NDVI June, 2009

Mid-latitude Afforestation: Consequences for General Circulation and Tropical Precipitation

1Harvard University, Organismic and Evolutionary Biology Dept. & Sustainability Science Prgm., Harvard Kennedy School2 University of California Berkeley, Dept. Earth & Planetary Science3 University of California Berkeley, Dept. of Geography

Abigail Swann1, Inez Fung2, John Chiang3

Land Model Working Group Meeting, March15th, 2011

Mid Latitude Ecosystems

NDVI June, 2009

model: National Center for Atmospheric Research Community Climate ModelAtmosphere: CAM 3.0, Land:CLM 3.5, run w/ CASA’ (biogeochemistry)Resolution: T42 L26Ocean: Slab Ocean Model

model spin-up: Land and carbon pools are set to equilibrium values from a long control run with fixed observed SST.

CO2 held fixed at 355ppm for all present day runs

equilibrium experiments: runs are 120 years, results averaged over 100 years.

Global Climate Model Details

Percent of gridcell afforested

0 12.5 25 37.5 50 62.5 75 87.5 100% of gridcellTotal area converted = 2.1 x 107 km2

Crops and C3 grass ⇒ Broadleaf Decid. Trees

Swann et al., in review

Mid Latitude Afforestation

NDVI June, 2009

Consequences of expanding deciduous tree cover in mid latitudes?

a. Climate response to afforestationb. Tropical circulation responsec. Implications for climate management

Surface Temp. Increases with Mid Latitude Trees

Kelvin

annual mean

K

Swann et al., in review

Trees

Trees Lower Albedo ⇒ More Absorbed Solar S

W N

et F

lux (

Wm

)

Latitude (deg)

Clear Sky Net Short Wave Flux at the Surface

DJF

MAM

JJA

SON

Swann et al., in review

Trees

Trees Lower Albedo ⇒ More Absorbed Solar

Sea Ice Loss

SW

Net F

lux (

Wm

)

Latitude (deg)

Clear Sky Net Short Wave Flux at the Surface

DJF

MAM

JJA

SON

Swann et al., in review

Sensible Heat

Short Wave

Latent Heat

Long Wave

Terrestrial Surface Energy Budget

Atmospheric Water Supply Gap

1− ET

PET

Measures the inability of the surface to meet the water demands of the atmosphere.

Widening Gap

Narrowing Gap∆(1− ET

PET) < 0

∆(1− ET

PET) > 0

Water Supply Gap

WET DRY

JJA

Swann et al., in review

Sensible Heat

Short Wave

Latent Heat

Long Wave

Terrestrial Surface Energy Budget

Sensible Heat removes absorbed Short Wave

5−12−20101 2 3 4 5 6 7 8 9 10 11 12

−0.02

0

0.02

0.04

0.06

0.08

Month

Δ T

herm

al R

atio

Climatology of ΔThermal Ratio

ΔV−IO+/− 1 σ

Short Wave

Sens

ible

Hea

tMid Latitiude Afforested points, JJA

Solar Absorbed at the Surface (Wm )

Sensib

le H

eat F

lux (

Wm

)

Swann et al., in review

Sensible Heat removes absorbed Short Wave

5−12−20101 2 3 4 5 6 7 8 9 10 11 12

−0.02

0

0.02

0.04

0.06

0.08

Month

Δ T

herm

al R

atio

Climatology of ΔThermal Ratio

ΔV−IO+/− 1 σ

Short Wave

Sens

ible

Hea

tMid Latitiude Afforested points, JJA

Solar Absorbed at the Surface (Wm )

Sensib

le H

eat F

lux (

Wm

)1:1 line

Swann et al., in review

Latent heat is curtailed by water limitation

Sensible heat removes most of the extra energy

Temperature increases most where water is limited

Mid Latitude Afforestation

dry ⇒ hot

Latent heat is curtailed by water limitation

Sensible heat removes most of the extra energy

Temperature increases most where water is limited

Mid Latitude Afforestation

dry ⇒ hot

⇒ soil moisture controls

the surface temperature response

NDVI June, 2009

1. Climate response to Forests2. Tropical Circulation and Precipitation3. Implications for climate management

Mid Latitude Afforestation

mm/day

Mid Latitude Trees modify Tropical Precipitation

mm/day

annual mean

WETDRYSwann et al., in review

mm/day

mm/dayWETDRY

mm/day

annual mean

Mid Latitude Trees modify Tropical Precipitation

Swann et al., in review

Hadley Circulation Streamfunction

ERA-40 Atlas0

0

0

0

0

00

0

0

0

0

0

0

00

00

0

-50

-50

-50

-50

-10

-10

-10

-10

-10

-10

-10

-10

-10

-10

-10

55

5

5

5

5

5

5

5

5

5

30

30

3030

3030

1000

900

800

700

600

500

400

300

200

100

80ON 60ON 40ON 20ON 0O 20OS 40OS 60OS 80OS

Annual mean

-300-250-200-150-100-75-50-30-20-10-5

Pre

ssur

e (h

Pa)

