 You are clear for launch. And with that, shut down your visors, O2 on, and prepare for ignition to O2. You can copy that and um... And we're back. Hi, I'm Mr. Ruchoff. In our last lesson, we went over what the reason is for the seasons, and we discussed the sun and the earth relationship that really drives the earth's climate. In this lesson, what we're going to do is we're going to look at all five factors that work together to create our climate. Of course, first of all, what we need to do is to find what is weather and what is climate. Weather is more of a snapshot of what's going on in the atmosphere at a particular place at a particular time. An example of weather might be that at 1049 on the 24th of July, the temperature was 90 degrees. It was partly cloudy with a 15% chance of rain. These are specific conditions of the atmosphere in a specific place at a specific time. That's weather. Climate, however, is the average weather conditions for a particular location over a period of time, usually over years. An example of climate would be if I told you that Brian, Texas, on average receives just over two inches of rain and has an average temperature of just about 81 degrees. We often use something called a climate graph like this one to be able to show these averages and to describe a climate of origin. We'll talk more about that in our next lesson. But right now we know the difference between climate and weather. Let's start looking at those factors that combine to create our climate. There's latitude, elevation, wind currents, ocean currents, and something called topography. We'll start a discussion by looking at latitude, which is by far the most important factor of climate. In fact, we just had an entire lesson that discusses how the seasons of the earth are different based upon latitude. This is, of course, due to the tilt of the earth and the earth's revolution around the sun. As we learn, the further away from the equator you are, the cooler you're going to be, and the closer to the equator you are, the warmer you're going to be. This is why Lagos, Nigeria, which is in the low latitudes, also known as the tropics, will be warm all year long. However, if you go to or maybe ask Russia, which is north of the Arctic Circle, the temperature year round will be much, much colder. Our next factor is elevation. Elevation essentially is how high above sea level you are, usually described in either feet or meters. Elevation impacts the climate by affecting the temperature. The higher you go in elevation, the colder it's going to be. But as you go down in evolution, it will become warm. To make this easy to remember, think of a mountain. Where do you usually find snow on a mountain? It's at the top. Why? Because at the top of a mountain, it's colder. It has more elevation. On its own, elevation will impact temperature by about 3.5 degrees Fahrenheit for every 1,000 feet. Take Africa's tallest mountain, Mount Kilimanjaro, which is found in the country of Tanzania. It towers over the African savannah at 19,564 feet. And if you're climbing Mount Kilimanjaro, you're probably going to stop at one of the camps at the foot of a mountain that sets at over 6,500 feet. Now, using our 3.5 degree temperature per every 1,000 foot of elevation calculation, we could tell you that the summit or at the top of the Kilimanjaro should be 44 degrees colder than at this camp. And how does this actually work in reality? Well, on the 24th of July, the temperature at the top of Mount Kilimanjaro was 19 degrees, and the camp at 6,500 feet was 63 degrees. That is a difference of 44 degrees, only about 1.5 degrees off of our calculation. So you can see in true terms the effect that elevation has on temperature. This is the reason why we see cold temperatures along the west coast of South America, even though that region is in the tropics. Because what is also on the west coast of South America are the Andes Mountains. Elevation impacts temperature. Then there are wind currents. These are very important as they move heat and water vapor around the world. And what creates wind? Well, it's time to break out the lava lamp again because we're going to talk about convection. We talked about convection before. Remember convection is that circular motion that happens when warmer air, liquid, or even rock, rises while cold material falls back to earth. The light bulb without lava lamp heats up wax, which makes that wax rise to the top. When it gets to the top of the lamp, it cools down and comes back down and the cycle begins. This is convection. Well, this also is what happens in the air and our atmosphere. As the sun beats down on the earth, the air near the surface heats up and begins to rise. But let's take this through. If the heating of the earth's surface causes the air to rise into the sky, it has to be replaced. Otherwise the people underneath are going to be suffocated and we know that's not the case. So what happens is there's rising air creates a low pressure cell that kind of works like a vacuum cleaner. As these air parcels move up, it creates a low pressure area that begins to suck in air from surrounding areas. This air rushing into the low pressure area actually is what creates the surface winds that causes wind erosion, fills