In the "Target Atmospheric CO2" paper by Hansen et al, methods of CO2 drawdown are discussed in section 4.4. http://dx.doi.org/10.2174/1874282300802010217
Air capture is mentioned, but I think the major focus is on reforestation, biochar agriculture, and carbon-negative biofuels. There may be a little more detail in the E3 Network's "Economics of 350" paper. http://www.e3network.org/papers/Economics_of_350.pdf On Oct 28, 3:59 am, Greg Rau <[email protected]> wrote: > We all saw the publicity surrounding 350.org's International Day of > Action last weekend insisting that we return the atmos CO2 to 350 > ppm. My point is: aren't they dreaming if they think this can happen > any time soon, even under the best of circumstances, unless we can > enhance air CO2 capture and storage -geoengineering? > > There's now about 3,000 GT CO2 in the air and that needs to be > reduced to about 2700 GT in order to have 350 ppm CO2, i.e. about a > 300 GT drop in air CO2 is needed. Current global net CO2 uptake > rates are roughly 15 GT CO2/yr, so one might argue that if we stopped > all emissions today we could get back to 350 ppm in 20 years. But we > are not stopping anthro emissions any time soon, and anyway as atmos > pCO2 declines, the net uptake rate will decline also because this is > largely driven by the pCO2 difference between the air and the ocean. > So as the air ppm declines so will the uptake rate. While they > didn't model a 350 scenario, Archer and Brovkin's (Climate Change > 90:283-) evaluation of atmospheric pCO2 relaxation time would seem to > imply hundreds of years would be need to reach 350 ppm from where we > are now. > > So the question to the higher authorities here is what is the natural > air CO2 relaxation rate even once anthro CO2 emissions are zero? If > 350 ppm is indeed some magic tipping point, I don't think we are > getting back there anytime soon under any positive or zero emissions > scenario, however well intentioned. That would leave enhanced air > capture (geoengineering) as the only (feasible) Plan B. Are 350.org > and Jim Hansen et al then advocating this approach and if so > shouldn't we team up - for an International Day of Geoengineering, > etc? > > Regards, > Greg Rau --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
