Keep the following things in mind as you watch this animation.
1) As the energy becomes more transparent, it represents the energy being absorbed by either the atmosphere or the ground. The more transparent it appears, the weaker it is.
2) Scattering and reflection of insolation (albedo) are not represented in this animation. Only absorption and radiation are shown.
3) The Play button must be pressed to go to the next piece of the topic.
This animation represents an ongoing process of energy exchange. In the animation several parts of the process are shown.
- The INcoming SOLar radiATION can be seen
entering the atmosphere. The ultraviolet rays (UV) can be seen getting
mainly absorbed by the ozone layer in the upper atmosphere. The
infrared (IR) can be seen getting mainly absorbed by the water molecules and
Carbon dioxide in the lower atmosphere. The ground then absorbs what
is left. (remember the reflected part is being ignored).
- Terrestrial Radiation
- The ground actually radiates energy whose frequency is related to its temperature. The temperature of the earth causes it to radiate in the infrared (IR) range. Keep in mind this is different than reflection. The majority of these radiated infrared rays get absorbed by the water molecules and carbon dioxide in the atmosphere, making it mainly opaque to IR. The earth actually contributes more energy to the atmosphere than the sun does. A very small amount of the radiation from the ground actually makes it to space.
- Atmospheric Radiation
- The atmosphere radiates energy whose frequency is also related to its temperature. The temperature of the atmosphere causes it to also radiate in the IR. As you can see in the animation, a large portion of this radiation goes to the ground while the remaining portion radiates out into space. The amount of energy the atmosphere radiates to the ground is actually more than the amount of energy the sun radiates to the ground.
- Latent Heat
- Water vapor has more energy than water (liquid) at the same temperature. As a result, when water evaporates from the surface of the earth, it takes energy form the ground. When the water vapor in the air condenses to form water it gives the energy to the atmosphere.
These processes do not follow a step by step process, they are each ongoing and not directly dependant on any of the other steps. They are related over time, but not dependant. If the sun went away, as it does every night, water still evaporates and condenses, the ground still radiates heat and the atmosphere continues to radiate.
It is important to notice that there is a balance. For the earth the amount of insolation is equal to the outgoing radiation. The same amount of energy absorbed by the atmosphere will also be radiated by it. The earth also loses as much energy as it gains. If more energy was coming in, the temperature would rise which would cause more energy to be radiated out. The amount of outward radiation would continue to increase until the two became equal and the temperature again became constant. If less energy were coming in than was being radiated, the temperature would drop, which would cause less energy to be radiated. The earth would cool until the incoming and outgoing radiation again became equal.
- What is the Greenhouse Effect?
- The green house effect, as it applies to
the earth, is that the surface of the earth is warmer than it would be if
it had no atmosphere. Notice in the animation above that the
atmosphere contributes a considerable amount of energy to the
ground. Without the atmosphere it is estimated that the surface of
the earth would be on average 30�C cooler than it is now. To put
this in perspective, in the last ice age, the average temperature of the
earth's surface was only half a degree Celsius less than it is presently.
- Is the Greenhouse Effect good?
- Life as we know it would not be possible
without it. The Greenhouse Effect is different from global
warming. Global warming is the theory that due to a buildup of certain gasses in the atmosphere,
the Greenhouse effect would increase and cause the temperature of the
earth's surface to increase. The theory is sound, global
warming could happen. The question is, "Is it happening
now?" The data is still being collected to answer the
question. While we wait, we should do what we can to avoid the
buildup of these gases.
- Does the atmosphere behave like a greenhouse or a blanket?
- No. The methods by which an actual greenhouse or blanket warms is to limit the exchange of air (convection) between the inside and out. Greenhouses themselves are often incorrectly explained and then used to teach the Greenhouse effect. Diagrams similar to this one often show visible light coming from the sun passing through the glass. No problem yet. Then, long wavelength infrared (IR) rays are shown popping off the point where the visible light hit. Here is where the train wreck starts. The infrared waves are created because the surfaces in the greenhouse have a temperature, not because visible light hit that very spot. It is not a one wave creates one wave relationship. Now for the real catastrophe. The infrared waves are then shown to reflect off the glass back into the greenhouse. Glass, as well as just about everything else, is opaque and black to infrared. Infrared is absorbed by the glass not reflected. The glass, because it has a temperature will radiate infrared just like every other object in the greenhouse. Some will be radiated into the greenhouse and some will be radiated out of the greenhouse. The air is warmed both by the radiation (from the floor, tables, plants, and even the glass) and by contact (conduction) with the same objects.
For more information on the greenhouse effect visit the Bad Greenhouse Explanations page.