Tuesday, April 27, 2010
Drawing Down CO2 by 2030 to Back Out of the Danger Zone for Abrupt Climate Shifts
Climate shifts are like heart attacks, striking suddenly and ranging from minor to catastrophic. (From 1950 to 1982, about 14% of global land surface was in serious drought at any one time. Then it suddenly doubled. It never recovered, stepping again to nearly triple in 1997, stepping down to double in 2005.) But there is nothing inevitable about them. The obvious course for prevention is analogous to drawing down a reservoir, done when an earthen dam is being undermined by a leak, threatening sudden collapse. To reverse global warming and back out of the danger zone for more abrupt climate shifts, an appropriate goal would be to remove nearly all of the atmosphere’s excess CO2 and put it back into long-term storage, finishing the job before 2030. The 30 GtC/yr drawdown would be an emergency repair, not a substitute for a low-carbon energy diet. Chemically scrubbing the atmosphere is unlikely to scale up fast enough. Though large enough, doubling forests is not secure enough, given that we cannot even protect rain forests from the trends in fire and drought. To avoid competing with the world’s food production, most sequestered carbon must come from new biomass grown in new places.
Here I explore how paired ocean pumps might uplift nutrients and then sink the new organic carbon into the ocean depths. Instead of sinking only the debris that is heavy enough to settle out, as in iron fertilization, we would be using bulk flow to sink the entire organic carbon soup (organisms plus the hundred-fold larger amounts of dissolved organic carbon) of the wind-mixed layer before its carbon reverts to CO2 and equilibrates with the atmosphere. The CO2 later produced in the depths will reach the surface 400–6,000 years later. Smearing it out over that period greatly reduces the damaging peaks in ocean acidification and global fever.