"Each year we pump at least six billion tons of heat-trapping carbon into the innermost layer of our atmosphere, whose outer extent is only about twelve miles overhead. According to an IPCC (United Nations' Intergovernmental Panel on Climate Change) report released this year, atmospheric CO2 will, if the buildup is left unchecked, double from its pre-industrial level within the next century. That doubling of CO2 correlates with an increase in the global temperature of at least three to eight degrees Fahrenheit. The last ice age was just five to nine degrees colder than our current climate."