An Introduction to CCSM http://www.ccsm.ucar.edu

Report
An Introduction to Climate Models:
Principles and Applications
William D. Collins
National Center for Atmospheric Research
Boulder, Colorado USA
Colloquium on Climate and Health
17 July 2006
Topics
• The climate-change context
• Components of the climate system
• Representation of climate in global models
• The NCAR climate model CCSM3
• Applications to global change
• Transition from climate models to Earth system models
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Climate Simulations for the IPCC AR4
(IPCC = Intergovernmental Panel on Climate Change)
IPCC Emissions Scenarios
Climate Change Simulations
IPCC 4th Assessment
Results:
• 10,000 simulated years
• Largest submission to IPCC
• 100 TB of model output
2007
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Exchange of Energy in the Climate
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Components of the Climate System
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Slingo
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Time Scales in the Climate System
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Configuration of NCAR CCSM3
(Community Climate System Model)
Atmosphere
(CAM 3.0)
T85 (1.4o)
Land
(CLM2.2)
T85
(1.4o)
Coupler
(CPL 6)
Ocean
(POP 1.4.3)
(1o)
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Sea Ice
(CSIM 4)
(1o)
Why are there multiple Climate Models?
• Ongoing research on processes:
– The carbon cycle
– Interactions of aerosols and clouds
– Interactions of climate and vegetation
• No “1st principles” theories (yet) for:
– Physics of cloud formation
– Physics of atmospheric convection
• Inadequate data to constrain models
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17 July 2006
Brief History of Climate Modeling
•
1922: Lewis Fry Richardson
–
•
1950: Charney, Fjørtoft and von Neumann (1950)
–
•
Results from about 30 atmospheric models from around the world
2001: IPCC Third Assessment Report
–
•
University of California Los Angeles (UCLA), National Center for Atmospheric Research (NCAR, Boulder, Colorado)
and UK Meteorological Office
1990s: Atmospheric Model Intercomparison Project (AMIP)
–
•
Nine level primitive equation model
1960s and 1970s: Other groups and their offshoots began work
–
•
1st general circulation experiment (two-layer, quasi-geostrophic hemispheric model)
1963: Smagorinsky, Manabe and collaborators at GFDL, USA
–
•
First numerical weather forecast (barotropic vorticity equation model)
1956: Norman Phillips
–
•
Basic equations and methodology of numerical weather prediction
Climate projections to 2100 from 9 coupled ocean-atmosphere-cryosphere models.
2007: IPCC Fourth Assessment Report
–
Climate projections to 2100+ from 23 coupled ocean-atmosphere-cryosphere models.
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Slingo
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Richardson’s Vision of a Climate Model
“Myriad computers are at work upon the
weather of the part of the map where each
sits, but each computer attends only to one
equation or part of an equation. The work of
each region is coordinated by an official of
higher rank. Numerous little 'night signs'
display the instantaneous values so that
neighboring computers can read them. Each
number is thus displayed in three
adjacent zones so as to maintain
communication to North and South of the
map…”
Lewis Fry Richardson
Weather Prediction by
Numerical Process (1922)
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Evolution of Climate Models
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Basic Equations for the Atmosphere
•
Momentum equation:
dV/dt = -p -2^V –gk +F +Dm
•
•
Thermodynamic equation:
dT/dt = Q/cp + (RT/p) + DH
•
•
Where =1/ ( is density), p is pressure,  is rotation rate of the Earth, g is acceleration due to gravity
(including effects of rotation), k is a unit vector in the vertical, F is friction and Dm is vertical diffusion of
momentum
where cp is the specific heat at constant pressure, R is the gas constant,  is the vertical velocity, DH is the
vertical diffusion of heat and Q is the internal heating from radiation and condensation/evaporation; Q =
Qrad + Qcon
Continuity equation for moisture (similar for other tracers):
dq/dt = E – C + Dq
•
where E is the evaporation, C is the condensation and Dq is the vertical diffusion of moisture
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Slingo
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Vertical Discretization of Equations
Vertical Grid for Atmosphere
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Horizontal Discretization of Equations
T31
T42
T85
T170
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Strand
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Physical Parameterizations
•
Processes that are not explicitly represented by the basic dynamical and
thermodynamic variables in the basic equations (dynamics, continuity,
thermodynamic, equation of state) on the grid of the model need to be
included by parameterizations.
