ERTH 535:
Planetary Climate Change
(Spring 2018)
Pre-class Quiz #5:
Feedback, Stability, and
Disturbances in Systems
Dr. Dave Dempsey
Dept. of Earth & Climate Sci.,
SFSU

This is a "preview" version of Pre-class Quiz #5. The preview version is suitable for printing and leisurely inspection before you submit your answers to the interactive or "live" version—that is, the real thing. When you feel ready to submit your answers, go to iLearn's ERTH 535 "Pre-class Quiz" section, select the interactive version, and follow its instructions.

Responses must be submitted via iLearn by 12:00 p.m. on Monday., April 16.

(Note: the order of the candidate responses to each question as they appear below might not be the same on the interactive version on iLearn. So, when submitting your responses on iLearn, pick your responses carefully!)

Description: The questions below address the concept of feedback. They are based on Reading Assignment #6.

Questions:

(1) Multiple Choice. Positive Coupling between System Components. When is a coupling between components in a system positive? (Pick the one correct answer.)

  1. A coupling is positive when a change in one component of a system directly causes a change in the same sense (same sign) in another component.
  2. A coupling is positive when a change in one component of a system directly causes an increase in another component.
  3. A coupling is positive when an increase in one component of a system directly causes a change in another component.
  4. A coupling is positive when a change in one component of a system directly causes a desirable change in another component.

(2) Multiple Choice. Positive Feedback Loop. What is a positive feedback loop in a system? (Pick the one correct answer.)

  1. When a change (increase or decrease) in one system component causes another component to change in the same sense.
  2. When a change (increase or decrease) in one system component causes another component to change in the opposite sense.
  3. When a change (increase or decrease) in one system component causes another component to change, which eventually (through couplings) causes the first component to change further in the same sense (sign, direction) as its initial change.
  4. When a change (increase or decrease) in one system component causes another component to change, which eventually (through couplings) causes the first component to change in a sense (sign, direction) opposite its initial change.

(3) Multiple Choice. Stable Systems. When is a system stable? (Pick the one best answer.)

  1. A system is stable when, disturbed away from equilibrium, negative feedbacks in the system cause it to achieve equilibrium in a new state.
  2. A system is stable when, disturbed away from equilibrium, negative feedbacks in the system tend to or "try" to return the system to its original equilibrium state.
  3. A system is stable when, if left undisturbed, it remains in an equilibrium state.
  4. A system is stable when it cannot be disturbed from its equilibrium state.

(4) Multiple Choice. Determining System Stability. The stability of some systems can be evaluated qualitatively simply by classifying the type of each feedback in the system as positive or negative (for example, from a system diagram). When can the stability of a system at equilibrium not be evaluated qualitatively and must instead be evaluated quantitatively (by determining the strength of each feedback in the system)? (Pick the one correct answer.)

  1. When feedbacks in a system are absent.
  2. When feedbacks in a system are very weak.
  3. When there is a mixture of both positive and negative feedbacks in the system.
  4. When feedbacks in a system are particularly strong.

(5) Multiple Choice. Negative Feedback with Forcing. Suppose that a system with only negative feedback, initially at equilibrium, is subjected to forcing. How would the system's response to the forcing differ if it didn't have the negative feedback? (Pick the one best answer.)

  1. Without the negative feedback, the system would return to its initial equilibrium state, whereas with the feedback it wouldn't return.
  2. Without the negative feedback, the system would not return to its initial equilibrium state, whereas with the feedback it would return.
  3. Without the negative feedback, the system would change less than it would with the feedback.
  4. Without the negative feedback, the system would change more than it would with the feedback.

(6) Multiple Answer. Climate System Feedbacks. The climate system contains many, many feedbacks, both positive and negative. Which of the example climate system feedbacks listed below are positive (and hence by themselves would tend to destabilize climate)? (Pick all answers that apply; there might be more than one.)

  1. water vapor feedback
  2. snow and ice albedo feedback
  3. temperature/radiative emission feedback
  4. feedback between global temperature, water vapor, and low (thick, liquid water) clouds
  5. feedback between global temperature, water vapor, and high (thin, ice) clouds

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