Atmospheric concentrations of carbon dioxide made history last month by climbing to their highest seasonal peak available in historical records, a team of researchers reported.
For the first time ever, these levels surpassed 430 parts per million (ppm) at the National Oceanic and Atmospheric Administration’s (NOAA) Mauna Loa Observatory in Hawaii, which is considered the global benchmark site for tracking atmospheric carbon dioxide.
The 430.2 ppm calculation for May marked a 3.5 ppm increase over May 2024’s reading of 426.7 ppm, according to scientists from the Scripps Institution of Oceanography at the the University of California, San Diego, who worked together with colleagues at NOAA.
“Another year, another record,” Ralph Keeling, director of the Scripps CO2 Program, said in a statement. “It’s sad.”
At an elevation of 11,141 feet above sea level, the observatory is located on the slopes of the Mauna Loa volcano and produces measurements that reflect the average state of the atmosphere for the Northern Hemisphere.
Carbon dioxide, the scientists explained, acts like a blanket — trapping heat and warming the lower atmosphere, as well as altering weather patterns and fueling extreme weather events.
The surge in CO2 concentrations is also contributing to acidification and causing changes in ocean chemistry that affect the survival of marine organisms, according to the researchers.
A half-century of sampling at Mauna Loa, conducted by researchers at both NOAA and Scripps, have provided a baseline for tracking the increase of human-generated carbon emissions, the scientists noted.
They acknowledged, however, that the station does not capture the full extent as to how carbon CO2 concentrations can vary across the planet — as stations in the Southern Hemisphere have yet to cross the 430-ppm threshold.
NOAA’s global sampling network, as well as 14 worldwide stations operated by the Scripps CO2 program, are also contributing to the broader planetary picture and helping identify locations of carbon sources and sinks, the researchers added.