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The Physics and Ecology of Mining Carbon Dioxide from the Atmosphere by Plants Dennis Baldocchi Professor of Biometeorology Ecosystem Sciences Division/ESPM University of California, Berkeley University of Illinois, Feb, 2011

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Contemporary CO 2 Record

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What We are Told Global Mean Temperature will Increase by about 2 C (3.6 F) if CO 2 Increases to 550 ppm by 2100 Current [CO2] is over 380 ppm, a 100 ppm increase over pre-industrial levels We are releasing more than 8 PgC/y (1Pg = 10 15 g) by Fossil Fuel Combustion and Cement Production

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Raupach, IBPG Newsletter Much Confusion about: How Much CO 2 We can Emit to Prevent Certain Temperature Increase? How Fast Must We Reduce C Emissions and to What Extent? How Do We Convert Information on Emissions from PgC/y to Atmospheric Pool Size in terms of ppm CO 2 ? Information is Needed to Guide What We should Do?

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ESPM 111 Ecosystem Ecology How much is C in the Air?: Resolving Differences between ppm and PgC? Mass of Atmosphere F=Pressure x Area=Mass x Acceleration=Mass x g Surface Area of the Globe = 4 R 2 M atmos = 101325 Pa 4 (6378 10 3 m) 2 /9.8 m 2 s -1 = 5.3 10 21 g air Compute C in Atmosphere @ 380 ppm (380 10 -6 ) PgC/ppm P: atmospheric pressure p c : partial pressure CO2 m c : molecular wt of C, 12 g/mole m a : molecular wt of air, 28.96 g/mole

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CO 2 in 50 years, at Steady-State 8 GtC/yr, Anthropogenic Emissions 45% retention; air-borne fraction 8 * 50 * 0.45 = 180 GtC, Net C Fossil Fuel Burden Each 2.19 GtC emitted causes a 1 ppm increase in Atmospheric CO 2 833 (@380 ppm) + 180 = 1013 GtC, atmospheric burden 450 ppm is thought to be Threshold to Keep Global Warming Below +2.0 C (3.6 F). 462 ppm with BAU in 50 years 1.65 times pre-industrial level of 280 ppm BAU C emissions will be ~ 16 to 20 GtC/yr in 2050 To stay under 462 ppm the world can only emit < 400 GtC of carbon, gross, into the atmosphere! Well Reach this Threshold in

Landscape Differences On Short Time Scales, Grass ET > Forest ET Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, 2008

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Role of Land Use on ET: On Annual Time Scale, Forest ET > Grass ET Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, 2008

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4a. U* of tall, rough Savanna >> short, smooth Grassland 4b. Savanna injects more Sensible Heat into the atmosphere because it has more Available Energy and it is Aerodynamically Rougher

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5. Mean Potential Temperature differences are relatively small (0.84 C; grass: 290.72 vs savanna: 291.56 K); despite large differences in Energy Fluxes--albeit the Darker vegetation is Warmer Compare to Greenhouse Sensitivity ~2-4 K/(4 W m -2 )

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Landscape Modification of Energy Exchange in Semi-Arid Regions: Theoretical Analysis with a couple Surface Energy Balance-PBL Model

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Conceptual Diagram of PBL Interactions H and LE: Analytical/Quadratic version of Penman-Monteith Equation

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The Energetics of afforestation/deforestation is complicated Forests have a low albedo, are darker and absorb more energy But, Ironically the darker forest maybe cooler (T sfc ) than a bright grassland due to evaporative cooling

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Forests Transpire effectively, causing evaporative cooling, which in humid regions may form clouds and increase planetary albedo Due to differences in Available energy, differences in H are smaller than LE Axel Kleidon

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Temperature Difference Only Considering Albedo Spring Conditions, Both Systems Green, Low Rc

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Theoretical Difference in Air Temperature: Considering differences in Albedo and Surface Resistances Savanna is Warmer than Grassland Summer Conditions, Grass Dead, Trees Transpiring Different Albedo and Rc

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And Smaller Temperature Difference considering PBL, Surface Roughness (R a ) and albedo.!! Summer Conditions Grass Dead, Trees Transpiring, Different Rc and Ra

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Rectifier Effect Prevents Strong Drawdowns in CO 2

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T sfc can vary by 10 C by changing albedo and Rs T air can vary by 3 C by changing albedo and Rs

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T air can vary by 3 C by changing Ra and Rs T sfc can vary by 10 C by changing Ra and Rs

