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 14 C inventory in the Earth System: a constraint on 14 C production

Production = - Decay of 14 C = 14 N Earth = 14 N Earth Decay rate:  =1/8267 yr 14 C Inventory, 14 N Earth :mainly from data

Atmosphere 590 GtC  820 GtC Vegetation/Soil 3000 to 4000 GtC Marine Biota 3 GtC Ocean 38‘000 GtC Sediments Carbon Pools Fossil 5000 GtC

Dissolved Inorganic Carbon in the ocean varies between 1.9 and 2.5 mmol/kg  mol/kg Sarmiento and Gruber, Ocean Biogeochemical Dynamics, 2006

Atmosphere  14 C~ 0 % o Vegetation/Soil  14 C~ -15 % o Ocean  14 C ~ % o Reactive Sediments ( CaCO 3, Organic)  14 C~ -200 % o 14 C/ 12 C in the Earth System

Observed Deep Ocean  14C Müller, et al., J. Climate, permil Simulated Deep Ocean  14C in the Bern3D model 14 C/ 12 C-ratio varies in ocean within 0.96 to 0.76

An estimate: Observation-based: [10 26 atoms] Ocean: 20,010 (85%) Atmosphere: 360 (2%) Model-supported: CaCO 3 Sediment 350 Organic Carbon Sediment 170 flux to litosphere · 920 (6%) vegetation 360 soils ~1,500 (8%) 14 N Earth 23, atoms Total Inventory 14 N Earth 23, atoms(100%)

An estimate: 14 N Earth 23, atoms Total Inventory 14 N Earth 23, atoms Total Production: 14 N Earth = atoms s -1 = 1.78 atoms cm -2 s -1 Next steps: estimate transient effects estimate transient effects using the Bern3D model using the Bern3D model (atmospheric variation (atmospheric variation in 14 C/ 12 C: 6%) and in 14 C/ 12 C: 6%) and link to solar modulation link to solar modulation improve terrestrial estimate improve terrestrial estimate (peat and permafrost) (peat and permafrost)

Solar activity reconstructed from 14 C and 10 Be for the past 6,000 years Wanner et al., 2008

How do past changes in radiative forcing compare with ongoing forcing changes? Cause effect chain: Perturbation in radiative balance Perturbation in radiative balance feedbacks feedbacks Climate Change Climate Change

Rates of Change CO 2 (ppm) Temperature anomaly ( o C) Today 800 ka BP Age Atmospheric CO 2 and Antarctic temperature covaried over the past 800,000 years. CO 2 acts as an amplifying feedback (Lüthi et al., 2008)

(IPCC, Time kyr latitude Summer insolation Variations in Earth‘s orbit control seasonal and latitudinal distribution of solar insolation and likely caused glacial-interglacial cycles 60 W/m W/m 2 Annual mean insolation Time scales: 20, years 10 W/m 2

(IPCC, 2007, Fig. 6.5) 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

Temperature response of the Bern model to orbital, greenhouse gas and ice sheet-albedo forcing Global Temperature ( o C) Today 800 ka BP (Ritz et al., 2010) Orbital only Orbital + CO 2 +ice

(IPCC, 2007, Fig. SPM-1a ) Time (years before present) Carbon Dioxide (ppm) Radiative Forcing (W m -2 ) 0 1 Atmospheric CO2 is rising and far above the preindustrial range: CO 2 from anthropogenic emissions causes warming and ocean acidification Time scale of increase: decadal-to-century Perturbation life time: millennial

N2ON2O CH 4 CO 2 Landuse CO 2 Fossil (IPCC, 2007, WGIII, Fig. SPM-1a ) Relative greenhouse gas emissions

Rates of climate change co-determine severity of impacts on socio-economic and natural systems Rates of Change

(Joos and Spahni, PNAS, 2008) Atmosphere Ice CO 2 CH 4 Results from a firn-diffusion and enclosure model How would the anthropogenic CO 2 and CH 4 peaks be recorded in Antarctic ice during the transition? Atmosphere Ice

(Joos and Spahni, PNAS, 2008) Time (thousand years before present) Spline fit to the greenhouse gas data

(Joos and Spahni, PNAS, 2008) Potential Smoothing of peak in ice Rates of change over the past 22,000 years inferred from splines through ice/atm. data The rate of increase in the combined radiative forcing from CO 2, CH 4 and N 2 O during the industrial era is very likely to have been unprecedented in more than 10,000 years (IPCC, SPM, 2007)

How do rates of change in anthropogenic forcing compare with solar and volcanic forcing of the last millennium?

