Beginning of Essay
Like the glass in a greenhouse, certain gases that occur naturally in the atmosphere tend to trap the sun's heat. This natural "greenhouse effect" helps keep the Earth's average temperature at a comfortable 59° Fahrenheit. Without these greenhouse gases, the Eart ....

Middle of Essay
.... life like today would not work. Instead, thanks to greenhouse gases, the earth's average temperature is better, 60°F. But, problems may happen when the amount of greenhouse gases increases. Since the beginning of the industrial revolution, great amounts of carbon dioxide have increased nearly 30%, methane concentrations have almost doubled, and nitrous oxide concentrations have risen about 15%. These increases have made the heat-trapping worse in the earth's atmosphere. Sulfate aerosols, a common air pollutant, cool the atmosphere by reflecting light back into space, but, sulfates do not live long in the atmosphere. Why are gree ....