The Physics and Ecology of Mining Carbon Dioxide from the Atmosphere by Plants

1. 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

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 Trees Really Offset Our Carbon Footprint? We can Plant Trees!

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: Plants/Trees/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: Plants/Trees/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 • Plants/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. Ecosystem Transpiration is Scale-Free Transpiration is not equal to the number of trees times their average Transpiration rate Enquist et al 1998 Nature ESPM 111 Ecosystem Ecology

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

20. Where the Sunshine Is Youngryel Ryu, D. Baldocchi, + Microsoft Azure Consortium

21. Theoretical and Potential Photosynthetic Efficiencies • 8 Photons per CO2 molecule fixed • 496 kJ/mole CO2, Energetics of photosynthesis • 13%, Maximum Efficiency of sunlight to stored carbon • 9%, Ideal photosynthetic efficiency • Considering photorespiration and leaf absorptance • 2%, Typical Maximum Efficiency Observed in the field • Potential Gross Primary Productivity • 12 g/mole C * 0.02 mol C/mole quanta * Rg/2 *4.6 (mole quanta m-2 ) • 12 * 0.02 * 341/2 * 4.6e-6 * 12*3600*365=2968 gC m-2 y-1 ESPM 2 The Biosphere

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

23. 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

24. Take Home Message: GPP of CornBelt + Annual Crops << Deciduous Forest Biome + Perennial Vegetation Missed Opportunities for Harvesting the Sun Youngryel Ryu, D. Baldocchi, + Microsoft Azure Consortium

25. Few Locales have 365 day Growing Seasons, unlike Solar Panels

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

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

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

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

30. ‘…the inescapable fact is that crop production is inextricably linked to crop transpiration. To increase crop biomass production, more water must be used in transpiration…’ Sinclair et al, 1983, Bioscience

31. How Much Water is Available, through Evaporation? Youngryel Ryu, D. Baldocchi, + Microsoft Azure Consortium

32. Corn Belt has High Water Use Efficiency Youngryel Ryu, D. Baldocchi, + Microsoft Azure Consortium

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

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

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

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

37. 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!

38. 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

39. Case Study, 1: Carbon Farming to Restore Peatland

40. Vulnerable Ecosystem via Severe Land Subsidence

41. Tower and AC Hut with Tunable Diode Laser Methane Spectrometer

42. Rice Production Trumps Business as Usual

43. Rice Cultivation vs Grazed Pasture Rice Cultivation Evaporates 2X the Water of a Degraded Pasture

44. Rice Promotes Methane Production, a Greenhouse Gas 21x CO2 Unpublished data: J Hatala, D Baldocchi

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

46. 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

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

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

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

50. 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