Think about the weather outside. Is it the same temperature as it was yesterday or last week or
six months ago? Chances are, the temperature has gone up and down a whole lot in that time.
But what causes the air temperature outside to change? When it cools off, where does the heat go?
To answer this question, we'll need to dig into two important ideas: matter and energy.
By the end of this lesson, you'll be able to describe how heat is
transferred through Earth's atmosphere and explain how heat transfer results in
temperature changes on Earth. So have your guided notes ready and let's get started.
We've learned that everything in our universe is either matter or energy. Our atmosphere,
or the sphere containing Earth's air, is made of matter primarily in the gaseous
state. But matter and the different kinds of energy are closely interconnected. In fact,
all matter also has energy. One of these kinds of energy is heat energy. This comes from the
movement of atoms and molecules. When they start to gain more heat energy, they start
moving around faster and faster. This movement is what causes a solid to melt into a liquid,
or a liquid to evaporate into a gas. At the same time, when atoms lose heat energy they
start moving slower. This is what happens when you freeze water into ice. The atoms slow down until
they're staying in place and forming a solid. That means matter doesn't gain or lose cold;
instead, it can only gain or lose heat energy. But where is this heat coming from?
There's an important rule called the Law of Conservation of Energy.
It tells us that energy can never be created or destroyed; it can only change between different
types of energy or be transferred between matter. This means when the air outside gets hotter,
it isn't making the energy, it's getting the energy from somewhere else. That's
where heat transfer comes in. Heat transfer is the movement of heat energy from one place to another,
like through the Earth's atmosphere. Heat transfer on a global scale causes temperature to change
from warm to cold and generally keeps the Earth at a comfortable temperature for us to live in.
There are three main ways that this heat transfer occurs.
Since energy is never created nor destroyed, where do you think the heat energy on Earth comes from?
Pause the video here and record your answer in your guided notes.
The heat energy on Earth comes from the Sun. It warms our atmosphere through a process called
radiation. This is when heat is transferred by waves of energy radiation from the Sun, reaches
all the way to Earth's surface, warms up the ground, and introduces heat to the Earth system.
The surface of the Earth absorbs a ton of heat energy from the Sun, so why isn't the
dirt burning hot every time we touch it? Well, it's because this isn't the only way radiation
leads to heat transfer in the atmosphere. The ground also radiates the heat it absorbed back
into the lower layers of the atmosphere. But what about when the sun sets? The temperature
is usually a bit cooler at night than it is during the day, but it isn't suddenly freezing
cold just because the radiation from the Sun is gone. During the night, the ground continues
radiating the heat absorbed but at a slower rate. It's like turning off the stove. The heat
source is no longer providing energy, but it's still hot for a while as it slowly cools down.
All this heat has to go somewhere, though, which is where our next type of heat transfer comes in.
Another way heat is transferred is through conduction. We know radiation is when heat is
transferred through energy waves, but conduction is when heat energy is transferred through matter.
Conduction is why a pan on a hot stove heats up. The energy is moving from the hot stove to the
cooler pan. In the atmosphere, the heat energy we get from the Sun radiates off the Earth's surface
and makes contact with the air molecules near the ground. Since conduction is the heat transfer
through matter, this means the energy continues to transfer outward to the nearby air molecules
and other sources of matter. Conduction is most effective in the lower atmosphere, but
why do you think that's the case? Pause the video here and record your answer in your guided notes.
Remember, this type of heat transfer requires direct matter-to-matter contact.
Since there are more air molecules in the lower atmosphere, there's more matter for the heat
energy to transfer to. The number of molecules decreases as you move further from the Earth's
surface. This makes conduction less effective in the upper atmosphere since the air molecules are
so far apart. The molecules up there might even be really high temperatures, but they're too spread
out to transfer their heat through conduction, so the upper atmosphere stays cold. Remember,
matter with more heat energy moves faster and that includes warm air. So where does it go?
The last way heat is transferred through our atmosphere is a process called convection.
Convection is when heat energy is transferred through the movement of a liquid or gas.
The heat energy moves through a liquid or gas as it heats up and rises. Then, as it cools, it
begins to sink back down. A pot of boiling water is a great example of convection. The moving,
swirling, bubbling, and boiling action of the water is convection. It's the heat energy moving
through the water. If you leave a pot of water on to boil without reducing the heat, it has the
potential to boil over the edge. That's because all of that heat energy is pushing the water up
and out. When you then turn the heat off entirely, this stops the flow of the heat energy and causes
the water to then settle back down. The same applies to the air in our atmosphere. The movement
of heat energy through convection causes the air to rise and fall. As the hot air rises up, cooler
air falls and takes its place. Can you think of what this movement of air is called? It's wind.
Like many processes on Earth, the processes that transfer heat through our atmosphere are
interconnected. Radiation transfers heat to and from the ground, conduction then
carries this heat into the air where it is then moved all over the planet by convection, and,
together, those three methods of heat transfer regulate the temperature of our entire planet.
So, let's go over what we learned today. You now know heat energy on Earth comes from the Sun.
Radiation, conduction, and convection transfer heat energy throughout Earth's atmosphere
and this movement of heat energy causes temperatures to change from warm to cold.
Ready to learn even more about our atmosphere? Be sure to check out the
practice questions and extension activities that go with this lesson. And remember,
in earth science as in life, you rock. We'll see you next time.