The "greenhouse effect" is the earth's increasing retention of solar energy. The phenomenon is primarily caused by the gases carbon dioxide (CO2), water vapor and methane in the atmosphere. Like the glass in a greenhouse, these gases surround the earth. They allow sunlight to pass through, but trap most of the heat reflected back by land and water. Though the effect is natural in part, humans have increased production of greenhouse gases to harmful levels.
Three fourths of man-made carbon dioxide (CO2) is created by burning fossil fuels, which include coal, fuel oil and natural gas. Land development and the destruction of the forests worsen the problem by getting rid of vegetation that naturally absorbs CO2. Methane is produced partly through livestock, wetlands, and the creation of landfills.
