For the first time, the seasonal peak of carbon dioxide concentrations in the atmosphere exceeded 430 parts per million (ppm) at NOAA’s Mauna Loa Observatory on Hawaii, scientists from NOAA and Scripps Institution of Oceanography at the University of California San Diego reported today.

Scripps Oceanography scientists calculated a May monthly average of 430.2 ppm for 2025, an increase of 3.5 ppm over May 2024’s measurement of 426.7 ppm. Scientists with NOAA’s Global Monitoring Laboratory reported an average of 430.5 ppm, an increase of 3.6 ppm over last year.

“Another year, another record,” said Ralph Keeling, director of the Scripps CO 2 Program . “It’s sad.”

Situated high on the slopes of the Mauna Loa volcano, the Mauna Loa Observatory is the global benchmark location for m

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