Greenhouse Effects on Earth

The heating of the Earth's surface and atmosphere is assisted by a natural phenomenon known as the greenhouse effect. As sunlight heats the surface of the Earth, the atmosphere absorbs the rising heat, creating an imbalance of energy. Gases in the Earth's atmosphere influence the greenhouse effect, which affects certain aspects of the Earth's climate.

The Process

• As solar energy from the sun penetrates the Earth's atmosphere, clouds and particles reflect some of the energy back into outer space. Solar energy that reaches the surface heats the ground and aids in the evaporation of water. Sunlight shines on the surface, generating heat that rises into the atmosphere where a majority of it is absorbed by atmospheric gases. As these gases warm, they act as a shield reflecting additional heat rising from the surface back toward the Earth.

  This greenhouse effect continues in a cycle, adding additional heat to the atmosphere. This cycle, and the amount of heat it generates, is controlled by the amount of solar energy reaching the surface and the concentration of various gases present in the atmosphere.

Natural Causes

• Chemical compounds in the Earth's atmosphere that absorb heat radiated from the surface are known as greenhouse gases, many of which occur naturally. Water vapor is the most common greenhouse gas. As the atmospheric temperature rises, evaporation of water from the surface increases, the air becomes warmer and is then able to hold more water vapor. This phenomenon allows water vapor to absorb additional heat radiated from the Earth's surface, thus increasing the overall temperature of the atmosphere.

  Carbon dioxide levels produced naturally, mainly through photosynthesis in plants, animal respiration, and the oceans' interaction with the atmosphere, fluctuate depending on the season and contribute to the greenhouse effect. In addition, methane, released into the atmosphere from certain biological processes, is a greenhouse gas.

  Other natural greenhouse gases include ozone, formed from the interaction of sunlight and oxygen, and nitrous oxide, produced from the interaction of soil and water with microorganisms.

Man-Made Causes

• Chlorofluorocarbons do not occur naturally, and although the use of this type of gas has been reduced due to the discovery of its harmful effects on the atmosphere, concentrations of chlorofluorocarbons remain as a man-made greenhouse gas.

  In addition to occurring naturally, levels of carbon dioxide increase from the burning of coal, oil, natural gas and wood, adding to the greenhouse effect. Methane gas levels in the atmosphere have increased due to coal mining, the raising of cattle and rice farming.

  Agriculture, by using fertilizers containing nitrogen, and certain industrial processes, such as power plants, using fossil fuels add to the level of nitrous oxide present in the atmosphere. Although not considered a greenhouse gas, carbon monoxide, created from the incomplete burning of fossil fuels, regulates the levels of methane and ozone, thus contributing to the greenhouse effect.

Possible Effects on Climate

• Some scientists predict that as greenhouse gas levels increase, the Earth's climate will warm. With the use of computer modeling, some predictions indicate the average temperature may increase about 2 to 5 degrees globally. However, an increase in the Earth's atmospheric temperature would create greater evaporation of water from the oceans, causing the formation of more clouds. Computer modeling does not take into account the effect increased cloud cover may have on the greenhouse effect by reducing the amount of solar energy reaching the Earth's surface.