sails of ships and even creates storms. Now as the air rises, it gradually cools down just like our wax and our lava lamp and this air comes back down to the surface. Now where the air presses down on the surface, the air pressure increases. We call these areas high pressure sails. Together this is actually what creates the winds through convection. But it just isn't air that is affected by these convection currents. Within these air parcels is water vapor that is either evaporated from surface water or plants have given off through what is known as transpiration. As this air and water vapor rises, the temperature falls and clouds are created. And after a while, the air can actually hold this liquid water and it falls through the surface as rain. This is the reason why low pressure areas typically have increased amounts of rain. But after losing its water vapor, the air that comes back down to earth is now dry and works to prevent any rain in these high pressure areas. This is the reason why high pressure areas do not have as much rain or precipitation as other areas. Now because of the uneven heating of the earth's surface, there are several of these large convection sails that create large global wind patterns. And of these probably the most important are the Hadley sails, which stretches from the low pressure area near the equator called the intercontinental convergence zone or you can just call it the itch for short. Where the area of the Hadley sail comes down is around 30 degrees north and 30 degrees south latitude. Now this constant dry air from the Hadley sails is the reason why so many of the world's deserts actually are found along 30 degrees north of 30 degrees south latitude. Now while the itch is found in the tropics as the seasons change, the itch will actually migrate north and south moving towards the hemisphere that has the most heat during that season. But while oceans and lands heat and cooled at different rates, the itch will not move uniformly around the world. In south and east Asia, the itch will move as much as 40 degrees of latitude between winter and summer. And over the South American and African continents, we find that the itch will actually move more in the eastern portion of the continents than they will find moving in the west. Now the seasonal migration of the itch is what gives the tropical latitudes their two seasons, their wet and the dry seasons. As the itch moves over an area, it brings rainfall with them and creates a wet season. But when the itch moves away, it takes the rains with them and that area is left with the dry season. Of course, in areas where the itch does not migrate very much such as the Congo rainforest in western Africa, there is no real dry season. Instead, these regions will only have one warm rainy season all year long. So those are wind currents, but ocean currents are also another important factor that drives our climate. Ocean currents operate like rivers in the ocean that affect the climate in terms of precipitation and in temperature. Warm currents are created by the heat of the tropics near the equator, and what will happen is those warm currents will move from the equator up to the poles. The water near the poles then cools down and now the cool currents will come from the poles and move towards the equators. But ocean currents don't travel straight north and south, rather, just as with wind currents, they will curve due to something known as the Correales effect. You might notice that the circumference of the Earth is larger at the equator than as you approach the poles. This means that in order to rotate in 24 hours, the surface of the Earth around the equator has to be moving much, much faster than the rest of the planet. In fact, the Earth at the equator is actually moving at over 1,000 miles an hour. But the surface near the poles doesn't have to move nearly as quickly. In fact, the Earth's surface at 60 degrees latitude is moving at half the speed of that at the equator. So as the wind and ocean currents move, the Earth's surface moves beneath them at different rates depending upon the latitude you're at. And it appears as if the wind and ocean currents actually curve. In the northern hemisphere, the currents are going to occur clockwise, and in the southern hemisphere, the currents are going to move counterclockwise. You can see how they're moving in this NASA animation, which also shows the temperature of the global sea currents. Orange and yellows are warm, green and some blue are cooler. And what does this matter? Well, it matters because the ocean currents off the east coast of continents will usually be warm, while the ocean currents off the west coast will usually be cold. The issue is that cool water doesn't evaporate at the same amount as warm water. So if you don't have very much evaporation, you do not have more humidity. If you don't have humidity, you don't have clouds. If you don't have clouds, you don't have precipitation. This is why states on the east coast of the United States receive order four times the amount of rain that states on the west coast do. And that doesn't even count the Gulf states. To further illustrate the effects of ocean currents, two of the driest deserts in the world are actually on the