What is a climate model? What is a climate model?

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

Jagadish ShuklaJagadish Shukla

CLIM 101: Weather, Climate and Global Society

Lecture 11: Oct 6, 2009

Reading for Week 6Reading for Week 6Lecture 11Lecture 11

What is a climate model?What is a climate model?

• GW Chapter 5• IPCC WG1 Chapter 8, FAQ 8.1 How Reliable

Are the Models Used to Make Projections of Future Climate Change?

IPCC has been established by WMO and UNEP to assess scientific, IPCC has been established by WMO and UNEP to assess scientific, technical and socio- economic information relevant for the technical and socio- economic information relevant for the understanding of climate change, its potential impacts and options for understanding of climate change, its potential impacts and options for adaptation and mitigation.adaptation and mitigation.

IPCC has been established by WMO and UNEP to assess scientific, IPCC has been established by WMO and UNEP to assess scientific, technical and socio- economic information relevant for the technical and socio- economic information relevant for the understanding of climate change, its potential impacts and options for understanding of climate change, its potential impacts and options for adaptation and mitigation.adaptation and mitigation.

Intergovernmental Panel Intergovernmental Panel on Climate Change (IPCC) on Climate Change (IPCC)

Working Group I: The Physical Science Basis

Working Group II: Impacts, Adaptation and Vulnerability

Working Group III: Mitigation of Climate Change

• Largest number of U.S. scientists: nominated by the U.S. Govt.

• Highest skepticism : “U.S. Govt.”

• 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

What is a Model?What is a Model?

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?What is a Model?

Dynamics

Physical processes

Climate System ModelingClimate System ModelingAtmospheric General Circulation Model

Basic Equations

CLIMATE DYNAMICS CLIMATE DYNAMICS OF THE PLANET EARTHOF 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 to predict rate of change of:

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

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

• With Time Steps of: ~ 10 Minutes

• Use Supercomputers

What is a Climate Model?What is a Climate Model?

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

Johnvon Neumann

Seymour Cray& Cray-1

ENIAC

IBM 360

Cray-2

ColumbiaNASA

Weather PredictionWeather PredictionFuture pressure = current pressure + (rate of change of pressure) x t

Future temperature = current temp. + (rate of change of temp.) x t

Current pressure & temperature: use global observations

For rate of change: use mathematical equations

For producing forecast: use supercomputers

Sea Level Pressure (mb) & Precipitation Rate Sea Level Pressure (mb) & Precipitation Rate (mm/12Hr)(mm/12Hr)

00Z Tue 10 Nov 199800Z Tue 10 Nov 1998

Sea Level Pressure (mb) & Precipitation Rate Sea Level Pressure (mb) & Precipitation Rate (mm/12Hr)(mm/12Hr)

12Z Tue 10 Nov 199812Z Tue 10 Nov 1998

Sea Level Pressure (mb) & Precipitation Rate Sea Level Pressure (mb) & Precipitation Rate (mm/12Hr)(mm/12Hr)

00Z Wed 11 Nov 199800Z Wed 11 Nov 1998

Numerical Weather Numerical Weather PredictionPrediction

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

Science

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

ForecastingForecasting

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

J. Shukla

Soil WetnessSoil Wetness

SST Anomalies (SST Anomalies (ooC)C)

1998 JFM SST [oC]

JFM SST Climatology [oC]

1998 JFM SST Anomaly [oC]

El Nino/Southern OscillationEl Nino/Southern Oscillation

El Nino/Southern OscillationEl Nino/Southern Oscillation

Rainfall AnomaliesRainfall Anomalies

Vintage 2000AGCM

Model Simulation of ENSO EffectsModel Simulation of ENSO Effects500 hPa Height Anomalies (ACC = 0.98)500 hPa Height Anomalies (ACC = 0.98)

European Heat Wave 2003European Heat Wave 2003

JJA 2003 SST AnomalyJJA 2003 SST Anomaly

JJA obs

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

• 2003

• Heat wave hits• Europe

• 30,000 people die• in Western

Europe

observationsHadCM3 Medium-High (SRES A2)

2003

2040s

2060sT

emp

erat

ure

an

om

aly

(wrt

196

1-90

) °

C

GEC is more acute than everGEC is more acute than ever

Courtesy of P. Houser (GMU)

200 km

Computing Capability & Global Model Grid Size (km)

Peak Rate: 10 TFLOPS 100 TFLOPS 1 PFLOPS 10 PFLOPS 100 PFLOPS

Cores(1st year available)

1,400

(2006)

12,000

(2008)

80-100,000

(2009)

300-800,000

(2011)

6,000,000?

(20xx?)

Global NWP0:

5-10 days/hr18 - 29 8.5 - 14

4.0 - 6.3(~20X106 points)

1.8 - 2.9 0.85 - 1.4

Seasonal1:

50-100 days/day17 - 28 8.0 - 13

3.7 - 5.9(~20X106 points)

1.7 - 2.8 0.80 - 1.3

Decadal1:

5-10 yrs/day57 - 91 27 - 42

12 - 20(~2X106 points)

5.7 - 9.1 2.7 - 4.2

Climate Change2:

20-50 yrs/day120 - 200 57 - 91

27 - 42(~0.5X106 points)

12 - 20 5.7 - 9.1

Range: Assumed efficiency of 10-40%0 - Atmospheric General Circulation Model (AGCM; 100 levels)1 - Coupled Ocean-Atmosphere-Land Model (CGCM; ~ 2X AGCM computation with 100-level OGCM)2 - Earth System Model (ESM; ~ 2X CGCM computation)

* Core counts above O(104) are unprecedented for weather or climate codes, so the last 3 columns require getting 3 orders of magnitude in scalable parallelization (scalar processors assumed; vector processors would have lower processor counts)

Thanks to Jim Abeles (IBM)

• Geographic resolution characteristic of the generations of climate models used in the IPCC Assessment Reports: FAR (IPCC, 1990), SAR (IPCC, 1996), TAR (IPCC, 2001a), and AR4 (2007).

• The figures above show how successive generations of these global models increasingly resolved northern Europe. These illustrations are representative of the most detailed horizontal resolution used for short-term climate simulations.

• The century-long simulations cited in IPCC Assessment Reports after the FAR were typically run with the previous generation’s resolution. Vertical resolution in both atmosphere and ocean models is not shown, but it has increased comparably with the horizontal resolution, beginning typically with a single-layer slab ocean and ten atmospheric layers in the FAR and progressing to about thirty levels in both atmosphere and ocean.

Center of Ocean-Land-Center of Ocean-Land-Atmosphere studiesAtmosphere studies

Projection of Global WarmingProjection of Global WarmingMean of 15 Models Surface Air Temperature Mean of 15 Models Surface Air Temperature

DifferenceDifference(Sresa1b YR 71-100) minus (20c3m 1969-98), Global Average = (Sresa1b YR 71-100) minus (20c3m 1969-98), Global Average = 2.612.61

IPCC 2007

1.0º C1.0º C

Increase in Surface TemperatureIncrease in Surface Temperature

ObservationsPredictions with Anthropogenic/Natural forcingsPredictions with Natrual forcings

Center of Ocean-Land-Atmosphere studies

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 ChangeClimate Model Fidelity and Projections of Climate Change

SummarySummary1. 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 “exteranal” forcings (Human: greenhouse gases, land cover change, etc.)

THANK YOU!

ANY QUESTIONS?