Th S i d E l f C b Off tThe Science and Ecology of Carbon Offsets

D i B ld hiDennis BaldocchiEcosystem Sciences Division/ESPM

University of California, Berkeley

2007 Max Planck Institute for Biogeochemistry, Jena

If Papal Indulgences can save us from burning in Hell:C C b I d l S l Gl b l W i ?Can Carbon Indulgences Solve Global Warming?

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 WaterBest Land is Vegetated and Ne Land needs to take p More Carbon– 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– Emission of volatile organic carbon compounds, ozone precursors– Changes in 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

Future Carbon Emissions: Kaya Identity

C Emissions = Population * (GDP/Population) * (Energy/GDP) * (Emissions/Energy)

•PopulationP l ti t d t t 9 10 billi b

(Energy/GDP) (Emissions/Energy)

•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•Rapid economic growth in India and China

•Energy intensity, the amount of energy consumed per unit of GDP.

•Can decrease with efficient technologyCan decrease with efficient technology•Carbon intensity, the mass of carbon emitted per unit of energy consumed.

•Can decrease with alternative energygy

CO2 in 50 years, at Steady-State2 y , y

• 8 GtC/yr Anthropogenic Emissions8 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• Each 2.19 GtC emitted causes a 1 ppm increase in

Atmospheric CO2• 833 (@380 ppm) + 180 = 1013 GtC, atmospheric

burdenburden• 462 ppm with BAU in 50 years

– 1.65 times pre-industrial level of 280 ppmBAU C emissions will be 16 to 20 GtC/yr in 2050• 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 cannot Afford Steady-State or BAU:We Must Consider the Integrated Path of Carbon EmissionsWe Must Consider the Integrated Path of Carbon Emissions

IPCC

Can we offset Carbon Growth by Planting Trees?Ca e o set Ca bo G o t by a t g ees

Yoda’s Self Thinning LawYoda s Self Thinning Law

• Planting trees is may be a ‘feel good’ solution but itfeel-good solution, but it is not enough– self thinning will occur

• Energetics of Solar• Energetics of Solar Capture Drives the Metabolism of the System

Enquist et al. 1998

Metabolic Scaling of Populations of g pOrganisms

Energy flux of a population per unit area (Bt) is scaleinvariant with mass of the system (M):

B N B M M M= ∝ =−3 4 3 4 0/ /B N B M M MT i i i i= ∝ =

All t l (2002)Allen et al. (2002)

Energy Drives Metabolism:How Much Energy is Available and Where

FLUXNET database

How Much Energy is Available and Where

8000

J m

-2 y

-1) 6000

Rg

(M

2000

4000

0 10 20 30 40 50 60 70 80 900

Latitude

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

How Does Energy Availability Compare with Energy Use?gy y p gy

• US Energy Use: 105 EJ/yeargy y– 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• 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, CAIone, CA• A solar system (solar panels, biomass) must be 0.1% efficient,

working year round, over the entire surface area of the US to capture the energy we use to offset fossil fuel consumptionAssuming 20% efficient solar system• Assuming 20% efficient solar system– 8.11 1010 m2 of Land Area Needed (8.11 105 km2, the size of South

Carolina)

Adler et al 2007 Ecol Appl

GPP has a Cost, in terms of Ecosystem Respiration

We need to Consider Net, not Gross, CO2 Exchange:, , 2 g

Fluxnet 2007 Database180 Sites across 600+ measurement-years

It’s a matter of scaleIt s a matter of scaleA lot of ‘trees’ need to be planted to offset our profligate carbon use

US t f b t 25% f Gl b l C i i• 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-2200 gC m

• Land Area Needed to uptake C emissions, per Person– 3.33 104 m2/person = 3.33 ha/person

US L d A• US Land Area – 9.8 108 ha– 10.0 108 ha needed by US population to offset its C emissions

N t ll !Naturally!

1. Carbon is Lost with Disturbance

2. Net Carbon Uptake Decline with Age

600 Sinkm

-2 y

-1)

200

400 OASOBSOJPNOBS

Interannual Variability

Flux

(g C

m

-200

0

NOBSHJP94F89F98HBS00WP39Gap

Car

bon

F

-600

-400

200DF49HDF88HDF00HJP02EOBSOMW

Source

St d A ( )0 20 40 60 80 100 120 140 160 180

-800

600HJP75BF67

Stand Age (years)Brian Amiro 2007 AgForMet

All Land is Not Available or Arable:Y d W t t G T !You need Water to Grow Trees!

