Transient Simulation of Northern African Climate ... · Summary Vegetation collapse Caused possibly...
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Transient Simulation of Northern African Climate Transient Simulation of Northern African Climate - - Ecosystem in the Holocene: Ecosystem in the Holocene: ---- ---- Climate Variability vs. Vegetation Feedback Climate Variability vs. Vegetation Feedback Z. Liu Z. Liu Center for Climatic Research Center for Climatic Research University of Wisconsin University of Wisconsin - - Madison Madison Collaborators Collaborators M M Notaro Notaro , Y., Wang, R. , Y., Wang, R. Gallimore Gallimore , , UW UW - - Madison Madison I.C. Prentice I.C. Prentice , Dept. Earth Sciences, Univ. Bristol, UK , Dept. Earth Sciences, Univ. Bristol, UK R. Jacob R. Jacob , Argonne National Laboratory, DOE , Argonne National Laboratory, DOE
Transcript of Transient Simulation of Northern African Climate ... · Summary Vegetation collapse Caused possibly...
Transient Simulation of Northern African ClimateTransient Simulation of Northern African Climate-- Ecosystem in the Holocene:Ecosystem in the Holocene:
--------Climate Variability vs. Vegetation FeedbackClimate Variability vs. Vegetation Feedback
Z. LiuZ. LiuCenter for Climatic ResearchCenter for Climatic Research
University of WisconsinUniversity of Wisconsin--MadisonMadison
CollaboratorsCollaboratorsM M NotaroNotaro, Y., Wang, R. , Y., Wang, R. GallimoreGallimore, , UWUW--MadisonMadisonI.C. PrenticeI.C. Prentice, Dept. Earth Sciences, Univ. Bristol, UK, Dept. Earth Sciences, Univ. Bristol, UKR. JacobR. Jacob, Argonne National Laboratory, DOE, Argonne National Laboratory, DOE
Abrupt !
Motivation for Transition Simulation
abrupt changes
paleo model-data comparison
Claussen et al., 1999, GRL
Int Atm.+ Int Veg (CLIMBER2)
Precipitation
Vegetation
Obs (dust)
InsolationPositive vegatation feedback
(Multiple equilibrium)
Abrupt
Change !
Unstable Collapse
Renssen et al., 2003, GRL
QG Atmosphere + Int Veg
Precipitation
VegetationAbrupt ?
June Temp
Wang et al., 2006
McGill Model: EBA + Int Veg
Precipitation
Desert fraction
Abrupt ?
Vegetation decrease
abruptly !
5000 yrs BP !!
Summer Insolation decrease
Area2: 23-27N/3W-5E Area3: 18-23N/3W-11EArea1: 18-23N/11E-36E
GrassTotal Veg
FOAM_LPJ Transient Simulation: 6500 0 yrs
0ka
6ka
0ka – 6ka
Liu et al., 2006, GRL, Liu et al., 2007, QSRLiu et al., 2006, GRL, Liu et al., 2007, QSR
Vegetation Cover
V
P
Observation
ModelPositive Vege Feedback??
Notaro et al., 2007
Global Change Biology
•Mechanism?
•Observation?
Implication:
⎪⎩
⎪⎨
⎧−=
0/)(
1)( 1 CCE DPPPV
VDtPtVP BdE += )(),(
A Conceptual Climate-Vegetation Model
Veg.
Atm.
Equilibrium
V
P
τVPV
dtdV E −
=)(
)(),(),( tPtVPtVP NE +=
Transient
PC1 PC2
Desert
Green
Unstable PE
Stable PE
VE
Unstable Case Stable Case
Steady Unstable Collapse Stable Decline
Forcing
Decadal StochasticUnstable Collapse Stable Collapse
Annual StochasticStochastic suppression Stochastic suppression
QG
FOAM_LPJ
CLIMBER2 McGill
Vegetation Cover: Sensitivity Experiments with Fixed Orbital Forcing
6ka:
650 yr
5.5ka:
450 yr
5ka:
350 yr
6000 5350
5550
5650
6000
6000
Cen-Est N. Afr
Timing ~ 5ka
An Early Try
N. Africa Vegetation
6.5ka
4.5ka
CCSM3-CLM-LPJ Simulation, 6000-3000 BP
Grass Change
6000 --- 3600 BP
Grass
Prep
CCSM PaleoWorking Group (Brady et al. Poster )
SummaryVegetation collapse
Caused possibly by strong decadal climate variability and soil moisture memory, in the absence of strong positive vegetation feedback, in FORM-LPJ.
Implication to Paleo-observationVegetation collapse,
is it accompanied by a gradual climate change?
Implication of Stable CollapseAbrupt change can occur even for a strongly nonlinear stable system, forced by strong low frequency variability. Climate variability and abrupt change are closely related to each other.
Implication to Long Term Transient Simulation
A Big Gamble!
Challenging: Abrupt changetimingmechanism
Can some acceleration methods help?
Small model drift matters!
Unstable Case Stable Case
Steady Unstable Collapse Stable Decline
Forcing
Decadal StochasticUnstable Collapse Stable Collapse
Annual StochasticStochastic suppression Stochastic suppression
Very Stable Green Very Stable Desert
Stable/Unstable Intermediate
Slow Stochastic
StableCollapse
Drying
Fast Stochastic
Stochastic Suppression
Very Stable Green Very Stable Desert
Stable/Unstable Intermediate
Drying
CCSMT31-CML+LPJ: Transient Holocene Run
Courtesy, B. Otto-Bliesner, and CCSM paleo working group
Abrupt ?
Sensitivty FOAM-LPJ Experiments with different Initial Conditions
Adkins et al., 2006
SST:
Even more gradual cooling
Upwelling:
Gradual Increase
Dust flux:
Abrupt Increase
ODP 658C: Marine Sediment
An Indirect Evidence?
Abrupt ?
Dust FluxSummer
Steady Forcing
Unstable Collapse and Stable Decline
VE
V
PPC1 PC2
Unstable Collapse
VE
V
PPC2
Stable Decline
PC1
FOAM-LPJ JJA Precipitation
0 ka
P, V
6ka
P, V
0ka --- 6 ka
P, V
0ka --- 6 ka
T
Evolution of Climate-Vegetation System (Central-East Africa)
V
P T
Grass
Tree
6.5ka 0ka 6.5ka 0ka
V
P
Observation
Model
Precipitation variability
