Atmospheric CO₂ Hits Record High: A Stark Warning from Mauna Loa
In May, the average monthly Keeling Curve was more than 430 parts per million.
Scientists from the Scripps Institution of Oceanography and the National Oceanic and Atmospheric Administration (NOAA) have reported that carbon dioxide concentrations have topped 430 parts per million (ppm) during their seasonal peak for the first time in history.
Mauna Loa Observatory, a worldwide standard for monitoring atmospheric CO₂, reported a May 2025 monthly average of 430.2 ppm, which was 3.5 ppm higher than May data from the previous year. A 3.6 ppm increase was also observed by NOAA’s Global Monitoring Laboratory.
The director of the Scripps CO₂ Program, Ralph Keeling, declared, “Another year, another record.” “It is depressing.”
Since scientist Charles David Keeling first noticed seasonal variations and annual rises in CO₂ levels in 1958, the observatory, which is perched on the slopes of Hawaii’s Mauna Loa volcano, has been monitoring CO₂ changes. One of the most important climatic records in existence, the Keeling Curve, was created as a result of his research.
In order to ensure an unbiased record of daily CO₂ observations, NOAA joined the program in 1974. Scientists resumed measurements at Maunakea using backup systems and alternate monitoring locations in spite of interruptions, including as the 2022 Mauna Loa eruption, which momentarily stopped observations.
The most important greenhouse gas produced by humans is CO₂, which acts as a blanket of heat trapping and contributes to extreme weather events including flooding, wildfires, droughts, and heatwaves. Additionally, it damages marine life including coral, crabs, and bivalves by causing ocean acidification.
Despite the fact that Mauna Loa offers an important snapshot, CO₂ levels differ throughout the world; stations in the Southern Hemisphere have not yet reached 430 ppm because of distinct seasonal cycles. Scientists can determine the sources and sinks of CO₂, from forests to oceans, with the aid of NOAA’s global sampling network and Scripps’ 14 global stations.
For academics and policymakers around the world, these growing CO2 levels are a serious warning. Leaders are assisted in navigating attempts to reduce emissions by the Global Greenhouse Gas Reference Network, which continues to be a fundamental instrument for climate science and includes Mauna Loa data.
Understanding the issue is the first step to taking action, which is why scientists are continuing to extend CO₂ tracking activities with assistance from Schmidt Sciences, Earth Networks, and the National Science Foundation.
