Climate Change: Demystifying the Application of Earth Systems Models for Climate Science

Richard B. Rood

Cell: 301-526-8572

2525 Space Research Building (North Campus)

rbrood@umich.edu

http://clasp.engin.umich.edu/people/rbrood

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June 20, 2017

Some Resources

• Gettelman and Rood: Demystifying Climate Models: A User’s Guide to Earth Systems Models
• Springer, Open Source, (It is free.)

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• Introductory Material OpenClimate Mini-page

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• Model Introduction OpenClimate Mini-page

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• Rood’s Class MediaWiki Site
• http://climateknowledge.org/classes/index.php/Climate_Change:_The_Move_to_Action

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Outline

• Models
• Definition
• Models and Scientific Investigation
• Models in Climate Science
• Establishing Trust: Numerical Experimentation
• Looking Towards the Future
• Summary

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Assumption

• I am talking to an audience that knows what “model” means in the context of weather and climate science.
• Knows the jargon of meteorology

From: http://www.halfhull.com/main.jpg

What is a Model?

• Model (Dictionary)
• A schematic description of a system, theory, or phenomenon that accounts for its known or inferred properties and may be used for further studies of its characteristics

We live lives full of models

• Models are everywhere in our lives and work
• Architecture
• Epidemiology
• Aerospace
• Computer assisted design
• Games
• The bridge over the Missouri River
• Landing things on Mars
• Investing my retirement account
• How much rent can I afford
• My digital thermometer

What is a Model?

• Model (Dictionary)
• A schematic description of a system, theory, or phenomenon that accounts for its known or inferred properties and may be used for further studies of its characteristics
• Weather and Climate
• Provide numerical approximations of the equations that describe the atmosphere, land, ocean, ice, biology of the Earth –
• process definition, diagnostics, predictions, and projections
• Solves conservation equations:
• energy, momentum, mass

Models and Scientific Investigation

OBSERVATIONS

THEORY

EXPERIMENT

Models and Scientific Investigation

OBSERVATIONS

THEORY

PREDICTION

Models and Scientific Investigation

OBSERVATIONS

PROCESSES

SIMULATION

Computational Science (Post and Votta, PhysToday, 2005)

• Computational Science & Numerical Simulation
• Given what we know, can we predict what will happen, and evaluate (validate) that what we predicted would happen, happened?
• Validation: Comparison with observations
• Philosophy: Do we ever know if we get the right answer for the right reason?
• Computational and natural science: Establish the credentials of a model to help inform us about the application for which the model was designed.

Models in Climate Science

Models and Model Infrastructure

Models & Model Simulations

Infrastructure

Solves the conservation equations

- Mass

- Momentum (~ weather)

- Energy (~climate)

Split into “processes”

- Fluid dynamics

- Radiation

- Moist physics

- Turbulence

Connects it all together. Critical for

- Scientific credibility

- Collaboration

- Development

- Efficiency

- Analysis

- End user

Observations and Models: Processes

Observations

Models & Model Simulations

Define & test model “physics”

Infrastructure

PROCESSES

DIAG. & TEST

Diagnostic applications

Observations and Models: Weather Forecasts

Observations

Models & Model Simulations

Start Forecasts

Infrastructure

INITIAL COND.

Validation

FORECASTS

Prognostic applications

Observations and Models: Assimilation

Observations

Models & Model Simulations

Assimilation & Reanalysis

Infrastructure

MELD

Initial Conditions

Validation

Scientific Investigation

Data System Monitoring

Observations and Models: Predictions and Projections

Observations

Models & Model Simulations

Assimilation & Reanalysis

Infrastructure

PROCESSES

INITIAL STATE

PREDICTIONS

PROJECTIONS

Diagnostic applications

Prognostic applications

Define & test model “physics”

Start Forecasts

Validation

Complexity / Types of Models�(Rood, Perspective)

• Conceptual / Heuristic Models
• Integrated, theory based (ex. Geostrophic balance)
• Statistical models
• Past behavior and correlated information used to make predictions
• Physical models: First principle tenets of physics (chemistry, biology)
• Mechanistic: some aspects prescribed
• Comprehensive: coupled interactions, self-determining

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(State Earth will Warm)

(Details of Warming, Feedbacks)

The Earth System Model: Climate Models

ATMOSPHERE

LAND

ICE

(cryosphere)

SUN

OCEAN

Establishing Trust: �Numerical Experimentation

• Hindcasting
• Historical simulation

Let’s look at observations from the last 1000 years

Surface temperature and CO₂ data from the past 1000 years. Temperature is a northern hemisphere average. Temperature from several types of measurements are consistent in temporal behavior.

