on and transport of coal, natural gas, and oil. Methane emissions also result from the decomposition of organic wastes in municipal solid waste landfills, and the raising of livestock. 3) Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels. Greenhouse gases that are not naturally occurring include byproducts of foam production, refrigeration, and air conditioning called chlorofluorocarbons (CFCs), as well as hydro fluorocarbons (HFCs) and per fluorocarbons (PFCs) generated by industrial processes. Each greenhouse gas differs in its ability to absorb heat in the atmosphere. HFCs and PFCs are the most heat-absorbent. Methane traps over 21 times more heat than carbon dioxide, and nitrous oxide absorbs 270 times more heat than carbon dioxide. Often, estimates of greenhouse gas emissions are presented in units of millions of metric tons of carbon equivalents (MMTEC), which weights each gas by its Global Warming Potential (GWP) value (Revkin, 1992).
             Energy from the sun drives the earth's weather and climate, and heats the earth's surface; in turn, the earth radiates energy back into space. Atmospheric greenhouse gases (water vapor, carbon dioxide, and other gases) trap some of the outgoing energy, retaining heat somewhat like the glass panels of a greenhouse. Without this natural greenhouse effect, temperatures would be much lower than they are now, and life as known today, would not be possible. Instead, the earth's average temperature is a more hospitable. However, problems may arise when the atmospheric concentration of greenhouse gases increases.
             According to Easterbook, around the mid-1800 with the beginning of the Industrial Revolution, carbon dioxide levels began increasing. The carbon dioxide concentration has risen sharply from 280 ppm (parts per million) to 360 ppm, or about 25 percent increase. The methane concentration has risen...