Carbon dioxide levels in Earth's atmosphere are at their highest point in human history, according to a study released in early December and published in Science. In fact, according to the study, it has been about 14 million years since the level of carbon dioxide (CO2) in our atmosphere was this high. That's long before modern humans appeared on the scene. Fourteen million years is much longer ago than earlier assessments have found. Find out more about the new findings in the link in bio.