Let’s look at just the last 1000 years

Surface temperature and CO₂ data from the past 1000 years. Temperature is a northern hemisphere average. Temperature from several types of measurements are consistent in temporal behavior.

Note that on this scale, with more time resolution, that the fluctuations in temperature and the fluctuations in CO₂ do not match one-to-one.

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What is the cause of the temperature variability? Can we identify mechanisms, cause and effect? How?

{

What do we do?

• We develop models based on the conservation of energy and mass and momentum, the fundamental ideas of classical physics. (Budget equations)
• We determine the characteristics of production and loss (forcing) from theory and observations of, for instance, the eruption of a major volcano and the temperature response as measured by the global observing system.
• We simulate the temperature (“Energy”) response.
• We evaluate (validate) how well we did, characterize the quality of the prediction relative to the observations, and determine, sometimes with liberal interpretation, whether or not we can establish cause and effect.

Schematic of a model experiment.

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Start model prediction

Observations

Statistical representation – not deterministic

What do we know from model experiments and evaluation (validation) with observations

• With consideration of solar variability and volcanic activity, the variability in the temperature record prior to 1800 can be approximated.
• After 1800 need to consider the impact of man
• Deforestation of North America
• Fossil fuel emission
• Change from coal to oil economy
• Clean Air Act
• Only with consideration of CO₂, increase in the greenhouse effect, can the temperature increase of the last 100 years be modeled.

Let’s look at the “modern” record.

• Modern ~ Industrial Revolution

~ Last half of 1800s

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• When we have direct temperature measures

Figure TS.23

20^th Century Simulations

Example of Attribution

20^th Century Simulations

Meehl et al., J. Climate (2004)

Look towards the future.

• Surface temperature anomaly
• Intergovernmental Panel on Climate Change (IPCC, every ~ 5 years)
• IPCC assesses, does not “do” research
• Coupled Model Intercomparison Project (CMIP)
• Scientist community designs protocol to evaluate and establish trustworthiness of climate models
• CMIP is not the same as IPCC, but are often conflated.

IPCC (2007) projections for the next 100 years.

Summary: Models

• Basic scientific principle or law used in climate science is conservation of energy
• Models are an accounting, or calculating the budget, of
• Energy
• Mass
• Momentum
• Credibility established by representation of the past, and, when possible, evaluating predictions and projections

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Summary: Energy Balance of Planet

• Earth’s energy balance
• Energy from Sun
• Energy sent back to space
• Things that absorb
• Things that reflect
• Moving energy around
• Storing energy at the surface of the Earth
• Greenhouse gases hold the energy a while
• Oceans pick it up and hold it longer
• Ice takes it up and melts 🡪 balances change

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A fundamental conclusion

• Based on the scientific foundation of our understanding of the Earth’s climate, we know with virtual certainty
• The average global temperature of the Earth’s surface has risen and will continue to rise due to the addition of gases (esp, carbon dioxide) into the atmosphere that hold heat close to the surface. The increase in greenhouse gases is due to human activities, especially, burning fossil fuels.
• Historically stable masses of ice on land have melted and will continue to melt.
• Sea level has risen and will rise.
• The weather has changed and will change.

Outline

• Models
• Definition
• Models and Scientific Investigation
• Models in Climate Science
• Establishing Trust: Numerical Experimentation
• Looking Towards the Future
• Summary

​

Some Resources

• Gettelman and Rood: Demystifying Climate Models: A User’s Guide to Earth Systems Models
• Springer, Open Source, (It is free.)

​

• Introductory Material OpenClimate Mini-page

​

• Model Introduction OpenClimate Mini-page

​

• Rood’s Class MediaWiki Site
• http://climateknowledge.org/classes/index.php/Climate_Change:_The_Move_to_Action

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Poll questions:

• I was formally introduced to weather or climate models in school.
• Our knowledge of climate change is adequate for us to take action to intervene to reduce carbon dioxide emissions.
• Climate models provide adequate information to inform decisions about adaptation.
• Climate models are trustworthy.
• Provide any comments, qualifications inspired by the questions above.
• Write any questions or comments about climate models and climate change you would like to make.
• What do you want to get from this presentation?

