Generalized diagram of the Earth system

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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 food
eaten Body weight A change in one component leads to a change of the same direction in the linked component

Positive Coupling Atmospheric CO2 Greenhouse effect
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 Car’s speed system Body weight Exercise
A change in one component leads to a change of the opposite direction in the linked component

Negative Coupling Earth’s Earth’s albedo surface (reflectivity)
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)

positive coupling childrens’ noise parents’ anger negative coupling

Negative Feedback Loops:
Electric Blankets person A’s body temperature person A’s blanket temperature person B’s blanket temperature person B’s body temperature

A Positive Feedback Loop: Mixed-up Electric Blankets
person A’s body temperature person A’s blanket temperature person B’s blanket temperature person B’s body temperature

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=0.75 albedo = 0.5

Systems diagram explicitly including albedo

Response of average surface temperature to daisy coverage
Systems diagram

completely covered planet

Equilibrium States: Graphical Determination
Overlay the two graphs (this is the graphical way of setting them equal to each other). The points where they meet are equilibrium points. Draw a systems diagram to determine whether each one is stable or unstable.

The Faint Young Sun Problem
More H2O Kasting et al., Scientific American (1988)

Response of average surface temperature to daisy coverage
Systems diagram

External Forcing: the response of Daisy World
Assume that the external forcing is an increase in solar luminosity The effect of temperature on daisy coverage should not change (this depends on the physiology of daisies) The effect of daisy coverage on temperature should change: for the same daisy coverage, higher temperature