Climate Models – Part II

GEO 458, Spring 2010Feb 9, 2010

Why do we need climate models?

� to gain physical insight into the behavior of the climate system.

� to get a complete spatial and temporal description of the climate.

� to predict future climate.

Simple Energy Balance Model:

No Atmosphere case: T = 255 K ----> Too coldAtmosphere case: T = 288 K ----> Greenhouse Effect!

Atmosphere opaque to outgoing (terrestrial) longwave radiation.

Atmosphere transparent to incoming (solar) shortwave radiation.

SWLW

Last Class

• Energy Balance Models (EBMs): 0-D/1-D

• Radiative-Convective Models (RCs): 1-D/2-D

• Statistical Dynamical Models (SDs): 2-D

• General Circulation Models (GCMs): 3-D

Types of Climate models

These models increase,

- in complexity, from first to last,

- in the degree to which they simulate particular processes, and

- in their temporal and spatial resolution.

The simplest models permit little interaction between the primary processes, radiation, dynamics and surface processes, whereas the most complex models are fully interactive.

0-D

1-D

Energy Balance Models (EBMs)

- simulate the global radiation balance and the latitudinal energy transfer.

- Radiation Balance

Radiative - Convective Models (RCs)

- simulate in detail the transfer of energy through depth of the atmosphere.

- Radiation Balance- Vertically Resolved Atmosphere

Statistical Dynamical Models (SDs)

- combine the horizontal energy transfer modeled by EBMs with the

radiative-convective approach of RCs.

- Radiation Balance- Vertically Resolved Atmosphere- Surface Processes and dynamics

General Circulation Models

The most ‘complete’ models constructed by discretizing and then solving equations which represent the basic laws governing the behavior of the atmosphere, ocean and land surface.

- Radiation Balance- Vertically Resolved Atmosphere- Surface Processes and dynamics- 3-D

Radiative - The way in which the input and absorption of solar radiation and the

emission of infrared radiation are handled.

Dynamic - The movement of energy around the globe (from low to high latitudes) and

vertical movements (convection).

Components of Climate Model

Three major sets of processes that must be considered when constructing a climate model:

Surface processes - Inclusion of

land/ocean/ice and the resultant change in albedo, emissivity, and surface-atmosphere exchanges.

GCMs Grid

Horizontal Resolution:~100 to 200 km

A complete spatial description of the climate.

� Conservation of energy

� Conservation of momentum

� Conservation of mass

� Equation of state

Parameterization

The method of incorporating a process by representing it as a simplified function of some other fully resolved variables.

• Sub-grid scale (small to be resolved in time and space) processes cannot be modeled, but must be parameterized.

• e.g. cloud formation, soil moisture transfer or oceanic eddies.

• Use of observed data as the basis of relationships.

• Time scale determines types of parameterizations needed (long term climate vs. weather prediction).

Physical Equations and Grid

Physical Equations

Parameterizations of Processes

FeedbacksSolved for each grid cell

3-D Grid

State of climateas a function

of time

� Conservation of energy

� Conservation of momentum

� Conservation of mass

� Equation of state

� External - solar, orbital.

� Internal - volcanic eruptions, ice-sheet changes, human-induced changes.

• BMRC: Bureau of Meteorology Research Center (Australia)• COLA: Center for Ocean-Land Atmosphere Studies (USA)• ECMWF: European Center for Medium Range Weather Forecasts• GFDL: Geophysical Fluid Dynamics Laboratory (USA)• GISS: Goddard Institute for Space Studies (USA)• GLA: Goddard Laboratory for Atmospheres (USA)• LLNL: Lawrence Livermore National Laboratories (USA)• MPI: Max Planck Institut (Germany)• MRI: Meteorological Research Institute (Japan)• NCAR: National Center for Atmospheric Research (USA)• NMC: National Meteorological Center (USA)• NTU: National Taiwan University• UKMO: United Kingdom Meteorological Office• UCLA: University of California Los Angeles

Climate Modeling Groups

The development of climate models

The development of climate models

Atmospheric GCMs (AGCMs)

consist of a three-dimensional representation of the atmosphere coupled to the land surface and cryosphere. AGCMs are useful for studying atmospheric processes, the variability of climate and its response to changes in sea-surface temperature.

• Dynamics

• General circulation (winds)

• Physics

• Radiation

• Clouds

• Thermodynamics

• Moisture

• Surface and oceans

• effects of ice, snow, vegetation on temperature, albedo, emissivity, roughness

• Chemisty

• composition of the atmosphere

Oceanic GCM

� The thermodynamic sea-ice model is an integral part of the OGCM in some cases.

� Initial condition given to the oceanic GCMs are surface temperature, sea-ice extent, surface albedo over ice-covered and ice-free regions, sea-surface salinity, partial pressure of CO2, wind stress at surface and fluxes at surface etc.

� The topography of oceanic basins is very important for getting the coastal circulation properly.

Initial Conditions for Atmospheric/Oceanic GCMs

Atmospheric GCM

� Land surface models are treated as integral components of the atmospheric model.

� Initial condition given to drive the atmospheric GCMs are winds, temperature profile, specific humidity, orography, radiativefluxes at surface and top of the atmosphere, land-sea mask, hydrological parameters, albedo, snow-ice extent etc.

� Surface boundary forcing given to the atmospheric models are through SST.

Equilibration Time of the Climate System

Equilibration Time is the response time (or relaxation time) of the components of the climate system.

Coupled Ocean Atmosphere Models (AOGCMs)

• Comparison with observations/measurements.

• Comparison with paleoclimate data.

• Comparison with regional patterns of change (“finge r-printing”).

Model Validation

how well it simulates reality…

TemperatureValidation

Precipitation ValidationPrecipitation Validation

Simulated

Observed

IPCC Special Report on Emissions Scenarios

Scenarios based on:

- Population- Economic growth- Technological Innovations- Energy use and sources of

energy generation

40 scenarios, all equally valid.

Future global emissions of GHG will depend on a variety of assumptions regarding human behavior and activities

A1B

A1T

A1FI

Emission ScenariosEmission Scenarios

Projected Surface WarmingProjected Surface Warming

Projections of Surface TemperaturesProjections of Surface Temperatures

Projected Patterns of Precipitation ChangesProjected Patterns of Precipitation Changes