Background Materials

Roles of Uncertainty / Variability at Different Times�Hawkins and Sutton, 2009

Conservation principle

• There are many other things in the world that we can think of as “conserved.” For example, money.
• We have the money that we have.
• If we don’t spend money or earn money, then the money we have today is the same as the money we had yesterday.

M_today = M_yesterday

That’s not very interesting, or realistic

Conservation principle�(with income and expense)

M_today = M_yesterday + I - E

Let’s get some money and buy stuff.

Income

Expense

Conservation principle�(with the notion of time)

M_today = M_yesterday + N(I – E)

Salary

Income per month = I

Rent

Expense per month = E

N = number of months

I = NxI and E= NxE

Income

Expense

Some algebra and some thinking

M_today = M_yesterday + N(I – E)

Rewrite the equation to represent the difference in money

(M_today - M_yesterday ) = N(I – E)

This difference will get more positive or more negative as time goes on.

Saving money or going into debt.

Divide both sides by N, to get some notion of how difference changes with time.

(M_today - M_yesterday )/N = I – E

Introduce a concept

• The amount of money that you spend is proportional to the amount of money you have:

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• How do you write this arithmetically?

E = e*M

Some algebra and some thinking

If difference does NOT change with time, then

M = I/e

Amount of money stabilizes

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Can change what you have by either changing income or spending rate

(M_today - M_yesterday )/N = I – eM

All of these ideas lead to the concept of a budget:

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What you have = what you had plus what you earned minus what you spent

Conservation principle

M_today = M_yesterday + I - E

Let’s get some money and buy stuff.

Income

Expense

Energy from the Sun

Energy emitted by Earth

(proportional to T)

Earth at a certain temperature, T

Some jargon, language

• Income is “production” is “source”
• Expense is “loss” is “sink”
• Exchange, transfer, transport all suggest that our “stuff” is moving around.

Equilibrium and balance

• We often say that a system is in equilibrium if when we look at everything production = loss. There might be “exchanges” or “transfers” or “transport,” but that is like changing money between a savings and a checking account.
• We are used to the climate, the economy, our cash flow being in some sort of “balance.”
• As such, when we look for how things might change, we look at what might change the balance.
• Small changes might cause large changes in a balance

Conservation of Energy

• Conceptual model of Earth’s temperature from space

Earth: How Change T?

Energy from the Sun

Energy emitted by Earth

(proportional to T)

Earth at a certain temperature, T

Stable Temperature of Earth could change from how much energy (production) comes from the sun, or by changing how we emit energy.

The first place that we apply the conservation principle is energy

• We reach a new equilibrium

Changes in orbit or solar energy changes this

The first place that we apply the conservation principle is energy

• We reach a new equilibrium

Balancing the Budget

• Today’s Money =

Yesterday’s Money + Money I Get – Money I Spend

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• Today’s CO₂ =

Yesterday’s CO₂ + CO₂ I Get – CO₂ I Spend

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• Today’s Energy =

Yesterday’s Energy + Energy I Get – Energy I Spend

Or Tomorrow?

Conservation principle

• Conserved Quantities:
• mass (air, ozone, water)
• momentum,
• Energy
• Need to Define System
• Need to count what crosses the boundary of the system
• System depends on your point of view

Point of View

SUN

EARTH

EARTH: EMITS ENERGY TO SPACE 🡪 BALANCE

PLACE AN INSULATING BLANKET AROUND EARTH

Simple earth 1

Models and Modeling

Models

• Blogs on Model Tutorial (Start with #3)
• Models are everywhere
• Ledgers, Graphics and Carvings
• Balancing the budget
• Point of View
• Cloak of Complexity

What is a Model?

• Model
• A work or construction used in testing or perfecting a final product.
• A schematic description of a system, theory, or phenomenon that accounts for its known or inferred properties and may be used for further studies of its characteristics.
• Numerical Experimentation
• Given what we know, can we predict what will happen, and verify that what we predicted would happen, happened?

Models are everywhere

http://www.halfhull.com/main.jpg

How Many Use Spread Sheets?

Ledgers, Graphics and Carvings

• Ledgers
• 🡪 Spreadsheets 🡪 Computers

Radiation Balance Figure

Let’s build up this picture

• Follow the energy through the Earth’s climate.
• As we go into the climate we will see that energy is transferred around.
• From out in space we could reduce it to just some effective temperature, but on Earth we have to worry about transfer of energy between thermal energy and motion of wind and water.

Building the Radiative Balance�

What happens to the energy coming from the Sun?