•
There are three types of parameterization;
1.
Processes taking place on scales smaller than the grid-scale, which are therefore
not explicitly represented by the resolved motion;
•
•
2.
Convection, boundary layer friction and turbulence, gravity wave drag
All involve the vertical transport of momentum and most also involve the transport of
heat, water substance and tracers (e.g. chemicals, aerosols)
Processes that contribute to internal heating (non-adiabatic)
•
•
3.
Radiative transfer and precipitation
Both require the prediction of cloud cover
Processes that involve variables additional to the basic model variables (e.g. land
surface processes, carbon cycle, chemistry, aerosols, etc)
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Slingo
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Parameterized Processes
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Slingo
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Processes Included in the CCSM Land Model
The current version includes:
• Biogeophysics
• Hydrology
• River routing
The next version will include:
• Natural and human-mediated changes in land cover
• Natural and human-mediated changes in ecosystem functions
• Coupling to biogeogeochemistry
Reflected Solar
Radiation
Absorbed Solar
Radiation
Photosynthesis
Sensible Heat Flux
Latent Heat Flux
Longwave Radiation
Hydrology
Momentum Flux
Wind Speed
0
ua
Precipitation
Evaporation
Interception
Canopy Water
Transpiration
Emitted Longwave Radiation
Diffuse Solar
Radiation
Biogeophysics
Throughfall
Stemflow
Sublimation
Melt
Evaporation
Infiltration
Surface Runoff
Snow
Soil Heat Flux
Soil Water
Heat Transfer
Redistribution
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Drainage
Subgrid Structure of the Land Model
Gridcell
Landunits
Glacier
Wetland
Vegetated
Lake
Columns
Soil
Type 1
PFTs
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Urban
“Products” of Global Climate Models
• Description of the physical climate:
–
–
–
–
Temperature
Water in solid, liquid, and vapor form
Pressure
Motion fields
• Description of the chemical climate:
– Distribution of aerosols
– Evolution of carbon dioxide and other GHGs
– Coming soon: chemical state of surface air
• Space and time resolution (CCSM3):
– 1.3 degree atmosphere/land, 1 degree ocean/ice
– Time scales: hours to centuries
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The CCSM Program
Scientific Objectives:
•
Develop a comprehensive climate model to
study the Earth’s Climate.
•
Investigate seasonal and interannual
variability in the climate.
•
Explore the history of Earth’s climate.
•
Estimate the future of the environment for
policy formulation.
Recent Accomplishments:
•
Release of a new version (CCSM3) to the
climate community.
•
Studies linking SST fluctuations, droughts,
and extratropical variability.
•
Simulations of last 1000 years, Holocene,
and Last Glacial Maximum.
•
Creation of largest ensemble of simulations
for the IPCC AR4.
