When we talk about weather, we're talking about the short-term atmospheric conditions in an area. These are going to be things like rainfall or what temperature it is outside. Now, climate is really looking at long-term weather patterns of an area. So, with weather, we wonder if it's raining outside, but with climate, we wonder how many inches of rain we received here in the past year? Something like that. Now, climate can actually be viewed from two different lenses: You can look at macroclimate, which is climate on the global, regional, and landscape scale. And, you can also look at microclimate, which is the climate of a small area, and this can be really small. I mean, we could be talking about a puddle. The thing about microclimates is they usually have a climate that differs from the surrounding macroclimates, so they kind of stand out for that reason.

Now, climographs are just representations of climate data. And we actually have a climate graph right here. This is from NASA, and it's showing global temperature averages for the year 2015. Now everything that is in color on this image, as in all the areas that aren't white, are different from the average. And hopefully, you can see that the Earth was quite a lot warmer than normal in 2015, and this is pretty alarming, you know. This is an aberration in average temperatures, and it's actually part of a trend that has been ongoing: the global temperature averages increasing.

Now, atmospheric conditions can lead to some pretty amazing phenomena. You know, we tend to think about physical processes like things moving due to differences in temperature, for example, on a small scale. But this kind of stuff is happening on a large scale across the planet at all times. So, I want to talk about this particular type of atmospheric circulation called Hadley cell that happens right around the equator. Now, the Hadley cell circulates air not only north and south on the globe but also up and down through the atmosphere. So the air in the Hadley cell is circulating north-south, but it's also circulating vertically, you know, it's moving up and down through the atmosphere as well. So hopefully, you can gather that from this image. These red arrows are trying to represent the movement of air in a Hadley cell.

And basically, what's going to happen is, at the equator, we get the strongest sunlight. So the air there is going to be hot, and it's going to be hotter than the air that's further away from the equator. Hopefully, you've followed me so far. Now, this warm air allows it, or this warmth in the air allows that air to hold more moisture. And hot things rise up. Right? So this air is going to rise up in the atmosphere. So basically around the equator, we get this hot warm air, and it rises up in the atmosphere. Now as it rises, as this air rises, it's going to cool. And as it cools, it's going to lose moisture as precipitation. So as this hot moist air rises, it's going to cause rainfall. Right? It's going to lose the moisture it's holding.

Now, this cooling air, not only so the air is rising up in the atmosphere as it cools, but as the air cools, it also gets pushed toward the poles. Right? So it's going to go up, and then also start to move either north or south. I'm showing an example going north could just as easily be working in this band down here, showing the opposite direction, like you can see here. However, I'm just going to keep working in this northern particular band. Now the cold air, as it's moving towards the pole, it will start to sink. Right? Cold things sink, hot things rise up, thermodynamics.

So as it moves towards the pole, it's going to sink down in the atmosphere. So, hopefully, you can see how these arrows are showing the movement of that air. Right? The hot air rises up, cools, moves towards the poles. Once it gets around this mid-latitude here, around 30 degrees, and again, this could either be north or south; you'll have them in both areas. You know, right when it gets around there, it's going to get cold enough that it's going to sink back down.

Now what's so cool about the Hadley cell is something we can literally see right here on this map. Notice how on the continent of Africa there's almost like a line right here. It's actually called the Sahel band, in case you're curious. And, basically, it's going to separate this jungle area, right, this green area from the desert up here. Now why is there such a stark division there? The answer is in part because of Hadley cells. Because the rainfall distribution is much higher around the equator and it's quite low in the peripheral areas. So these areas around the equator get all the rainfall. And look, this area of desert exists right in essentially the part where the Hadley cell has, or rather the air moving, has given off all its moisture. It's going to be dry. Right? And it's going to be dry air that's moving over this area, this desert. So the point being that these atmospheric circulations, and there's more than just the Hadley cell, this is just one to illustrate a point, you know, there's more than just this. But these atmospheric circulations have a major impact on the ecosystems of our planet, and, you know, you can't really make it any more apparent than right here, this line through the continent. So with that, let's go ahead and flip the page.