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Generalized diagram of the Earth system
Systems Notation
= system component
= positive coupling
= negative coupling
Positive Coupling
Car’s gas pedal Car’s speed
Amount of foodeaten
Body weight
A change in one component leads to a change of the same direction in the linked component
Positive Coupling
AtmosphericCO2
Greenhouseeffect
• An increase in atmospheric CO2 causes a corresponding increase in the greenhouse effect, and thus in Earth’s surface temperature• Conversely, a decrease in atmospheric CO2
causes a decrease in the greenhouse effect
Negative Coupling
Car’s break system
Car’s speed
Exercise Body weight
A change in one component leads to a change of the opposite direction in the linked component
Negative Coupling
Earth’s albedo(reflectivity)
Earth’ssurface
temperature
• An increase in Earth’s albedo causes a corresponding decrease in the Earth’s surface temperature by reflecting more sunlight back to space• Or, a decrease in albedo causes an increase in surface temperature
Increasing carbon dioxide: forcing (long term)
Volcanic eruption: perturbation (short term)
childrens’noise
parents’ anger
negative coupling
positive coupling
person A’sbodytemperature
person A’sblankettemperature
Negative Feedback Loops:Electric Blankets
person B’sblankettemperature
person B’sbodytemperature
person A’sbodytemperature
person A’sblankettemperature
A Positive Feedback Loop:Mixed-up Electric Blankets
person B’sblankettemperature
person B’sbodytemperature
A simplified climate system: Daisyworld
Average Temperature = 30 oC No clouds, no ocean Soil = light gray (absorbs some light) Life = white daisies (reflects all light) Sun = like Earth’s Daisy growth = changes with temperature
Albedo: measure of reflectivity of a surface, expressed as a % of reflected insolation to incoming insolation.
(Christopherson, Elemental Geosystems, 2004)
albedo = 0.5
albedo=0.75
Systems diagram explicitly including albedo
Systems diagram
Response of average surface temperature to daisy coverage
22.5 °C
5 °C40 °C
completely covered planet
Equilibrium States: Graphical Determination
1. Overlay the two graphs (this is the graphical way of setting them equal to each other).
2. The points where they meet are equilibrium points.
3. Draw a systems diagram to determine whether each one is stable or unstable.
The Faint Young Sun Problem
Kasting et al., Scientific American (1988)
More H2O
Systems diagram
Response of average surface temperature to daisy coverage
External Forcing: the response of Daisy World
1. Assume that the external forcing is an increase in solar luminosity
2. The effect of temperature on daisy coverage should not change (this depends on the physiology of daisies)
3. The effect of daisy coverage on temperature should change: for the same daisy coverage, higher temperature