Gaby
For the first time since precise measurements began, the average monthly concentration of carbon dioxide in the atmosphere has topped 430 parts per million (ppm). Researchers at the Scripps Institution of Oceanography in San Diego said the May 2025 average reached 430.2 ppm, the highest level in 67 years of records. Why this matters: more CO2 accelerates global warming and could make parts of Earth’s surface uninhabitable for humans. High concentrations of carbon dioxide can also cause health problems, including cognitive impairment, drowsiness, nausea, and, in extreme cases, death. “Another year, another record. And it’s sad,” said Ralph Keeling, director of the Scripps CO2 program, which studies carbon dioxide. He added that CO2 levels in the Northern Hemisphere peak in May.
Carbon dioxide, like other greenhouse gases, traps heat in the lower atmosphere. That changes weather patterns and drives extreme events such as heatwaves, drought, wildfires, heavy rainfall, and floods, the Daily Mail reported. Rising CO2 also contributes to ocean acidification, making it harder for marine life like crustaceans and corals to build shells and skeletons.
Alarming Figures
New measurements came from the Mauna Loa Observatory, a research station on the slopes of the Mauna Loa volcano in Hawaii at about 11,000 feet (3,400 meters). The May 2025 average at Mauna Loa — 430.2 ppm — is 3.5 ppm higher than the May 2024 value. CO2 is the most abundant greenhouse gas produced by human activities, and it can remain in the atmosphere and oceans for thousands of years. Scientists say the current CO2 concentration in Earth’s atmosphere matches levels from roughly 4.1 to 4.5 million years ago, during the Pliocene climatic optimum. Back then, sea levels were about 24 meters higher than today, and the global average temperature was roughly 3.9 °C warmer than preindustrial levels. The climate was so warm that vast forests grew in parts of the Arctic that are now tundra.
Researchers said the Mauna Loa readings reflect the average state of CO2 in the Northern Hemisphere; the Southern Hemisphere has not yet passed 430 ppm. Ralph Keeling’s father, Charles David Keeling, first showed that CO2 levels in the Northern Hemisphere peak in May. In 1958 he began measuring CO2 at Mauna Loa and documented the long-term increase now called the Keeling Curve.
