File:Historical CO2 levels based on proxy (indirect) measurements.png

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Description	English: This graph shows CO2 (carbon dioxide, a "greenhouse gas") levels during the last three glacial cycles, as reconstructed from ice cores. Based on research and data from the National Oceanic and Atmospheric Administration (NOAA)
Date	10 April 2018
Source	https://climate.nasa.gov/resources/graphics-and-multimedia/ https://climate.nasa.gov/scientific-consensus/ https://climate.nasa.gov/vital-signs/
Author	Earth Science Communications Team, Jet Propulsion Laboratory/California Institute of Technology, National Aeronautics and Space Administration (NASA), 4800 Oak Grove Drive, Pasadena, CA 91109; (818) 354-4321

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