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Greenhouse Effect

Earth is so "COOL"! (Heating the Atmosphere)

Our atmosphere is really unique. Itís not too hot, and not too cold. It has oxygen, which is a big bonus for breathing. And it has just the right mixture of gases and water to drive the water (hydrologic) cycle. We are not bombarded with solar radiation because we have ozone, which many other planets do not. There are a lot of really cool things about planet Earth.

One of the coolest things about Earth is the way air is heated and how it helps to drive the water cycle.

When you view Earth from other space it looks like a big blue globe, covered with white, swirling patterns (weather systems). Air is the medium through which that occurs, in the lowest layer of the atmosphere (the troposphere). Letís check out how that occurs.

All forms of matter, whether a solid, liquid, or gas, are composed of atoms or molecules in constant motion. Because of this constant motion, all atoms have thermal (heat) energy. Whenever a substance is heated, the atoms move faster and faster. When a substance is cooled, the atoms move slower and slower. The "average motion" of the atoms that we sense is what we call temperature.

On a sunny winter day, you park your car in the sun, lock it, and go cruise the local shopping mall for a couple of hours. When you come back later and climb into your car, what do you notice? Is the interior of the car hot or cold? How does the temperature inside of your car compare to the temperature outside?

If you have ever been inside of a greenhouse, especially when the sun is out, what have you observed? It is definitely warm, and usually the air is moist. A greenhouse is commonly warmer than the outside air because a greenhouse has the ability to trap heat inside of it. This phenomenon is called the greenhouse effect.

This same phenomenon occurs on the Earth. What causes this? Well, letís take a look at how a greenhouse works to give you some ideas.

Click the picture to learn how the Earth's
atmosphere works like a greenhouse.

Radiation is the primary way that air is heated. Convection currents move that heated air around the earth, and the difference between warm and cold air provide the energy needed to create weather.

The ability of the Earth to absorb heat from the Sun and "hold onto" or re-radiate that heat is important for night-time, when there is no solar radiation reaching a given area. For example, the moon has essentially little or no atmosphere. The side of the moonís surface facing the sun would get all radiation all of the time, and the side of the moonís surface facing away from the sun would get no radiation. That means that the temperature differences between sides of the moon would be huge, because there is little to no atmosphere keep and hold heat. If a planet had a very thick atmosphere, especially one that absorbed a lot of solar radiation, temperatures would be very hot. If a planet had a very thin atmosphere that wasnít that efficient at reradiating heat, temperatures would be cooler on average. It seems such a simple thing, and yet small atmospheric differences (like the composition of the atmosphere, how thick it is, etc.) make huge differences in temperature ranges and pressure readings.

Next: Comparing the Atmosphere of Earth, Venus and Mars



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