Corporate ppt template

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Vegetation dynamics in simulations of
radiatively-forced climate change Richard A.
Betts, Chris D. Jones, Peter M.
Cox chris.d.jones_at_metoffice.com Met
Office Hadley Centre for Climate Prediction and
Research Terrestrial Carbon Sinks Workshop,
Wengen, Sept. 2002
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Simulating global vegetation in the Hadley Centre
coupled climate-carbon cycle model

• Compare simulated vegetation with global
  observational datasets
• In simulations of future global change,
  investigate interactions and feedbacks
• direct effects of CO2 on vegetation
• biogeophysical feedbacks (through water cycle)
• biogeochemical feedbacks (through carbon cycle)

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Hadley Centre Coupled Climate-Carbon Cycle Model
(Biogeophysical)
(Biogeochemical)
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TRIFFID vegetation model

• Competition between 5 plant functional types
• Broadleaf tree, Needleleaf tree, C3 grass, C4
  grass, shrub
• Carbon balance computed within GCM land surface
  scheme
• Interacts with atmospheric CO2
• Vegetation distribution and leaf area determine
  land surface characteristics in atmosphere model

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TRIFFID-GCM coupling
Photosynthesis, respiration, transpiration
(30 minutes)
Litter (1 day)
Broadleaf Tree
Shrub
C3 Grass
LAI, albedo, roughness(1 day)
Soil
Competition (10 days)
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Coverage of vegetation types, control simulation
Fraction of gridbox
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Vegetation cover simulated - observed (IGBP-DIS)
Fraction of gridbox
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Surface temperature changes (K)relative to
200030-year means
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Precipitation changes relative to 2000mm
day-130-year means
2020
2050
2080
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Changes in tree coverGridbox fraction
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What is the role of plant physiological responses
to CO2?

• TRIFFID includes direct effects of CO2 on
  vegetation
• CO2 fertilization
• size of stomatal openings
• 3 simulations, IS92a concentration scenario
• (a) CO2 exerts radiative forcing only
  (vegetation given constant present-day CO2)
• (b) CO2 exerts radiative and physiological
  forcings (vegetation responds directly to
  rising CO2)
• (c) Other GHGs included as well as CO2

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Broadleaf tree Net Primary Productivity(NPP) in
central Africa
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Changes in broadleaf tree cover due to
physiological responses to CO2
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Precipitation difference (mm day-1)due to plant
physiological responses to CO2
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How do biogeophysical feedbacks affect Amazon
drying?

• Changes in land surface characteristics
• albedo
• moisture availability (roots, canopy)
• aerodynamic roughness
• 2 simulations, IS92a GHG concentration scenario
  (prescribed CO2 and other GHGs)
• (a) Vegetation fixed at present-day state
• (b) Dynamic vegetation updates land surface
  characteristics
• NB. No direct anthropogenic deforestation-
  natural responses only

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Precipitation changes (mm day-1) due to
biogeophysical feedbacks
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How do carbon cycle feedbacks affect Amazon
drying and dieback?

• Further simulation fully interactive carbon
  cycle
• IS92a emissions scenario
• atmospheric CO2 calculated within GCM
• (other GHGs prescribed)
• vegetation and soil feedbacks on CO2
• physical and biological ocean carbon feedbacks on
  CO2

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Vegetation soil carbon changesGtCInteractive
CO2
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Effects of climate-carbon cycle feedbacks on
atmospheric CO2 rise
with CO2-climate feedbacks
1000
without CO2-climate feedbacks
800
CO2 concentrations (ppmv)
600
400
200
1900
1950
2000
2050
2100
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Effects of climate-carbon cycle feedbacks on land
temperature rise
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with CO2-climate feedbacks
without CO2-climate feedbacks
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4
Temperature rise (C)
2
0

2
1850
1900
1950
2000
2050
2100
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Further precipitation changes with CO2-climate
feedback(compared to prescribed CO2 dynamic veg
simulation)mm day-130-year means
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Further changes in tree cover with CO2-climate
feedbacksGridbox fraction
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Broadleaf tree cover (gridbox fraction) in
coupled climate-carbon cycle simulation
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Conclusions

• CO2 physiological effects enhance NPP through
  fertilization but also exert climatic effect
• relative importance for vegetation varies from
  place to place
• Biogeophysical feedbacks modify local climate
  change
• enhance Amazon drying
• Carbon cycle feedbacks accelerate global climate
  and vegetation change
• enhance Amazon drying and dieback
• Vegetation carbon sink may not be robust to
  climate change