> Carbon Dioxide Removal (CDR) techniques involves to processes that are in >>> principle separable: >>> >>> 1. Carbon dioxide removal from the atmosphere (or oceans) >>> 2. Storage of that carbon in a long-lived pool. >>> >>> Carbon can be removed from the atmosphere using biological strategies >>> (e.g., land plants, phytoplankton) or chemical strategies (e.g., direct air >>> capture, accelerated chemical weathering). >>> >>> Carbon so removed must then be stored in a long-lived reservoir. Carbon >>> can be stored in a reduced form (e.g., biochar, living forests) or in an >>> oxidized form (e.g., CO2 injected in geologic reservoirs, Fe-fertilized >>> biomass that has oxided into dissolved inorganic carbon in the deep ocean). >>> >>> Carbon stored in an oxidized form can be largely in the form of molecular >>> CO2 (perhaps dissolved) or can be part of another compound such as CaCO3 >>> (perhaps dissolved). >>> >>> What makes something CDR approach is a system property (i.e., air capture >>> that vents back to the atmosphere is not a CDR approach; geologic CO2 >>> storage without air capture is not a CDR approach; but put the two together >>> and you have a CDR approach). >>> >>> On this taxonomy, I would consider biochar as a way of storing reduced >>> carbon for long periods of time. Under this interpretation, biochar could be >>> part of a CDR system, but as a process in-and-of-itself, biochar is an >>> approach for carbon storage. Biochar does no carbon dioxide removal, so >>> cannot itseld be a CDR technique. >>> >>> Therefore, it may make sense to talk about biochar as a carbon dioxide >>> storage approach. As part of a system of biological carbon capture by land >>> plants and storage using biochar, biochar can be part of a CDR system, but >>> biochar itself is not a CDR system. >>> >>> Maybe we should be talking about CDRS (Carbon Dioxide Removal and Storage) >>> instead of CDR. We should then specifiy both the Carbon Dioxide Removal >>> (CDR) approach and the Storage (S) approach. >>> >>> Biochar is an S approach, not a CDR approach. >>> >>> Best, >>> >>> Ken >>> >>> _______________ >>> Ken Caldeira >>> >>> Carnegie Institution for Science >>> Dept of Global Ecology >>> 260 Panama Street, Stanford, CA 94305 USA >>> +1 650 704 7212 [email protected] >>> http://dge.stanford.edu/labs/caldeiralab >>> https://twitter.com/KenCaldeira >>> >> -- >> 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. >> 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. 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