The Physics and Ecology of Carbon Offsets

1. 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

2. Contemporary CO2 Record

3. What We are Told • Global Mean Temperature will Increase by about 2 C (3.6 F) if CO2 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 = 1015g) by Fossil Fuel Combustion and Cement Production

4. Much Confusion about: • How Much CO2 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 CO2? • Information is Needed to Guide What We should Do? Raupach, IBPG Newsletter

5. 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 = 4p R2 • Matmos = 101325 Pa 4p (6378 103 m)2/9.8 m2 s-1= • 5.3 1021 g air • Compute C in Atmosphere @ 380 ppm (380 10-6) P: atmospheric pressure pc: partial pressure CO2 mc: molecular wt of C, 12 g/mole ma: molecular wt of air, 28.96 g/mole PgC/ppm ESPM 111 Ecosystem Ecology

6. CO2 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 CO2 • 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! • 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??

7. If Papal Indulgences Saved Them from burning in Hell:Can Carbon Indulgences save Us from Global Warming? Alexander VI Sixtus IV Innocent VIII Julius II Leo X

8. Does Planting a Tree Really Offset Your Carbon Footprint?

9. 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

10. 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

11. 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

12. Can we offset Carbon Growth by Planting Trees?

13. All Seedlings Do Not Grow to Maturity Pine Seedlings in Finland Old Growth Forest in Finland http://www.helsinki.fi/~korpela/forestphotos.html ESPM 111 Ecosystem Ecology

14. 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

15. 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

16. 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 ESPM 111 Ecosystem Ecology

17. Energetics at Landscape scale is Scale Invariant • Energetics/Metabolism of the System <B> 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

18. Energy Drives Metabolism: How Much Energy is Available and Where

19. Light vs Canopy CO2 Uptake by Closed Forests and Crops Peak Light Use Efficiency, Forests: ~0.01 (A); Crops: ~0.015 (B)

20. Potential and Real Rates of Gross Carbon Uptake by Vegetation: Most Locations Never Reach Upper Potential GPP at 2% efficiency and 365 day Growing Season tropics GPP at 2% efficiency and 182.5 day Growing Season FLUXNET 2007 Database

21. Annually-Integrated Measured GPP ~ 1000 gC m-2 y-1; Peak GPP < 3500 gC m-2 y-1 Global GPP = 1033 * 110 1012 m2 = 113.6 PgC/y

22. Ecosystem Respiration (FR) Scales Tightly with Ecosystem Photosynthesis (FA), But Is with Offset by Disturbance Baldocchi, Austral J Botany, 2008

23. Net Ecosystem Carbon Exchange << GPP Probability Distribution of Published NEE Measurements, Integrated Annually Baldocchi, Austral J Botany, 2008

24. Net Carbon Exchange is a Function of Time Since Disturbance Baldocchi, Austral J Botany, 2008

25. It’s a matter of scaleA 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 1015gC = 2.0 1015gC • Per Capita Emissions, US • 2.0 1015gC/300 106 = 6.66 106gC/person • Ecosystem Service, net C uptake, above current rates • ~200 gC m-2 • Land Area Needed to uptake C emissions, per Person • 3.33 104 m2/person = 3.33 ha/person • US Land Area • 9.8 108 ha • 10.0 108 ha needed by US population to offset its C emissions Naturally!

26. All Land is Not Available or Arable: You need Water to Grow Trees! Scheffer al 2005

27. Carbon sequestration by plantations can dry out streams [Jackson, et al., 2005, Science].

28. Its not Only Carbon Exchange:Albedo, Surface Roughness and Energy Partitioning Changes with planting Forests, too

29. Forests are Darker and Possess Lower Albedos than Crops/Grasslands Deciduous Forest Crop Conifer Forest Evergreen Broadleaved Forest O’Halloran et al. NCEAS Workshop

30. Forest Albedo Changes with Stand Age Amiro et al 2006 AgForMet

31. Should we cut down Dark Forests to Mitigate Global Warming?:UpScalingAlbedo 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 CO2 • 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!

32. 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

33. Case Study on Energetics of Land Use Change: Comparative study of an Annual Grassland and Oak Savanna

34. Case Study: Savanna Woodland adjacent to Grassland • Savanna absorbs much more Radiation (3.18 GJ m-2 y-1) than • the Grassland (2.28 GJ m-2 y-1) ; DRn: 28.4 W m-2

35. 2. Grassland has much great albedo than savanna;

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

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

38. 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

39. 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)

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

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

42. 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 (Tsfc) than a bright grassland due to evaporative cooling

43. 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

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

45. 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

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

47. Tsfc can vary by 10 C by changing albedo and Rs Tair can vary by 3 C by changing albedo and Rs

48. Taircan vary by 3 C by changing Ra and Rs Tsfc can vary by 10 C by changing Ra and Rs

49. Closing Comments • 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?

50. Knobs We Can TurnFuture Carbon Emissions: Kaya Identity C Emissions = Population * (GDP/Population) * (Energy/GDP) * (C Emissions/Energy) • 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