Global warming is an environmental disaster caused by humans. The net increase in temperature over the last hundred years has fallen within this range, measuring roughly .5 degrees Centigrade. Global Warming is melting the polar ice caps, and causing sea levels to rise. Although increases in the concentration of any greenhouse gas will affect temperatures, the effects of carbon dioxide are minor. Increases in the level of carbon dioxide in the atmosphere can largely be attributed to humans.
Nature produces the rest through geysers, the respiration of organisms, springs, and volcanoes.