Making sense of change

Don Barber, assistant professor of geology, BMC

Global change examples of systems analysis, equilibriums, feedbacks and thresholds

Hands-on experiments: • How much salt is in seawater? • How does salt content affect water density?• Illustrate how density differences drive convection. • Also: why is convection so important for global change?

A question for reflection:A question for reflection:

List a global environmental change issue.

After each one, write the number one question/piece of information you think would help you make sense of this issue.

List a global environmental change issue.

After each one, write the number one question/piece of information you think would help you make sense of this issue.

my philosophy…

I view Spaceship Earth as one Global Ecosystem…

Very beautiful, but very complex… just like the human mind/body system. Hard to understand how it all works!

Systems analysis breaks this beautifully complex system into simpler components.

We graphically examine how changes in one part of the system influence other parts of the system.

Concepts and content:Concepts and content:Part 1: Part 1: • Define system properties and behavior. • Make sense of (and use) x-y graphs.Make sense of (and use) x-y graphs.• Learn and apply rules for drawing systems diagrams. • Use graphs and diagrams to make sense of a few systems.

Part 2: • Illustrate how much salt is in ocean water.• Examine consequences of water density differences, example: fluids layered by density; buoyancy effects.• Illustrate density driven convection.

Systems- your classroom as example:

Types of systems:

• Open: matter & energy can flow to/from

• Closed: no matter transfer, but energy can

come and go

• Isolated: neither energy nor matter flows

into or out of the system “box.”

Systems- your classroom as example:• couplings between system components, how things

interact “change in X directly causes a change in Y”

ClassroomVariable A

X

Classroom variable B

Y

coupling

Systems- your classroom as example:• couplings are analyzed as X-Y graphs showing

how things interact: “change in X directly causes a

change in Y” example below is negative coupling

Classroom temperature

Stu

dent

att

enti

on s

panlong

short

cool warm

System feedbacks and feedback loops:

ClassroomTemperature X1

Y2

Student attention span Y1

X2

Coupling 1

Coupling 2

System feedbacks and feedback loops:

• two negative couplings

Classroom temperature

Stu

dent

att

enti

on s

pan

long

short

cool warmro

om te

mp.

attention spanlongshort

cool

hot

1

2

ClassroomTemperature X1

Y2

Student attention span Y1

X2

System feedbacks and feedback loops:• Analyze by multiplying signs of couplings around loop, e.g., negative times negative equals positive• two negative couplings create one positive feedback loop… but it’s not a good thing!

Systems-

• system equilibrium: (stable / unstable)

• perturbations & forcing(s)

• thresholds

Systems- your classroom as example:

• example of stable equilibrium…

negative feedbacks tend to minimize

perturbations and restore system to

original state

Systems- example of unstable equilibrium…

positive feedback reinforces (exacerbates) even

small perturbations, pushing system far away

from original previous state, possibly into a new

stable equilibrium

1

2

How does the temperature/attention span classroom system behave?

How does the temperature/attention span classroom system behave?

What happens if a perturbation occurs… a distraction, or a temperature change?What happens if a perturbation occurs… a distraction, or a temperature change?

Earth system behavior and feedbackEarth albedo example

How does Earth’s reflectiveness, or albedo, affect the capture of incoming solar radiation (insolation), which thence influences Earth’s surface temperature?

Albedo = fraction of incoming solarenergy that is reflected away

total reflection: albedo = 1total absorption: albedo = 0

Albedo: fraction of incomingenergy that is reflected

total reflection: albedo = 1total absorption: albedo = 0

Rank from highest to lowest:

Forest

Snow

Water

Land surfaces exhibitvarious albedos

Water’s albedo varies greatly

Albedo: surface reflectivity

total reflection = 1total absorption =0

Sand ~0.26Grass ~0.23Forest ~0.07Water 0.03 - 0.80 (note large range)Snow ~0.82Cloud ~0.75

Concepts:Concepts:

System properties and behavior: definitions

Rules for Rules for drawingdrawing and interpreting systems and interpreting systems diagrams (albedo example)diagrams (albedo example)