Mean meridional streamfunction109 kg/sec

51020305075100150200250300

NORTH SOUTH

Winter Cell Does the Transport0

0

00

0

0

0

0

0

0

0

0

00

0

0

00

-10

-10

-10

-10

-10

-10

-10

-10

-10

5

5

5

5

5

5

5

5

5

5

5

30

30

30

30

30

30

30

100

100

100

100

1000

900

800

700

600

500

400

300

200

100

80ON 60ON 40ON 20ON 0O 20OS 40OS 60OS 80OS

December-February

-300-250-200-150-100-75-50-30-20-10-5

Pre

ssur

e (h

Pa)

Mean meridional streamfunction

109 kg/sec

51020305075100150200250300

0

00

0

0

0

0

0

0

0

0

0

0

00

-150

-150

-50

-50

-50

-50

-10

-10

-10

-10

-10

-10

-10

-10

-10

-10

-10

5

5

5

5

5

5

5

5 30

30

1000

900

800

700

600

500

400

300

200

100

80ON 60ON 40ON 20ON 0O 20OS 40OS 60OS 80OS

June-August

-300-250-200-150-100-75-50-30-20-10-5

Pre

ssur

e (h

Pa)

Mean meridional streamfunction

109 kg/sec

51020305075100150200250300

NH Summer

NH Winter

ERA-40 Atlas

NORTH SOUTH

Winter

WinterSummer

Summer

0

0

0

0

0

00

0

0

0

0

0

0

00

00

0

-50

-50

-50

-50

-10

-10

-10

-10

-10

-10

-10

-10

-10

-10

-10

55

5

5

5

5

5

5

5

5

5

30

30

3030

3030

1000

900

800

700

600

500

400

300

200

100

80ON 60ON 40ON 20ON 0O 20OS 40OS 60OS 80OS

Annual mean

-300-250-200-150-100-75-50-30-20-10-5

Pre

ssur

e (h

Pa)

Mean meridional streamfunction109 kg/sec

51020305075100150200250300

NORTH SOUTH

NORTH SOUTH

1. dark trees = NH warm*because the surface is water limited*

Hypothesized Mechanism

20eq 6040

20eq 6040

grass

treesHOT

Hypothesized Mechanism

20eq 6040

20eq 6040

grass

treesHOT

1. dark trees = NH warm

2. Energy gradient (N-S) between the Hemispheres increases

1. dark trees = NH warm

2. Energy gradient (N-S) between the Hemispheres increases

3. Hadley Cell moves north to increase southward heat transport

Hypothesized Mechanism

20eq 6040

20eq 6040

grass

trees

Nor

thw

ard

ATM

Tra

nspo

rt (P

W)

Latitude (deg)

Total Northward Atmospheric Energy Transport

Circulation shift moves energy Southward

Southward Energy flux0.17 PW Anomaly

13% change at the Equator

Swann et al., in review

1. dark trees = NH warm

2. Energy gradient (N-S) between the Hemispheres increases

3. Hadley Cell moves north to increase southward heat transport

4. ITCZ shifts North

Hypothesized Mechanism

20eq 6040

20eq 6040

grass

trees

1. dark trees = NH warm

2. Energy gradient (N-S) between the Hemispheres increases

3. Hadley Cell moves north to increase southward heat transport

4. ITCZ shifts North

Hypothesized Mechanism

20eq 6040

20eq 6040

grass

treesTropical productivity follows changes in precipitation

⇒

g/C/m

annual mean

gC/m2/yr

NPP

Mid Lat. Afforestation modifies Tropical Productivity

Swann et al., in review

1. dark trees = NH warm

2. Energy gradient (N-S) between the Hemispheres increases

3. Hadley Cell moves north to increase southward heat transport

4. ITCZ shifts North

Hypothesized Mechanism

20eq 6040

20eq 6040

grass

treesTropical productivity follows changes in precipitation

⇒

NDVI June, 2009

1. Climate response to Forests2. Tropical Circulation and Precipitation3. Implications for climate management

Mid Latitude Afforestation

Afforestation Carbon Budget

Change in Carbon Pools:

∆M Afforested: 270 PgC

∆M Mid-lat: -3 PgC

∆M High-lat: -28 PgC

∆M Tropics: -9 PgC

Total ∆M: 228 PgC

Carbon is taken up by switching from grass to trees, 1/2 above ground

1/2 below ground

2 PgC => 1ppm

ΔCarbon ~ 228 PgC

2 PgC => 1ppm

-114 ppm -2.23-2.1 Wm-2ΔCO2: Δclimate forcing:

Climate Response to ΔCarbon

ΔCarbon ~ 228 PgC

2 PgC => 1ppm

-114 ppm -2.2 Wm-2ΔCO2: Δclimate forcing:

Climate Response to ΔCarbon

-1.10 ˚C ΔT:assume climate feedback: 0.5 degrees/Wm-2 (2 ˚C for 2xCO2)

0.75 degrees/Wm-2 (3 ˚C for 2xCO2)

1 degrees/Wm-2 (4 ˚C for 2xCO2)

-1.65 ˚C

-2.20 ˚C

ΔCarbon ~ 228 PgC

2 PgC => 1ppm

-114 ppm -2.2 Wm-2ΔCO2: Δclimate forcing:

Climate Response to ΔCarbon

-1.10 ˚C ΔT:assume climate feedback: 0.5 degrees/Wm-2 (2 ˚C for 2xCO2)

0.75 degrees/Wm-2 (3 ˚C for 2xCO2)

1 degrees/Wm-2 (4 ˚C for 2xCO2)

-1.65 ˚C

-2.20 ˚C

Equilibrium Experiment:

if we account for ocean response, the net drawdown of atmospheric CO2 is only 14%-40% =>~16-46ppm.

ΔCarbon ~ 228 PgC

2 PgC => 1ppm

-114 ppm -2.2 Wm-2ΔCO2: Δclimate forcing:

Climate Response to ΔCarbon

-1.10 ˚C ΔT:assume climate feedback: 0.5 degrees/Wm-2 (2 ˚C for 2xCO2)

0.75 degrees/Wm-2 (3 ˚C for 2xCO2)

1 degrees/Wm-2 (4 ˚C for 2xCO2)

-1.65 ˚C

-2.20 ˚C

Equilibrium Experiment:

if we account for ocean response, the drawdown of atmospheric CO2 is only 30Pg/15ppm.

Climate Response from ΔCO2 ~ -0.2 to -0.7 ˚C

Climate Response from albedo and transpiration = + 0.3 ˚C

Afforestation leads to little temperature change, but gradients in temperature can still drive

changes in circulation and precipitation

NDVI June, 2009

1. Climate response to mid latitude Afforestation• Soil moisture status controls climate response (dry = hot)

2. Tropical Circulation and Precipitation• Circulation shifts northward to transport more energy to the south

3. Implications for Future Climate• Circulation could still change despite global ∆T

Mid Latitude Afforestation

Latent Heat fluxes occur where water is not limited

5−12−20101 2 3 4 5 6 7 8 9 10 11 12

−0.02

0

0.02

0.04

0.06

0.08

Month

Δ T

herm

al R

atio

Climatology of ΔThermal Ratio

ΔV−IO+/− 1 σ

Long Wave

Late

nt H

eat

Mid Latitiude Afforested points, JJA

Net Longwave at the Surface (Wm )

Late

nt H

eat F

lux (

Wm

)

Latent Heat fluxes occur where water is not limited

5−12−20101 2 3 4 5 6 7 8 9 10 11 12

−0.02

0

0.02

0.04

0.06

0.08

Month

Δ T

herm

al R

atio

Climatology of ΔThermal Ratio

ΔV−IO+/− 1 σ

Long Wave

Late

nt H

eat

Mid Latitiude Afforested points, JJA

Net Longwave at the Surface (Wm )

Late

nt H

eat F

lux (

Wm

)

1:1 line

2−15−2011

PRECIP somcontrol annual mean

0 1 2 3 4 5 6 7 8 9 10

2 4 6−90−75−60−45−30−15

0153045607590

mm/day

Annual Mean Precipitation

mm/day