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 Colloquium on Climate and Health 17 July 2006

Climate Simulations for the IPCC AR4

(IPCC = Intergovernmental Panel on Climate Change)

IPCC Emissions Scenarios Climate Change Simulations IPCC 4 th Assessment

Results:

• 10,000 simulated years • Largest submission to IPCC • 100 TB of model output Colloquium on Climate and Health 17 July 2006 2007

Exchange of Energy in the Climate

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Components of the Climate System

Slingo Colloquium on Climate and Health 17 July 2006

Time Scales in the Climate System

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Configuration of NCAR CCSM3

(Community Climate System Model)

Atmosphere

(CAM 3.0) T85 (1.4

o )

Land

(CLM2.2) T85 (1.4

o )

Coupler

(CPL 6)

Sea Ice

(CSIM 4)

(



1 o )

Ocean

(POP 1.4.3) (  1 o ) Colloquium on Climate and Health 17 July 2006

Why are there multiple Climate Models?

•

Ongoing research on processes:

– The carbon cycle – Interactions of aerosols and clouds – Interactions of climate and vegetation •

No “1 st principles” theories (yet) for:

– Physics of cloud formation – Physics of atmospheric convection •

Inadequate data to constrain models

Colloquium on Climate and Health 17 July 2006

Brief History of Climate Modeling

• • • • • • • •

1922: Lewis Fry Richardson

– Basic equations and methodology of numerical weather prediction

1950: Charney, Fj ørtoft and von Neumann (1950)

– First numerical weather forecast (barotropic vorticity equation model)

1956: Norman Phillips

– 1 st general circulation experiment (two-layer, quasi-geostrophic hemispheric model)

1963: Smagorinsky, Manabe and collaborators at GFDL, USA

– Nine level primitive equation model

1960s and 1970s: Other groups and their offshoots began work

– University of California Los Angeles (UCLA), National Center for Atmospheric Research (NCAR, Boulder, Colorado) and UK Meteorological Office

1990s: Atmospheric Model Intercomparison Project (AMIP)

– Results from about 30 atmospheric models from around the world

2001: IPCC Third Assessment Report

– 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.

Colloquium on Climate and Health 17 July 2006 Slingo

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) Colloquium on Climate and Health 17 July 2006

Evolution of Climate Models

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Basic Equations for the Atmosphere

• • •

Momentum equation:

d

V

/dt = •  p -2  Where  =1/  ^

V

(  –g

k

+F +D m is density), p is pressure,  (including effects of rotation),

k

is rotation rate of the Earth, g is acceleration due to gravity is a unit vector in the vertical, F is friction and D m is vertical diffusion of momentum

Thermodynamic equation:

dT/dt = Q/c p • + (RT/p)  + D H where c p is the specific heat at constant pressure, R is the gas constant,  is the vertical velocity, D H is the vertical diffusion of heat and Q is the internal heating from radiation and condensation/evaporation; Q = Q rad + Q con

Continuity equation for moisture (similar for other tracers):

dq/dt = E – C + D q • where E is the evaporation, C is the condensation and D q is the vertical diffusion of moisture Colloquium on Climate and Health 17 July 2006 Slingo

Vertical Discretization of Equations

Vertical Grid for Atmosphere Colloquium on Climate and Health 17 July 2006

Horizontal Discretization of Equations

T31 T42 T85 T170 Strand Colloquium on Climate and Health 17 July 2006

•

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

.

• 1.

There are three types of parameterization; • • Processes taking place on scales smaller than the grid-scale, which are therefore not explicitly represented by the resolved motion; 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) 2.

3.

