Earth System Science - · PDF fileGreenland and rain evaporation Antarctic ice caps ......

Earth System ScienceEarth System Science

Today: “Systems”Today: “Systems”

Basic questions/Goals:To Understand:• Why is the Earth System so Complex.• Basics of how systems work. • How systems can be “self-regulating”• How you might make predictions about

system behavior

Outline for todayOutline for today (don’t have to write this all down..)(don’t have to write this all down..)

• 1) What makes up a “System”? - Couplings, feedback loops, and stability vs. instability?

2) Stability of Systems - Equilibrium states , perturbation and forcing

3) Daisy- World! - Self Regulating Systems, and tipping points..

4) Predictions and complexity

Part 1) What is a “System”Part 1) What is a “System”

• Topics: • What makes up a system?• Couplings: a positive vs. negative

coupling (relationship)• Feedback loops: a positive/negative• Stability and instability?

1) What is a System?1) What is a System?

• Collection of parts with flow between the parts– Flow of matter (for example: water, air, carbon)– Flow of energy (for example: sunlight)

Ocean water

River & Lake water

AtmosphereWater vapor

Greenland andAntarctic ice capsevaporationrain

rain snow

evaporation sublimation

melting

river flow

Systems: box modelsSystems: box models

• “Flux”: Flow of matter/ energy is also called ‘flux’

• Storage parts are also called ‘reservoirs’• Together, this is a ‘box model’

Ocean water

River & Lake water



rain snow


melting

river flow

SystemsSystems

• If we understand these processes, we can make educated guesses or predictions of how the system will respond to change.

Ocean water

River & Lake water



rain snow


melting

river flow

How does a system work?How does a system work?

• 1) “couplings” (relationships) between parts of a system:– A) Positive coupling

• A change in one part of the system results in a change in another part, in the same direction

• If X increases, does Y? YES• If X decreases, does Y? YES

Sun’s energy Earth’s temperature+

A Positive RelationshipA Positive Relationship

Or to follow more closely from the book..Or to follow more closely from the book..

• Consider the relationship between your body temperature and…

an electric blanket…?

Blanket get warmer.... Blanket get warmer....

Makes YOU warmer.Makes YOU warmer.

Converse: negative coupleConverse: negative couple

– Negative coupling• A change in one part of the system results in a change

in another part, but in the opposite direction• If X increases, does Y? NO- it goes down. • If X decreases, does Y? NO – it goes up.

Temperature Snow cover-

Negative couplingNegative coupling

Notation noteNotation note

In the book:

This means “negative coupling”

In other books/ literature:

This means “positive coupling”+

This means “negative coupling”-

This means “positive coupling”

But then.. YOU get too hot.. But then.. YOU get too hot..

(You turn the darn thing down..) (You turn the darn thing down..)

Blanket gets colder.. Blanket gets colder..

Back under the blanket..

Add together two or more Add together two or more couplings (or links) and you couplings (or links) and you get…get…

“Feedback”“Feedback”

• “Feedback loop” is a combination of positive and/or negative relationships thatconnects part of the system back to itself

Feedback loops are made Feedback loops are made up of multiple couplings up of multiple couplings

(positive or negative)(positive or negative)

OVERALL Feedback OVERALL Feedback loops loops can also be eithercan also be either: :

* positive* positiveor or

*negative*negative

Negative FeedbackNegative Feedback

• Negative Feedback loop: diminishes the initial change

Reflectivity of sun’sEnergy

(Albedo)

+-

Temperature Evaporation and cloudformation

+increase increase

increase

then decrease

Note: Note: The property of being a “positive” or The property of being a “positive” or

“negative” feedback“negative” feedback is independent of the is independent of the couplingscouplings

Reflectivity of sun’sEnergy

(Albedo)

+-

Temperature Evaporation and cloudformation

+increase increase

increase

then decrease

Its about how the whole system Its about how the whole system behaves in response to a forcingbehaves in response to a forcing

Negative feedbackNegative feedback

• Negative Feedback loop: diminishes the initial change

The Simons Blanket Feedback loop! The Simons Blanket Feedback loop!

