Afforestation and global climate

Yadvinder MalhiEnvironmental Change Instiuuk School of

Geography and the EnvironmentUniversity of Oxford

GPP The Carbon Cycle of a Forest

R leaf

R stem

R CWD

Fdoc

DFine litterfall

DCWD

R roots

R soil

DRoot

R soil het

NPP coarse roots

NPP fine roots

NPP VOCNPP leaves,flowers,fruit

NPP wood (Branch + Stem)

Intact forest Converted to grassland

Carbon stocks in mature and converted forests (Mg C ha-1)

House and Prentice 2002

The global carbon cycle

Foley et al (2003)

Dense forest: 0.05-0.20

Pasture and croplands: 0.3-0.4

Snow albedo: 0.8

Bala et al 2007, Proceedings of the National Academy of Sciences

Surface Albedo

Net AlbedoCloudiness

Evaporation

Modelled effects of global deforestation on albedo

9

CO2 emissions from Land Use Change (1850-2009)

R.A. Houghton 2010, personal communication; GFRA 2010

-400-200

0200400600800

10001200140016001800

1850

1860

1870

1880

1890

1900

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

2010

Tropical

Temperate

CO2 e

miss

ions

(TgC

y-1)

Time (y)

Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS

Human Perturbation of the Global Carbon Budget

Sink

Sour

ce

Time (y)

5

10

10

5

1850 1900 1950 2000

1.1±0.7deforestation

CO2 f

lux

(PgC

y-1)

2000-2009(PgC)

Human Perturbation of the Global Carbon Budget

Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS

5

10

10

5

1850 1900 1950 2000

7.7±0.5

deforestation

fossil fuel emissions

Sink

Sour

ce

Time (y)

CO2 f

lux

(PgC

y-1)

1.1±0.7

2000-2009(PgC)

Human Perturbation of the Global Carbon Budget

Time (y)

Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS

5

10

10

5

1850 1900 1950 2000

deforestation

fossil fuel emissions

Sink

Sour

ce

CO2 f

lux

(PgC

y-1) 7.7±0.5

1.1±0.7

2000-2009(PgC)

Human Perturbation of the Global Carbon Budget

Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS

5

10

10

5

1850 1900 1950 2000

4.1±0.1

fossil fuel emissions

deforestation

atmospheric CO2

Sink

Sour

ce

Time (y)

CO2 f

lux

(PgC

y-1) 7.7±0.5

1.1±0.7

2000-2009(PgC)

Human Perturbation of the Global Carbon Budget

Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS

5

10

10

5

1850 1900 1950 2000

atmospheric CO2

fossil fuel emissions

deforestation

ocean2.3±0.4

oceanSink

Sour

ce

Time (y)

CO2 f

lux

(PgC

y-1)

(5 models)

4.1±0.1

7.7±0.5

1.1±0.7

2000-2009(PgC)

Human Perturbation of the Global Carbon Budget

Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS

5

10

10

5

1850 1900 1950 2000

2000-2009(PgC)

atmospheric CO2

oceanland

fossil fuel emissions

deforestation

(Residual)

Sink

Sour

ce

Time (y)

CO2 f

lux

(PgC

y-1)

2.3±0.4(5 models)

4.1±0.1

7.7±0.5

1.1±0.7

2.4

Fate of Anthropogenic CO2 Emissions (2000-2009)

1.1±0.7 PgC y-1

+7.7±0.5 PgC y-1

2.4 PgC y-1

27%Calculated as the residual of

all other flux components

4.1±0.1 PgC y-1

47%

26%2.3±0.4 PgC y-1

Average of 5 models

Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS

Carbon sources and sinks over the last two centuries (Pg C)

How much can afforestation contribute to climate change mitigation?

Carbon and biophysical effects of an extreme afforestation scenario

Carbon sources and sinks over the last two centuries (Pg C)

Arora and Montenegro 2011

Arora and Montenegro 2011

Global average temperature rise under A2 emissions scenario

Arora and Montenegro 2011 Nature Geoscience

Global mean: -0. 11 oC; Global land mean: -0.16 oC

Arora and Montenegro 2011 Nature Geoscience

Global mean: -0.04 oC; Global land mean: +0.01 oC

Arora and Montenegro 2011 Nature Geoscience

Global mean: -0. 16 oC; Global land mean: -0.25 oC

Climate effectiveness of afforestation per unit area

100% global afforestation of croplands

100% global afforestation of croplands

100% global afforestation of croplands

But can we afford to regrow forests in a world on 9+ billion?Would afforestation compete with food supply?

New England 1900 New England 2000

Many temperate regions have already been undergoing afforestation

Other regions lock out afforestation for cultural reasons, not resource supply ones

Or for historical legacies and minority interests…

In many tropical regions cultural factors also dominate over food economics

Conclusions

Afforestation can be a relatively low component of a climate mitigation strategy (except in regions with substantial winter snow)

If appropriately done, it brings many co-benefits including biodiversity, watershed protection and soil protection.

Tropical afforestation (and avoided deforestation) is particularly effective.

It is possible to afforest and reforest in a food-demanding world.