The term greenhouse effect has become a way of saying global warming. These terms both are used to imply the Earth’s atmosphere has been warming, with the slight difference being the cause. Global warming does not require a specific cause, while the greenhouse effect clearly implies the connection with the gas content of our atmosphere and the increase in warming. Since the control man has upon our planet is limited, most people are content to consider only what man has an ability to change, and that is mostly the content of the gases we add to the atmosphere.
The Greenhouse Effect Made Simple
Many people have heard of the greenhouse effect, but too often it is not understood. The similarity with a greenhouse is limited, both have different mechanisms for heating up.
Is It Really Like a Greenhouse?
Well, both a greenhouse and the atmosphere retain heat, so there is a similarity. However, the mechanism by which this is done is completely different.
How Does a Greenhouse Trap Heat?
A greenhouse is a structure with glass, or some other transparent substance, making up much of its walls and roof. Light easily passes through glass. Once light enters the greenhouse much of it is absorbed by the floor and the tables and plants within it. It is a natural process for things to give off heat via infrared waves, a group of waves similar to light but with a lower frequency. But, glass reflects infrared rays, so the energy they carry is returned to the ground and contents within the structure. This inability for the energy to escape causes the temperature to rise. This is quite useful in keeping temperatures high enough for plants to grow.
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How Does the Greenhouse Effect Work?
Just as a surface within the greenhouse gives off infrared rays in an effort to come to thermal equilibrium with the environment, the Earth itself and the things on it give off heat via infrared rays. These rays should work to bleed off energy to outer space. But, with the greenhouse effect the energy is trapped. Here is the difference. The Earth has no glass wall to reflect the energy back.
Gases absorb certain frequencies. And each gas absorbs its own special frequencies. Certain gases absorb infrared very well. And yes, the gas molecules will give off that energy in an effort to come into thermal equilibrium with outer space, but the energy is not always given off in the direction of outer space. Some is aimed back at the Earth. And what is aimed outward is subject to being absorbed by another gas molecule. So, energy is absorbed and reemitted until it either gets past the greenhouse gases or is again absorbed by the Earth. This reduces the efficiency of the Earth being able to come into a balance where the atmosphere gains and gives up equal amounts of energy each year. A similar daily balance is also almost obtained with the temperature gradually changing some with the seasons.
What Gases Should We Consider?
The gas most often associated with the greenhouse, and the one individuals are often concerned with, is carbon dioxide. Another common gas that causes problems is methane. Indeed, there are many greenhouse gases, including water vapor. Yes, places with dry climates can see a daily temperature change of sixty degrees in a day while damp places might have little change on a given day.
Is the Ozone Layer Involved in Global Warming?
The ozone layer absorbs ultraviolet rays, which have more energy than visible light per photon. If these rays were to come in unimpeded they would be absorbed by the ground and the things upon it, and this energy would heat the Earth.
Why Does the Earth Emit Infrared?
When a solid absorbs energy its molecules move faster. It would seem that it might emit the same frequencies that were absorbed, but before that can happen the energy is shared by molecules bumping each other. So, when it comes time to emit the energy back to space the molecules have less than what is needed for visible light. Remember, some molecules sharing the energy are below the surface, so many more molecules have some of the incoming energy than those that were in the sunlight.
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