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Keywords:

  • carbon dioxide (CO2);
  • daily mean concentration;
  • increase

The daily mean concentration of carbon dioxide (CO2) in the atmosphere at Mauna Loa, Hawaii, hit 400.03 parts per million (ppm) on 9 May, marking the first time the concentration there has topped 400 ppm since measurements began at Mauna Loa in 1958, the U.S. National Oceanic and Atmospheric Administration (NOAA) announced on 10 May. NOAA scientists with the agency's Global Monitoring Division have made measurements of CO2 at the NOAA Mauna Loa Observatory since 1974.