* You get too hot* You get too hot••Turn the blanket Turn the blanket down down ((-- coupling)coupling)••Blanket heats your body less strongly (+ Blanket heats your body less strongly (+ coupling) coupling)

In book, this (-) in the middle means the ENTIRE lOOP is negative

Positive FeedbacksPositive Feedbacks

• Positive Feedback loop: amplifies the initial change

Reflectivity of sun’sEnergy(Albedo)

+-

Temperature Snow cover-increase decrease

decrease

more

Bit tricky here to follow coupling signs..

Positive FeedbacksPositive Feedbacks

• Positive Feedback loop: amplifies the initial change

Electric Blanket Positive Feedbacks?Electric Blanket Positive Feedbacks?

The somewhat loopy “presidential crossed controllers” example The somewhat loopy “presidential crossed controllers” example

Note: Positive vs. negative & systemsNote: Positive vs. negative & systems

• Negative feedbacks help make a system stable because they diminish changes

Topic 2) Stability of systemsTopic 2) Stability of systems

• Perturbations and forcings• “Equilibrium states”• degrees of stability vs. instability

– Resilience and resistance

Perturbations and forcingsPerturbations and forcings

• Forcing: Typically something constant, or cyclical, that drives as system.– Part of the equilibrium balance it comes to

• Perturbation: more of a “one time” forcing. Ie, something that pushes a system away from equilibrium

Example of Perturbation:Example of Perturbation: Volcanic eruption, Volcanic eruption, influence on global temp. influence on global temp.

• 1) Volcanic eruption releases sulphate aerosol into the stratosphere.

• 2) Sulphate aerosol reflects incoming solar radiation back to space – so earth cools.

• 3) Eventually aerosol settles into the troposphere and is rained out and earth returns to equilibrium.

The average effect on global average surfacetemperature due to volcanic eruptions

How a system responds to a DisturbanceHow a system responds to a Disturbance

Instability:inability to return to initial state

Example of a SYSTEM: A ball in a bowl

Stability: ability to return to initial stateBecause of the force of gravity, this system/bowl design

forces ball back into initial state

How Stable is a System?How Stable is a System?

Resistant:Ball can’t go far

Resistance: ability of system to withstand disturbance

Less Resistant: Ball can gofurther away


Resilient:Even if ball is far, it will come back

Resilience: ability of system to recover from disturbance, tells you how far a system can be pushed

Less Resilient: If pushed to far, the ball will not come back


• Even stable systems can be disturbed to the point that they become unstable!

Resilient System

Resistant System

““Equilibrium” state:Equilibrium” state:when a system (or given part of it) is in when a system (or given part of it) is in balancebalance

*=*= forcingsforcings are balanced are balanced

* won’t change until new forcing or * won’t change until new forcing or perturbation perturbation

NOTE: Can have NOTE: Can have both stable and both stable and unstable unstable equilibrium equilibrium states!states!

Overall: Overall:

• If we understand these processes (couplings, feedbacks, equilibrium states) we can make educated guesses or PREDICTIONS of how the system will respond to changes.

Ocean water

River & Lake water



rain snow


melting

river flow

Topic 3) complexity (briefly)Topic 3) complexity (briefly)

• stochastic (random) behavior?• variance (scatter or variability)?• time lags?• model simulations

RandomnessRandomness

• But, there can be random disturbances to a system that can’t be predicted: Stochastic behavior

Ocean water

River & Lake water



rain snow


melting

river flow

ComplexityComplexity

• most systems have lots of parts and feedback loops that interact with each other.

Time LagsTime Lags

• most relationships between parts take time to happen.• cause and effect don’t happen at the same time.• makes it difficult to study.

Why use a ‘system’ approach?Why use a ‘system’ approach?

• Reductionist Approach: Study single relationships, oftenwithin one discipline

• System Approach: Need to understand relationships and feedbacks with multidisciplinary perspective

How do we handle all this complexity?How do we handle all this complexity?

• Computer models (big)– Equations that represent each relationship– Primary way that predictions are made

4) “Daisy world”4) “Daisy world”

• An example of a seemingly simple system that can be “self-regulating”

• Also: An example of how pushing systems past certain “tipping points” can result in drastic changes..

