Paleoclimate Models

1
Paleoclimate Models (Chapter 12)
2
The Climate System
(IPCC TAR, Ch. 1)
3
The Climate System
(IPCC TAR, Ch. 1)
4
Feedbacks
Internal couplings through linking
processes Amplify or diminish initial induced
climate change
5
Adjustment Time Scales
300-3000 yr
6
Climatic Variation and Change

• Additional Factors
• Abrupt change
• external conditions (e.g., solar output)
• internal feedbacks
• passing a threshold (e.g. ice caps melting)
• 2. Multiple climate states from the same
  external conditions

7
How can a numerical model represent all of this?

• Options
• Full complexity - short time scales
• Simplified - long time scales

8
Simplified Models

• Climate simulation in general - 1960s
• Paleoclimate applications
• Barry Saltzman (1931-2001)

e.g., Saltzman Maasch (1991)
9
Simplified Models

• Three-variable model for slow climate
  variability

I ice mass, ? atmospheric CO2, ? mean ocean
temperature R(t) solar variation at 65 N ?i,
?i, ?I - constants that can distill into 7
tunable parameters
10
Simplified Models

• Three-variable model for slow climate
  variability

(Saltzman, 1986)
CO2 parameter (?) from ??13C core data
(dashed) and simulation (solid)
11
Simplified Models

• Three-variable model for slow climate
  variability

(Saltzman, 1986)
?18O from SPECMAP ?18O (dashed) and simulation
(solid)
12
Intermediate Models

• Global, 2-5 dimensional model
• 5 latitudinal bands
• In each band
• 2 continental sectors (Eurasia-Africa, Americas)
• 3 ocean sectors (Atlantic, Indian, Pacific)
• Circulation dynamics 2-level, Q-G
• winds at 250 hPa, 750 hPa
• temperature at 500 hPa
• plus - Hadley Cell transport in tropics
• 2-D ocean model for each basin
• Land-atmosphere coupling processes

(Crucifix et al., 2002)
13
Intermediate Models
Simulation versus observations
(Crucifix et al., 2002)
14
Intermediate Models
(Crucifix et al., 2002)
15
Intermediate Models
Prescribed Changes
(Crucifix et al., 2002)
16
Intermediate Models
Prescribed Changes and Responses
(Crucifix et al., 2002)
17
Intermediate Models
Response
(Crucifix et al., 2002)
18
Intermediate Models
Prescribed Changes - Sensitivity
(Crucifix et al., 2002)
19
Intermediate Models
Sensitivity
(Crucifix et al., 2002)
20
Global Climate Models
21
Global Climate Models
Differing scales distributed surface properties
22
Global Climate Models
23
GCM Simulation

• Paleo-Simulation Projects
• Cooperative Holocene Mapping Project (COHMAP)
• COHMAP extension
• Paleoclimate Model Intercomparison Project (PMIP)

24
GCM Simulation

• Cooperative Holocene Mapping Project (COHMAP)
• NCAR CCM0
• Prescribed changes in
• Insolation
• SST
• Ice sheets
• CO2
• Time slices every 3,000 yr (18k BP, 15k BP, )
• Perpetual January or July

25
GCM Simulation

• Cooperative Holocene Mapping Project (COHMAP)
• Ice sheets cold ocean
• colder, drier climate
• intensified jet stream
• Amplified annual cycle
• Intensified summer monsoons

26
GCM Simulation

• COHMAP Extension
• NCAR CCM1
• Computed
• SST (slab ocean, prescribed heat transport)
• Sea ice
• Soil moisture
• Seasonal snow
• Time slices every 3,000 yr
• Full annual cycle simulated

27
GCM Simulation
(Kutzbach et al., 1998)
28
GCM Simulation
(Kutzbach et al., 1998)
29
GCM Simulation

• 25-yr simulation
• Last 5 yr analyzed

(Kutzbach et al., 1998)
30
GCM Simulation
Longitudinal average overturning circulation
(mean meridional circulation)
(Kutzbach et al., 1998)
31
Spruce
GCM Simulation
Present-Day Results
Douglas Fir
Sagebrush
(Bartlein et al., 1998)
32
GCM Simulation
Changes with Climate
(Bartlein et al., 1998)
33
GCM Simulation
Paleoclimate Model Intercomparison
Project Tropical Changes _at_ LGM

• 17 GCMs
• 9 slab ocean
• 8 prescribed SST
• Prescribed changes in
• - insolation
• - CO2
• - ice sheets

34
GCM Simulation
PMIP LGM vs. Present Day
(Pinot et al., 1999)
35
GCM Simulation
PMIP Present Day
Sea-surface temperature
Land-surface temperature
(Pinot et al., 1999)
36
GCM Simulation
PMIP Present Day
(Pinot et al., 1999)
37
GCM Simulation
PMIP Present Day
Ocean precipitation
Land precipitation
(Pinot et al., 1999)
38
GCM Simulation
PMIP LGM vs. PD (30 S - 30 N)
(Pinot et al., 1999)
39
GCM Simulation
Paleoclimate Model Intercomparison
Project Tropical Changes _at_ LGM
Top Sfc T change - prescribed SST
RMS spead among models
Bottom Sfc T change - computed SST
40
GCM Simulation
Paleoclimate Model Intercomparison
Project Tropical Changes _at_ LGM
Difference in simulated SST changes from
reconstructed changes (LGM-PD)
41
GCM Simulation
PMIP LGM-PD Comparison with proxies
(Pinot et al., 1999)
42
GCM Simulation
Paleoclimate Model Intercomparison
Project Tropical Changes _at_ LGM
Model changes vs. pollen record Coldest month
temperature
43
Paleoclimate Model Intercomparison
Project Tropical Changes _at_ LGM
GCM Simulation
Model changes vs. pollen record Annual surface
temperature
44
Precipitation changes vs. lake records
prescribed SST models
45
Precipitation changes vs. lake records computed
SST models
46
Paleoclimate Models (Chapter 12) END