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Richard A. Betts & Pete Falloon Hadley Centre for Climate Prediction and Research Met Office Expert Meeting on the Contribution of Agriculture to the State of Climate – PowerPoint PPT presentation

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Title: Corporate ppt template


1
Biophysical forcing of climate by anthropogenic
vegetation change Richard A. Betts Pete
Falloon Hadley Centre for Climate Prediction and
Research Met Office Expert Meeting on the
Contribution of Agriculture to the State of
Climate Ottawa, Canada 28 September 2004
2

IPCC 2001
3
Photo Centre for Ecology and Hydrology
4
Photo Tim Hewison
5
Fraction of land used by agriculture(crops
grazing)
Ramankutty Foley 1999 Klein Goldewijk 2000
6
Forest and grassland albedo Delta Junction,
Alaska, 1991-1993
Sharratt 1998
7
Modelling surface albedo a
a a0 (aD - a0)(1 - e-0.2S) a0 snow-free
albedo Forest 0.15 Grassland 0.2 aD
deep-snow albedo Forest 0.25 Grassland
0.8 (also some temperature dependence) S snow
amount (kg m-2)
Hansen et al 1983
8
Radiative forcing (Wm-2) by surface albedo
changeactual - natural vegetation
Global mean - 0.24 Wm-2
9
Vegetation-atmosphere interactions
CO2
Latent heat / moisture
Sensible heat
Surface albedo
LW emissivity
Aerodynamic roughness
Moisture availability
10
Simulated 1.5m temperature difference (K)
Actual - Natural vegetation (annual mean)
11
Simulated seasonal differencesActual (ACT) -
Natural (NAT) vegetation
12
Simulated seasonal differencesdue to albedo
change alone
ALBNAT albedo of natural veg
13
Changes in fraction of land disturbed by
agriculture
Ramankutty Foley 1999 Klein Goldewijk 2000
14
Surface albedo forcing (Wm-2) 1750 - natural
Global mean - 0.06 Wm-2
15
Surface albedo forcing (Wm-2) 1850 - natural
Global mean - 0.10 Wm-2
16
Surface albedo forcing (Wm-2) 1900 - natural
Global mean - 0.14 Wm-2
17
Surface albedo forcing (Wm-2) 1950 - natural
Global mean - 0.18 Wm-2
18
Surface albedo forcing (Wm-2) 1990 - natural
Global mean - 0.24 Wm-2
19
1990 forcing relative to natural global mean
-0.24 Wm-2
1990 forcing relative to 1750 global mean -0.18
Wm-2
Wm-2
20
Time evolution of shortwave radiative forcings
(Wm-2)
Surface albedo
Ramaswamy et al 2001
21
But what about Cool the Earth - plant a tree?
22
Carbon sink plantationsestimated sequestration
potentials
Carbon uptake (trees soil) over 1 harvest
rotation period
From regional/national estimates of annual
increment (Nilsson Schopfhauser 1995, Nabuurs
Mohren 1995)
23
Radiative forcing due to carbon sequestration
24
Radiative forcing due to surface albedo change
25
Net forcing due to carbon sink plantations
26
Rates of change of forest cover
Temperate forests 1.3 million ha
yr-1 Tropical forests - 12.6 million ha yr-1
UN Food and Agriculture Organization 1997
27
Temperature change (K) due to Amazon deforestation
1.25
Contour interval 0.25K
Kleidon and Heimann 2000
28
150hpa circulation response to Amazon
deforestation
Streamfunction deviation from zonal mean Contour
interval 5105 m2s-1
Gedney Valdes 2000
29
Conclusions (i)
  • Model results suggest that past deforestation has
    affected global climate mainly through surface
    albedo change
  • Radiative forcing (-0.18 Wm-2 since 1750)
    therefore seems to be a reasonable indicator of
    land use effects on global climate
  • Surface albedo change may affect estimates of
    aerosol forcing

30
Conclusions (ii)
  • Carbon sink afforestation will also affect
    climate via surface albedo
  • carbon accounting may overestimate negative
    forcing
  • in cold regions, forcing may even be positive!
  • Tropical deforestation forces climate
    non-radiatively
  • how do we quantify this?

31
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