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Vegetation dynamics in simulations of radiatively-forced climate change Richard A. Betts, Chris D. Jones, Peter M. Cox [ [email protected]] Met Office Hadley Centre for Climate Prediction and Research Terrestrial Carbon Sinks Workshop, Wengen, Sept. 2002. - PowerPoint PPT Presentation
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1Hadley Centre for Climate Prediction and Research
Vegetation dynamics in simulations of radiatively-forced climate change
Richard A. Betts, Chris D. Jones, Peter M. Cox[[email protected]]
Met OfficeHadley Centre for Climate Prediction and Research
Terrestrial Carbon Sinks Workshop, Wengen, Sept. 2002
2Hadley Centre for Climate Prediction and Research
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)
3Hadley Centre for Climate Prediction and Research
Hadley Centre Coupled Climate-Carbon Cycle Model
(Biogeophysical)
(Biogeochemical)
4Hadley Centre for Climate Prediction and Research
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
5Hadley Centre for Climate Prediction and Research
TRIFFID-GCM coupling
Photosynthesis, respiration,
transpiration (30 minutes)
Litter (1 day)
Competition (10 days)
LAI, albedo,
roughness(1 day)
Broadleaf Tree
C3 Grass
Shrub
Soil
6Hadley Centre for Climate Prediction and Research
Coverage of vegetation types, control simulation
Fraction of gridbox
7Hadley Centre for Climate Prediction and Research
Vegetation cover: simulated - observed (IGBP-DIS)
Fraction of gridbox
8Hadley Centre for Climate Prediction and Research
Surface temperature changes (K)relative to 2000
30-year means
9Hadley Centre for Climate Prediction and Research
Precipitation changes relative to 2000
mm day-1
30-year means
2020
2050
2080
10Hadley Centre for Climate Prediction and Research
Changes in tree cover
Gridbox fraction
11Hadley Centre for Climate Prediction and Research
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
12Hadley Centre for Climate Prediction and Research
Broadleaf tree Net Primary Productivity(NPP) in central Africa
13Hadley Centre for Climate Prediction and Research
Changes in broadleaf tree cover due to physiological responses to
CO2
14Hadley Centre for Climate Prediction and Research
Precipitation difference (mm day-1)due to plant physiological responses to CO2
15Hadley Centre for Climate Prediction and Research
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
16Hadley Centre for Climate Prediction and Research
Precipitation changes (mm day-1) due to biogeophysical feedbacks
17Hadley Centre for Climate Prediction and Research
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
18Hadley Centre for Climate Prediction and Research
Vegetation & soil carbon changes
GtC
Interactive CO2
19Hadley Centre for Climate Prediction and Research
Effects of climate-carbon cycle feedbacks on atmospheric CO2 rise
1000
800
600
400
200
with CO2-climate feedbackswithout CO2-climate feedbacks
1900 1950 2000 2050 2100
CO
2 c
on
cen
trati
on
s (
pp
mv)
20Hadley Centre for Climate Prediction and Research
with CO2-climate feedbackswithout CO2-climate feedbacks
1850–2
0
2
4
6
8
1900 1950 2000 2050 2100
Tem
pera
ture
ris
e (
°C)
Effects of climate-carbon cycle feedbacks on land temperature rise
21Hadley Centre for Climate Prediction and Research
Further precipitation changes with CO2-climate feedback
(compared to prescribed CO2 dynamic veg simulation)
mm day-1
30-year means
22Hadley Centre for Climate Prediction and Research
Further changes in tree cover with CO2-climate feedbacks
Gridbox fraction
23Hadley Centre for Climate Prediction and Research
Broadleaf tree cover (gridbox fraction) in
coupled climate-carbon cycle
simulation
24Hadley Centre for Climate Prediction and Research
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
