1. The Physics and Ecology of Carbon Offsets
Dennis Baldocchi
Professor of Biometeorology
Ecosystem Sciences Division/ESPM
University of California, Berkeley
UC Merced Feb 24, 2010

2. If Papal Indulgences can save us from burning in Hell: Can Carbon Indulgences save us from Global Warming?
Alexander VI
Sixtus IV
Innocent VIII
Julius II
Leo X

3. Does Planting a Tree Really Offset your Carbon Footprint?

4. Haiti vs Dominican Republic

5. 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, and water vapor is a greenhouse gas and scarce resource in semi-arid regions, eg California

6. Issues of Concern and Take-Home Message
Trees are 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
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

7. Can we offset Carbon Growth by Planting Trees?

8. ESPM 111 Ecosystem Ecology
All Seedlings Do Not Grow to Maturity
Pine Seedlings in Finland
Old Growth Forest in Finland
ESPM 111 Ecosystem Ecology

9. Yoda’s Self Thinning Law
#N ~ Mass -3/4
Mass ~ #N -4/3
Planting trees may be a ‘feel-good’ solution, but it is not enough
self thinning will occur
Energetics of Solar Capture Drives the Metabolism of the System
Enquist et al. 1998

10. 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
ESPM 111 Ecosystem Ecology

11. 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

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

13. 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 day Growing Season
FLUXNET 2007 Database

14. Probability Distribution of Published GPP Measurements, Integrated Annually
Global GPP = 1033 * m2 = PgC/y

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

16. Probability Distribution of Published NEE Measurements, Integrated Annually

17. US accounts for about 25% of Global C emissions
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
m2/person = 3.33 ha/person
US Land Area ha
ha needed by US population to offset its C emissions Naturally!

18. 1. Carbon is Lost with Disturbance
2. Net Carbon Uptake Decline with Age
Sink
Interannual
Variability
Gap
Source
Brian Amiro 2007 AgForMet

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

20. Carbon sequestration by plantations can dry out streams
Plantations decreased stream flow by 220 mm per year globally
[Jackson, et al., 2005, Science].

21. 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

22. Land Use Affects Mass and Energy Exchange

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

24. Its not Only Carbon Exchange: Albedo Changes too with planting Forests
Get albedo data from O’Hallaran
Amiro et al 2006 AgForMet

25. Average Solar Radiation: ~95 to 190 W m-2
Should we cut down Dark Forests to Mitigate Global Warming?: UpScaling Albedo Differences Globally, part 1
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

26. Nutrient Requirements Ecosystem Sustainability
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

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

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

29. Savanna Woodland adjacent to Grassland
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

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

31. Landscape Differences On Short Time Scales, Grass ET > Forest ET
Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, 2008 31

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

33. 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

34. 5. Mean Potential Temperature differences are relatively small (0
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)

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

36. 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

37. 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

38. Theoretical Difference in Air Temperature: Grass vs Savanna
Summer Conditions

39. Temperature Difference Only Considering Albedo
Spring Conditions

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

41. Tair can vary by 3 C by
changing Ra and Rs
Tsfc can vary by 10 C
by changing Ra and Rs

42. Future 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

43. CO2 in 50 years, at Steady-State
8 GtC/yr, Anthropogenic Emissions
45% retention
8 * 50 * 0.45 = 180 GtC, integrated Flux
Each 2.19 GtC emitted causes a 1 ppm increase in Atmospheric CO2
833 ppm) = 1013 GtC, atmospheric burden
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!

44. How Does Energy Availability Compare with Energy Use?
US Energy Use: 105 EJ/year
1018J per EJ
US Population:
J/capita/year
US Land Area: km2= m2 = 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
m2 of Land Area Needed ( km2, the size of South Carolina)

46. 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