By:- Robert Monroe
Scientists at Scripps Institution of Oceanography at the University of California San Diego reported today that carbon dioxide levels at Mauna Loa Observatory reached 432.00 parts per million (ppm) in May, continuing a long trend of record-breaking annual peak readings.
The level is an increase of 1.8 ppm over May 2025’s measurement of 430.2 ppm. Scientists with NOAA’s Global Monitoring Laboratory reported an average of 432.3 ppm, an increase of 1.8 ppm over last year.
“Atmospheric CO₂ has continued its relentless rise over the past year, reaching yet another record high and moving us deeper into a high-CO₂ world,” said Ralph Keeling, director of the Scripps CO2 Program. “I wish we had better news.”
Situated high on the slopes of the Mauna Loa volcano, the Mauna Loa Observatory is the global benchmark location for monitoring atmospheric CO2. At an elevation of 11,141 feet above sea level, the observatory produces measurements that represent the average state of the atmosphere in the northern hemisphere.
In 1958, Scripps scientist Charles David Keeling, father of Ralph Keeling, began monitoring CO2 concentrations at the NOAA weather station located at the observatory site, recording an initial measurement of 313 ppm on March 29 of that year. Keeling was the first to recognize that CO2 levels in the Northern Hemisphere peaked in May, fell during the growing season, and rose again as plants died in the fall. He documented these CO2 fluctuations in a record that came to be known as the Keeling Curve. He was also the first to recognize that, in addition to the seasonal fluctuation, CO2 levels rose every year.
NOAA initiated daily CO2 measurements in 1974 and has maintained a complementary, independent measurement record ever since.
For several decades, continuous daily sampling by both NOAA and Scripps at Mauna Loa has provided an ideal baseline for establishing a long-term time series of the increase in the most important human-caused greenhouse gas. In November 2022, the eruption of Mauna Loa volcano buried over a mile of the access road to the observatory in lava. After a brief pause, Scripps and NOAA established measurements at the summit of nearby Maunakea as an alternative to Mauna Loa. Later in 2023, NOAA staff accessing the observatory by helicopter installed a solar power and battery backup system that allowed them to restart CO2 measurements at Mauna Loa. Earlier this year, NOAA announced that road access has been re-established, but work at the observatory remains limited to mission-critical functions while planned renovations are completed.
Like other greenhouse gases, CO2 acts like a blanket, trapping heat and warming the lower atmosphere. This changes weather patterns and fuels extreme events, such as heat waves, droughts and wildfires, as well as heavier precipitation and flooding. Rising CO2 levels also contribute to ocean acidification, a change in ocean chemistry that makes it more difficult for marine organisms like crustaceans, bivalves and coral to grow hard, carbonate skeletons or shells.
The Mauna Loa data, together with measurements from sampling stations around the world, are incorporated into NOAA’s Global Greenhouse Gas Reference Network, a foundational research dataset for international climate scientists and a benchmark for policymakers attempting to address the causes and impacts of climate change.
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