Do emissions of carbon dioxide from human activities have a big impact on Earth’s climate?
Plants, oceans, and soils release and absorb large quantities of carbon dioxide as a part of the Earth’s natural carbon cycle. These natural emissions and absorptions of carbon dioxide on average balance out over time. However, the carbon dioxide from human activities is not part of this natural balance. According to the United States Environmental Protection Authority (EPA) Ice core measurements reveal that carbon dioxide levels in the atmosphere are higher than they have been for at least 800,000 years (http://www3.epa.gov/climatechange/science/causes.html#GreenhouseRole). The global warming that has been observed in recent decades was caused by elevated levels of carbon dioxide and other greenhouse gases in the atmosphere, due primarily to human activities.