The greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (water vapor, carbon dioxide, nitrous oxide, and methane, for example) trap energy from the sun. Without these gases, heat would escape back into space and Earth’s average temperature would be about 60ºF colder. Because of how they warm our world, these gases are referred to as greenhouse gases.
There is mounting evidence that our own activities, most significantly the burning of fossil fuels, are a major contributor to this effect. The predicted consequences are quite sever, including major changes in climate which will have impact on food production, and rising sea levels which will submerge coastal and other low lying communities. Lurking in the background hauntingly are the facts we have discovered about our near neighbor, the planet Venus. Because of its dense atmospheric gases, Venus has what has been described as having a runaway greenhouse effect, giving surface temperatures of about 8000F. Now I love the warm summer weather, but that is a little too hot for me.
The usual villains in the greenhouse scenario are gases such as carbon dioxide. Carbon dioxide, which, incidentally, we all exhale, has the unusual habit of absorbing infra-red radiation. Infra-red radiation for those of you less scientifically minded is actually heat radiating away from a warm object. During the day, sunlight warms the earth and during the night the Earth cools by radiating heat into space in the form of infra-red radiation. Carbon dioxide, and to a lesser extent other gases, absorb this radiation, limiting its exit out into space, and thus limiting the natural cooling effect.
Greenhouse gases in the atmosphere behave much like the glass panes in a greenhouse. Sunlight enters the Earth’s atmosphere, passing through the blanket of greenhouse gases. As it reaches the Earth’s surface, land, water, and biosphere absorb the sunlight’s energy. Once absorbed, this energy is sent back into the atmosphere. Some of the energy passes back into space, but much of it remains trapped in the atmosphere by the greenhouse gases, causing our world to heat up.
Would it be safer if we had no greenhouse effect at all? Well, no, we do not want that either. Without the greenhouse effect, the Earth would not be warm enough for humans to live.
There is another member of the heat absorbing clan. This is water vapor. There is a large amount of water vapor in the atmosphere at any time, which is why we have rain. The presence of water vapor as a heart absorbing gas keeps the Earth comfortably warm. Without this warmth, the planet would freeze, and life as we know it would not be possible. We therefore do need some greenhouse effect, just not too much.
Mother Nature is again telling us what we should already know; in any situation, both of the extremes are harmful.