coast of an ocean. On the west coast of South America, we find the Atacama Desert, which is actually the driest desert in the world. And if we look on the west coast of Africa, we find the Namibian Desert. Both of these deserts owe their dryness to the cool water of the Atlantic and the Pacific oceans on the west coast. But there are exceptions to this pattern. Off the west coast of the Americas, every say two or ten years, there is El Nino. Now ocean currents are greatly influenced by surface winds and trade winds. These are the west blowing winds that are caused by the high pressure cell caused by the Hadley cells around 30 degrees latitude. These trade winds are usually pushing warmer Pacific water to the west. However, in El Nino occurs when these trade winds weaken and the other winds now start to push the warm water to the west coast of South America. This impacts the climate of all the Americas as El Nino's warm water allows for increased water vapor, creating humidity that creates clouds which provides for flooding and precipitation along the west coast of the Americas. Now another exception to the rule is the North Atlantic Drift. The Gulf Stream is the warm ocean current that starts when the equator flows through the Caribbean and then flows up the eastern coast of the United States. But as it leaves the eastern coast of the United States, it begins to move. You can see it drifts. It drifts across the Atlantic, not any portion of the Atlantic, but the North Atlantic, see, North Atlantic Drift. But this warm water drifts and moves over to Europe. It is this North Atlantic Drift that gives Europe a northern climate despite the continent being at about the same latitude as Canada. For example, due to the North Atlantic Drift, Dublin, Ireland is on average about eight and a half degrees warmer than St. George Newfoundland even though Dublin is a full six degrees latitude closer to the North Pole. Another way that ocean currents impact weather is that because water heats and cools slower than land or air, places near the oceans tend to not have as much of a swing of temperature. Take San Francisco, California and my hometown of Wichita, Kansas. Now both these cities are pretty much the same latitude. But San Francisco, California is on the western coast in Wichita the smack dab in the middle of the country. But they also have a similarity in that both of these cities have an average temperature throughout the year of 57 degrees. But Wichita, which is far from the ocean, has nearly a 49 degree temperature change from January to July. However, San Francisco's average temperature throughout the year changes by less than 12 degrees. The ocean waters moderate San Francisco's climate. This effect that being in the interior of the continent away from oceans is called continentality. Not only does continentality mean that these inland areas have much more of a temperature swing as it comes through the seasons, we also find that these inland areas have less precipitation because they're further away from oceans. This is all in what we call continentality. And the last factor of climate we'll look at is topography. Now the term topography actually means the arrangement of physical features on the earth. But mostly when we use it to determine the causes of climate we're talking about the impact of mountains outside of elevation has on the climate. Now we've already seen how the temperature drops 3.5 degrees for every 1,000 feet of elevation gain. Topography now looks at how mountains can block precipitation from reaching an area through something called the rain-shadow effect. And the rain-shadow effect is something that we're going to be discussing quite a bit in this course because it shapes so many different regions of the world that we're going to cover. When the winds blow water vapor on clouds they become blocked by mountains. Now the wind can get onto the other side but the only way it can get onto the other side is it has to go over the mountain. As the air pushed by the wind moves up into elevation the temperature falls, the water vapor condenses and it falls as rain on what is known as the windward side of the mountain. Now when the air finally makes its way over the mountain it has dumped all of its moisture on the windward side leaving nothing for the other side of the mountain. This other side of the mountain is known as the leeward side and it tends to be fairly dry. The Tibetan Plateau in China is a perfect example of the rain-shadow effect in action. To the south of the Tibetan Plateau are the Himalayan Mountains which blocks any of this precipitation from being able to get to the northern or the leeward side of the Himalayas. Consequently the southern side or the windward side of the Himalayas receive large amounts of rain or a lush with vegetation but the Tibetan Plateau again the leeward side is dry. This is an example of the rain-shadow effect in action. So we've discussed the five factors of climate. Latitude, elevation, wind and ocean currents and topography or the rain-shadow effect. Each of these factors works together to be able to create the world's climate. In our next lesson we'll talk about the specific climate types that we find around the world. But until then, keep on learning.