Image caption
Global atmospheric carbon dioxide concentrations (CO2) in parts per million (ppm) for the past 800,000 years. The peaks and valleys track ice ages (low CO2) and warmer interglacials (higher CO2). During these cycles, CO2 was never higher than 300 ppm. On the geologic time scale, the increase (orange dashed line) looks virtually instantaneous. Graph by NOAA Climate.gov based on data from Lüthi et al., 2008, provided by the NOAA NCEI Paleoclimatology Program.