Qualitatively evaluate:

1. Effect of temperature on snow coverage?

2. Effect of snow amount on albedo?

3. Effect of albedo on temperature?

Tsurface

snow

Planetaryalbedo

coupling 1

coupling2

coupling3

systemcomponent

systemcomponent

systemcomponent

Exercise: Draw quantitative graphs relating:1. Temperature (200-400 K) is coupled to

snow coverage (0 - 100%)

2. Snow cover (0 - 100%) --> albedo (0 - 1)

3. Albedo (0 - 1) --> temperature (200-400 K)

Don’t confuse COMPONENTS with COUPLINGS !

Tsurface

snow

albedo

graph1

graph2

graph3

Exercise: Draw three quantitative graphs relating:

1. Temperature (200-400 K) to snow coverage (0 - 100%)

2. Snow cover (0 - 100%) to albedo (0 - 1)

3. Albedo (0 - 1) to temperature (200-400 K)

?1

Tsurface

snow

snow

?2

alb

edoalbedo

Tsu

rfac

e ?3

Tsurface

snow

snow

alb

edoalbedo

Tsu

rfac

e

Slope of lines on these graphs set the SIGN (+ or -) of couplings.

Symbol use for systems diagrams

negative coupling

positive coupling

ALSO NOTE DIRECTION OF COUPLING… the x (independent) variable dictates to the y (dependent) variable. So the coupling direction on your systems boxdiagram goes from x to y.

Tsurface

snow

snow

alb

edo

albedo

Tsu

rfac

e negative

negative positive

Systems diagram symbols

negative coupling

positive coupling

NOTE COUPLING DIRECTION !

Tsurface

snowcoverage

albedo

(—)

(—)

(+)

Is this a positive ornegative feedback loop?

multiply it out, see if positive or negative, e.g.: (—) x (+) x (—) = +

This is a positive feedback loop.

Tsurface

snowcoverage

albedo

(—)

(—)

(+)

Tsurface

snow

albedo

Feedback factorratio: > 1 or < 1 ?

PERTURBATIONS AND FORCINGS

What is the effect of external

warming (forcing)? (e.g., 2°C)

Think about classroom as systemThink about classroom as system

Describe system (interactions among components). [Keep it simple. Remember there

must be feedback to make a feedback loop.]

Draw graphs and diagrams and analyze.

Positive or negative feedback loop?

Describe system (interactions among components). [Keep it simple. Remember there

must be feedback to make a feedback loop.]

Draw graphs and diagrams and analyze.

Positive or negative feedback loop?

Concepts and content:Concepts and content:Part 1: Part 1: • Make sense of (and use) x-y graphs.Make sense of (and use) x-y graphs.• Define system properties and behavior.• Learn and apply rules for drawing systems diagrams. • Use graphs and diagrams to make sense of a few systems.

Part 2: • Illustrate how much salt is in ocean water.• Examine consequences of water density differences, example: fluids layered by density; buoyancy.• Illustrate density driven convection.

Global change- water density, salt and convection

Ocean circulation, weather and climate

Ocean consists of a thin, well stirred layer of surface water and a much thicker mass of deep water that is cold, “calm” and relatively slow moving.

• What stirs the surface water?

• What makes the deep ocean water move around?

Saltiness of the ocean is about 35 gmsalt/kgsea water, or 35 parts

per thousand.

• How much salt is that?

The salt in seawaterThe salt in seawater

Water density and convectionWater density and convection Fresh water… warm water is less dense; maximum density at 4°C; ice is much less dense (tricky!).

Salt water (simpler)… warm water less dense, cold water is more dense; higher salt concentration means more dense.

Fresh water… warm water is less dense; maximum density at 4°C; ice is much less dense (tricky!).

Salt water (simpler)… warm water less dense, cold water is more dense; higher salt concentration means more dense.

Fresh water

Salt water

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Air convection patternsAir convection patterns

Global wind patterns result from heating and convectionGlobal wind patterns result from heating and convection

These winds drive the surface ocean currents