It seems like every day, there is something regarding greenhouse gases and the greenhouse effect mentioned in the news. However, many people are a bit confused when it comes to the greenhouse effect and what it is.
The simple fact is that without the greenhouse effect, the Earth would probably be an uninhabitable ball of ice.
Defining greenhouse effect
In its simplest terms, the greenhouse effect occurs when the rays of the sun pass through the atmosphere, reflecting back up from the ground; water, snow, ice and plant life are then prevented from escaping back into space by various gases and dust in the atmosphere. This is very similar to what happens in a greenhouse, where the light and heat from the sun shines through the glass of the greenhouse, but the heat is prevented from leaving by the glass. If this didn't happen in our atmosphere, more of the heat would be likely be reflected into space than the Earth receives.
The radiation from the sun reaches the earth in a broad spectrum, defined by specific wavelengths...the range from very long wavelengths like radio, to very short ones like gamma rays. This is measured by the distance from the peak of one wave to the peak of the next. For example, radio waves have wavelengths that range from several millimeters to hundreds of kilometers. This is important because it means that for an object to stop the waves, it needs to be as large or larger than the wavelength.
In the case of the topic of the greenhouse effect, infrared or heat waves are of prime importance. These waves measure from just under a micron to about 350 microns in size or wavelength. For something to block these waves, thus preventing them from reflecting right back out in space, a substance such as a greenhouse gas or the molecules of glass in the windows of a greenhouse must be larger than this.
Loss of energy
One key is that when the radiation strikes something, it usually loses some energy, which lowers the wavelength. In the process, the radiation has the effect of heating the object, which re-radiates some of the energy as infrared energy, at a wavelength that is longer than it originally was. It is this that makes it possible for sunlight to pass through the atmosphere and yet to be prevented from leaving again by the greenhouse gas (or the glass) that was previously mentioned.
The references in the news about the greenhouse effect often revolve around certain gases, such as carbon dioxide. Carbon dioxide is a naturally occurring greenhouse gas that prevents some of the infrared radiation from being reflected right back into space. Water vapor is another, more abundant greenhouse gas. According to the United States Geological Survey (USGS), at any given time, there is approximately 12,900 cubic kilometers of water in the atmosphere.
Without the greenhouse effect
Without the glass or plastic on a greenhouse, the structure would have nearly the same temperature as the surroundings. Likewise, without the greenhouse gases in Earth's atmosphere, such as water vapor, carbon dioxide, methane and so forth, there would be little to prevent much of the received solar radiation to be simply reflected back into space. If this happened, global temperatures at the surface would most likely be very similar to the space surrounding the planet, which is far colder than would be necessary for all the water on the globe to freeze solid. For that matter, it would probably be so cold that even the gases in the atmosphere would freeze.
We owe our lives to the greenhouse effect, and this is something we should never lose sight of, or make slight of. It is one more of the fantastic wonders of nature.