http://www.ccsm.ucar.edu
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The CCSM Community
Development Group
NCAR
Universities
CCSM3
Atmosphere
Labs
(CAM 3)
Land
(CLM 3)
Physics
Coupler
Sea Ice
(CPL 6)
(CSIM 4)
Ocean
Applications Chemistry
(POP 1)
Model Users
Climate Community
Current Users:
• Institutions: ~200
Publications:
• NCAR:
• Universities:
• Labs/Foreign:
Downloads of CCSM3:
• Users:
~600
Total:
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87
94
48
229
Changes in Atmospheric Composition
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Forcing: Changes in Exchange of Energy
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17 July 2006
Components of Aerosol Forcing
Back Scattering (Cooling)
Absorption
(Atmospheric Warming)
Absorption
(Column
Warming)
Cloud Evaporation
(Warming)
Cloud Seeding
(Cooling)
Suppression of Rain;
increase of life time
(Cooling)
Forward
Scattering
Dimming of Surface
Surface Cooling Colloquium on Climate and Health
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Ramaswamy
Simulations of Aerosol Distributions
1995-2000
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Fidelity of 20th Century Simulations with the CCSM3
• Criteria for the ocean/atmosphere system
– Realistic prediction of sea-surface temperature given realistic
forcing
– Realistic estimates of ocean heat uptake
Effects of ocean on transient climate response
– Realism of ocean mixed layer and ventilation
Ocean uptake of CO2 and passive tracers (CFCs)
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17 July 2006
Simulation of Sea-Surface Temperature
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Increases in Global Ocean Temperatures
(Results from CCSM3 Ensemble)
L = Levitus et al (2005)
Ensemble
Members
Relative Model
Error < 25%
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Gent et al, 2005
17 July 2006
Global Ocean Inventory of CFC-11
(Passive tracer proxy for CO2)
}
Ensemble
Members
Data
CCSM3
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Gent et al, 2005
17 July 2006
Penetration Depth of CFC-11
WOCE data (Willey et al, 2004)
m
CCSM3 Simulation
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Gent et al, 2005
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Projections for Global Surface Temperature
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Meehl et al, 2005
17 July 2006
Projections for Regional
Surface Temperature Change
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Meehl et al, 2005
17 July 2006
Projections for Global Sea Level
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Meehl et al, 2005
17 July 2006
Committed Change:
Global Temperature and Sea Level
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Teng et al, 2005
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Changes in Sea Ice Coverage
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Meehl et al, 2005
17 July 2006
Changes in Permafrost Coverage
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Lawrence and Slater, 2005: Geophys. Res. Lett.
17 July 2006
Scientific objectives for the near future
• Major objective:
Develop, characterize, and understand
the most realistic and comprehensive model of the
observed climate system possible.
• Subsidiary objectives:
– Analyze and reduce the principal biases in our
physical climate simulations using state-of-the-art
theory and observations.
– Simulate the observed climate record with as much fidelity
as possible.
– Simulate the interaction of chemistry, biogeochemistry, and
climate with a focus on climate forcing and feedbacks.
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Recent evolution of climate forcing
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Hansen and Sato, 2001
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Simulating the chemical state of the climate system
Emissions
Chemistry + BGC +
Physics + Ecosystems
Concentrations
Forcing
Climate
Response
Feedbacks
Offline models
Chemical
Reservoirs
• In the past, we have generally used offline models to predict concentrations
and read these into CCSM.
• This approach is simple to implement, but
 It cuts the feedback loops.
 It eliminates the chemical reservoirs.
• The next CCSM will include these interactions.
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17 July 2006
CCSM4: a 1st generation Earth System Model
Coupler
Land
C/N
Cycle
Dyn.
Veg.
Ocean
Atmosphere
Land Ice
Gas chem. Prognostic
Use Sheets
Aerosols
Upper
Atm.
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Ecosystem
& BGC
Sea Ice
Historical changes in agricultural land use
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Johan Feddema
17 July 2006
Changes in surface albedo by land use
Johan Feddema
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17 July 2006
Evolution of tropospheric ozone
(1890-2100, following A2 scenario)
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Lamarque et al, 2005
Flux of CO2 into the world oceans
(Ocean ecosystem model)
Moore, Doney, and Lindsay
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Conclusions
• Modern climate models can be applied to:
– Studying the integrated climate system
– Modeling climates of the past
– Projecting future climate change and its impact
• Challenges ahead for modelers:
– Process-oriented modeling of the climate
– Coupled chemistry/climate modeling
• Challenges ahead for the community:
– Better linkages between modelers, health specialists, & policy makers
– Better modeling of chemical and biological climate change
Colloquium on Climate and Health
17 July 2006

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