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A paleoperspective on the carbon cycle-climate system Fortunat Joos Climate and Environmental Physics and Oeschger Centre of Climate Change Research University of Bern The 14C inventory in the Earth System: a constraint on 14C production Production = - Decay of 14C = l 14NEarth Decay rate: l=1/8267 yr 14C Inventory, 14N Earth :mainly from data Carbon Pools Atmosphere 590 GtC 820 GtC Fossil 5000 GtC Vegetation/Soil 3000 to 4000 GtC Ocean 38‘000 GtC Sediments Marine Biota 3 GtC Dissolved Inorganic Carbon in the ocean varies between 1.9 and 2.5 mmol/kg Sarmiento and Gruber, Ocean Biogeochemical Dynamics, 2006 mmol/kg 14C/12C in the Earth System Atmosphere D14C~ 0 %o Vegetation/Soil D14C~ -15 %o Ocean D14C ~ - 152.2 %o Reactive Sediments ( CaCO3, Organic)D14C~ -200 %o 14C / 12C ( 13C 25) D C (1 2 ) 1 1000permil 1000 Rstd 14 permil Observed Deep Ocean D14C -50 14C/12C-ratio varies in ocean within 0.96 to 0.76 -150 -250 Simulated Deep Ocean D14C in the Bern3D model Müller, et al., J. Climate, 2005 An estimate: Observation-based: Ocean: Atmosphere: Model-supported: CaCO3 Sediment Organic Carbon Sediment flux to litosphere · l vegetation soils Total Inventory 14N Earth [1026 atoms] 20,010 (85%) 360 (2%) 350 170 920 (6%) 360 ~1,500 (8%) 23,670 1026 atoms (100%) An estimate: Total Inventory 14N Earth 23,670 1026 atoms Total Production: l 14NEarth = 9.079 1018 atoms s-1 = 1.78 atoms cm-2 s-1 Next steps: • estimate transient effects using the Bern3D model (atmospheric variation in 14C/12C: 6%) and link to solar modulation • improve terrestrial estimate (peat and permafrost) How do past changes in radiative forcing compare with ongoing forcing changes? Cause effect chain: Perturbation in radiative balance feedbacks Climate Change Rates of Change +4 -10 CO2 (ppm) 300 Temperature anomaly (oC) Atmospheric CO2 and Antarctic temperature covaried over the past 800,000 years. CO2 acts as an amplifying feedback 180 Today 800 ka BP Age (Lüthi et al., 2008) Variations in Earth‘s orbit control seasonal and latitudinal distribution of solar insolation and likely caused glacial-interglacial cycles Annual mean insolation Time scales: 20,000 ++ years Summer insolation latitude 60 W/m2 10 W/m2 -500 Time kyr 0 100 -60 W/m2 (IPCC, 2007 Changes in greenhous gas concentration and ice sheet growth acted as amplifying feedbacks Radiative Forcing at the Last Glacial Maximum Orbital: large distributional effects, but small change in global annual mean insolation (IPCC, 2007, Fig. 6.5) Temperature response of the Bern model to orbital, greenhouse gas and ice sheet-albedo forcing Orbital only Global Temperature (oC) +16 Orbital + CO2 +ice +10 800 ka BP Today (Ritz et al., 2010) 350 Time scale of 1increase: decadal-to-century 300 0 250 Radiative Forcing (W m-2) Carbon Dioxide (ppm) Atmospheric CO2 is rising and far above the preindustrial range: CO2 from anthropogenic emissions causes warming and ocean acidification Perturbation life time: millennial 5000 10000 0 Time (years before present) (IPCC, 2007, Fig. SPM-1a) Rates of Change Rates of climate change co-determine severity of impacts on socio-economic and natural systems Rates of change over the past 22,000 years inferred from splines through ice/atm. data The rate of increase in the combined Potential Smoothing radiative forcing of peak in ice from CO2, CH4 and N2O during the industrial era is very likely to have been unprecedented in more than 10,000 years (IPCC, SPM, 2007) (Joos and Spahni, PNAS, 2008) How do rates of change in anthropogenic forcing compare with solar and volcanic forcing of the last millennium? Rates of decadal-scale change: Natural (solar, volcanoes) versus human made volcanoes Solar (MM 0.25%) sum of current rates in anthropogenic forcings Trend in solar irradiance over satellite period: 10-6 W m-2 yr-1 (Joos and Spahni, PNAS, 2008) Last millennium: Are suggestions of a small influence of solar changes on climate over the past millennium plausible? A carbon cycle-climate perspective Data-based reconstructions Today‘s solar activity is not unusual in the context of the last millennium: solar modulation from 14C tree ring record and carbon model 1600 AD Muscheler et al., 2005 Different solar forcing reconstructions from 10Be,14C, sunspot records differ in amplitude (not in evolution) Volcanic, solar and other forcings Bard et al., 2000 (MM: -0.25%) 1000 1500 Wang et al., 2005 (MM -0.08%) 2000 Year (IPCC, 2007, Fig. 6.14) Reconstructed ranges for low frequency variations in NH temperature are between ~ 0.3oC and 1oC Temperature anomaly (oC) Northern Hemisphere temperature reconstructions (IPCC, 2007, Fig. TS-20) 800 1200 Year 1600 2000 Preindustrial CO2 variations: an additional constraint (Etheridge al.) (Neftel al.) Siegenthaler et al., 2004 Climate model results Climate models forced with prescribed forcing (low and high solar): simulated versus reconstructed NH temperature Temperature anomaly (oC) Anthropogenic Forcing With Without 1000 1400 1600 AD Year 1800 (IPCC, 2007, Fig. 6.14) Temperature anomaly (oC) Simulated temperatures with and without anthropogenic Aforcing significant of theorreconstructed interdecadal andfraction with weak strong solarNH irradiance variations temperature variability over at least the seven centuries prior to Anthropogenic 1950 is very likely attributable to volcanic eruptions and changes in Forcing solar irradiance 1000 1400 Year 1800 (IPCC, 2007, Fig. 6.14) Modelled versus measured CO2 Simulated atmospheric CO2 Simulated versus ice core CO2 versus ice core data Model results: smoothed with DML age distribution Probabilistic estimates of the sensitivity of CO2 to temperature from reconstructions DCO2/DT (ppm/K) Probability A probabilistic assessment of the CO2-temperature sensitivity based on different temperature and CO2 reconstructions 0 20 40 60 Sensitivity (ppm per oC) (Frank et al., 2010) Comparison of data-based estimates of the sensitivity of CO2 to temperature with model results Probability Reconstructed 20th century C4MIP models 0 20 Sensitivity (ppm per oC) (Range of median values) 40 (Frank et al.,2010) • The amplitudes of the preindustrial decadal-scale Northern Hemisphere temperature changes from the proxy-based reconstructions (<1oC) are broadly consistent with the ice core CO2 record and our quantitative understanding of the carbon cycle and reconstructions of solar and volcanic forcing • The small changes in CO2, CH4, and N2O over the last millennium also suggest a limited range of climate variability over this period • A small solar influence on climate, despite large variations in solar modulation, is consistent with the climatic records of the last millennium Thank you for your attention! Surface temperature anomaly after a collapse of the North Atlantic Circulation The power spectrum of the 14C and 10Be solar modulation records shows common peaks Wanner et al., 2009 Low solar forcing: Simulated atmospheric CO2 versus ice core data Model results: smoothed with DML age distribution High Solar Forcing Large low frequency temperature variations are not compatible with the ice core CO2 record Natural forcings: contribution to 20th century warming is less than 0.15 K for all solar scalings