Measurements are taken in May because it is the month when CO2 peaks in the Northern Hemisphere. The outpost on Mauna Loa has measured atmospheric CO2 since 1958, when the level was less than 320 ppm, and shown a steady increase since then in what NOAA Administrator Rick Spinrad called "a direct result of human activity." NOAA began collaborating with Scripps on the measurements in 1974. This year's measurements were taken from a temporary site because lava flows cut off access to the Mauna Loa observatory in November 2022, NOAA said. (This story has been corrected to change NOAA's previously reported figure as 424 ppm and not 423 ppm, in paragraph 2.

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Persons: Rick Spinrad, David Keeling, Keeling's, geochemist Ralph Keeling, Keeling, Daniel Trotta, Marguerita Choy Organizations: U.S . National Oceanic, Atmospheric Administration, Scripps Institute of Oceanography, Scripps, Northern Hemisphere, NOAA, Thomson Locations: Mauna Loa, Loa