Presentation on theme: "The Physics and Ecology of Carbon Offsets Dennis Baldocchi Professor of Biometeorology Ecosystem Sciences Division/ESPM University of California, Berkeley."— Presentation transcript:
The Physics and Ecology of Carbon Offsets Dennis Baldocchi Professor of Biometeorology Ecosystem Sciences Division/ESPM University of California, Berkeley COAS Frontiers Seminar Series Oregon State, June, 2010
Contemporary CO 2 Record
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 = g) by Fossil Fuel Combustion and Cement Production
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?
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 = Pa 4 ( m) 2 /9.8 m 2 s -1 = – g air Compute C in 380 ppm ( ) 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, g/mole
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 ppm) = 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! We’ll Reach this Threshold in << 50 years as Current Rates of C emissions Continue to Grow via growth in population and economy What Can We Do??
If Papal Indulgences Saved Them from burning in Hell: Can Carbon Indulgences save Us from Global Warming? Sixtus IV Alexander VI Innocent VIII Julius II Leo X
Does Planting a Tree Really Offset Your Carbon Footprint?
Ecological Engineering 101 The Answer Depends on the Specifics of the Question… Be Wary of Unintended Consequences –A Ubiquitous Feature of Complex, Non-Linear Systems with many Feedbacks…like Ecosystems! We often need to manage an Ecosystem for more than one service, some which may have counter-acting effects on the original goal
Working Hypotheses H1: Forests Can Mitigate Global Warming –Forests are effective and long-term Carbon Sinks –Land-use change (via afforestation/reforestation) can help offset greenhouse gas emissions and mitigate global warming –Forests transpire water effectively, producing clouds, rainfall and a lower planetary albedo H2: Forests Contribute to Global Warming –Forests are optically dark and absorb more energy than short vegetation –Forests convect more sensible heat into the atmosphere than grasslands, warming the atmosphere Landuse change (more forests) can help promote global warming –Forests use more water than other vegetation water vapor is a greenhouse gas It is a scarce resource in semi-arid regions, eg California
Issues of Concern and Take-Home Message Trees May Be Inefficient Solar Collectors –Much vegetation operates less than ½ of the year and is a solar collector with less than 2% efficiency –The Ability of Forests to sequester Carbon declines with stand age –Solar panels work 365 days per year and have an efficiency of 20%+ Ecological Scaling Laws Must be Obeyed when Planting Trees and Cultivating Plantations –There is only So Much Solar Energy Available to a unit Area of Land! –Self-Thinning Occurs with Time –Mass scales with the -4/3 power of tree density There Must be Available Land and Water –You need more than 500 mm of rain per year to grow Trees –Best and Moistest Land is Already Vegetated –New Forested Lands needs to take up More Carbon than current land use –It’s a matter of scale, A lot of ‘trees’ (more than the US land area) is needed to be planted to offset our profligate carbon emissions There are Energetic and Environmental Costs to soil, water, air by land use change –Forests are Darker than Grasslands, so they Absorb More Energy –Changes in Surface Roughness and Conductance and PBL Feedbacks on Energy Exchange and Evaporative cooling may Dampen Albedo Effects –Forest Albedo changes with stand age –Forests Emit volatile organic carbon compounds, ozone precursors –Forests reduce Watershed Runoff and Soil Erosion Societal/Ethical Costs and Issues –Land for Food vs for Carbon and Energy –Energy is needed to produce, transport and transform biomass into energy –Better to Reduce C Emissions than Increase C Sinks
Can we offset Carbon Growth by Planting Trees?
ESPM 111 Ecosystem Ecology Pine Seedlings in Finland Old Growth Forest in Finland All Seedlings Do Not Grow to Maturity
Yoda’s Self Thinning Law Energetics of Solar Capture by the Landscape Drives the Metabolism of the System Only So-Much Sunlight Available to a unit area of Land Planting trees may be a ‘feel-good’ solution, but it is not enough –self thinning will occur so only a fraction of trees will grow to maturity
You can sustain a lot of little trees or a few Big Trees, but not a lot of Big Trees! #N ~ Mass -3/4 Mass ~ #N -4/3 Enquist et al. 1998, Nature
ESPM 111 Ecosystem Ecology Kleiber’s Law Metabolic rate (B) of an organism scales to the 3/4 power of its mass (M) The Metabolic Energy needed to Sustain an organism INCREASES with Mass, to the ¾ power
Energetics at Landscape scale is Scale Invariant Energetics/Metabolism of the System is weighted by the sum of the product of the Energetics of class, i, times the number of individuals in this class, N Energy/Metabolism, B, scales with Mass, M, to the ¾ power, Kleiber’s Law Number of Individuals scales with Mass to the -3/4 power, modified Yoda’s Law Energy/Metabolism of the System is scale invariant with Mass, exponent equals zero
Energy Drives Metabolism: How Much Energy is Available and Where
Peak Light Use Efficiency, Forests: ~0.01 (A); Crops: ~0.015 (B) Light vs Canopy CO 2 Uptake by Closed Forests and Crops
FLUXNET 2007 Database GPP at 2% efficiency and 365 day Growing Season Potential and Real Rates of Gross Carbon Uptake by Vegetation: Most Locations Never Reach Upper Potential tropics GPP at 2% efficiency and day Growing Season
Global GPP = 1033 * m 2 = PgC/y Annually-Integrated Measured GPP ~ 1000 gC m-2 y-1; Peak GPP < 3500 gC m -2 y-1
Baldocchi, Austral J Botany, 2008 Ecosystem Respiration (F R ) Scales Tightly with Ecosystem Photosynthesis (F A ), But Is with Offset by Disturbance
Probability Distribution of Published NEE Measurements, Integrated Annually Baldocchi, Austral J Botany, 2008 Net Ecosystem Carbon Exchange << GPP
Net Carbon Exchange is a Function of Time Since Disturbance Baldocchi, Austral J Botany, 2008
It’s 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* gC = gC Per Capita Emissions, US – gC/ = gC/person Ecosystem Service, net C uptake, above current rates –~200 gC m -2 Land Area Needed to uptake C emissions, per Person – m 2 /person = 3.33 ha/person US Land Area – ha – ha needed by US population to offset its C emissions Naturally!
