There are four ways that Heat can be transferred, as radiation, conduction, convection, or advection.

Conduction
 
Heat is a form of energy and all molecules contain heat energy, it is what makes them vibrate. When we put more heat energy into an object, its individual molecules begin to vibrate faster. Molecules are always bumping into one another. When two molecules with different amounts of heat energy collide heat energy will be transferred from the high energy molecule to the low energy molecule. In other words, when the molecules collide, the one that was vibrating a lot will slow a little and the vibration of the slower one will speed up. This is called convection.

Consider heating a iron bar:
 

Initially all the atoms are moving the same speed as they are all the same temperature:
As we heat the bar the atoms near the flame start to heat up, vibrating faster. As they start to vibrate faster, they begin to bump into other atoms more often, causing them to vibrate faster:
Eventually, through billions of collisions, the atoms heated by the flame have affected the vibrations of all the atoms in the iron bar:

In conduction the heat is moving, from one location to another, but the atoms are not. They are vibrating but stay in the same location.

Convection and Advection
 
Have you ever heard someone say "heat rises?" They are referring to what is known as convection. Convection is the vertical movement of fluids (gases or liquids). When a fluid becomes warm it expands, this causes it to become less dense, the warm fluid then rises above the cooler, more dense, fluid around it. This principle is what allows people who are hang gliding to stay in the air for several hours when it should only take minutes to fall to the ground. The glider looks for a warm current that is directed up a mountain cliff. If the hang glider is falling slower than the air around him is moving upward, he will continue to gain altitude.

Often when we have a column of fluid rising, we also have a void left behind. This is where advection comes into play. Advection is the horizontal movement of a fluid. When warm air rises it creates a vacuum that has to be filled, so air is rushed to that area to fill the void. That is what causes mush of the wind that we experience. As warm air rises, cooler air sweeps across the land looking to fill that void. Usually the area that is under the column of warm air that is rising experiences no wind...but this is also true of the area under the column of air that is returning from the upper atmosphere after cooling.

On the graphic of the globe to the right you can see what is called a "cell." The cells contain air that gain heat as they move along the Earth's surface and the air interacts with the land/sea (conduction). At the same time the horizontal air movement brings in cooler air molecules all the time cooling the land (advection). The air then turns upward toward the outer atmosphere (convection). Once in the upper atmosphere the air is moving horizontally again (advection) where its heat is lost to space as radiation. Once it cools, the air begins to sink back to Earth again (convection).


Radiation
Until now, all we have talked about is energy transfer through the interaction and movement of particles. We know that most of our Energy comes from the sun...so how does it get here if there are no particles linking us or being transferred to us? The answer is radiation. The radiation that travels to earth is in the form of waves. The waves we are most familiar with are the light waves. Radiation with a shorter wavelength include UV rays and longer wavelengths are microwaves and infrared light.

All of these are emitted by the sun. When you are out in the middle of nowhere and you turn on the radio and all you hear is static. That is your radio picking up solar and cosmic radiation.

The radiation that comes to Earth from the sun hits gas molecules in the atmosphere and heats them up (makes them vibrate faster). Some also make it to the Earth's surface where they warm the objects on the Earth's surface up.

The first thing the solar radiation encounters when it reaches Earth is the atmosphere. The atmosphere absorbs 1/5 of this energy, reflects 1/4 back into space, and lets 1/2 pass through to the Earth's surface. Most of the sun that hits the Earth's surface is absorbed, only 3% is reflected back into space.

An objects ability to reflect light is known as its albedo. Snow has a high albedo because it can reflect most of the light that hits it back into the atmosphere. This helps to keep the poles cool. As the solar radiation hits the snow covered poles, most of that energy is reflected back towards space and the poles remain cool. In recent years the polar caps have been receding due to Global Warming. As the polar caps recede, more water and rock is exposed. These water and rock are much better at absorbing solar radiation and in turn are warming the poles causing the snow at the poles to melt. That's right, the more the poles warm up, the more the ice caps recede, the more the ice caps recede, the more the poles warm up. One feeds the other. It is predicted that in the not to distant future there may no longer be ice at the poles year long which could mean extinction for many animals including the polar bear and many penguin species.

Questions: You may cut and paste these questions into a word document. Make sure that you put your answers between each question, the final copy contains your name, and that all the information fits on one sheet of paper. 1. What is the difference between convection and advection? 2. Does the atmosphere absorb more solar energy than it reflects? 3. Does the atmosphere absorb more solar energy than it allows to pass through? 4. Why do you hear static on the radio when you are not receiving a station? 5. How is heat energy transferred from one molecule to another? 6. The data table to the right shows the percentage of solar energy reflected by a number of different materials. Based on this information:   a) What material would you consider to have the highest albedo?   b) What material would you consider to have the lowest albedo?   c) We know a desert is known to be hotter than a forest, then       how can a forest absorb more solar radiation than a desert yet       it remains cooler? What explanations can you think of?
7. Above is a picture of a sea breeze. The sun warms the land, the land then warms the air that is sitting over the land. As that air warms it rises and cooler air that is sitting over the ocean flows inland to take the place of the warm air that is rising. This is a sea breeze and it cools land near the ocean on hot, sunny days so the costal areas do not become too hot. Looking at the picture above, describe where you would find an example of each of the following occurring in the diagram: radiation, conduction, convection, and advection.
8. Above is a picture of an off shore breeze. When the sun sets the land begins to cool rapidly. The ocean has been absorbing heat energy all day. As the atmosphere cools the ocean passes heat to the air that rests on top of it. As this air warms it begins to rise. As this warm air rises, cooler air over the land rushes out to sea to fill the place of the warm rising air. This is an off shore breeze and it keeps costal areas from getting too cold in the evening. Look at the picture above, describe where you would find an example of each of the following occurring: radiation, conduction, convection, and advection.