Making sense of change Don Barber, assistant professor of geology, BMC
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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?
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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.
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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.
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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.
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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.”
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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
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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
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System feedbacks and feedback loops:
ClassroomTemperature X1
Y2
Student attention span Y1
X2
Coupling 1
Coupling 2
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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
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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!
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Systems-
• system equilibrium: (stable / unstable)
• perturbations & forcing(s)
• thresholds
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Systems- your classroom as example:
• example of stable equilibrium…
negative feedbacks tend to minimize
perturbations and restore system to
original state
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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
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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?
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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
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Albedo: fraction of incomingenergy that is reflected
total reflection: albedo = 1total absorption: albedo = 0
Rank from highest to lowest:
Forest
Snow
Water
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Land surfaces exhibitvarious albedos
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Water’s albedo varies greatly
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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
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Concepts:Concepts:
System properties and behavior: definitions
Rules for Rules for drawingdrawing and interpreting systems and interpreting systems diagrams (albedo example)diagrams (albedo example)
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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
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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
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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
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Tsurface
snow
snow
alb
edoalbedo
Tsu
rfac
e
Slope of lines on these graphs set the SIGN (+ or -) of couplings.
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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.
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Tsurface
snow
snow
alb
edo
albedo
Tsu
rfac
e negative
negative positive
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Systems diagram symbols
negative coupling
positive coupling
NOTE COUPLING DIRECTION !
Tsurface
snowcoverage
albedo
(—)
(—)
(+)
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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
(—)
(—)
(+)
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Tsurface
snow
albedo
Feedback factorratio: > 1 or < 1 ?
PERTURBATIONS AND FORCINGS
What is the effect of external
warming (forcing)? (e.g., 2°C)
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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?
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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.
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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?
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The salt in seawaterThe salt in seawater
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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.
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Fresh water
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Salt water
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QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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Air convection patternsAir convection patterns
Global wind patterns result from heating and convectionGlobal wind patterns result from heating and convection
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These winds drive the surface ocean currents