 feedbacks are really important to a number of natural processes. And in general, there are two types of feedbacks, positive and negative feedbacks. Positive feedbacks are ones that amplify a change. And so an example would be if something causes the temperature to go up a little bit, and the response of the system is to raise the temperature even more. That small change in temperature is amplified by a positive feedback, or an amplifying feedback. In contrast, a negative feedback dampens those changes. So if we take a small increase in temperature again, if the system responds so that the temperature decreases and that small change is reversed or reduced in size, we say that that's a negative feedback or a dampening feedback. One of the interesting things about these two is that if small changes are amplified, they can grow and grow and grow. And the system can end up in a whole new place. If they're dampened, that tends to keep a system in the state that it exists in. It's a stable state that doesn't respond very much to changes. Okay, so let's talk about an amplifying feedback example. Let's say we have some ground here. And on that ground, we have some ice, so we're in a polar area. So we have some dark ground and we have some ice, which will be the light blue here, since white doesn't show up on white. So in our world, we have some sunlight. And that sunlight has a lot of heat associated with it. And so when that sunlight comes down onto the ice, a lot of it is reflected back, whereas if it comes down on the ground, a lot of it is absorbed and it heats up the ground. So this difference in ability to absorb the light is called albedo. And something with a low albedo heats up because it absorbs that energy from the sunlight, whereas something with a high albedo reflects a lot of light. So we have this situation where we have the ground and some ice. And so what happens if the temperature goes up a little bit? So let's say that the temperature increases maybe due to some carbon dioxide in the atmosphere, which is a greenhouse gas. What happens is some of the ice melts back, right? And it produces water and if we actually erase it here, right? As some of the ice melts, there's more ground exposed and less ice exposed. So as the ice melts, you end up with more of the sunlight hitting the ground and you end up with more heat and that causes the temperature to go up even more. So that causes, again, more ice to melt. And as that ice melts, more and more of the sunlight gets absorbed. And so you end up with the temperature going up even more and more. So this is a case of an amplifying feedback. A small change in the temperature causes a set of processes that lead to a greater and greater change in temperature through time. So let's talk about an example of a dampening feedback where an increase in temperature gets dampened back by different processes. So if we take our example of carbon dioxide in the atmosphere, that creates a greenhouse effect and it causes the temperature to increase when there's an increase in carbon dioxide. This carbon dioxide can be removed in different ways. One of those ways is by the growth of plants and photosynthesis. So let's say we have some plants here. The carbon dioxide can go into the organic matter of the plants. And so plant growth can remove carbon dioxide from the atmosphere. And so often plants grow faster when there's more carbon dioxide in the atmosphere. And so this would reduce the effect of an increase of carbon dioxide, which would reduce the effect of a temperature increase. The carbon dioxide can also go into the soil. And in the soil there are weathering processes. And those are reactions between these carbon dioxide and minerals. And the thing that comes out is bicarbonate ion that is in the water. And so this process of weathering takes carbon dioxide out of the atmosphere and puts it into the water. And then this can actually be used by organisms to form carbonate minerals that make up a lot of their shells. So this is another process that on the long term acts as a dampening feedback because when the carbon dioxide goes up and the temperature increases, these soil reactions occur more quickly and they pull the carbon dioxide out of the atmosphere. And so both the growth of plants and these reactions reduce CO2 in the atmosphere and dampen the effects of the greenhouse effect. Thanks for watching.