EPS 106 Lecture 12

Feedback and Daisyworld

Nov. 2^nd, 1999

FEEDBACK:

Feedback is a very important phenomenon in the Geological sciences. It is a method of self regulation, either stabilizing or destabilizing.

Stabilizing systems are negative feedbacks:

• A thermostat in the house.
• A ruler between two fingers.
• “Get’s hotter, more clouds”. Albedo

Negative feedback.

• A microphone placed before a speaker.
• Albedo on the Earth’s surface.
• Jimmy and Rosilyn’s electric blanket.

Daisyworld.

The idea of temperature vs. Daisy coverage.

Increasing daisy coverage decreases temperature.

The complication is that there is an optimal growth temperature for daisy coverage given by a parabola.

When we combine the two curves, we get

Now it turns out that P1 is a stable configuration, where if we change the abundance of daisies, we will quickly come back to the equilibrium position.

On the other hand, at P2, we are at

an unstable 'equilibrium', where

any purtubation will cause a change

to either catastrophe or position P1.

If we increase the solar radiation, we will shift the position of curve 1, but not change 2. There will be a buffering effect as seen in the following figure:

CONCLUSIONS:

· A planetary system is not passive in the face of internal or external influences.

· The response of life to pertubations is 'intelligent'. Self-regulation is a common property to many natural systems.

Another example of positive feedback is the Earth's temperature in response to glacial ice. More on this later!