What is a System? Definition: A system is a group of different components that interact with each other Example: The climate system includes the atmosphere, oceans, polar caps, clouds, vegetation…and lots of other things

How do we study systems? Identify the components Determine the nature of the interactions between components

Systems Notation = system component = positive coupling = negative coupling

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 An increase in Earth’s albedo causes a (reflectivity) Earth’s surface 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

The interesting thing to do is to put couplings together in feedback loops…

A Harmonious Family childrens’ noise parents’ anger

A Harmonious Family parents’ childrens’ anger noise positive coupling negative coupling

A negative feedback loop: A Harmonious Family positive coupling childrens’ noise parents’ anger negative coupling street noise A negative feedback loop: Stable system which resists change following a perturbation

NOT A Harmonious Family positive coupling childrens’ noise parents’ anger positive coupling street noise A positive feedback loop: Unstable system which changes further following a perturbation

The Non-Harmonious Family Two possible states following perturbation: 1) Complete silence 2) Infinite noise Positive feedback loops are unstable or not homeostatic.

The Harmonious Family Noise levels return to near starting conditions following perturbation. Negative feedback loops are stable or homeostatic.

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 Positive Feedback Loop: Mixed-up Electric Blankets Any perturbation will cause both people to adjust their blanket controls, but with undesired consequences. Ultimately, one person will freeze (become infinitely cold) and the other person to swelter (become infinitely hot).

Conditions under which the system will remain indefinitely Equilibrium State: Conditions under which the system will remain indefinitely --If left unperturbed

An Unstable Equilibrium State

An Unstable Equilibrium State Perturbation

When pushed by a perturbation, an unstable equilibrium state shifts to a new, stable state.

A Stable Equilibrium State

A Stable Equilibrium State Perturbation

When pushed by a perturbation, a stable equilibrium state, returns to (or near) the original state.

Daisy World

A simplified climate system: Daisy World Daisyworld, originally proposed by Watson & Lovelock in 1983, is a simple model of a planet that illustrates systems behavior and shows how climate can be considered in terms of systems concepts. Daisyworld has only two species of life on its surface, white and black daisies. The planet is assumed to be well-watered, with all rain falling at night so that the days are cloudless. The atmospheric water vapor and CO2 are assumed to remain constant, so that the greenhouse gas effect of the planet does not change.

Accessing the Daisyworld Model: 1)Go to the class website and access the daisyworld model link or type in http://www.carlachi.com/daisyworld.html 2) Click on Daisyworld in the left column. 3) Click on “Go” at the lower right.

Parameter Explanation Valid Numerical Values* Black Daisy Heat Rate (BDHR) Fraction of solar energy absorbed by black daisies: default 0.001 Range = 0 - 1 0=No energy absorbed 1=All energy absorbed White Daisy Cool Rate (WDCR) Fraction of solar energy reflected by white daisies: default 0.001 Range = 0 – 1 0=No energy reflected 1=All energy reflected Temperature for White Daisy Life Minimum and maximum temperatures for survival of white daisies: default min 40 to max 50 T min < T max Temperature for Black Daisy Life Minimum and maximum temperatures for survival of black daisies: default min 20 to max 30 Sun Heat Rate in Different Climates Fraction of solar energy received in each latitude zone: default: Pole=0.4, Zone 2=0.6, Zone 3=0.8, Equator=1 0 = No energy received 1 = All energy received Initial Temperature of the World Initial temperature in each latitude zone: default Pole-8, 2-10, 3-12, equator-17

Test 1 Black Daisies Only Case: Set BDHR to 0.1 temperature for white daisy life to 4000 (min) and 5000 (max). Leave all other settings as the default This scenario explores the case of only black daisies growing on the planet.

Discussion questions What do you notice first? B) What patterns do you notice about the black daisies colonization of the planet? C) Do the black daisies act as a positive feedback or as a negative feedback on the planet’s temperature? How do you know? D) Do the black daisies cause the planet’s temperature to become more stable (i.e., toward equilibrium) or less stable (i.e., away from equilibrium)?

Test 2 White Daisies Only Case: Set WDCR to 0.1 and the temperature for black daisy life to 2000 (min) and 3000 (max). This scenario explores the case of only white daisies growing on the planet. Leave the “sun heat rate in different climates” and the “initial temperature of the world” unchanged (i.e. at their default settings).

Discussion On the line graph, after the white daisies colonize the planet, the temperature of the planet is lower with the white daisies than with no daisies. How do the white daisies cool the planet? B) Do the white daisies act as a positive feedback or negative feedback on the planet’s temperature? C) Do the white daisies cause the planet’s temperature to be more stable or less stable? D) Do the white daisies ever colonize all zones of the planet (i.e., from the equator to the poles) simultaneously? Why or why not?

Test 3 Default Case: Return the parameters to the default setting. Then set both BDHR and WDCR to 0.1.

Discussion What type of daisies grow first? Why? What type of daisies die off first? Why? C) What type of daisies populate the planet’s surface for the longest amount of time? Why? D) Compare the temperature versus time graph for the “without daisies” case and the case with both black and white daisies that you just ran. How does the growth of daisies cause the large difference between these two cases? E) Describe how what you’ve modeled here can be extended and used to understand Earth and its systems.

What kind of feedback loop is represented below?

What kind of feedback loop is shown below?