Greenhouse gases trap heat in the atmosphere. Some of these gases, such as carbon dioxide and methane, are emitted into the atmosphere naturally from the decay of organic waste. Others, like the synthetic fluorinated gases, are the direct result of human industrial activities. Even water vapor is a greenhouse gas. It is the accumulation of these greenhouse gases that are believed to be responsible for climate change.
The principal greenhouse gases that enter the atmosphere from industrial activities are carbon dioxide, nitrous oxide, methane and fluorinated gases. Carbon dioxide and nitrous oxide enter the atmosphere from burning of fossil fuels and solid waste. Methane is emitted during the combustion of coal, natural gas and oil. Though fluorinated gases--hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride--are emitted in smaller quantities, they are so potent they are referred to as High Global Warming Potential gases.
Greenhouse gases have a direct effect on the environment. Each year, a typical 500-megawatt coal plant burns 1,430,000 tons of coal to produce electricity. That process generates 10,000 tons of sulfur dioxide, 10,200 tons of nitrogen oxide, and 220 tons of hydrocarbons. All three greenhouse gases are the main cause of smog, and sulfur dioxide is also responsible for the damaging effects of acid rain. The same coal plant also generates 3.7 million tons of carbon dioxide, another greenhouse gas.
The Greenhouse Effect
The greenhouse effect is a natural event that heats the Earth's surface and atmosphere. As energy from the sun passes through the atmosphere, 19 percent is absorbed by clouds and atmospheric gases while 26 percent of the energy is reflected back into space. Most of the remaining solar energy reaches the Earth’s surface and heats the ground. This heating causes the Earth's surface to radiate heat energy back toward space, but the majority of that heat is absorbed by the greenhouse gases. This causes more heat energy to be added to the Earth's atmosphere and directed back to the Earth's surface, where it once again heats the ground. This cycle continues to repeat, resulting in an accumulative build-up of heat in the atmosphere that can affect the balance of ecosystems worldwide and is believed to causing global warming.
Industrial and human activities have caused the major greenhouse gases to build up in the atmosphere. As a result of the higher concentrations of these gases, computer modeling predicts that the greenhouse effect will increase and the Earth's climate will become warmer. These predictions suggest that by the middle of the next century the Earth's average temperature may rise 2 to 5 degrees higher than it is today.