The entire warming effect of the earth’s atmosphere is referred to as the greenhouse effect because heat-trapping gases in the atmosphere behave like the glass of a greenhouse. When the greenhouse effect first became a controversial issue, the increased levels of carbon dioxide was the major concern of scientist. However, over the past years scientists start noticed that the levels of the other less abundant greenhouse gases started to increase also. Most of the greenhouse gases form naturally on earth, but there are also man-made substances that we created which absorbs the long-wave radiation. Thus they trap heat near the earth’s surface and contribute to the green- house effect. Some of the less abundant greenhouse gases include methane, nitrous oxide, and a group of chemicals called chlorofluorocarbons, or CFCs.
Next to carbon dioxide, methane gas is the second most important greenhouse gas. Even though there is far less methane in the air than carbon dioxide, a methane molecule absorbs twenty times more infrared rediation than one molecule of carbon dioxide. Methane is produced by several natural sources such as cattle, termites, and microorganisms that live in waterlogged soils. The burning of grasslands and rainforests also contributes to the methane in the air because it causes the soil microorganisms to increase their methane-producing activities.
Nitrous oxide is another greenhouse gas that is becoming more abundant in our atmosphere. It is a colorless gas known to most people as laughing gas. Nitrous oxide is released into the atmosphere through automobile exhaust, the burning of fossil fuels, and through farmers spreading nitrogen fertilizer on open fields. As these fertilizers break down into the soil, nitrous oxide is released into the air.
Scientists have analyzed air trapped in ice cores and found that the atmospheric concentration of nitrous oxide was about 0.20 ppm around the year 1900. However eighty years later they found that the atmospheric concentration of nitrous oxide had increased to 3.0 ppm. This may not seem alarming, but nitrous oxide has the potential to stay in the troposphere anywhere from 120 to 175 years before moving into the stratosphere. Therefore, the gas nitrous oxide has the potential to become extremely abundant in our atmosphere since we place an additional five million tons of this gas into our environment each year.