Our planets climate is predicted to change because human activities are altering the chemical composition of the atmosphere through the buildup of greenhouse gases – primarily carbon dioxide, methane and nitrous oxide. Although scientists yet haven't agreed on exactly how earth's climate responds to these gases, we just have to face the fact – global temperatures are rising.
             Our sun is the source to all weather and climate on earth, and when the sun heats the surface of earth, the earth radiates energy back into space. Different kinds of gases in the atmosphere trap some of the outgoing energy, retaining heat and this makes earth with its atmosphere with all its gases work like an enormous greenhouse, and therefore the name "greenhouse effect".
             Without this "natural" greenhouse effect, temperatures would be much lower than they are today, and life would not be possible.
             However, problems may still arise when the concentration of atmospheric gases increases.
             The connection with the increasing concentration of greenhouse gases and human activities is obvious: concentrations of carbon dioxide in the atmosphere have increased with 30% since the beginning of the industrial revolution.
             Scientists generally believe that the combustion of fossil fuels and other human activities are the primary reason for the increased concentration of carbon dioxide. For example plant respiration release more than 10 times the carbon dioxide released by human activities, but these releases have always been in balance with the carbon dioxide absorbed by plant photosyntesis.
             Energy burned for example to run cars and trucks, and heat and power homes and factories is the responsible for about 80% of society's carbon dioxide emissions and about 20% of global nitrous oxide emissions.
             In 1994, the USA emitted about one fifth of total global greenhouse gases.
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