Buffers and Feedback Loops

Cla

ss N

otes

1:6

Buffers and Feedback Loops

Buffersare agents or

regulatorymechanisms

that reduce or minimize

fluctuations and change

A forest experiences less fluctuation

in temperature, wind, and humidity than an

unforested area

Example

Buffers and Feedback Loops

Because the trees cool with their shade, block winds, and their fallen

leaves help keep the soil moist

Thus the microclimate in the forest is buffered against extremes

Less fluctuation….. Less change……

How Feedback Loops Function – Example One

A feedback is a signal that can be detectedand can trigger a response

Imaginean air-conditioner

regulatedby a

thermostattime

1

How Feedback Loops Function

As the room warms, the thermostat

detectsthe change,

and causes theair-conditioner to

switch ontime

2

and in response, the temperature begins to fall

time

3 As temperaturescool, the thermostat

again detectsthe change

and shuts off theair-conditioner

and, in response, the room begins to warm again

How Feedback Loops Function

time

4These repeated reversals

illustrate the usefulness of

negative feedbacks

Negative feedback loops help bring constancy to a systemand help buffer the system against

Extremes Fluctuations, and Change

* Remember, negative does not mean ”bad” and positive does not mean “good”

Negative feedback loops help bring constancy to a system

time

Extremes Fluctuations and Change

Reducing

They help produce and maintain an active stateof constancy known as.

time

Homeostasis

:the tendency of a system, esp. the physiological system of higher animals, to maintain internal stability.

Some Feedback Loops Can Destabilize

What is the oppositeof a negative feedback loop?

Answer:

A positive feedback loop

When a signal is detected in a

positive feedback system

The system responds by

Amplifying Intensifying Magnifying or Accelerating

the original trend

We all know, snow reflects sun back into space

-if the planet gets a little warmer, snow melts

-with less snow, more sunlight is absorbed by planet

-the increased absorption accelerates warming

-etc., etc., etc.

Positive Feedback Loop

Living systemstend to benefit

because the interactions of many species help maintain

from

Negative Feedback Loops

Stability Constancy and Homeostasis in the system

Buffers and Feedbacks on a Planetary Scale

Buffers and Feedbacks on a Planetary Scale

NASA consultant James Lovelock helps us see

buffers and negativefeedback systems at work on a

planetary scale

First, envision an imaginary planet that is perfectly

round, smooth, grey and lifeless

He calls his imaginary planet

"Daisyworld"

If Daisyworld'ssun heats up and

emits more radiation, what will happen to Daisyworld's

temperature?

The planetary temperature will increase

Decreased Solar Output

What will happen toDaisyworld's temperature if its star becomes cooler and emits

less radiation?

The planetary temperature will go down

Next imagine thatDaisyworld is inhabited by two species of organisms

White daisies that reflect light energy

And dark daisies that absorb light energy

Imagine that 100% of Daisyworld's surface is coveredwith equal numbers of these two species

What happensif Daisyworld's

sun becomescooler?

Will both daisy species be affected in the same way?

Decreased Solar Output

As a result, dark daisies increase in numbers

because theyabsorb

the energy that arrives

The dark daisies are better able to survivea decrease in solar radiation

Decreased Solar Output

In contrast, thelight daisies reflect the

light that arrivesand their

numbers decline

Decreased Solar Output

Daisyworld remains warmer than it would be if it were entirely lifeless

With so many additional dark daisies absorbing solar radiation,

Increased Solar Output

This time the dark daisies absorb too much of the

extra solar output

What if Daisyworld's star heats up?

and their numbers decline

and cover a greater portionof Daisyworld's surface

The light daisies, however,

reflectmuch of the excess heat so

that they survive

Significance

The presence of life

helps moderate planetary conditions

helps reduce fluctuations and change

buffers Daisyworld’s temperature

( in this case, two mindless species of daisies)

Positive and Negative feedback loops in Global Warming

Both negative and positive feedback processes occur in the atmosphere. If negative feedback loops are strong, then global

warming will be more moderate. If positive feedback loops prevail, global warming could be catastrophic for life as we

know it.

1. Increased algae populations reduce [CO2] in atmosphere and causes cooling.

2. Increased plant growth will reduce [CO2] in atmosphere and causes cooling.

3. Increased water evaporation will increase cloud cover and cause cooling.

The Negative Feedback loop

The Positive Feedback Loop

4. Increased evaporation adds more water vapor to atmosphere causing warming

5. Melting of permafrost releases more methane gas causing warming

6. Reduced summer snow-pack decreases Earth’s albedo causing warming

7. Increased use of air conditioning using more fossil fuels causes warming