Scheffer al 2005

Leaf Area Index scales with:Precipitation, Evaporation and Nutrition

10

various functional types:Baldocchi and Meyers (1998)

p , p

y ( )savanna:Eamus et al. 2001

LAI

1b[0] -0.785b[1] 0.925r ² 0.722

[N]ppt/Eeq

0.1 1 10 1000.1

Carbon sequestration by plantations can dry out streamsq y p y

[Jackson, et al., 2005, Science].

Other Complications associated with li C b t tireliance on Carbon sequestration

• FireFire• Nutrient Requirements

S il E i• Soil Erosion• Ecosystem Sustainability• Deleterious effects of Ozone, Droughts

and Heat Stress• Length of Growing Season

Energetics of Greenhouse Gas Forcing:Doubling CO2 provides a 4 Wm-2 energy increase, Worldwide

Myhre et al 1998 GRL

Its not Only Carbon Exchange:Alb d Ch t ith l ti F tAlbedo Changes too with planting Forests

bedo

0.15

0.20AKMBSKSOA

ertim

e A

lb

0.10

Sum

me

0.05

Time since disturbance (years)0 25 50 75 100 125 150 175

0.00

Time since disturbance (years)

Amiro et al 2006 AgForMet

Randerson et al 2006 Science

Should we cut down dark forests to Mitigate Global Warming?:UpScaling Albedo Differences Globally part 1UpScaling 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 weight change in incoming Solar Radiation: 0 8 W• Area weight change in incoming 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 waterIgnores role of forests on planetary albedo, as conduits of water

vapor that form clouds and reflect light

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

km2 MJ m-2 y-1 albedo albedoarea rad change wt value

tropical 1.75E+07 6.00E+09 0.05 0.15 5.25E+15temperate 1.00E+07 5.00E+09 0.05 0.15 2.50E+15boreal 1.30E+07 4.00E+09 0.1 0.1 5.20E+15

Earth 5.10E+08 sum 1.30E+16ave time/land 0.805 W m-2

Case Study:

Energetics of a Grassland d O k Sand Oak Savanna

Measurements and Model

Case Study:Savanna Woodland adjacent to Grassland

35

Solar RadiationNet Radiation, GrasslandNet Radiation, Savanna

Savanna Woodland adjacent to Grassland

2006

m-2

d-1

)

25

30

ux D

ensi

ty (M

J

15

20

Ene

rgy

Flu

5

10

Day

0 50 100 150 200 250 300 3500

1. Savanna absorbs much more Radiation than grassland

0.30Grassland

2006

0.20

0.25

GrasslandSavanna

PA

R A

lbed

o

0 10

0.15

0.05

0.10

Day

0 50 100 150 200 250 300 3500.00

2. Grassland has much great albedo than savanna

2006

m-2

d-1

)

10

12GrasslandSavanna 2006

m-2

d-1

)

12

14GrasslandSavanna

at F

lux

Den

sity

(MJ

m

4

6

8

eat F

lux

Den

sity

(MJ

6

8

10

0 50 100 150 200 250 300 350

Late

nt H

ea

0

2

4

0 50 100 150 200 250 300 350

Sen

sibl

e H

e

0

2

4

Day Day

3. Savanna evaporates more, but it also injects more sensible heat into the t hatmosphere

2006

2006

C)

30

40GrasslandSavanna

2006

30

35

40

Coefficients:b[0] 0.419b[1] 1.011r ² 0.952

Air

Tem

pera

ture

(C

20

Tair,

Sav

anna

10

15

20

25

Day

0 50 100 150 200 250 300 3500

10

Tair, Grassland

0 5 10 15 20 25 30 35 400

5

10

Day

4 But air temperature differences are small (15 7 vs 16 4

,

4. But air temperature differences are small (15.7 vs 16.4 C) despite large differences in Energy Fluxes

Annual budget of energy fluxes

EF: 0.23Ω: 0.16

EF: 0.29Ω: 0.27

6.6 GJ/m2/yr 6.6 GJ/m2/yr

Gs: 3.42 mm/secGa: 50.64 mm/secSWC at surface: 0.19

Gs: 3.95 mm/secGa: 25.14 mm/secSWC at surface: 0.12

1.93 GJ/m2/yr

H

0.97 GJ/m2/yr

LE

1.45 GJ/m2/yr

H

0.75 GJ/m2/yr

LERnet3.18 GJ/m2/yr

Rnet2.28 GJ/m2/yr

Tonzi site Vaira site

-0.01 GJ/m2/yr 0.05 GJ/m2/yr

G G

ET-PBL O ak-G rass Savanna Land U se

e 300

310

Th E ti f

T su

rfac

e

290

300

albedo = 0.3; R c=2560 s /malbedo = 0.15; R c = 320 s /m

•The Energetics of afforestation/deforestation is complicated

Tim e

6 8 10 12 14 16 18 20280

800

•Forests have a low albedo, are darker and absorb more energy

(W m

-2)

