The Earth's climate has always warmed and cooled. These temperatures are normal and natural and have existed for three thousand years. “Increasing atmospheric CO2 levels do not necessarily cause global warming, which contradicts the basic thesis of human-caused climate change” (Moore). There is little evidence that CO2 is the direct cause of global warming. More than half of the CO2 emitted by humans has already been reabsorbed by terrestrial carbon sinks. Carbon sinks are elements that absorb more carbon than they produce. CO2 is also already infused into Earth's atmosphere, so more natural or artificial CO2 will have little impact on the climate. According to Doctor William