Explain Like I'm 5: What's a Feedback Loop?
Today we’re making another installment in the Explain Like I’m 5 series! As we touched on in ELI5: Climate Change, the environment is a complicated amalgam (mixture) of different processes that all work together to regulate the planet. I’m sure you’ve already heard about lots of processes in nature, like photosynthesis, respiration, and the water cycle. You also know about how lots of things in nature can affect each other - when there’s no rain, plants can’t grow, etc. Today we’re going to introduce a very special type of interaction you probably aren’t as familiar with: feedback loops. These loops are found all over the place on our planet and this is a topic that you’ll find yourself coming back to the more you dive into environmental topics. Today we’re just going to tackle Feedback Loops 101, then later on we can dive a little deeper. So strap in Scouts, you’re gonna learn today!
The environment is made up of lots and lots of “earth systems.” These systems operate on big scales; for example, the water cycle that changes rivers and lakes into rain and back again can be called one system. There are systems that regulate the earth’s revolution around the sun, systems that change magma into rocks and then into different rocks, systems that change the course of rivers, and even systems that turn cow farts into fish food. These earth systems never act all alone in a vacuum; they always have effects on other systems. Sometimes, two systems talk back to each other and start a conversation. This conversation can either escalate, like 2 people trying to shout over each other, or they can be a calm exchange. When two systems have a long conversation, we say that they occur in a feedback loop. If each system gets ramped up during the conversation, they are said to be in a “positive feedback loop.” If the systems balance one another out as they go back and forth, this is a “negative feedback loop.” This all gets easier to understand when we look at some examples.
Let’s start with a positive feedback loop. One of the most talked-about positive feedback loops is that of glacial melt and global surface temperature. To really understand this loop, we need to learn a new word! Albedo. Albedo is not a European style of men’s swimsuit or a Victorian name for fancy boys. Albedo is the measurement of how much light a surface reflects. When you wear a black shirt in the summertime, you get hot really fast. This is because black fabrics tend to have very low albedos - meaning they absorb a ton of light energy instead of reflecting it back out into the world. As a general rule, lighter color objects usually have higher albedos and so stay cooler (of course there are exceptions but we don’t need to worry about them right now). Glaciers and ice sheets have a high albedo, meaning they reflect a lot of solar energy back away from the planet. The ocean is dark and has a much lower albedo than ice, which means ocean water tends to absorb solar energy and warm up, which warms up the overall surface temperature of the planet. When glaciers are big, they help keep the earth cool, which then allows the glaciers to grow even bigger, which makes the earth cooler, etc. On the other hand, when glaciers start to melt they get smaller and reflect less energy away, allowing temperatures to rise, causing more ice to melt. When these two systems talk to each other, they each get amplified. Even though these two scenarios go in opposite directions (in one the ice grows and temperatures lower, and in the other ice melts and temperatures rise), they are both “positive” feedback loops; the effects get more extreme the longer they talk to each other. This mutual amplification is what makes a positive feedback loop, not whether the loop results in more of something or less of something. Don’t forget there are always lots of systems at play, so there is no single loop that acts all by itself like a runaway train. Even so, feedback loops make big impacts on the planet, climate, and our lives.
Now we’ll take a look at an example of a negative feedback loop. Negative feedback loops act like checks and balances on earth processes. One famous example is population overshoot and dieback. I know, I know, more new words. Overshoot is when a population grows so big that there are not enough basic resources like food and water to support everyone. The maximum amount of resources that land can produce is called the carrying capacity, and when the population overshoots that capacity, some of the population dies. Let’s illustrate this with rabbits. The rabbits are going to wind up dying, so try not to picture really cute ones in your head while you follow along: Every year, plants get eaten by rabbits and the rabbits get eaten by coyotes. That is until one year, when humans hunt all of the coyotes until they’re gone from the area. Now there is no predator that regulates the rabbit population. Lots and lots of rabbits are born and grow up and have more rabbit babies and the population explodes. The problem is that there is only so much room for rabbit food to grow; the area has a limited carrying capacity. The rabbit population grows so much that there is not enough food for all of them and lots of rabbits die of starvation. The main systems at play here are population growth and carrying capacity. When population growth talks too much, carrying capacity levels things out again. These two systems interact in a negative feedback loop and ultimately balance each other out. Again, the loop is “negative” because the systems keep one another balanced, not because you might think of bunny death as something that is negative.
And there you have it! Your main takeaways from this article should be:
Lots of different systems work together to make our environment/climate/planet what it is
When two earth systems cause each other to have amplified effects or feed each other, they are acting in a positive feedback loop
When two earth systems act to keep each other in check, they are acting in a negative feedback loop
For bonus Scout points, try to remember the new words we learned today like albedo, overshoot, and carrying capacity. I find that the best way to remember new words is to teach them to other people. So share what you learned today with your friends and family, and keep an eye out for feedback loops! Now that you know what they are, I bet you’ll spot some in your daily life. If any of the main points still feel a little fuzzy or if you want to share another example of a feedback loop, leave a comment here or in the Troop 7B facebook group! Your fellow Scouts and I would be happy to talk through it some more!
