TAG 166 - Geological Society of Australia

Relations between CO 2 rise rates and mean global temperature rise rates during warming periods including the Paleocene–Eocene Thermal Maximum (PETM),Oligocene, Miocene, glacial terminations, Dansgaard–Oeschger (D–O) cycles and the post-1750 period (after Glikson, 2012).Since the 18th century, and in particular since about 1975, theEarth system has been shifting away from Holocene (10 000 yearsago to the present) conditions that allowed agriculture, previouslynot possible due to instabilities in the climate and extreme weatherevents. The shift is most clearly manifested by the loss of polar ice(Loss of polar ice article, 2001). Sea-level rises have beenaccelerating, with a total of more than 20 cm since 1880 and about6 cm since 1990 (CLIM 012, 2012; Rahmstorf et al, 2012).For a temperature rise of 2–3°C, to which the climate iscommitted if sulfur aerosol emission discontinues (see accompanyingfigure on mean CO 2 from ice cores), sea levels would reachPliocene-like levels of 25 ± 12 m, with lag effects due to ice sheethysteresis. With global CO 2 -e levels at about 470 ppm, just underthe upper stability limit of the Antarctic ice sheet, and with thecurrent rate of CO 2 emissions from fossil-fuel combustion, cementproduction, land-clearing and fires of about 9.7 GtC in 2010(Raupach, 2011), it is clear that global civilisation is at a tippingpoint, facing the following alternatives:l With carbon reserves sufficient to raise atmospheric CO 2 levelsto above 1000 ppm, continuing business-as-usual emissions canonly result in advanced melting of the polar ice sheets, acorresponding rise of sea level on the scale of metres to tens ofmetres and continental temperatures rendering agriculture, in itspresent distribution and extent, unlikely.l With atmospheric CO 2 at about 400 ppm, abrupt decrease incarbon emissions may no longer be sufficient to prevent currentfeedbacks (melting of ice, methane release from permafrost,fires). Attempts to stabilise the climate would require globalefforts at CO 2 drawdown, using a range of methods includingglobal reforestation, extensive biochar application, chemical CO 2sequestration (using sodium hydroxide, serpentine and newinnovations) and burial of CO 2 .SO 2 injectionsSpace sunshades/mirrorsOcean iron filing fertilisation enhancingphytplanktonOcean pipe system for verticalcirculation of cold water to enhance CO 2sequestration‘Sodium trees’–NaOH liquid in pipe systemsequestering CO 2 to Na2CO3, separation and burialof CO 2Soil carbon burial/biocharSerpentine CO 2 sequestrationCheap and rapid applicationRapid application. No direct effect on oceanchemistryCO 2 sequestrationCO 2 sequestrationCO 2 sequestration estimated by Handsen et al.(2008) at $300 per ton CO 2Effective means of controlling the carbon cycle(plants+soil exchange more than 100 GtC/year withthe atmosphere)CO 2 sequestrationShort multi-year atmospheric residence time;ocean acidification; retardation of precipitationand of monsoonsLimited space residence time. Uncertain positioningin space. Does not mitigate ongoing oceanacidification by carbon emissionsNo evidence that dead phytoplankton would notrelease CO 2 back to the ocean surfaceNo evidence of cold water would circulate back toocean depths where CO 2 is prevented fromreturning to the surfaceUnproven efficiency; need for CO 2 burial; $trillionsexpense (though no more than current militaryexpenses)Requires a huge international effort by a workforceof millions of farmersPossible scale unknownMain proposed solar mitigation and atmospheric carbon sequestration methods.TAG March 2013| 37