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Are Ecological Solutions to Mitigating Global Warming a Band-Aid? Are they Necessary because they Buy us Time? Or, do they give Us, as a society, a False Sense of Security to Continue doing Nothing, or Little? Will They, the Carbon Sinks, be Permanent? Will Engineering the Environment for Carbon Capture Alone Engender Unexpected Consequences on the Climate System? Closing Comments

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Knobs We Can Turn Future Carbon Emissions: Kaya Identity Population Population expected to grow to ~9-10 billion by 2050 Per capita GDP, a measure of the standard of living Rapid economic growth in India and China Energy intensity, the amount of energy consumed per unit of GDP. Can decrease with efficient technology Carbon intensity, the mass of carbon emitted per unit of energy consumed. Can decrease with alternative energy C Emissions = Population * (GDP/Population) * (Energy/GDP) * (C Emissions/Energy)

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Quo Vadis? Sure we'll live, we'll survive, it just might not be a very nice world., DDB, KTVU Interview, April 18, 2010 We must Reduce Carbon Emissions Immediately and Dramatically, rather than looking for Ecological Band Aids To Remove our Dependence on Fossil Fuel, We Will Need to Re- Design Society which Depends on Energy for All its Work This will involve Redesigning Energy Production and Infrastructure, Housing, Transportation Soon! At the most radical stage, it may even require major Economic (e.g. Internalizing Externalities) and Government Changes and Major Reductions in Population Growth Unintended Consequences include Poverty, Famine, and Conflict whether we make Changes, or Not Vested Interests are Reluctant to Change Energy/Cost Savings and Efficiencies Could be Positive

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Concluding Issues to Consider Vegetation operates less than of the year and is a solar collector with less than 2% efficiency Solar panels work 365 days per year and have an efficiency of 20%+ Ecological Scaling Laws are associated with Planting Trees Mass scales with the -4/3 power of tree density Available Land and Water Best Land is Vegetated and New Land needs to take up More Carbon than current land You need more than 500 mm of rain per year to grow Trees The ability of Forests to sequester Carbon declines with stand age There are Energetics and Environmental Costs to soil, water, air and land use change Changes in Albedo and surface energy fluxes Emission of volatile organic carbon compounds, ozone precursors Changes in Watershed Runoff and Soil Erosion Societal/Ethical Costs and Issues Food for Carbon and Energy Energy is needed to produce, transport and transform biomass into energy Forests play positive roles for habitat, biodiversity, carbon storehouses and resources

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How Does Energy Availability Compare with Energy Use? US Energy Use: 105 EJ/year 10 18 J per EJ US Population: 300 10 6 3.5 10 11 J/capita/year US Land Area: 9.8 10 6 km 2 =9.8 10 12 m 2 = 9.8 10 8 ha Energy Use per unit area: 1.07 10 7 J m -2 Potential, Incident Solar Energy: 6.47 10 9 J m -2 Ione, CA A solar system (solar panels, biomass) must be at least 0.1% efficient, working year round, over the entire surface area of the US to capture the energy we use to offset fossil fuel consumption Assuming 20% efficient solar system 8.11 10 10 m 2 of Land Area Needed (8.11 10 5 km 2, the size of South Carolina)

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NASA GISS CO2, ppm + 2C Case

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Working Hypotheses H1: Forests have a Negative Feedback on Global Warming Forests are effective and long-term Carbon Sinks Landuse change (more forests) can help offset greenhouse gas emissions and mitigate global warming H2: Forests have a Positive Feedback on Global Warming Forests are optically dark and Absorb more Energy Forests have a relatively large Bowen ratio (H/LE) and convect more sensible heat into the atmosphere Landuse change (more forests) can help promote global warming

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Should we cut down dark forests to Mitigate Global Warming?: UpScaling Albedo Differences Globally, part 2

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Global GPP = 1033 * 110 10 12 m 2 = 113.6 PgC/y Annually-Integrated Measured GPP ~ 1000 gC m-2 y-1; Peak GPP < 3500 gC m -2 y-1

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Its a matter of scale A lot of trees need to be planted to offset our profligate carbon use US accounts for about 25% of Global C emissions 0.25*8.0 10 15 gC = 2.0 10 15 gC Per Capita Emissions, US 2.0 10 15 gC/300 10 6 = 6.66 10 6 gC/person Ecosystem Service, net C uptake, above current rates ~200 gC m -2 Land Area Needed to uptake C emissions, per Person 3.33 10 4 m 2 /person = 3.33 ha/person US Land Area 9.8 10 8 ha 10.0 10 8 ha needed by US population to offset its C emissions Naturally!