400

600

absorb more energy

•But, Ironically the darker forest maybe cooler than a

Rne

t

0

200

albedo = 0 .3; R c=2560 s /malbedo = 0 .15; R c = 320 s/m

ybright grassland due to evaporative cooling

T im e

6 8 10 12 14 16 18 20

250ET-PBL Oak-Grass Savanna Land Use

F t T i

W m

-2) 150

200

•Forests Transpire effectively, causing evaporative cooling, which in humid regions may form

LE (W

50

100 albedo = 0.3; Rc=2560 s/malbedo = 0.15; Rc = 320 s/m

in humid regions may form clouds and reduce planetary albedo

Time

6 8 10 12 14 16 18 200

500

m-2

) 300

400

H (W

m

100

200

albedo = 0.3; Rc=2560 s/malbedo = 0.15; Rc = 320 s/mAxel Kleidon

Time

6 8 10 12 14 16 18 200

PBL feedbacks affect Tair

310

300

305PBL Feedbackno PBL feedbackair temperature with feedback

T sfc (o

K)

290

295

285

290

Time

6 8 10 12 14 16 18280

Fig. 1. Simulated temporal evolution of atmospheric CO2 (Upper) and 10-year running mean of surface temperature change (Lower) for the period 2000-2150 in the Standard and deforestation experiments

Copyright ©2007 by the National Academy of Sciences

Bala, G. et al. (2007) Proc. Natl. Acad. Sci. USA 104, 6550-6555

Fig. 4. Simulated spatial pattern differences (Global minus Standard) in the decade centered on year 2100 for the surface albedo (fraction) (A), evapotranspiration rates (cm/day) (B), cloudiness (fraction)

(C), and planetary albedo (fraction) (D) differences(C), and planetary albedo (fraction) (D) differences

Bala, G. et al. (2007) Proc. Natl. Acad. Sci. USA 104, 6550-6555

Copyright ©2007 by the National Academy of Sciences

• “Finally, we must bear in mind that preservation of ecosystems is a primary goal of preventing global warming, and the destruction of ecosystems to prevent global warming would be a counterproductive and perverse strategy. p gy

• Therefore, the cooling that could potentially arise from deforestation outside the tropics should not necessarily be viewed as a strategy for mitigating climate change because, apart from their potential climatic role forests are valuable in many aspectsclimatic role, forests are valuable in many aspects.

• They provide natural habitat to plants and animals, preserve the biodiversity of natural ecosystems, produce economically valuable timber and firewood, protect watersheds through prevention of soil erosion and indirectly prevent ocean acidification by reducingerosion, and indirectly prevent ocean acidification by reducing atmospheric CO2.

• In planning responses to global challenges, therefore, it is important to pursue broad goals and to avoid narrow criteria that may lead to

i t ll h f l ”environmentally harmful consequences”. • Bala et al 2007 PNAS

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 WaterBest Land is Vegetated and Ne Land needs to take p More Carbon– 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– 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– Role of forests for habitat and resources

Contemporary Radiative Forcing

Hansen et al 2005 JGRHansen et al 2005 JGR

Energy fluxesEnergy fluxes

• Potential Energy Production by EnergyPotential Energy Production by Energy Crops, 2025

2 22 EJ yr-1– 2-22 EJ yr 1

– Offsets 100-2070 Mt CO20 564 Gt C/yr-1– 0.564 Gt C/yr-1

Sims et al 2006 Global Change Biology

You Need Water to Grow Trees!You Need Water to Grow Trees!

10

various functional types:Baldocchi and Meyers (1998)savanna:Eamus et al. 2001

LAI

1b[0] -0.785b[1] 0.925r ² 0.722

[N]ppt/E

0.1 1 10 1000.1

[N]ppt/Eeq

Chapin et al 2005 Science