transient simulation of northern african climate ... · summary vegetation collapse caused possibly...
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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
Claussen et al., 1999, GRL
Int Atm.+ Int Veg (CLIMBER2)
Precipitation
Vegetation
Obs (dust)
InsolationPositive vegatation feedback
(Multiple equilibrium)
Abrupt
Change !
Unstable Collapse
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
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 ?
Adkins et al., 2006
SST:
Even more gradual cooling
Upwelling:
Gradual Increase
Dust flux:
Abrupt Increase
ODP 658C: Marine Sediment
An Indirect Evidence?
Abrupt ?
Steady Forcing
Unstable Collapse and Stable Decline
VE
V
PPC1 PC2
Unstable Collapse
VE
V
PPC2
Stable Decline
PC1