WHAT CAUSES GLOBAL WARMING?

Until very recently, scientists thought carbon dioxide was the main culprit behind a warming Earth. But new evidence shows other gases may be just as harmful.

Black Carbon Soot (Not a gas) is made of particles produced by burning coal and diesel fuel in populated areas. Soot reduces the amount of cloud cover in the sky. Since clouds reflect 40 to 90 percent of the sun's radiation (heat rays) back to space, fewer or thinner clouds mean more heat is trapped in the air.

Sulfur Hexafluoride (SF6) is a gas released by the production of energy, such as to insulate electrical switches or cables. It has a heat-trapping potential 25,000 times greater than carbon dioxide--and is increasing in the atmosphere at a rate of 8 percent each year.

CFCs (chlorofluorocarbons) are gases used in aerosol sprays or refrigerants. They are the atmosphere's biggest heat trappers. CFCs were banned for use in aerosols in the U.S. in 1978, but still linger in the atmosphere.

Nitrous Oxide (N2O) is a gas found naturally in Earth's soils and oceans. But use of [N.sub.2]O in fertilizers, chemical manufacturing, and car emissions has increased its amount in the air. [N.sub.2]O traps 270 times more heat than carbon dioxide.

Methane (CH4) is a natural gas emitted by livestock, rice paddies, and wetlands. But the use of methane in natural gas and oil production has caused its amount in the air to soar. Methane traps 20 times more heat than carbon dioxide.

Carbon Dioxide (CO2) is a natural gas released in the atmosphere by animal respiration and the burning of wood. But the use of [CO.sub.2] in oil, gas, factories and refineries has led to a 30 percent increase of the gas in the atmosphere over the last 150 years.