The Philosophy of Climate ModelingThe Philosophy of Climate Modeling

Jeffrey T. KiehlClimate Change Research

SectionNCAR

Jeffrey T. KiehlClimate Change Research

SectionNCAR

OutlineOutline

Philosophy & Climate Modeling Climate Science Finding a Research Problem Why Model the Climate System? The Way of Climate Modeling Summary

Philosophy & Climate Modeling Climate Science Finding a Research Problem Why Model the Climate System? The Way of Climate Modeling Summary

Philosophy & Climate Modeling

Philosophy & Climate Modeling

Epistemology - What can we know? Models as representations

Metaphysics - What is? How real are the representations?

Ethics - What is Good/Evil? What do we choose to present?

Aesthetics - What is Beauty? How do we present our results?

Politics - Ethics of Groups What are the social implications of our results?

Epistemology - What can we know? Models as representations

Metaphysics - What is? How real are the representations?

Ethics - What is Good/Evil? What do we choose to present?

Aesthetics - What is Beauty? How do we present our results?

Politics - Ethics of Groups What are the social implications of our results?

Climate ScienceClimate Science

Forcing Feedbacks Response

Variability

We all fit in here somewhere!

Finding a Research Problem

Finding a Research Problem

Something that Really Grabs You (Follow Your Bliss)

Tractable (be aware of timescales involved, complexity of system)

Affordable (can you pay for it?)

Valuable (to whom?)

Something that Really Grabs You (Follow Your Bliss)

Tractable (be aware of timescales involved, complexity of system)

Affordable (can you pay for it?)

Valuable (to whom?)

Why Model the Climate System?

Why Model the Climate System?

Develop a fundamental understanding of Earth’s climate system (What Ifs)

To look at mechanisms in the system To look at interactions within the system To replicate reality (past, present, future)

To provide information for policy decisions

Can you think of others?

Develop a fundamental understanding of Earth’s climate system (What Ifs)

To look at mechanisms in the system To look at interactions within the system To replicate reality (past, present, future)

To provide information for policy decisions

Can you think of others?

Climate What IfsClimate What Ifs

What if the solar output decreased? What if there were no mountains? What if Earth rotated twice as fast? What if aerosol loading doubled? What if cloud drop size decreased? What if tropical forests disappeared?

What if the solar output decreased? What if there were no mountains? What if Earth rotated twice as fast? What if aerosol loading doubled? What if cloud drop size decreased? What if tropical forests disappeared?

The Way of Climate Modeling

The Way of Climate Modeling

Forming a Question Setting up a simulation Simulation Strategy What do you look for? What can you explain, or not? Looking at the process level Forming a new question

Forming a Question Setting up a simulation Simulation Strategy What do you look for? What can you explain, or not? Looking at the process level Forming a new question

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Forming a QuestionForming a Question

Decides the Model Configuration Individual or Group Needed?

Decides the Model Configuration Individual or Group Needed?

Don’t get involved in partial problems, but always take flightto where there is a free view over the whole single greatproblem, even is the view is still not a clear one.

Ludwig Wittgenstein

Setting up a Simulation

Setting up a Simulation

Boundary Conditions Initial Conditions Model Spin up Defining the control simulation

To tune or not to tune

Boundary Conditions Initial Conditions Model Spin up Defining the control simulation

To tune or not to tune

Energy Balance

Surface Temperature

Sea Ice Area

Spin-up~100 yr

CCSM3T31X3 Control

To Tune or Not?To Tune or Not?

ocean

atmosphere

The great Way is easy,yet people prefer the side paths.Be aware when things are out of balance.

Tao Te Ching 53

ocean

atmosphere

ρCp∂T

∂t≈ 0 ρCp

∂T

∂t> 0

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Net Energy Flux into Earth System

Net Energy Flux into Ocean

Simulation StrategySimulation Strategy

Length of simulation Transient Steady State

Time scales of problem When do you stop the simulation?

Length of simulation Transient Steady State

Time scales of problem When do you stop the simulation?

What do you look for?What do you look for?

Are there optimal metrics? Model versus data Model versus control

Don’t be narrowly focused on a few metrics Global Regional Mean state Variability

How to display your metrics?

Are there optimal metrics? Model versus data Model versus control

Don’t be narrowly focused on a few metrics Global Regional Mean state Variability

How to display your metrics?

What can(‘t) you explain?

What can(‘t) you explain?

Where to look? Budgets and Causality (the chicken and the egg)

What tools are available? Process studies Sensitivity studies Temporal evolution

Where to look? Budgets and Causality (the chicken and the egg)

What tools are available? Process studies Sensitivity studies Temporal evolution

Kiehl and Shields (2005)

Inefficient mixingin Permian ocean indicativeof anoxia

10XCO2

1XCO2

∂ρd∂z

∂ρd∂z

Process StudiesProcess Studies

Temporal Evolution and Correlation

Regional Analysis Sensitivity of Parameterizations

Single Column Model Data Assimilation CAPT: A CAM Forecast Model

Temporal Evolution and Correlation

Regional Analysis Sensitivity of Parameterizations

Single Column Model Data Assimilation CAPT: A CAM Forecast Model

CCPP ARM Parameterization Testbed (CAPT)

Hannay, Williamson, Kiehl

SummarySummary

Big challenges in model biases: Tropical mean state Tropical variability (e.g. ENSO) Cold polar tropopause Continental precipitation High latitude continental temperatures

Big challenges in model biases: Tropical mean state Tropical variability (e.g. ENSO) Cold polar tropopause Continental precipitation High latitude continental temperatures

SummarySummary

Big Challenges Model Processes Fully interactive biogeochemical, atmospheric chemical system model

Regional Simulation of the 20th century climate

Aerosol indirect effect

Big Challenges Model Processes Fully interactive biogeochemical, atmospheric chemical system model

Regional Simulation of the 20th century climate

Aerosol indirect effect

In the beginner’s mind there are many possibilities,but in the expert’s mind there are few.

Shunryu Suzuki