For the first time on record, monthly average CO2 levels exceeded 430 parts per million (ppm), according to experts at Scripps Institution of Oceanography in San Diego.
The experts’ new measurements come from Mauna Loa Observatory, a research station situated high on the slopes of the Mauna Loa volcano, Hawaii.
However, CO2 concentrations have not yet passed the 430 ppm mark in the Southern Hemisphere, which has a reversed cycle.
In 1958, he began monitoring CO2 concentrations at Mauna Loa Observatory and documented a long-term increase, known as the Keeling Curve.
NOAA’s Global Monitoring Laboratory, meanwhile, begun daily CO2 measurements in 1974 and has maintained a complementary, independent measurement record ever since.
Scientists have discovered that the amount of carbon dioxide (CO2) in the atmosphere is higher now than it has ever been.
According to scientists at Scripps Institution of Oceanography in San Diego, monthly average CO2 levels surpassed 430 parts per million (ppm) for the first time ever.
May 2025 saw the highest monthly average since precise measurements started 67 years ago, at 430 point 2 ppm.
Global warming, which could eventually make the Earth’s surface too hot for people, is accelerating with increasing CO2 levels in the atmosphere.
At much higher levels, CO2 can also lead to a number of health problems.
This includes, concerningly, cognitive impairment, nausea, drowsiness, and in the worst situations, death.
“Another year, another record,” said Ralph Keeling, the Scripps CO2 Program director.
And it’s sad, he added. “…
Similar to other greenhouse gases, CO2 warms the lower atmosphere by trapping heat.
This alters weather patterns and contributes to extreme events like flooding, heat waves, droughts, wildfires, and heavy rains.
Moreover, ocean acidification brought on by rising CO2 levels hinders the development of hard skeletons or shells in marine life, such as coral and crustaceans.
The new measurements from the experts were taken at Mauna Loa Observatory, a research facility located high on the slopes of Hawaii’s Mauna Loa volcano.
The Mauna Loa Observatory, located 11,141 feet above sea level, uses various forms of light and radiation to measure the various gases in the air.
The experts say that the monthly average for May 2025 at the observatory is 430.2 ppm, which is 3.5 ppm higher than the measurement for May 2024, which was 426.7 ppm.
A separate report from NOAA’s Global Monitoring Laboratory in Boulder, Colorado, states that the average was 430 ppm, which is 3 ppm higher than it was the previous year.
Jeff Berardelli, a meteorologist and climate specialist for WFLA Tampa Bay, described the new record as “concerning” in a post on X.
The most common greenhouse gas produced by humans is CO2, which can linger in the atmosphere and oceans for thousands of years.
Scientists estimate that the amount of carbon in the Earth’s atmosphere today is equivalent to what would have existed between 4 and 5 million years ago, during what they call the “Pliocene Climatic Optimum.”.
The average global temperature was 7°F (3point 9°C) higher than it was prior to the Industrial Revolution, and the sea level was an astounding 78 feet (24 meters) higher than it is today.
It was actually so hot at the time that vast forests covered parts of the Arctic that are now cold, arid tundra.
Even though human activity emits CO2 continuously throughout the year, the Northern Hemisphere experiences its highest levels of atmospheric CO2 in the spring, specifically in May.
Many plants in the hemisphere break down between autumn and spring, releasing carbon dioxide into the atmosphere.
Before plants come to life and absorb CO2 to support their growth, May typically represents the highest amount of CO2 in the atmosphere.
This starts the process of reducing the atmospheric concentration of CO2 until the autumn, when the plants begin to die, thus continuing the cycle.
Scientists say the new measurements from Mauna Loa Observatory show the average level of CO2 in the Northern Hemisphere’s atmosphere.
However, the Southern Hemisphere, which has a reversed cycle, has not yet seen CO2 concentrations surpass the 430 ppm threshold.
The first person to realize that CO2 levels in the Northern Hemisphere peaked in May was Charles David Keeling, a Scripps scientist and Ralph Keeling’s father.
He started keeping an eye on CO2 levels at Mauna Loa Observatory in 1958 and recorded a sustained rise that became known as the Keeling Curve.
In contrast, NOAA’s Global Monitoring Laboratory started measuring CO2 on a daily basis in 1974 and has since kept an independent, complementary measurement record.
