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 -~----------~----~----~----~------~----~------~--~---
