an introduction to climate models: principles and applications

Colloquium on Climate and Health17 July 2006

An Introduction to Climate Models:Principles and Applications

William D. CollinsNational Center for Atmospheric Research

Boulder, Colorado USA


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


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


Exchange of Energy in the Climate


Components of the Climate System

Slingo


Time Scales in the Climate System


Configuration of NCAR CCSM3(Community Climate System Model)

Atmosphere(CAM 3.0)

T85 (1.4o)

Ocean(POP 1.4.3)

(1o)

Coupler(CPL 6)

Sea Ice(CSIM 4)

(1o)

Land(CLM2.2)

T85 (1.4o)


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


• 1922: Lewis Fry Richardson– Basic equations and methodology of numerical weather prediction

• 1950: Charney, Fjørtoft and von Neumann (1950)– First numerical weather forecast (barotropic vorticity equation model)

• 1956: Norman Phillips– 1st 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.

Brief History of Climate Modeling

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 threeadjacent zones so as to maintain communication to North and South of the map…”

Lewis Fry RichardsonWeather Prediction by Numerical Process (1922)


Evolution of Climate Models


• Momentum equation:

dV/dt = -p -2^V –gk +F +Dm

• 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

• Thermodynamic equation:

dT/dt = Q/cp + (RT/p) + DH

• 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

Basic Equations for the Atmosphere

Slingo


Vertical Discretization of Equations

Vertical Grid for Atmosphere


Horizontal Discretization of Equations

T31 T42

T85 T170

Strand


• 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;• 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. Processes that contribute to internal heating (non-adiabatic)• Radiative transfer and precipitation

• Both require the prediction of cloud cover

3. Processes that involve variables additional to the basic model variables (e.g. land surface processes, carbon cycle, chemistry, aerosols, etc)

Physical Parameterizations

Slingo


Parameterized Processes

Slingo


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

Drainage

Hydrology

Canopy Water

Evaporation

Interception

SnowMelt

Sublimation

ThroughfallStemflow

Infiltration Surface Runoff

Evaporation

Transpiration

Precipitation

Soil Water

Redistribution

Direct Solar

Radiation

Absorbed SolarRadiation

Diff

use

Sol

ar

Rad

iatio

n

Long

wav

e R

adia

tion

Reflected Solar Radiation

Em

itted

Lon

g-w

ave

Rad

iatio

n

Sen

sibl

e H

eat

Flu

x

Late

nt H

eat

Flu

x

ua0

Momentum FluxWind Speed

Soil Heat Flux

Heat Transfer

Pho

tosy

nthe

sis

Biogeophysics

Processes Included in the CCSM Land Model


Subgrid Structure of the Land Model

Gridcell

Glacier Wetland Lake

Landunits

Columns

PFTs

UrbanVegetated

Soil Type 1


“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


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


The CCSM Community

Atmosphere(CAM 3)

Ocean(POP 1)

Coupler(CPL 6)

Sea Ice(CSIM 4)

Land(CLM 3)

CCSM3

Model Users Climate Community

Development Group

NCAR Universities Labs

Physics Applications Chemistry

Current Users:• Institutions: ~200

Downloads of CCSM3:• Users: ~600

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

Total: 229


Changes in Atmospheric Composition


Forcing: Changes in Exchange of Energy


Back Scattering (Cooling)

Absorption(Atmospheric Warming)

Dimming of Surface Surface Cooling

Absorption (Column Warming)

Cloud Evaporation(Warming)Cloud Seeding(Cooling)

Suppression of Rain; increase of life time (Cooling)

Forward Scattering

Components of Aerosol Forcing

Ramaswamy


Simulations of Aerosol Distributions

1995-2000


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 uptakeEffects of ocean on transient climate response

– Realism of ocean mixed layer and ventilationOcean uptake of CO2 and passive tracers (CFCs)


Simulation of Sea-Surface Temperature


Increases in Global Ocean Temperatures(Results from CCSM3 Ensemble)

Gent et al, 2005

L = Levitus et al (2005)

EnsembleMembers

Relative ModelError < 25%


Global Ocean Inventory of CFC-11(Passive tracer proxy for CO2)

Gent et al, 2005

EnsembleMembers}

Data

CCSM3


Penetration Depth of CFC-11

WOCE data (Willey et al, 2004)

Gent et al, 2005

CCSM3 Simulation

m


Projections for Global Surface Temperature

Meehl et al, 2005


Projections for Regional Surface Temperature Change

Meehl et al, 2005


Projections for Global Sea Level

Meehl et al, 2005


Committed Change:Global Temperature and Sea Level

Teng et al, 2005


Changes in Sea Ice Coverage

Meehl et al, 2005


Changes in Permafrost Coverage

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.


Recent evolution of climate forcing

Hansen and Sato, 2001


Simulating the chemical state of the climate system

EmissionsChemistry + BGC +

Physics + Ecosystems

ChemicalReservoirs

Concentrations ForcingClimateResponse

Feedbacks

• In the past, we have generally used offline models to predict concentrationsand 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.

Offline models

Feedbacks

ChemicalReservoirs


CCSM4: a 1st generation Earth System Model

Atmosphere Ocean

Coupler

Sea IceLand

C/NCycle

Dyn.Veg.

Ecosystem & BGCGas chem.Prognostic

AerosolsUpperAtm.

LandUse

IceSheets


Historical changes in agricultural land use

Johan Feddema


Changes in surface albedo by land use

Johan Feddema


Evolution of tropospheric ozone(1890-2100, following A2 scenario)

Lamarque et al, 2005


Flux of CO2 into the world oceans(Ocean ecosystem model)

Moore, Doney, and Lindsay


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

an introduction to climate models: principles and applications

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