The problem: global warming and the greenhouse effect

Climate change is the result-yet the term is often interchanged with the popular phrases "global warming" and "greenhouse effect."

The greenhouse effect describes the increased warming of the planet's surface and lower atmosphere due to heightened levels of carbon dioxide and other gases in the earth's atmosphere. Similar to the windowpanes of a greenhouse, these gases let in the sun's rays but prevent some of the heat from leaking out.

The greenhouse effect is a natural phenomenon - without it the earth's surface temperatures would be 60º F (33° C) colder than they are now. However, since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide have increased 30 percent, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by 15 percent.

Why are greenhouse gases increasing? Scientists generally agree that fossil fuel combustion and past clearing of forests are the primary reasons for increasing levels of carbon dioxide. Fuels burned to run cars and trucks, heat homes and businesses, and power factories account for 80 percent of our carbon dioxide emissions. Tropical deforestation also accounts for significant CO2 emissions.

Climate change. Our climate is predicted to change because humans are altering the chemical composition of the atmosphere. Already, global mean surface temperatures have increased 0.6°F to 1.2°F (about 0.5° C) in the past 150 years. (To put this in perspective, the difference in temperature from the last ice age-10,000 years ago-to now is about 9° F (4.5-5.5° C.)

The 20th century's 10 warmest years all occurred within the last 15 years and 1998 was the warmest year on record.

Armed with a growing body of evidence, leading scientists point to predictions of further warming in the new century of between 3° F and 9 °F (1.6° and 5 C°). And the most advanced computer models project that greenhouse emissions would have to be lowered more than 60 percent in order to stabilize global warming.

While no reputable scientist will link individual weather events to global warming, the body of science does agree that we will experience changes in the earth's climate over the next century.