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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). D Fine litterfall. R stem.
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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 NPPleaves,flowers,fruit R leaf NPPwood (Branch + Stem) DFine litterfall R stem R soil R CWD DCWD R roots NPPcoarse roots NPPfine roots DRoot R soil het Fdoc
Carbon stocks in mature and converted forests (Mg C ha-1) Intact forest Converted to grassland House and Prentice 2002
Dense forest: 0.05-0.20 Pasture and croplands: 0.3-0.4 Snow albedo: 0.8
Surface Albedo Evaporation Cloudiness Net Albedo Modelled effects of global deforestation on albedo Bala et al 2007, Proceedings of the National Academy of Sciences
1800 1600 Tropical 1400 1200 Temperate 1000 800 CO2 emissions (TgC y-1) 600 400 200 0 -200 -400 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Time (y) CO2 emissions from Land Use Change (1850-2009) R.A. Houghton 2010, personal communication; GFRA 2010
2000-2009 (PgC) 10 5 Source deforestation CO2 flux(PgC y-1) 1.1±0.7 5 Sink 10 1950 2000 1900 1850 Time (y) 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
2000-2009 (PgC) 10 fossil fuel emissions 7.7±0.5 5 Source deforestation CO2 flux(PgC y-1) 1.1±0.7 5 Sink 10 1950 2000 1900 1850 Time (y) 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
2000-2009 (PgC) 10 fossil fuel emissions 7.7±0.5 5 Source deforestation CO2 flux(PgC y-1) 1.1±0.7 5 Sink 10 1950 2000 1900 1850 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
2000-2009 (PgC) 10 fossil fuel emissions 7.7±0.5 5 Source deforestation CO2 flux(PgC y-1) 1.1±0.7 atmospheric CO2 4.1±0.1 5 Sink 10 1950 2000 1900 1850 Time (y) 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
2000-2009 (PgC) 10 fossil fuel emissions 7.7±0.5 5 Source deforestation CO2 flux(PgC y-1) 1.1±0.7 atmospheric CO2 4.1±0.1 5 Sink ocean 2.3±0.4 ocean (5 models) 10 1950 2000 1900 1850 Time (y) 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
2000-2009 (PgC) 10 fossil fuel emissions 7.7±0.5 5 Source deforestation CO2 flux(PgC y-1) 1.1±0.7 atmospheric CO2 4.1±0.1 land 5 2.4 (Residual) Sink ocean 2.3±0.4 (5 models) 10 1950 2000 1900 1850 Time (y) 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
1.1±0.7 PgC y-1 4.1±0.1 PgC y-1 47% 2.4 PgC y-1 27% Calculated as the residual of all other flux components + 7.7±0.5 PgC y-1 26% 2.3±0.4 PgC y-1 Average of 5 models Fate of Anthropogenic CO2 Emissions (2000-2009) Global Carbon Project 2010; Updated from Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS
How much can afforestation contribute to climate change mitigation? Carbon and biophysical effects of an extreme afforestation 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
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
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.