global carbon cycling where does it all go?

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Global Carbon Cycling Where does it all go?. Main Concepts. Pre-anthropogenic CO 2 fluxes in and out Current CO 2 fluxes What are C reservoirs? Carbon Residence time? Timescales of carbon removal from the atmosphere. Carbon: Ins and Outs. IPCC AR5 (2013). Atmospheric CO 2. - PowerPoint PPT Presentation


  • Global Carbon CyclingWhere does it all go?

  • Main Concepts

    Pre-anthropogenic CO2 fluxes in and outCurrent CO2 fluxesWhat are C reservoirs?Carbon Residence time?Timescales of carbon removal from the atmosphere.

  • IPCC AR5 (2013)Carbon: Ins and Outs

  • Atmospheric CO2What are the major sources of C emissions? How unique are modern CO2 levels? Where does it all go?How long will it stick around?

  • Fossil fuel CO2 emissions: Burning buried sunshine

  • Carbon emissions rising faster than estimates

  • Global C emissions mapWhere emissions come from

  • Atmospheric CO2:Last 50 years (2.0 ppm/year increase, or 0.5%)400 ppm

  • Its alive! Seasonal cycle

  • CO2 growth rates

  • CO2 growth rates

  • What do we know aboutgreenhouse gases and past climate change?

  • Glacial ice traps ancient airSnow accumulatesSnow becomes ice Pore spaces are sealed and they trap ambient air.

    Up to 800,000 year old ice with ancient trapped air bubbles!

    Free air

  • Atmospheric CO2: Last 250 years

  • Atmospheric CO2: last 400,000 years!

  • Atmospheric CO2:Last 50 MILLION yearsHow unusual are modern CO2 levels?

  • Carbon fluxes (in Gt/yr), reservoirs (bold, Gt), and residence times (years)Note: 2010 emissions were 9 Gt / year 1990s data

  • How much is a gigaton (Gt)?One billion metric tons (1012 kg)

    It is about 2750 Empire State Buildings.Global C emissions are about 9 Gt as of 2012.

    How much does global population weigh?7 x 109 people x 102 kg/person7 x 1011 kg = 0.7 Gt

  • AR5 Observed carbon fluxes

    Negative (positive) means removed from (added to) the atmosphere; IPCC AR5 data)

    ReservoirPre-Ind Fluxes (Gt/year)Current Flux (Gt/year)Photosynthesis-108.9-123.0Respiration+107.2+118.7Ocean+0.7-2.3Fossil fuels emissions+7.8Land Use changes+1.1Other (volcanoes, lakes, rivers)+1.0 +0.3Atmosphere CO2 increase- 0 -+4

  • Carbon ins and outsSource:Carbon Emissions 7.8 Gt/yearDeforestation 1.1 Gt/year

    Sink:Obs. Atm increase -4.0 Gt/yearOcean uptake -2.3 Gt/yearmissing sink -2.6 Gt/yearIPCC AR5 data

  • Human Carbon emissions2012 emissions are ~9 Gt were about 6 Gt when I started teaching this course !

  • Deforestation accounts for an additional +1.1 Gt / yearDeforestation

    - Mainly tropical rainforests

    - Cutting down forests to make agricultural land is a net source of carbon to the atmosphere.

    CH2O + O2 CO2 + H2OBolivia (1984-1998)

  • Where do our carbon emissions go?Ocean takes up about -2.3 Gt / yearRoughly one-third of our fossil fuel emissions

  • Why does the ocean take up CO2?CO2 gas is soluble in the oceanGas solubility is highest in colder waterCO2 enters the oceans at the polesCO2 is converted to HCO3- by buffer reactionThe ocean acidifies as a direct result

    Ocean buffer chemistry can take up only a finite amount of CO2.

  • Air-Sea CO2 fluxesOcean uptakeOcean releaseGases are more soluble in COLD waterOcean uptakeOcean uptakeOcean releaseNet:-2 Gt/yr

  • Where is our carbon in the oceans ?Vertical Sections through the oceansTotal ocean uptake is about -2.5 Gt / year

  • Carbon ins and outsSource:Carbon Emissions 7.8 Gt/yearDeforestation 1.1 Gt/year

    Sink:Obs. Atm increase -4.0 Gt/yearOcean uptake -2.3 Gt/yearmissing sink -2.6 Gt/yearIPCC AR5 data

  • What is the missing sinkThe missing sink is the amount of carbon required to balance sources and sinks.

    It is a big number: -2.6 Gt Carbon / year !

    What is it ???

  • The Missing Sink (history)

  • Missing C sink: 1-2 Gt CO2 fertilizationCO2 fertilization of high-latitude forests Plants grow faster/better at higher CO2But the effect is assymptotic (not linear)Atm CO2 levelPlant Cuptake

  • Other things we need to knowNot only Fluxes of carbon in/out (Gt / year)

    Sizes of the carbon reservoirsResidence Time of carbon in each reservoir

    These additional factors determine who the biggest players are and how quickly they will act.

  • Why these things matterWhat would happen to CO2 levels if we stopped all emissions today?What if the ocean warms up a lot?What if deep ocean circulation were to change ?Does Arbor day matter ?