James LovelockJames Lovelock““Famous independent natural scientist”Famous independent natural scientist”

“The Earth is Alive…”

GaiaGaia HypothesisHypothesis

Gaia: Greek Mother Goddess, or Goddess of Earth

One end of spectrum:One end of spectrum:

*Focus on observation that feed-back driven systems can become intrinsically self-regulating (in specific stable states) *idea that earth is one such system

Other end of spectrum: Other end of spectrum:

•Earth is “a living being” ( Gaia?) – regulates itself (climate) for the benefit of life

•(Just one uncomfortable Implication: never mind pollution, or CO2 emissions.. Earth can fix itself .. )

“Daisy “Daisy world”world”

• Lovelock’s simple feedback-model simulation of effect of life & Albedo on climate

• Illustrates that natural feedbacks can control the climate of a planet without recourse to intelligent intervention (or design).

AlbedoAlbedo

• The primary controlling influence on Daisyworld is the surface “albedo.”

• Albedo=the fraction of incident solar radiation that is reflected back to space.

• Some examples from the climate system are …

Albedo Albedo tabletable

Welcome to Daisy world!

Simplest version: There are only two types of surface on Daisy world:

(1)Gray soil(2)White daisies

The feedbackThe feedback

• As daisy coverage increases, Albedoincreases

• Net solar radiation absorbed at the surface decreases

• Surface temperature decreases• What kind of coupling is this? “+” or “-

”?

Control Response

Negative!

Simple animation..Simple animation..

1) http://library.thinkquest.org/C003763/flash/gaia1.htm

The Basic Idea:The Basic Idea:

Control Response

But to be more realistic.. But to be more realistic.. there are feedbacks toothere are feedbacks too-- since since temperature affects daisies! temperature affects daisies!

DaisyworldDaisyworld equilibriaequilibria

• Daisy coverage also depends on surface temperature.

• If it is too hot or too cold, daisies will not survive – hence there are critical thresholds for the daisies.

• Assume: There is an “optimum” temperaturefor daisy growth – a temperature which is “just right” for daisies (the “Goldilocks” effect).

Control ControlResponse Response

Equilibrium ClimateEquilibrium Climate

• We now have two relationships:(i) Surface temp vs daisy coverage

(i) Daisy coverage vs surface temp.

Clearly they are not independent so we can combine them to determine the states of the system when they are both satisfied simultaneously. This occurs at the equilibrium points.

+

Surface temp vs daisy coverage

Daisy coverage vs surface temp

What about What about Stability Stability of the equilibrium climate?of the equilibrium climate?

If you like math, you can combine these relationships into a series of equations.

System of equations = ultraSystem of equations = ultra--simple “climate simple “climate model” model”

We can then use it to ask questions about climate change, given new forcings!

What would be a realistic What would be a realistic longlong--term change in basic term change in basic

forcing ? forcing ?

( Solar Luminosity )( Solar Luminosity )

Climate forcing: Solar Luminosity Climate forcing: Solar Luminosity increasing..increasing..

Climate forcing: Solar Luminosity Climate forcing: Solar Luminosity

• What will be the response of Daisyworldto a steady increase in the solar luminosity?

• What will be the ultimate of fate of daisyworld?

For a given daisy coverage,temperature increases withincreasing solar luminosity.

• So what happens as solar luminosity continues to increase into the far future of daisy world?

1) Change in daisy coverage versus solarluminosity.

Once surface temp passes theoptimum value, all feedbacks become positive andall daisies rapidly perish.

This is called a “tipping point”: where the basics of an entire system rapidly change..

No daisies No daisies

“Tipping point”

2)Temperature vs. Luminosity: As solar luminosity increases, temp increases.However as daisies begin to grow the albedo reduces the surface temperature compared to the that if there were no daisies. (note dotted line= no life)

Again once the optimum temperature is reached, all feedbacks are positive and the daisies rapidly perish so temp continues to rise because the albedo is nowlower. No daisiesNo daisies

Important point: the system is only “self regulating” within certain boundaries

Animation:Animation:

2) http://ccl.northwestern.edu/netlogo/models/Daisyworld

More Realistic Model:More Realistic Model:

You can play with this one .. Change a lot of parameters..

Review of important ideasReview of important ideas

• There are natural feedbacks in the climate system.

• Negative feedbacks can lead to stable equilibria.

• Positive feedbacks often lead to unstable equilibria.

• Feedbacks can very naturally control climate in a self-governing way..within limits.

ENDEND

Earth System Science - · PDF fileGreenland and rain evaporation Antarctic ice caps ......

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