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

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

Does Planting a Tree Really Offset your Carbon Footprint?

Haiti vs Dominican Republic

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

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

Can we offset Carbon Growth by Planting Trees?

ESPM 111 Ecosystem Ecology 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

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

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

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

Energy Drives Metabolism: How Much Energy is Available and Where

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

Probability Distribution of Published GPP Measurements, Integrated Annually Global GPP = 1033 * 110 1012 m2 = 113.6 PgC/y

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

Probability Distribution of Published NEE Measurements, Integrated Annually

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*8.0 1015 gC = 2.0 1015 gC Per Capita Emissions, US 2.0 1015 gC/300 106 = 6.66 106 gC/person Ecosystem Service, net C uptake, above current rates ~200 gC m-2 Land Area Needed to uptake C emissions, per Person 3.33 104 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!

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

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

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

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

Land Use Affects Mass and Energy Exchange

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

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

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

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

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

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

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

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 31

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

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 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)

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 (Tsfc) 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

Theoretical Difference in Air Temperature: Grass vs Savanna Summer Conditions

Temperature Difference Only Considering Albedo Spring Conditions

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

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

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

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 (@380 ppm) + 180 = 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!

How Does Energy Availability Compare with Energy Use? US Energy Use: 105 EJ/year 1018J per EJ US Population: 300 106 3.5 1011 J/capita/year US Land Area: 9.8 106 km2=9.8 1012 m2 = 9.8 108 ha Energy Use per unit area: 1.07 107 J m-2 Potential, Incident Solar Energy: 6.47 109 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 1010 m2 of Land Area Needed (8.11 105 km2, the size of South Carolina)

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