Climate ModelingClimate Modeling

Idania Rodriguez

EEES PhD Student Idania Rodriguez

EEES PhD Student

“Science Explorations Through the Lens of Global Climate Change” Workshop

OutlineOutline

• Introduction• Motivation • Building a Climate Model• Model Complexity• Model Uncertainty• Model Validation

• Introduction• Motivation • Building a Climate Model• Model Complexity• Model Uncertainty• Model Validation

What is a Climate Model?What is a Climate Model? a mathematical representation of

physical, biological and chemical processes that determine climate

a mathematical representation of physical, biological and chemical processes that determine climate

• Mathematical Equationso Ordinary Differential time-dependento Partial Diff. time- & space-dependento Parameterized 1 parameter in terms of 2+o Empirical reproduce observed results

Computers are needed to solve the equations arising from climate models

• Mathematical Equationso Ordinary Differential time-dependento Partial Diff. time- & space-dependento Parameterized 1 parameter in terms of 2+o Empirical reproduce observed results

Computers are needed to solve the equations arising from climate models

MotivationMotivationHumans have affected and will likely continue to affect Earth’s climate

Climate models can• Help us understand sensitivities of

climate system• Project future changes from plausible

scenarios• Illustrate benefits of mitigating impacts

caused by these potential changes as an instrument of climate policy

Humans have affected and will likely continue to affect Earth’s climate

Climate models can• Help us understand sensitivities of

climate system• Project future changes from plausible

scenarios• Illustrate benefits of mitigating impacts

caused by these potential changes as an instrument of climate policy

Global Mean Radiative Forcing by 2005 (WmGlobal Mean Radiative Forcing by 2005 (Wm-2-2) )

Cloud Processes

Surface Processes

RadiativeProcesses

Meteorological Processes

Transport Processes

GasProcesses

AerosolProcesses

Building a Climate ModelBuilding a Climate Model

Source: Adapted from IPCC, 2001a

Model ComplexityModel ComplexityFrom the simplest model…

to an AOGCM

From the simplest model…

to an AOGCM

Source: IPCC 2001

EiE

Ein Eout

Tempave

[CO2]

Model ComplexityModel ComplexityHow do these models differ?• Space Resolution

How do these models differ?• Space Resolution

Land/Land/OceanOcean

AtmosphereAtmosphereEnergy & Energy & MassMassTransferTransfer

2-Box 2-Box No land/ocean distinctionNo land/ocean distinction

LandLand

AtmosphereAtmosphere

OceanOcean

3-Box 3-Box No vertical or horizontal distinctionNo vertical or horizontal distinction

Model ComplexityModel Complexity• Inclusion/Complexity of Processes• Input Properties• Inclusion/Complexity of Processes• Input Properties

Multi-box multi-layerMulti-box multi-layer

LandLand

AtmosphereAtmosphere

OceanOceanAOGCM AOGCM Each 3D cell - few Each 3D cell - few o o of latitude & of latitude & longitude / 10-40 layerslongitude / 10-40 layers

Model ComplexityModel Complexity• Space/Time Scale

Inputs to a climate model depend on what we want to learn from it…

• Space/Time Scale

Inputs to a climate model depend on what we want to learn from it…

Million-year global projectionMillion-year global projection

AtmosphereAtmosphere

OceansOceans

Cryosphere (sea ice/glaciers)Cryosphere (sea ice/glaciers)

Land surface & biotaLand surface & biota

Biogeochem cyclesBiogeochem cycles

Solar input long-term Solar input long-term variation variation

Regional climate over next Regional climate over next centurycentury

AtmosphereAtmosphere

OceansOceans

Day to night variationsDay to night variations

More geographic detail More geographic detail of region of region

More temporal detail of More temporal detail of regionregion

Model ComplexityModel Complexity• Sub-grid scale effects

o Partial differential eqns arising from processes cannot be solved analytically

o GCMs break the atmosphere, land and oceans on grid boxes & average processes to that scale to approximate solutions

But many events relevant to climate happen on smaller scales, e.g. clouds

Solution: treat implicitly using “parameterizations”

• Sub-grid scale effectso Partial differential eqns arising from

processes cannot be solved analyticallyo GCMs break the atmosphere, land and

oceans on grid boxes & average processes to that scale to approximate solutions

But many events relevant to climate happen on smaller scales, e.g. clouds

Solution: treat implicitly using “parameterizations”

Grid sky half-Grid sky half-covered bycovered bycloudsclouds

Grid skyGrid skyuniformly uniformly lightly lightly covered - covered - 1/2 sunlight1/2 sunlight

Model UncertaintiesModel Uncertainties• Future emissions• Future emissions

Model UncertaintiesModel Uncertainties

• Approximations/Simplifications to Chemical, Physical & Biological Processes• Example: GATOR-GCMM includes organic

chemistry using a condensed mechanism OLE + O3 CH3CHO + H2COO + XOP

vs. C2H4 + O3 HCHO + H2COO (explicit)

• Using numerical methods to solve ODEs/PDEs instead of analytical solutions

• Sub-grid scale effects / Parameterizations

• Approximations/Simplifications to Chemical, Physical & Biological Processes• Example: GATOR-GCMM includes organic

chemistry using a condensed mechanism OLE + O3 CH3CHO + H2COO + XOP

vs. C2H4 + O3 HCHO + H2COO (explicit)

• Using numerical methods to solve ODEs/PDEs instead of analytical solutions

• Sub-grid scale effects / Parameterizations

C=C

Model UncertaintiesModel Uncertainties

• Poorly understood phenomenao Cloud effects on climate (aerosol

indirect)

• Poorly understood phenomenao Cloud effects on climate (aerosol

indirect)

Model ValidationModel ValidationHow can we know the model works?Diverse Techniques• Climatic response to volcanic eruptions

How can we know the model works?Diverse Techniques• Climatic response to volcanic eruptions

Volcanoes effect on global temperature

Black: actual temperature

Yellow: 14 different models

Red: averageof all simulations

Source: AR4WG1, IPCC, 2007

Model ValidationModel Validation• Modeling past climate trends• Modeling past climate trends

Source: IPCC, 2001

Model ValidationModel ValidationOther Techniques• Modeling seasonal temperature variations• Comparing to geographical patterns

o Precipitation

• Comparing to effects of climate predictedo Animal & plant response to climate change

Other Techniques• Modeling seasonal temperature variations• Comparing to geographical patterns

o Precipitation

• Comparing to effects of climate predictedo Animal & plant response to climate change

Questions?Questions?

Thank you for your attention

Thank you for your attention