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Global Warming refers to the sustained increase in the average temperature of the earth's atmosphere. Human activity contributes to this change through the buildup of heat-trapping greenhouse gases. Over time, this increase may be sufficient to cause climatic change, including raising sea levels, altering precipitation patterns and changing water supplies and crop yields. It is also an increase in the near surface temperature of the Earth. Global warming has occurred in the distant past as a result of natural influences, but the term is most often used to refer to the warming; predicted to occur as a result of increased emissions of greenhouse gases. Scientists generally agree that the Earth's surface has warmed by about 1 degree Fahrenheit in the past 140 years.
The Intergovernmental Panel on Climate Change (IPCC) recently concluded that increased concentrations of greenhouse gases are causing an increase in the Earth's surface temperature and that increased concentrations of sulfate aerosols have led to relative cooling in some regions, generally over and downwind of heavily industrialized areas. The usual method to research about this phenomenon is to measure the surface-air temperature over long period of time. Some people blame the nature for the temperature increase while other points at human causes, such as our cars, industries, farmers in the third world countries. It is because car pollutes the air with Carbon Dioxide and farmers in the third world countries pollutes the air with methane gas. Both Carbon Dioxide and Methane are Greenhouse gases. Since the late 19th century, we have experienced a rise in average global temperatures approximated between 0.6C and 0.2C.