Top of Atmosphere / Edge of Space

Building the Radiative Balance

What happens to the energy coming from the Sun?

We also have the atmosphere.

Like the surface, the atmosphere can:

Top of Atmosphere / Edge of Space

Building the Radiative Balance

What happens to the energy coming from the Sun?

In the atmosphere, there are clouds which :

Top of Atmosphere / Edge of Space

Building the Radiative Balance

What happens to the energy coming from the Sun?

For convenience “hide” the sunbeam and reflected solar over in “RS”

Top of Atmosphere / Edge of Space

RS

Building the Radiative Balance

What happens to the energy coming from the Sun?

Consider only the energy that has been absorbed.

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What happens to it?

Top of Atmosphere / Edge of Space

RS

Building the Radiative Balance

Conversion to terrestrial thermal energy.

1) It is converted from solar radiative energy to terrestrial thermal energy.

(Like a transfer between accounts)

Top of Atmosphere / Edge of Space

RS

Building the Radiative Balance

Redistribution by atmosphere, ocean, etc.

2) It is redistributed by the atmosphere, ocean, land, ice, life.

(Another transfer between accounts)

Top of Atmosphere / Edge of Space

RS

Building the Radiative Balance

Terrestrial energy is converted/partitioned into three sorts

SURFACE

3) Terrestrial energy ends up in three reservoirs

(Yet another transfer )

Top of Atmosphere / Edge of Space

ATMOSPHERE

CLOUD

RS

Building the Radiative Balance

Which is transmitted from surface to atmosphere

SURFACE

3) Terrestrial energy ends up in three reservoirs

Top of Atmosphere / Edge of Space

ATMOSPHERE

CLOUD

RS

(THERMALS)

(LATENT HEAT)

(infrared or thermal)

CLOUD

Building the Radiative Balance

And then the infrared radiation gets complicated

SURFACE

Top of Atmosphere / Edge of Space

ATMOSPHERE

CLOUD

RS

(THERMALS)

(LATENT HEAT)

(infrared or thermal)

CLOUD

Want to consider one more detail

• What happens if I make the blanket thicker?

Thinking about the greenhouse

A thought experiment of a simple system.

SURFACE

Top of Atmosphere / Edge of Space

ATMOSPHERE

(infrared or thermal)

1. Let’s think JUST about the infrared radiation
• Forget about clouds for a while

2) More energy is held down here because of the atmosphere

• It is “warmer”

3) Less energy is up here because it is being held near the surface.

• It is “cooler”

Thinking about the greenhouse

Why does it get cooler up high?

SURFACE

Top of Atmosphere / Edge of Space

ATMOSPHERE

(infrared or thermal)

1) If we add more atmosphere, make it thicker, then

The real problem is complicated by clouds, ozone, ….

Think about that warmer-cooler thing.

• Addition of greenhouse gas to the atmosphere causes it to get warmer near the surface and colder in the upper atmosphere.
• This is part of a “fingerprint” of greenhouse gas warming.
• Compare to other sources of warming, for example, more energy from the Sun.

Think about a couple of details of emission.

• There is an atmospheric window, through which infrared or thermal radiation goes straight to space.
• Water vapor window
• Carbon dioxide window is saturated
• This does not mean that CO₂ is no longer able to absorb.
• It means that it takes longer to make it to space.

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Thinking about the greenhouse

Why does it get cooler up high?

SURFACE

Top of Atmosphere / Edge of Space

ATMOSPHERE

(infrared or thermal)

The real problem is complicated by clouds, ozone, ….

So what matters?

Think about the link to models

• energy reflected = (fraction of total energy reflected) X (total energy)
• energy absorbed = total energy - energy reflected = (1-fraction of total energy reflected) X (total energy)
• fraction of total energy reflected 🡪
• Clouds
• Ice
• Ocean
• Trees
• Etc.

Radiation Balance Figure�In this figure out = in

Energy in Earth System: Basics

Can we measure the imbalance when the Earth is not in equilibrium?

Science 🡪 Observations 🡪 Evaluation 🡪 Measurement

Can we do the counting to balance the budget?

Radiative Balance (Trenberth et al. 2009)�In this figure out does not = in

IPCC (2001) projections for the next century

IPCC (2007) projections for the next century

IPCC (2013) projections for the next three centuries

Radiative Forcing Changes

Interesting History of This Plot at RealClimate

• Questionnaire: Kansas City, AMS, Broadcast Meteorologists, Model Short Course