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Video transcript

- [Narrator] What's the weather usually like in the winter where you live? If you asked someone in Fairbanks, Alaska they might describe below freezing days and navigating through huge drifts of snow. If you asked someone else in Miami, Florida they might tell you that most days it was warm enough to go to the beach. How can two places on the same continent be so different? Well, it all comes down to regional climates. Climate is the long term pattern of weather in a particular region. You can think of it as the average weather. A region's climate depends on many factors, including its latitude, elevation, and surrounding geographic features, such as oceans or mountains. Let's look at how regional climates depend on latitude first. Latitude refers to imaginary lines that measure how far north or south a place is from the Equator, which equally divides the earth in half. The Equator is marked at zero degrees latitude and the mid-latitudes increase north or south until they reach the poles, which are marked at 90 degrees north and 90 degrees south. The sun heats the planet unevenly. So places at higher latitudes, which are farther from the Equator, get less direct sunlight and solar energy on average, resulting in lower average annual temperatures. Places at lower latitudes, being closer to the Equator, get more direct sunlight and solar energy on average, which results in higher average annual temperatures. This uneven heating creates a pattern of low and high air pressure bands from the Equator to the poles, affecting the amount of precipitation that the different latitudes receive. In bands where moist air is rising, mainly at zero degrees latitude and 60 degrees north and south, places experience a lot of rainfall, especially around the Equator. And bands where dry air is sinking, like at the poles and 30 degrees north and south, places experience very little rainfall. This creates dry conditions at the cold poles and desert conditions in regions near the 30 degree latitude lines. Another important influence on regional climates is elevation or how high a place is above sea level. As air rises from lower to higher elevations, it expands and cools. That's why regions at higher elevations, like mountains, tend to have lower average air temperatures than regions at lower elevations. Speaking of mountains and seas, the presence of geographic features can also influence a region's climate. Let's start by diving into the impact of water first. Water heats and cools slowly while land heats and cools quickly. As a result, temperature variations tend to be much smaller for cities near large bodies of water than for cities surrounded by land. For example, let's compare the yearly temperature ranges for Vancouver, which is close to Canada's Pacific Coast and Winnipeg, which is further East in the interior of the country. This line graph follows the average temperature in Celsius for each city throughout the months of the year. Vancouver starts at the year mildly chilly. Temperatures rise a bit for a warmer summer. And then slope gradually back down. Overall, the city sees a pretty small range of temperatures throughout the year because the nearby ocean influences the local climate as it gradually warms and cools. Compared to Vancouver, Winnipeg has a much colder winter and a slightly hotter summer resulting in a more dramatic range of temperatures throughout the year. We call a climate like Vancouver's a Marine Climate and a climate like Winnipeg's a Continental Climate. Things get pretty interesting when we combine the impact of water with land forms. One unique example is a rain shadow, which can be found in places where mountains are relatively close to the ocean. For example, here's a satellite image of the Andes Mountain Range in south America. The mountains run north to south in this image and they're close to the Pacific Ocean. Notice how the area between the Pacific and the Andes is green and lush, but the area behind the Andes is brown and dry. That's the rain shadow. What causes such a huge change? Well, when warm moisture rich air from the ocean meets the mountain it's forced upward. As it rises the air expands and cools causing the moisture to condense and fall as precipitation. Now, the air is much drier, which allows it to change temperature much faster. As that dry air descends down the other side of the mountain it compresses and quickly becomes warmer, which leads to increased evaporation. Overall, this results in a cool and wet climate on the ocean side of the mountain and a warm and dry climate inside the rain shadow, which is what we saw on the satellite view. As you can see, regional climates can get pretty complicated when you consider all of the factors that can go into them. Depending on the exact region, one factor may be more responsible for the local climate than the others. Like how the presence of the Andes Mountains contributes to the rain shadow climate beyond them. Let's look back at our two very different cities from before so we can see how the factors we discussed affect their winter climates. Fairbanks is at a very high northern latitude which helps explain why it's so freezing in the winter. Miami is much closer to the Equator and near an ocean, so it experiences a very warm and mild winter. Which of these cities would you like to visit in the winter? Whether you prefer hanging out on sunny shorelines or exploring frosty winter wonderlands, there's a regional climate somewhere in the world that you'd probably enjoy.