(This is the third post in the “feedback loops” series)
Ever used a bad eraser in your life? One that has been used so much that it’s become completely black?
What happens when you erase something with that eraser?
Instead of cleanly removing everything you have written on the page, it just makes your page more and more dirty! The harder you rub the eraser, the dirtier it gets!
This, my friends, is a small and significant example of a positive feedback loop.
Positive feedback: Ever present in nature
When you get an initial force, there are two responses. I covered the negative feedback response in my previous post in this series. Now that was a response that was ideal to the functioning of humans as well as the ecosystem of the world. It does it’s best to keep the environment under control; to keep things as they are.
Negative feedback loops are like the control freaks of nature. Positive feedback loops, on the other hand, are the carefree leaves that go where the strong wind takes them!
There are many examples of positive feedback loops in nature, most of which are not something humans appreciate. The classic example of positive feedback is of soil erosion…
When it rains, water collects on the ground. Eventually, a point is reached where the amount of water collected is greater than the water that can infiltrate the soil. So, instead of going downwards, water begins to flow laterally. Along with it, it takes away the topsoil.
When this topsoil is removed, it exposes the harder soils/rocks below. These layers have even less pores for water to infiltrate. So, even more water collects and begins to flow, increasing the amount of soil erosion.
In fact, in the above example of the eraser, there is another positive loop at work. When you take a new eraser and begin to use it, it gets progressively blacker the more you use! So the initial force (rubbing), intensifies the response (the eraser becoming blacker)!
I’ve given other examples of positive feedback loops in many of the posts in this blog. You can check them out here.
Why are positive loops seen as a drawback?
They are a drawback because they completely change the conditions in the system it acts. Positive feedback loops intensify the initial response. Therefore, more of what was already taking place happens. Eventually, you reach a point where the environment of the system in which the loop was acting will become completely different!
More often than not, this is not what we want. All of the activities we pursue require a certain set of conditions for them to work. We, as organisms of Earth, have adapted to these conditions. If everything changes, what will we do?
Interestingly, this is probably the reason why people hate change. We never know what will happen, and more often than not, the change usually creates completely new conditions!
Does positive feedback continue forever?
No, they do not. The principle behind this is the same as that of a chemical reaction. When the reacting chemicals finish, the product also stops to form, doesn’t it?
In positive feedback loops, there is a concept called threshold. This is the limit where the feedback loop begin to stop working. From here on, new feedback loops begin to work, which may be positive or negative. That will depend on the conditions created by the first feedback loop.
For example, if we continue to erase with the blackened eraser, sure, the paper continues to become dirty. But you will reach a point where all the black is now rubbed onto the page and the eraser becomes white again! You can then, start erasing cleanly.
Generally, after the threshold is reached, positive feedback loops reverse themselves. This reversal is of prime importance in climate change studies, because unlike negative feedback loops, positive feedback is what control the climate! Hint: yes, it is related to global warming 😉
More on this in a future post!