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Global warming refers to an increase in the earth’s temperature which is believed to be caused in part by the greenhouse effect or the excessive releases of gasses such as carbon dioxide, methane and nitrous oxides as well as the depletion of the ozone layer which is mainly the result of chlorofluorocarbons and halocarbons that are released into the atmosphere.
Many people believe that global warming is largely due to the effects of human activities, especially industry and agriculture. However, while human activity is very likely a big contributing factor, we are not the sole cause of global warming. In addition, the issue of rising global temperatures is not an exact science.
Scientists believe that over the last 400,000 years, there have been four almost identical weather cycles, lasting a little over 100,000 years each. During each cycle it was cold for almost 100,000 years. Then there was a much warmer period lasting 10 to 20 thousand years with average temperatures comparable to the present. By studying weather patterns in terms of 10’s of thousands of years, it is likely that year to year fluctuations in temperature and a gradual increase in the average global temperature indicates a natural "global warming" cycle.
In the past few hundred thousand years, the major cause of climate change has been due to the cyclic variation of earth's orbit around the sun which has changed the average amount of energy that the earth receives from the sun. These variations in earth's orbit have created some very long lasting "astronomic seasons", similar to "regular seasons" over a year. They have been the major cause of climate change and have generated the series of ice ages and "warm" periods like the ones we are now experiencing.
This natural astronomical cycle has a domino effect on the planet which further increases the incident of global warming. One very important factor involves the arctic regions. The slight rise in temperatures is enough to begin to melt the earth’s permafrost which is the ground that has been frozen since the last ice age. When this happens, the layers of dead plant material and other organic compounds in the soil begin to decay which creates byproducts of carbon dioxide and methane gases. This process releases more greenhouse gases into the atmosphere creating a vicious cycle that snowballs global warming. Volcanic eruptions also contribute to the presence of gases in the atmosphere.