  • Ocean and Atmoshere C reservoirsAtmosphere: 1580 Gt (as CO2)Ocean C: 39,000 Gt (as HCO3-, CO32-)

    Ocean has 50x more carbon than the atmosphere.

  • Residence timeResidence time is a replacement time: time required to affect a reservoir given a certain flux. (years) = reservoir / input rate

    Example: Residence time of a CU undergradReservoir: Size of Columbias UG Student Body?Input rate: Incoming 1st-year class size

  • Calculating residence time of Carbon due to air-sea exchangeOcean uptake rate: -2.0 Gt / yearTotal Ocean C reservoir : 39,000 GtSurface Ocean C reservoir : 600 Gt

    C residence time (surface only) = ?C residence time (whole ocean) = ?

  • The fate of fossil fuel CO2Q: How quickly will the planet take up our CO2?A: Not very quickly

    Fast: solubility pump Air-Sea CO2 exchange (centuries)Moderate: Deep ocean acid neutralization (tens of thousands of years)Really slow: Weathering of continental rocks (millions of years)

  • Fastest response (decades to centuries): The CO2 solubility pumpAir-Sea gas exchange

  • Medium response time (104 years): Neutralize ocean acidityNeutralize deep ocean acidity by Dissolving ocean CaCO3 sedimentsCaCO3 Ca2+ + CO32-

  • Really Slow response time (106 years)Continental weathering (dissolves mountains!)Urey reaction - millions of yearsCaSiO3 + CO2 --> CaCO3 + SiO2

  • 75% in 300 years25% foreverTime of removal

  • Bottom LineHuman C Emissions are largeNature cant keep upNatural C sinks are diminishing

    Lifetime of CO2 from your tailpipe: 300 years, plus 25% that lasts forever

  • Radiative ForcingHelps us quantify how global climate responds to an imposed change (forcing).

  • What is Radiative Forcing? Radiative forcing: An imposed change in Earths radiative energy balance. Measured in Watts per square meter (W/m2)

    Radiative because these factors change the balance between incoming solar radiation and outgoing infrared radiation within the Earths atmosphere. This radiative balance sets the Earths surface temperature.Forcing indicates that Earths radiative balance is being pushed away from its normal state.

    Examples: Solar variability, volcanic emissions, greenhouse gases, ozone, changes in ice cover (albedo), land use changes.

  • Our first climate modelRecall how to calculate Earths effective temperature

    The Stefan-Bolzmann equation:

    Blackbody radiation I (w/m2) = s T4

    Earth incoming radiation (a = Earth albedo, or reflectivity)I incoming = (1-a) Isolar = (1-a) s Tsun4

    a Is ~0.3, or 30%

  • Our first climate modelEarth incoming radiation (a = Earth albedo, or reflectivity)I incoming = ((1-a) Isolar ) / 4, or ((1-a) s Tsun4 )/ 4

    Earth outgoing radiation

    I outgoing = s Tearth4

  • Earths temperature with no greenhouse effect

    Teffective = 254.8K (-18C)At equilibrium, I incoming = I outgoing

    Set Sunlight = Earthlight

    Solve for Tearth

    Eqn. 3.1 in Archer Chapter 3

  • Volcanic eruption can change albedo by 1% = ~30% on averageTeffective = 254.8K

    Increase to 31%New Teffective = 253.9K

    or -1C cooler due a volcanic eruptionRecalling I = (1-a) s T4

  • Adding an atmosphere

  • Greenhouse gases are selective absorbersof outgoing long wavelength radiation (Earthlight) Spectrum of IR light emitted from earth to space

  • Water Vapor Molecule (H2O)Vibrational modesH2O bendH2Ostretch

  • Carbon Dioxide Molecule (CO2)Vibrational mode (~15m)CO2 bend

  • Natural CO2 radiative forcingMakes Earth habitable

    Pre-Industrial CO2 level of ~280 ppm

    Increases surface temperature from -18C (effective temperature) to +15C

    (Water vapor is also important)

  • CO2 Band SaturationMore CO2 warms the Earth less and less10 ppm1000 ppm100 ppmNo CO2Notice the CO2 absorption band

  • CO2 and surface warming just due to radiation changes - no feedbacksAbout 1C per 100 ppm

    Pre-Industrial = 280 ppmToday = 390 ppm

    So, w/o feedbacks: ~1.2CWith feedbacks: ~3C(Feedbacks include water vapor and sea ice changes)CO2 ppmTemp (K)

  • Atmospheric CO2 CO2 has increased by about +40%Long term average growth rate is +1.4% per yearLast decade growth rate is +2.0% per year

    CO2 (ppm)

  • All Radiative Forcing factors (1750-2005)Sum = +1.6 W/m2

  • Radiative Forcing ContributionsGHGs warm (CO2, CH4, N2O)H2O (vapor) warmsTropospheric O3 warms, Strat O3 coolsHuman and natural Aerosols coolSolar irradiance warms

    Net Effect: +1.6 W/m2

    *************Global population = 6 x10^9 people * 100 kg/person = 600 x10^9 kg, or 0.6 x 10^12 kg (~0.5 Gt)**********************Prism analogy*******


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