All Land is Not Available or Arable: You need Water to Grow Trees! Scheffer al 2005
Carbon sequestration by plantations can dry out streams [Jackson, et al., 2005, Science].
Its not Only Carbon Exchange: Albedo, Surface Roughness and Energy Partitioning Changes with planting Forests, too
O’Halloran et al. NCEAS Workshop Forests are Darker and Possess Lower Albedos than Crops/Grasslands Crop Deciduous Forest Conifer Forest Evergreen Broadleaved Forest
Amiro et al 2006 AgForMet Forest Albedo Changes with Stand Age
Should we cut down Dark Forests to Mitigate Global Warming?: UpScaling Albedo Differences Globally: Devil’s Advocate Average Solar Radiation: ~95 to 190 W m -2 Land area: ~30% of Earth’s Surface Tropical, Temperate and Boreal Forests: 40% of land Forest albedo (10 to 15%) to Grassland albedo (20%) Area-weighted change in Net Solar Radiation: 0.8 W m -2 –Smaller than the 4 W m -2 forcing by 2x CO 2 –Ignores role of forests on planetary albedo, as conduits of water vapor that form clouds and reflect light –Discounts Ecological Services provided by Forests I Argue that the Environmental Costs Far Outweigh the Climate Benefits: Don’t Cut the Forests!
Other Complications associated with Reliance on Forest/Carbon Sequestration Fire Nutrient Requirements Ecosystem Sustainability Deleterious effects of Ozone, Droughts and Heat Stress Length of Growing Season Ecosystem Services –Habitat, Soil Erosion Prevention, Biodiversity
Case Study on Energetics of Land Use Change: Comparative study of an Annual Grassland and Oak Savanna
Case Study: Savanna Woodland adjacent to Grassland 1.Savanna absorbs much more Radiation (3.18 GJ m -2 y -1 ) than the Grassland (2.28 GJ m -2 y -1 ) ; Rn: 28.4 W m -2
2. Grassland has much great albedo than savanna;
Landscape Differences On Short Time Scales, Grass ET > Forest ET Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, 2008
Role of Land Use on ET: On Annual Time Scale, Forest ET > Grass ET Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, 2008
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
5. Mean Potential Temperature differences are relatively small (0.84 C; grass: vs savanna: K); despite large differences in Energy Fluxes--albeit the Darker vegetation is Warmer Compare to Greenhouse Sensitivity ~2-4 K/(4 W m -2 )
Landscape Modification of Energy Exchange in Semi-Arid Regions: Theoretical Analysis with a couple Surface Energy Balance-PBL Model
Conceptual Diagram of PBL Interactions H and LE: Analytical/Quadratic version of Penman-Monteith Equation
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
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
Temperature Difference Only Considering Albedo Spring Conditions, Both Systems Green, Low Rc
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
And Smaller Temperature Difference considering PBL, Surface Roughness (R a ) and albedo….!! Summer Conditions Grass Dead, Trees Transpiring, Different Rc and Ra
T sfc can vary by 10 C by changing albedo and Rs T air can vary by 3 C by changing albedo and Rs
T air can vary by 3 C by changing Ra and Rs T sfc can vary by 10 C by changing Ra and Rs
Are Ecological Solutions to Mitigating Global Warming a Band-Aid? Do they Buy us Time? Or, do they give us a False Sense of Security to Continue doing Nothing, or Little? Will They be Permanent? Will They Engender Unexpected Consequences? Closing Comments
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)
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, 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
Concluding Issues to Consider Vegetation operates less than ½ 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
How Does Energy Availability Compare with Energy Use? US Energy Use: 105 EJ/year –10 18 J per EJ –US Population: – J/capita/year US Land Area: km 2 = m 2 = ha Energy Use per unit area: J m -2 Potential, Incident Solar Energy: 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 – m 2 of Land Area Needed ( km 2, the size of South Carolina)
NASA GISS CO2, ppm + 2C Case
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
Should we cut down dark forests to Mitigate Global Warming?: UpScaling Albedo Differences Globally, part 2