Carbon dioxide levels usually peak in May, but 2025's reading was like no other

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An observatory high on Hawaii's Mauna Loa volcano that measures carbon dioxide in the atmosphere has reported its highest ever seasonal peak concentration of the greenhouse gas.
For the first time, the May average exceeded 430 parts per million, reported scientists from the National Oceanic and Atmospheric Administration's Mauna Loa Observatory and the Scripps Institution of Oceanography at the University of California San Diego.
"Another year, another record," said Ralph Keeling, director of the Scripps CO2 Program. "It's sad."
Carbon dioxide and other gases function like a blanket around the Earth, holding in heat and warming the atmosphere above the surface, scientists say. A broad consensus of international scientists say the rise in carbon dioxide concentrations is responsible for the globe's changing climate, helping to make natural weather events such as rainfall, drought and heat waves more extreme.
While carbon dioxide is naturally present in Earth's atmosphere, scientists say the problem is the rate at which it's increasing, driven by fossil fuel emissions. Geoscientists at the University of Utah, who participated in a 2023 study with more than 90 scientists in 16 countries, previously stated that CO2 levels in the atmosphere are higher than they've been in human history and highest in at least 14 million years.
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Last year, the average level of carbon dioxide rose faster over the previous year than at any other point since the recordings began, Scripps reported in January. The average readings for the 12 months was 3.58 parts per million higher than the previous year's average, breaking a record set in 2016.
In both years, the climate pattern El Niño played a role, Keeling said in January. "Although this El Niño event ended early in 2024, it is often the case that El Niño events are associated with higher than normal CO2 growth extending into the northern hemisphere summer following the El Niño event."
The historic 67-year-old laboratory at elevation 11,141 feet is the global benchmark location for monitoring carbon dioxide in the atmosphere. Its measurements represent the average state of the atmosphere in the northern hemisphere.
Scripps scientist Charles David Keeling, Ralph Keeling's father, began monitoring CO2 concentrations there in 1958. He was the first to realize CO2 levels peak in May in the northern hemisphere, fall during the growing season and rise again after plants die in the fall, according to Scripps. The fluctuations were presented in a record that became known as the Keeling Curve, which demonstrated carbon dioxide concentrations in the atmosphere were increasing every year.
NOAA initiated daily measurements at Mauna Loa in 1974 and has maintained a complementary, independent measurement record ever since. A global network that includes NOAA and Scripps, forms a dataset used by climate scientists internationally. Eruptions at Mauna Loa caused an interruption to power at the observatory in 2022, NOAA said. Scientists established a temporary measurement site at Mauna Kea nearby.
Dinah Voyles Pulver, a national correspondent for USA TODAY, covers climate change, wildlife and the environment. Reach her at [e-mail] or @dinahvp on Bluesky or X or dinahvp.77 on Signal.
This article originally appeared on USA TODAY: Carbon dioxide levels hit new record in May Mauna Loa observation