# Positive feedbacks and negative feedbacks (global warming)

1. Oct 15, 2015

### TheMathNoob

1. The problem statement, all variables and given/known data
Consider the feedback loop involving Clouds, Rainfall and forest area.
All the relationships represented in this figure show positive couplings between the components:
Forest area is positively coupled to rainfall, plant evapotranspiration is positively coupled to forest area, and rainfall is positively coupled to plant evapotranspiration.

Is this a positive or negative feedback loop
2. Relevant equations
Forest Area-> Plant evapotranspiration and rain cloud formation
Plant evapotranspiration and rain cloud formation->Rainfall
Rainfall->Forest Area

3. The attempt at a solution
I don't actually understand that loop because I cant see the invariant. In my class we are analyzing how those feedbacks influence the variation of the temperature. In this case, I cant see the invariant or I dont know if this loop is related to the temperature. Can someone explain me how this loop works?

2. Oct 15, 2015

### Buzz Bloom

Hi MathNoob:

I confess I also find this loop a bit puzzling.

I added number in brackets to your quote for ease of reference.

First I would think that [1] involved 2 distinct steps:
[1a] Forest Area-> Plant evapotranspiration
[1b] Plant evapotranspiration -> cloud formation​

Next, [3] has a limit.
[3x] If rain fall rate grows too much, flooding will reduce forest areas.​
Also,
[3y] If rain fall rate diminishes too much, drought will reduce forest areas.​
Therefore, rainfall rate has an optimum range, and less or more is bad for the forest growth. I think this is sufficient to break the loop.

Also, the is another link in the opposite direction, that is a negative feedback effect..
[1bx] Cloud formation -> Plant evapotranspiration​
If cloud formation increases, Plant evapotranspiration will decrease due to reduced sunlight.
So now there is a negative feedback loop:
Increasing Plant evapotranspiration -> Increasing cloud formation -> Decreasing Plant evapotranspiration​

All in all I think this "All the relationships represented in this figure show positive couplings between the components" is seriously flawed.

I also don't understand the following:
3. The attempt at a solution
I cant see the invariant or I dont know if this loop is related to the temperature. Can someone explain me how this loop works?​
I don't understand what you mean by "invariant", or what "the solution" is supposed to solve. I am guessing the solution is supposed to determine the trend of something, and that is some variable lioke temperature.

So, as I discussed above, I don't think this "loop" works. I am guessing that:
(1) the student is supposed to ignore reality facts that contradict the premises of the "loop", and
(2a) that the (unrealistic) never ending increase in forests, clouds and rain causes a never ending increase in water vapor in the atmosphere, and
(2b) the increase of water vapor (a greenhouse gas) causes an increase in temperature.

Regards,
Buzz

Last edited: Oct 15, 2015
3. Oct 15, 2015

### TheMathNoob

Never mind what I said. I understand now what is going on, but consider just the positive feedbacks. The problem is telling us that there is just positive feedbacks between the events, so it would be a positive or a negative feedback loop?

4. Oct 15, 2015

### Buzz Bloom

Hi MathNoob:

I edited some addition to my previous post while you were posting #3. Your #3 seems to confirm some of my guesses.

Regards,
Buzz