Afforestation and global climate
Yadvinder Malhi
Environmental Change Instiuuk School
of Geography and the Environment
University of Oxford
GPP
The Carbon Cycle of a
Forest
NPP VOC
NPP leaves,flowers,fruit
R leaf
NPP wood (Branch + Stem)
DFine litterfall
R stem
R soil
R CWD
DCWD
R roots
NPP coarse roots
R soil het
DRoot
NPP fine roots
Fdoc
Carbon stocks in mature and converted forests (Mg C ha-1)
Intact forest
Converted to grassland
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
Surface Albedo
Cloudiness
Evaporation
Net Albedo
Modelled effects of global deforestation on albedo
Bala et al 2007, Proceedings of the National Academy of Sciences
CO2 emissions (TgC y-1)
CO2 emissions from Land Use Change (1850-2009)
1800
1600
1400
1200
1000
800
600
400
200
0
-200
-400
Tropical
Temperate
Time (y)
R.A. Houghton 2010, personal communication; GFRA 2010
9
Human Perturbation of the Global Carbon Budget
2000-2009
(PgC)
Source
Sink
CO2 flux (PgC y-1)
10
5
deforestation
5
10
1850
1900
1950
Time (y)
Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS
2000
1.1±0.7
Human Perturbation of the Global Carbon Budget
2000-2009
(PgC)
10
Source
Sink
CO2 flux (PgC y-1)
fossil fuel emissions
7.7±0.5
5
deforestation
5
10
1850
1900
1950
Time (y)
Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS
2000
1.1±0.7
Human Perturbation of the Global Carbon Budget
2000-2009
(PgC)
10
Source
Sink
CO2 flux (PgC y-1)
fossil fuel emissions
7.7±0.5
5
deforestation
5
10
1850
1900
1950
Time (y)
Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS
2000
1.1±0.7
Human Perturbation of the Global Carbon Budget
2000-2009
(PgC)
10
Source
7.7±0.5
5
deforestation
atmospheric CO2
Sink
CO2 flux (PgC y-1)
fossil fuel emissions
5
10
1850
1900
1950
Time (y)
Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS
2000
1.1±0.7
4.1±0.1
Human Perturbation of the Global Carbon Budget
2000-2009
(PgC)
10
Source
7.7±0.5
5
deforestation
atmospheric CO2
Sink
CO2 flux (PgC y-1)
fossil fuel emissions
1.1±0.7
4.1±0.1
5
ocean
ocean
10
1850
1900
1950
Time (y)
Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS
2000
2.3±0.4
(5 models)
Human Perturbation of the Global Carbon Budget
2000-2009
(PgC)
10
Source
7.7±0.5
5
deforestation
atmospheric CO2
Sink
CO2 flux (PgC y-1)
fossil fuel emissions
land
5
ocean
2.4 (Residual)
2.3±0.4
(5 models)
10
1850
1.1±0.7
4.1±0.1
1900
1950
Time (y)
Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS
2000
Fate of Anthropogenic CO2 Emissions (2000-2009)
1.1±0.7 PgC y-1
4.1±0.1 PgC y-1
47%
7.7±0.5 PgC y-1
+
2.4 PgC y-1
27%
Calculated as the residual of
all other flux components
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
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
Arora and Montenegro 2011 Nature Geoscience
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?
Many temperate regions have already been undergoing afforestation
New England 1900
New England 2000
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.