• • Processes that contribute to internal heating (non-adiabatic) 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) Colloquium on Climate and Health 17 July 2006 Slingo

Parameterized Processes

Slingo Colloquium on Climate and Health 17 July 2006

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

Biogeophysics Hydrology Reflected Solar Radiation Absorbed Solar Radiation Soil Heat Flux Momentum Flux Wind Speed 0 u a Precipitation Interception Evaporation Canopy Water Transpiration Heat Transfer Melt Sublimation Snow Throughfall Stemflow Evaporation Infiltration Surface Runoff Soil Water Redistribution Drainage Colloquium on Climate and Health 17 July 2006

Subgrid Structure of the Land Model

Gridcell

Landunits Glacier Columns Wetland Vegetated Lake 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 Colloquium on Climate and Health 17 July 2006

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

Colloquium on Climate and Health 17 July 2006

The CCSM Community

NCAR Development Group Universities Labs Physics Applications Chemistry

Land (CLM 3)

CCSM3

Atmosphere (CAM 3) Coupler (CPL 6) Ocean ( POP 1) Sea Ice (CSIM 4)

Model Users

Current Users:

• Institutions: ~200

Downloads of CCSM3:

• Users: ~600

Climate Community

Publications:

• NCAR: 87 • Universities: 94 • Labs/Foreign: 48

Total:

229 Colloquium on Climate and Health 17 July 2006

Changes in Atmospheric Composition

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Forcing: Changes in Exchange of Energy

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Components of Aerosol Forcing

Back Scattering (Cooling) Absorption (Atmospheric Warming) Forward Scattering Absorption (Column Warming) Cloud Evaporation (Warming) Cloud Seeding (Cooling) Suppression of Rain; increase of life time (Cooling) Dimming of Surface Surface Cooling

Colloquium on Climate and Health 17 July 2006 Ramaswamy

Simulations of Aerosol Distributions

1995-2000 Colloquium on Climate and Health 17 July 2006

Fidelity of 20 th 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 CO 2 and passive tracers (CFCs)

Colloquium on Climate and Health 17 July 2006

Simulation of Sea-Surface Temperature Colloquium on Climate and Health 17 July 2006

Increases in Global Ocean Temperatures

(Results from CCSM3 Ensemble)

L = Levitus et al (2005) Ensemble Members Relative Model Error < 25% Gent et al, 2005 Colloquium on Climate and Health 17 July 2006

Global Ocean Inventory of CFC-11

(Passive tracer proxy for CO 2 )

} Ensemble Members Data CCSM3 Gent et al, 2005 Colloquium on Climate and Health 17 July 2006

Penetration Depth of CFC-11 WOCE data (Willey et al, 2004) m CCSM3 Simulation Colloquium on Climate and Health Gent et al, 2005 17 July 2006

Projections for Global Surface Temperature Meehl et al, 2005 Colloquium on Climate and Health 17 July 2006

Projections for Regional Surface Temperature Change Meehl et al, 2005 Colloquium on Climate and Health 17 July 2006

Projections for Global Sea Level Meehl et al, 2005 Colloquium on Climate and Health 17 July 2006

Committed Change: Global Temperature and Sea Level Teng et al, 2005 Colloquium on Climate and Health 17 July 2006

Changes in Sea Ice Coverage

Meehl et al, 2005 Colloquium on Climate and Health 17 July 2006

Changes in Permafrost Coverage

Colloquium on Climate and Health 17 July 2006 Lawrence and Slater, 2005: Geophys. Res. Lett.

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.

Colloquium on Climate and Health 17 July 2006

Recent evolution of climate forcing

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Hansen and Sato, 2001

17 July 2006

Simulating the chemical state of the climate system

Emissions Chemistry + BGC + Physics + Ecosystems Concentrations Forcing Climate Response 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.

Colloquium on Climate and Health 17 July 2006

CCSM4: a 1

st

generation Earth System Model

Coupler Land

C/N Cycle Dyn.

Veg.

Land Use Ice Sheets

Atmosphere

Upper Atm.

Ocean

Ecosystem & BGC

Sea Ice Colloquium on Climate and Health 17 July 2006

Historical changes in agricultural land use

Colloquium on Climate and Health

Johan Feddema

17 July 2006

Changes in surface albedo by land use

Johan Feddema

Colloquium on Climate and Health 17 July 2006

Evolution of tropospheric ozone

(1890-2100, following A2 scenario)

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Lamarque et al, 2005

17 July 2006

Flux of CO

2

into the world oceans

(Ocean ecosystem model) Moore, Doney, and Lindsay

Colloquium on Climate and Health 17 July 2006

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