(Joos and Spahni, PNAS, 2008) volcanoes Solar ( MM 0.25% ) sum of current rates in anthropogenic forcings Trend in solar irradiance over satellite period: W m -2 yr -1 Rates of decadal-scale change: Natural (solar, volcanoes) versus human made

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 Data-based reconstructions

Muscheler et al., 2005 Today‘s solar activity is not unusual in the context of the last millennium: solar modulation from 14 C tree ring record and carbon model 1600 AD

Different solar forcing reconstructions from 10 Be, 14 C, sunspot records differ in amplitude (not in evolution) (IPCC, 2007, Fig. 6.14) Year Volcanic, solar and other forcings Bard et al., 2000 (MM: -0.25%) Wang et al., 2005 (MM -0.08%)

(IPCC, 2007, Fig. TS-20) Northern Hemisphere temperature reconstructions Year Temperature anomaly ( o C) Reconstructed ranges for low frequency variations in NH temperature are between ~ 0.3 o C and 1 o C

Siegenthaler et al., 2004 (Etheridge al.) (Neftel al.) Preindustrial CO 2 variations: an additional constraint

Climate model results Climate model results

With Without Anthropogenic Forcing (IPCC, 2007, Fig. 6.14) Year Temperature anomaly ( o C) Climate models forced with prescribed forcing (low and high solar): simulated versus reconstructed NH temperature 1600 AD

Anthropogenic Forcing (IPCC, 2007, Fig. 6.14) Simulated temperatures with and without anthropogenic forcing and with weak or strong solar irradiance variations Year Temperature anomaly ( o C) A significant fraction of the reconstructed NH interdecadal temperature variability over at least the seven centuries prior to 1950 is very likely attributable to volcanic eruptions and changes in solar irradiance

Modelled versus measured CO 2

Simulated atmospheric CO 2 versus ice core data Model results: smoothed with DML age distribution Simulated versus ice core CO 2

Probabilistic estimates of the sensitivity of CO 2 to temperature from reconstructions  CO 2 /  T (ppm/K)

A probabilistic assessment of the CO 2 -temperature sensitivity based on different temperature and CO 2 reconstructions Probability (Frank et al., 2010) Sensitivity (ppm per o C)

Comparison of data-based estimates of the sensitivity of CO 2 to temperature with model results

02040 Probability (Frank et al.,2010) Sensitivity (ppm per o C) (Range of median values) Reconstructed 20 th century C4MIP models

The amplitudes of the preindustrial decadal-scale Northern Hemisphere temperature changes from the proxy-based reconstructions (<1 o C) are broadly consistent with the ice core CO 2 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

(IPCC, 2007, Fig. TS-20) Locations of temperature-sensitive proxy records Average Northern Hemisphere temperatures during the second half of the 20 th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1300 years (SPM, 2007).

Normalisation to Neutron and Ionisation Chamber Data

Solar Modulation Parameter and Group Sun Spot Number

Different proxies of solar activity Agreement /Disagreement

The power spectrum of the 14 C and 10 Be solar modulation records shows common peaks Wanner et al., 2009

C4MIP range: (20th century simulations: ΔCO2 / ΔT = [4 – 16 ppm/K] Linking variations in CO 2, in NH temperature, and the carbon cycle-climate feedback:

Low solar forcing: Simulated atmospheric CO 2 versus ice core data Model results: smoothed with DML age distribution

Large low frequency temperature variations are not compatible with the ice core CO 2 record High Solar Forcing

Solar Forcing, Volcanic Forcing and Simulated Temperature Decoupling of solar forcing and global temperature consistent with proxy data Volcanic Forcing (VOD)

Natural forcings: contribution to 20 th century warming is less than 0.15 K for all solar scalings