For the first time in history, carbon dioxide concentrations have surpassed 430 parts per million (ppm) during their seasonal peak, according to scientists from the National Oceanic and Atmospheric Administration (NOAA) and the Scripps Institution of Oceanography.
Measurements from Mauna Loa Observatory—a global benchmark for tracking atmospheric CO₂—showed a May 2025 monthly average of 430.2 ppm, up 3.5 ppm from last year’s May measurements. NOAA’s Global Monitoring Laboratory reported a similar rise, marking a 3.6 ppm increase.
“Another year, another record,” said Ralph Keeling, director of the Scripps CO₂ Program. “It’s sad.”
Perched on the slopes of Hawaii’s Mauna Loa volcano, the observatory has been tracking CO₂ trends since 1958, when scientist Charles David Keeling first identified seasonal fluctuations and yearly increases in CO₂ levels. His findings led to the creation of the Keeling Curve, one of the most critical climate records in existence.
NOAA joined the effort in 1974, ensuring an independent record of daily CO₂ measurements. Despite disruptions, such as the 2022 Mauna Loa eruption, which temporarily halted observations, scientists resumed measurements using backup systems and alternative monitoring sites at Maunakea.
Carbon dioxide in the atmosphere just exceeded the highest level in human history
CO₂ is the most significant human-caused greenhouse gas, acting like a heat-trapping blanket that fuels extreme weather events, including heatwaves, droughts, wildfires, and flooding. It also contributes to ocean acidification, harming marine life, such as coral, crustaceans, and bivalves.
Although Mauna Loa provides a crucial snapshot, CO₂ levels vary globally—stations in the Southern Hemisphere have yet to reach 430 ppm due to different seasonal cycles. NOAA’s global sampling network and Scripps’ 14 global stations help scientists identify the sources and sinks of CO₂, from forests to oceans.
These rising CO₂ levels serve as a critical warning for policymakers and researchers worldwide. The Global Greenhouse Gas Reference Network, which incorporates Mauna Loa data, remains a foundational tool for climate science, helping leaders navigate efforts to curb emissions.
With support from the National Science Foundation, Schmidt Sciences, and Earth Networks, scientists continue expanding CO₂ tracking efforts because understanding the problem is the first step toward action.
