According to the Intergovernmental Panel on Climate Change (IPCC), global emissions of greenhouse gases resulting from human activity have grown 70 percent since 1970. During that same time, carbon dioxide (CO2) emissions increased by 80 percent, due primarily to the use of fossil fuels and land-use changes. In 2005, atmospheric concentrations of CO2 reached 379 ppm (parts per million), far outside the natural range scientists have documented for the last 650,000 years. The IPCC Report, Climate Change 2007, goes on to state that this increase in anthropogenic greenhouse gases is very likely the cause of the observed increase in global average temperature since the mid-twentieth century, and that this warming has had “a discernible influence on observed changes in many physical and biological systems.”
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