Center of Ocean-Land- Atmosphere Studies CLIM101: Global Warming - Weather, Climate and Global Society What is a climate model? What is a climate model?

Center of Ocean-Land-Atmosphere Studies CLIM101: Global Warming - Weather, Climate and Global Society

What is a climate model?

If we cannot predict weather, how can we predict climate?


Reading for Week 6Lecture 11

What is a climate model?

• RG 227-244• GW Chapter 5• IPCC WG1 Chapter 8, FAQ 8.1 How Reliable Are the

Models Used to Make Projections of Future Climate Change? – ftp://iges.org/pub/emilia/CLIM101_2010/reading/

IPCC_WG1_FAQ8.1.pdf


• Substitute for reality• Closely mimics some

essential elements• Omits or poorly

mimics non-essential elements

What is a Model?


What is a Model?

• Quantitative and/or qualitative representation of natural processes (may be physical or mathematical)

• Based on theory• Suitable for testing “What if…?” hypotheses• Capable of making predictions


Input Data Model Output Data

Tunable Parameters

What output data might we consider for

a typical climate model?

What input data might we consider for a

typical climate model?

What are the tunable parameters of interest?

What is a Model?


Input Data Model Output Data

Tunable Parameters

What is a Model?

• Temperature, Pressure, Humidity, Wind Velocity, Salinity, Ice Mass, …

• Averaged by Day, Month, Season, Year, …

• Need verification with obs

• Energy flux from Sun• Atmospheric

constituents (CO2, etc.)

• Landscape features (geography, topography, land use, etc.)

• Initial conditions of all predicted variables

Properties of:Clouds, Ice, Aerosol …

CLIMATE DYNAMICS OF THE PLANET EARTH

S

Ω

a

g

T4

WEATHER

CLIMATE .

hydrodynamic instabilities of shear flows; stratification & rotation; moist thermodynamics

day-to-day weather fluctuations; wavelike motions: wavelength, period, amplitude

T_

y,U_

yT_

z,U_

z

S, , a, g, ΩO3

H2OCO2

stationary waves (Q, h*), monsoons

h*: mountains, oceans (SST)w*: forest, desert (soil wetness)

(albedo)




(approximation)

Mass conservation

Energy conservation

Newton’s law

= p / ps


Equations of motions and laws of thermodynamics predict rate of change of:

T, P, V, q, etc. (A, O, L, CO2, etc.)


Equations of motions and laws of thermodynamics predict rate of change of:



Discretization

Atmosphere and ocean are continuous fluids … but computers can only represent discrete objects


Discretization

Atmosphere and ocean are continuous fluids … but computers can only represent discrete objects


• Equations of motions and laws of thermodynamics to predict rate of change of:


• 10 Million Equations: 100,000 Points × 100 Levels × 10 Variables

• With Time Steps of: ~ 10 Minutes

• Use Supercomputers

What is a Climate Model?


Numerical Weather Prediction

1. Determine (continuous) equations to be solved– Equation of state or Ideal Gas Law (Boyle’s Law relates P V, Charles’

Law relates V T, Gay-Lussac’s Law relates T P)– Conservation of mass (dry air, water)– Conservation of energy– Conservation of angular momentum– Result: set of coupled, nonlinear, partial differential equations

2. Discretize the equations for numerical solution (typically requires computer)

3. Measure current state of global atmosphere to obtain initial conditions

4. Solve the initial value problem to produce a forecast5. Take into account uncertainty in measured atmospheric state by

repeating step 4 over an ensemble of slightly different initial conditions




Climate Predictability: Averages in space and/or time are more predictable than instantaneous values.

Energy balance sets the range of weather variation.


Science

Predictability in the Midst of Chaos: A Scientific Basis for Climate

Forecasting23 October 1998, Volume 282, pp. 728-731

J. Shukla

Soil Wetness

SST Anomalies (oC)


1998 JFM SST [oC]

JFM SST Climatology [oC]

1998 JFM SST Anomaly [oC]

El Nino/Southern Oscillation


El Nino/Southern Oscillation


Rainfall Anomalies


ca 2000AGCM

Model Simulation of ENSO Effects500 hPa Height Anomalies (ACC = 0.98)


Moore’s “Law”

IPCC-1

IPCC-2

IPCC-3

IPCC-4

103-fold jump since 1st IPCC106-fold jump in last 30 years

Latest advance due to dual-core chipsNear-term advance w/quad-core chips


Johnvon Neumann

Seymour Cray& Cray-1

ENIAC

IBM 360

Cray-2

ColumbiaNASA


Climate Models circa early 1990s Global coupled climate models in 2007 and new ESMs

New decadal prediction modelsGlobal coupled models in 5 yrs post-AR5

~500 km ~100 – 200 km

~50 km ~10 km


European Heat Wave 2003


JJA 2003 SST Anomaly


JJA obs

OBS.SST-CLIM.SST exp. result significant at more than 90% sig.lev.








J. Shukla, T. DelSole, M. Fennessy, J. Kinter and D. PaolinoGeophys. Research Letters, 33, doi10.1029/2005GL025579, 2006

Climate Model Fidelity and Projections of Climate Change


Regional Climate Change – Beyond Today’s Models’ Ability?


Annual Mean Precipitation ChangeEurope: 21st C minus 20th C

T159 (125-km) T1279 (16-km)

“Time-slice” runs of the ECMWF IFS global atmospheric model with observed SST for the 20th century and CMIP3 projections of SST for the 21st century at two different model resolutions

The continental-scale pattern of precipitation change associated with global warming is the same, but the regional details are quite different, particularly in southern Europe.


Summary1. Weather prediction depends on initial conditions (global

observations).

2. Short-term climate (seasonal-decadal) depends on boundary conditions (SST, soil wetness, snow, sea ice, etc.), which depends on ocean-atmosphere interactions.(natural forcings: sun, volcanoes, etc.)

3. Long-term climate change depends on “external” forcing (Human: greenhouse gases, land cover change, etc.)

Center of Ocean-Land- Atmosphere Studies CLIM101: Global Warming - Weather, Climate and Global Society What is a climate model? What is a climate model?

Documents

global warming weather

climate dynamics

typical climate model

global society substitute

center of ocean

g t4t4 weatherweather

land use

aerosol slide